[Federal Register Volume 75, Number 239 (Tuesday, December 14, 2010)]
[Proposed Rules]
[Pages 78094-78146]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 2010-31000]



[[Page 78093]]

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Part V





Department of the Interior





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Fish and Wildlife Service



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50 CFR Part 17



Endangered and Threatened Wildlife and Plants; 12-Month Finding on a 
Petition To List the Sonoran Population of the Desert Tortoise as 
Endangered or Threatened; Proposed Rule

  Federal Register / Vol. 75, No. 239 / Tuesday, December 14, 2010 / 
Proposed Rules  

[[Page 78094]]


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DEPARTMENT OF THE INTERIOR

Fish and Wildlife Service

50 CFR Part 17

[Docket No. FWS-R2-ES-2009-0032; MO 92210-0-008]


Endangered and Threatened Wildlife and Plants; 12-Month Finding 
on a Petition To List the Sonoran Population of the Desert Tortoise as 
Endangered or Threatened

AGENCY: Fish and Wildlife Service, Interior.

ACTION: Notice of 12-month petition finding.

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SUMMARY: We, the U.S. Fish and Wildlife Service, announce a 12-month 
finding on a petition to list the Sonoran population of the desert 
tortoise (Gopherus agassizii) as endangered or threatened and to 
designate critical habitat under the Endangered Species Act of 1973, as 
amended (Act). After review of all available scientific and commercial 
information, we find that listing the Sonoran population of the desert 
tortoise is warranted. Currently, however, listing the Sonoran 
population of the desert tortoise is precluded by higher priority 
actions to amend the Lists of Endangered and Threatened Wildlife and 
Plants. Upon publication of this 12-month petition finding, we will add 
the Sonoran population of the desert tortoise to our candidate species 
list. We will develop a proposed rule to list the Sonoran population of 
the desert tortoise as our priorities allow. We will make any 
determination on critical habitat during development of the proposed 
listing rule. In any interim period we will address the status of the 
candidate taxon through our annual Candidate Notice of Review (CNOR).

DATES: The finding announced in this document was made on December 14, 
2010.

ADDRESSES: This finding is available on the Internet at http://www.regulations.gov at Docket Number FWS-R2-ES-2009-0032. Supporting 
documentation we used in preparing this finding is available for public 
inspection, by appointment, during normal business hours at the U.S. 
Fish and Wildlife Service, Arizona Ecological Services Office, 2321 
West Royal Palm Road, Suite 103, Phoenix, Arizona 85021. Please submit 
any new information, materials, comments, or questions concerning this 
finding to the above address.

FOR FURTHER INFORMATION CONTACT: Steven L. Spangle, Field Supervisor 
Arizona Ecological Services Office (see ADDRESSES); by telephone at 
(602) 242-0210; or by facsimile at (602) 242-2513. If you use a 
telecommunications device for the deaf (TDD), please call the Federal 
Information Relay Service (FIRS) at 800-877-8339.

SUPPLEMENTARY INFORMATION:

Background

    Section 4(b)(3)(B) of the Endangered Species Act of 1973, as 
amended (Act) (16 U.S.C. 1531 et seq.), requires that, for any petition 
to revise the Federal Lists of Endangered and Threatened Wildlife and 
Plants that contains substantial scientific or commercial information 
that listing the species may be warranted, we make a finding within 12 
months of the date of receipt of the petition. In this finding, we 
determine that the petitioned action is: (a) Not warranted, (b) 
warranted, or (c) warranted, but the immediate proposal of a regulation 
implementing the petitioned action is precluded by other pending 
proposals to determine whether species are threatened or endangered, 
and expeditious progress is being made to add or remove qualified 
species from the Federal Lists of Endangered and Threatened Wildlife 
and Plants. Section 4(b)(3)(C) of the Act requires that we treat a 
petition for which the requested action is found to be warranted but 
precluded as though resubmitted on the date of such finding, that is, 
requiring a subsequent finding to be made within 12 months. We must 
publish these 12-month findings in the Federal Register.

Previous Federal Actions

    On October 15, 2008, we received a petition dated October 9, 2008, 
from WildEarth Guardians and Western Watersheds Project (petitioners) 
requesting that the Sonoran population of the desert tortoise be listed 
under the Act as a distinct population segment (DPS), as threatened or 
endangered rangewide (in the United States and Mexico), and critical 
habitat be designated. The petition contained detailed information on 
the natural history, biology, current status, and distribution of the 
Sonoran population of the desert tortoise. It also contained 
information on what the petitioners reported as potential threats to 
the Sonoran population of the desert tortoise, such as livestock 
grazing, urbanization and development, mining, international border 
patrol activities, illegal collection, inadequacy of existing 
regulations, altered fire regimes, off-highway vehicle use, drought, 
and climate change. We acknowledged the receipt of the petition in a 
letter to the WildEarth Guardians and Western Watersheds Project, dated 
November 26, 2008. In that letter we also stated that we had reviewed 
the information presented in the petition and determined that issuing 
an emergency regulation temporarily listing the species as per section 
4(b)(7) of the Act was not warranted. We also stated that we intended 
to make our finding on whether the petition presented substantial 
information that the requested action may be warranted, to the maximum 
extent practicable within 90 days of receipt of the petition, according 
to the provisions of section 4(b)(3) of the Act.
    On August 28, 2009, we made our 90-day finding that the petition 
presented substantial scientific information indicating that listing 
the Sonoran population of the desert tortoise (Gopherus agassizii) may 
be warranted. The finding and notice of our initiation of a status 
review was published in the Federal Register on August 28, 2009 (74 FR 
44335).
    On April 10, 2010, a stipulated settlement agreement (WildEarth 
Guardians and Western Watersheds Project v. Salazar, 10-cv-86-ACT-RHS 
(D. NM)) was filed. In this agreement, we agreed to submit a 12-month 
finding to the Federal Register on or before December 5, 2010. The 
stipulated settlement agreement was signed and adopted by the District 
Court of New Mexico on April 15, 2010.
    This notice constitutes our 12-month finding for the petition to 
list the Sonoran population of the desert tortoise as threatened or 
endangered.
Other Federal Actions
    Throughout this finding, we use ``Mojave'' to describe desert 
tortoise populations north and west of the Colorado River, as well as 
any reference to the biotic community known as the ``Mojave Desert'' or 
``Mojave desertscrub.'' These uses are consistent with the previous and 
current spelling of the common name in Federal actions that have 
addressed this population. We use ``Mohave'' in the geographic context 
to remain consistent with its reference by the U.S. Board of Geographic 
Names (e.g., Mohave County). In addition, while the Sonoran population 
of the desert tortoise is not currently formally recognized as a unique 
taxonomic entity, for ease of reference, we refer to the Sonoran 
population of the desert tortoise as the ``Sonoran desert tortoise'' in 
this finding.
    On December 30, 1982, we published a notice of review which 
determined the desert tortoise throughout its range in the United 
States and Mexico to be a Category 2 Candidate species (47 FR

[[Page 78095]]

58454); this was reaffirmed on September 18, 1985 (50 FR 37958). 
Category-2 status was granted to species for which information in our 
possession indicated that a proposed listing as threatened or 
endangered was possibly appropriate, but for which sufficient data were 
not available to make a determination of listing status under the Act.
    On April 2, 1990, we issued a final rule designating the Mojave 
population of the desert tortoise (occurring north and west of the 
Colorado River) as a threatened species under the Act (55 FR 12178; see 
final rule for a summary of previous actions regarding the Mojave 
population of the desert tortoise). Currently, the Mojave population of 
the desert tortoise is recognized as a distinct population segment 
under the Act. As part of that rulemaking, we designated any desert 
tortoise from the Sonoran population as threatened when observed 
outside of its known range, due to similarity of appearance under 
section 4(a) of the Act.
    On December 5, 1996, we published a rule that discontinued the 
practice of keeping a list of Category 2 Candidate species (61 FR 
64481). Since that time, the Sonoran desert tortoise observed inside 
its known range has had no Federal Endangered Species Act status.
    For a detailed account of previous Federal actions that pertained 
to the desert tortoise in the United States, please review the 
following Federal Register documents: ``Proposed Endangered Status and 
Critical Habitat for the Beaver Dam Slope Population of the Desert 
Tortoise'' (43 FR 37662, August 23, 1978); ``Requirement to withdraw or 
supplement proposals to determine various U.S. taxa of plants and 
wildlife as Endangered or Threatened or to determine Critical Habitat 
for such species'' (44 FR 12382, March 6, 1979); ``Reproposal of 
Critical Habitat for the Illinois mud turtle and Beaver Dam Slope 
population of the desert tortoise'' (44 FR 70680, December 7, 1979); 
``Listing as Threatened With Critical Habitat for the Beaver Dam Slope 
Population of the Desert Tortoise in Utah'' (45 FR 55654, August 20, 
1980); ``Review of Vertebrate Wildlife for Listing as Endangered or 
Threatened Species'' (47 FR 58454, December 30, 1982); ``Notice of 
Findings on Four Petitions, and Review of One Species'' (50 FR 13054, 
April 2, 1985); ``Review of Vertebrate Wildlife'' (50 FR 37958, 
September 15, 1985); ``Finding on Desert Tortoise Petition'' (50 FR 
49868, December 5, 1985); ``Findings on Pending Petitions and 
Description of Progress of Listing Actions'' (53 FR 25511, July 7, 
1988); ``Findings on Pending Petitions and Description of Progress of 
Listing Actions'' (53 FR 52746, December 29, 1988); ``Emergency 
Determination of Endangered Status for the Mojave Population of the 
Desert Tortoise'' (54 FR 32326, August 4, 1989); ``Desert Tortoise'' 
(54 FR 42270, October 13, 1989); ``Determination of Threatened Status 
for the Mojave Population of the Desert Tortoise'' (55 FR 12178, April 
2, 1990); ``Finding on a Petition to List the Sonoran Desert Tortoise 
as Threatened or Endangered'' (56 FR 29453, June 27, 1991); ``Proposed 
Determination of Critical Habitat for the Mojave Population of the 
Desert Tortoise'' (58 FR 45748, August 30, 1993); ``Determination of 
Critical Habitat for the Mojave Population of the Desert Tortoise'' (59 
FR 5820, February 8, 1994); ``Determination of Critical Habitat for the 
Mojave Population of the Desert Tortoise'' (59 FR 9032, February 24, 
1994); ``Notice of Final Decision on Identification of Candidates for 
Listing as Endangered or Threatened'' (61 FR 64481, December 5, 1996); 
and ``90-Day Finding on a Petition To List the Sonoran Population of 
the Desert Tortoise (Gopherus agassizii) as a Distinct Population 
Segment (DPS) with Critical Habitat'' (74 FR 44335, August 28, 2009).

Species Information

Taxonomy
    The desert tortoise is in the genus Gopherus (Rafinesque 1832), or 
gopher tortoises, and is a member of the Testudinidae family, or 
terrestrial tortoises. The North American tortoises formerly comprised 
two genera, Gopherus and Xerobates, with the latter including X. 
agassizii, the desert tortoise (Crumly 1994, pp. 7-8). Scientific 
nomenclature assigned to the desert tortoise has undergone a series of 
changes since its initial description by Cooper (1863) as X. agassizii 
(Barrett and Johnson 1990, p. 5); the currently recognized scientific 
name for the desert tortoise is Gopherus agassizii. Further information 
is available in Barrett and Johnson (1990, p. 5) or in the detailed 
account of desert tortoise phylogeny (evolutionary development) and 
systematics (taxonomic classification) by Crumly (1994, pp. 7-32). The 
desert tortoise is known in Mexico with the common names of ``tortuga 
del monte,'' ``Gal[aacute]pago de desierto,'' or the 
``xtam[oacute]osni'' (Rorabaugh 2008, p. 35).
Physical Description of Sonoran Desert Tortoises
    Adult Sonoran desert tortoises range in total carapace (straight-
line top shell) length from 8 to 15 inches (in) (20 to 38 centimeters 
(cm)), with a relatively high domed shell (AGFD 2001, p. 1; Brennan and 
Holycross 2006, p. 54). The record length for a Sonoran desert tortoise 
is 19.4 in (49 cm) total carapace length (Jackson and Wilkinson-Trotter 
1980, p. 430). The carapace is usually brownish with a definite pattern 
and prominent growth lines (AGFD 2001, p. 1). The plastron (bottom 
shell) is yellowish and is not hinged (AGFD 2001, p. 1; Brennan and 
Holycross 2006, p. 54). The hind limbs are very stocky and elephantine; 
forelimbs are flattened for digging and covered with large conical 
scales (AGFD 2001, p. 1; Brennan and Holycross 2006, p. 54). Male 
Sonoran desert tortoises are differentiated from females by having 
elongated gular (throat) shields, chin glands visible on each side of 
the lower jaw (most evident during the breeding season), a concave 
plastron, and larger overall size (AGFD 2001, p. 1).
Distribution
    The desert tortoise includes portions of southern California, 
southern Nevada, southwestern Utah, and the western, northwestern, and 
southern portions of Arizona in the United States, and also includes 
the Mexican State of Sonora into the northern portion of Sinaloa. One-
third of the geographic range of the desert tortoise occurs in 
northwestern Mexico (Bury et al. 2002, p. 86). The specific 
distribution of desert tortoise is influenced by habitat and climatic 
characteristics (vegetation community for food), soil and substrate 
characteristics (for shelter), and precipitation pattern (for water 
availability) within the appropriate elevation range.
    The distribution of the Sonoran desert tortoise in the United 
States is considered to be entirely within Arizona and comprises 
approximately 26.8 million acres (ac) (10.8 million hectares (ha)); 
east and south of the Colorado River (Barrett and Johnson 1990, pp. 4-
5; Lamb et al. 1989, p. 84). Sonoran desert tortoise distribution in 
Arizona is limited to the northeast by the limits of the Sonoran 
Desert. The Arizona portion of their range constitutes approximately 52 
percent of their total distribution. In Arizona, the Sonoran desert 
tortoise occurs primarily on Federal land but also occurs on a variety 
of non-federal lands as well as on ten Native American reservations: 
(1) Fort Mojave Indian Tribe; (2) Colorado River Indian Tribe; (3) 
Hualapai Tribe; (4) Fort McDowell Yavapai Nation; (5) Salt River Pima-
Maricopa Indian Community; (6) Gila River Indian Community; (7) Ak 
Chin; (8) Tohono O'odham Nation; (9) Pasqua Yaqui Tribe; and, (10) San 
Carlos Apache Tribe (AIDTT 2000, p. 40).

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    In Mexico, where 48 percent of their range occurs, the distribution 
of the Sonoran desert tortoise extends from the international border of 
Sonora and Arizona, south to the vicinity of Guaymas, and north of the 
R[iacute]o Yaqui (the southern and southeastern-most border of their 
distribution), in southern Sonora (Germano et al. 1994, p. 77; Fritts 
and Jennings 1994, p. 51; Bury et al. 2002, p. 88; Van Devender 2002a, 
p. 5; Edwards et al. 2009, pp. 7-8). This includes approximately the 
western half of the State of Sonora from the Gulf of California coast 
east roughly to the transition to unsuitable woodland and conifer 
forest areas in the higher elevations of the Sierra Madre Occidental. 
In 30 timed searches conducted August to September 1983, and beyond the 
known distribution of Sonoran desert tortoises in Sonora, Mexico, 
Fritts and Jennings (1994, p. 52) found several patterns in Sonoran 
desert tortoise distribution. First, most Sonoran desert tortoises in 
the eastern and northern extent of their distribution in Mexico occur 
below the 2,600 foot (ft) (790 meters (m)) elevation contour (Fritts 
and Jennings 1994, p. 52). Second, populations may be the densest and 
the least patchy between elevations of 900 and 1,600 ft (270 and 490 m) 
(Fritts and Jennings 1994, p. 52). They were also not found in habitat 
in Mexico that received an average of 3.9 in (10 cm) or less of rain 
annually (Fritts and Jennings 1994, p. 53).
    One question about the distribution of the Sonoran desert tortoise 
concerns the origin of a small number of tortoises that have been found 
in far southeastern Cochise County, Arizona, an area generally 
considered well east of the known distribution. There is some evidence 
that these tortoises may represent a naturally occurring population 
based on the presence of suitable habitat (Rorabaugh 2009, pers. 
comm.), similar animal communities (Rosen 2009, pers. comm.), and 
historic and current observations of tortoises in the area (Hulse and 
Middendorf 1979, p. 546; Radke 2009, pers. comm.; Van Devender et al. 
1976, pp. 300-303). However, these observations have traditionally been 
discounted as released pets rather than a natural population (AIDTT 
2000, p. 3; Germano et al. 1994, p. 81). Also, recent genetic analysis 
of a Sonoran desert tortoise collected from this area in 2009 indicated 
it was most closely related to tortoises in the Phoenix, Arizona, area 
and is likely, therefore, a ``released or escaped captive'' tortoise 
(Edwards 2010, pers. comm.). We recognize there is a fair amount of 
uncertainty regarding the origin of this population. However, because 
Sonoran desert tortoises are infrequently documented from this area and 
recent genetic testing indicated that observations represent released 
captives, we conclude that desert tortoises from this area do not 
represent a naturally-occurring, disjunct population. Consequently, we 
will not evaluate potential threats to the tortoises in this area of 
Cochise County in this finding.
Habitat
    Sonoran desert tortoises are most closely associated with the 
Arizona Upland and Lower Colorado River subdivisions of Sonoran 
desertscrub and Mojave desertscrub vegetation types. They occur most 
commonly on rocky (predominantly granitic rock), steep slopes and 
bajadas (lower mountain slopes often formed by the coalescing of 
several alluvial fans (fan-shaped deposits at the ends of canyons 
formed when fast flowing streams slow and widen)) and in paloverde-
mixed cacti associations (Ortenburger and Ortenburger 1927, p. 120; 
Burge 1979, p. 49; 1980, p. 48). Sonoran desert tortoise density has 
been observed to be higher in the Arizona Upland subdivision of the 
Sonoran desertscrub than in the Lower Colorado subdivision of the 
Sonoran desertscrub or in Mojave desertscrub (Berry 1984, p. 434; AIDTT 
2000, p. 4; Boarman and Kristan 2008, p. 19). In addition to the use of 
vegetation to meet energy and nutritional needs, the Sonoran desert 
tortoise uses vegetation for predator avoidance, thermal protection, 
and in social behaviors (Avery and Neibergs 1997, p. 13; Grandmaison et 
al. in press, p. 3). An important attribute of Sonoran desert tortoise 
habitat is the presence of cryptogamic crusts (soil crusts with unique, 
microscopic association of flora and fauna) (Bowker et al. 2008, p. 
2309). These occur on the surface of Sonoran Desert soils and assist 
with nitrogen-fixing to enhance soil fertility, improve water 
infiltration into soils, and prevent or lessen effects from wind and 
water erosion, all of which help to sustain vegetation vital to the 
Sonoran desert tortoise (DeFalco 1995, p. 22; DeFalco et al. 2001, pp. 
1, 9).
    Sonoran desert tortoises rarely occur in oak woodland habitat. 
However, one such population occurs at approximately 5,000-ft (1,500-m) 
elevation in Chiminea Canyon in the Rincon Mountains of Pima County, 
Arizona (Van Devender 2002a, p. 23), and they are also known from 
similar elevation in the Atascosa and Pajarito Mountains in south-
central Arizona. Zylstra and Steidl (2008, p. 747) found that habitat 
selection by Sonoran desert tortoises was most closely associated with 
topographic (degree of steepness of slope) and geomorphologic (rock 
type and structure) influences rather than by vegetation type. 
Specifically, Zylstra and Steidl (2008, p. 747) found that the 
likelihood of observing Sonoran desert tortoises increased with 
increasing slope, with a strong association to aspect (the direction to 
which a slope faces), with east-facing slopes preferred over north-
facing slopes. However, the season of use may affect which slope-
aspects (the direction a particular slope faces) Sonoran desert 
tortoises are likely to use based on their needs at that time (Zylstra 
and Steidl 2008, p. 752). Specifically, Sonoran desert tortoises have 
different thermoregulatory and physiological needs based upon their 
seasonal behaviors, such as hibernation or seeking temporary shelter 
during the tortoise's surface-active seasons.
    In addition to steep, rocky slopes and bajadas, Sonoran desert 
tortoises also use inter-mountain valleys as part of their home ranges 
and for dispersal at all age classes (Averill-Murray and Averill-Murray 
2002, p. 16). In the Ironwood National Forest, Averill-Murray and 
Averill-Murray (2005, p. 65) found tortoises or their signs (such as 
scat (droppings) and burrows) on 92 percent of transects in boulder 
habitat, on 71 percent of transects that included incised washes (dry 
stream beds that flow in response to precipitation), and on 25 percent 
of transects that had neither boulder habitat nor incised washes. 
Sonoran desert tortoises were found up to one mile (mi) (1.6 kilometers 
(km)) away from the nearest slope, indicating that they occur in low 
densities in inter-mountain valleys. Averill-Murray and Averill-Murray 
(2005, p. 65) stated that maintaining these areas ``may be important 
for long-term population viability.'' Washes might also be selectively 
chosen by reproductive female Sonoran desert tortoises as all eggs and 
hatchling desert tortoises observed by Barrett (1990, p. 205) occurred 
there. Sonoran desert tortoises on the 40-square-mile (sq mi) (64-
square-kilometer (sq km)) Florence Military Reservation in Pinal 
County, Arizona, primarily use xeroriparian habitat (a habitat 
association with plant species tolerant to hyper-arid conditions) along 
washes, with caliche caves (caves formed along steep banks of washes 
within cemented, sedimentary rock formations of calcium carbonate) 
within washes being an important component to occupied habitat (Lutz et 
al. 2005, p. 22; Riedle et al. 2008, p. 418). Another frequently

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used habitat type on the Florence Military Reservation included gently 
rolling alluvial fans dominated by creosote bush (Larrea tridentata) 
and white bursage (Ambrosia dumosa) during all periods of the year; 
somewhat atypical for Sonoran desert tortoises in other portions of its 
range (Lutz et al. 2005; p. 22; Grandmaison et al. in press, p. 4). In 
this habitat, Sonoran desert tortoises often used packrat middens 
(organic debris piles constructed for nesting purposes which often are 
comprised of wood material, cactus pads, etc.) as shelter sites, 
especially those with suitable canopy cover, an absence of cattle 
activity, and proximity to roads and washes (Lutz et al. 2005, p. 22; 
Grandmaison et al. in press, p. 2).
    Sonoran desert tortoises in Arizona generally occur within 
elevations from 510 to 5,300 ft (155 to 1,615 m) (Barrett and Johnson 
1990, p. 7; AGFD 2001, p. 4). According to the AGFD's Heritage Data 
Management system, 95 percent of Sonoran desert tortoise observations 
in Arizona have occurred at an elevation of 904 to 4,198 ft (275 to 
1279 m) (Zylstra and Steidl 2009, p. 8). However, one example of an 
extreme exception was a Sonoran desert tortoise observed at 7,808 ft 
(2,379 m) in a ponderosa pine-dominated coniferous community in the 
Rincon Mountain District of Saguaro National Park in Pima County, 
Arizona (Aslan et al. 2003, p. 57). The nearest road was 8.6 mi (13.9 
km) away by trail and nearly 2,000 ft (610 m) lower in elevation from 
the observed location of the tortoise, which strongly dismisses any 
notion that human activity was responsible for its location at such a 
high elevation (Aslan et al. 2003, p. 57).
    Sonoran desert tortoises in Mexico are generally found at lower 
elevations, ranging from approximately 1,000 to 1,640 ft (305 to 500 m) 
in elevation in rocky outcrops in desertscrub and foothills thornscrub 
habitat (Bury et al. 2002, p. 89). As in Sonoran desertscrub habitat in 
Arizona, Sonoran desert tortoises in Mexico often use shrubs as 
temporary shelter sites, and species such as mesquite (Prosopis spp.) 
and ironwood (Olneya tesota) may play important roles in the natural 
history of Sonoran desert tortoises in Mexico (Bury et al. 2002, p. 
100). Sonoran desert tortoises in Mexico have not been documented in 
flatter areas between mountain ranges (Bury et al. 2002, p. 89), 
although we presume they use these areas to some extent for dispersal 
much like they do in similar inter-mountain basins of Arizona. With the 
exception of the El Pinacate Desert Bioreserve in northwestern Sonora, 
Sonoran desert tortoises have not been documented using the extremely 
arid Lower Colorado subdivision of the Sonoran Desert in Mexico (Bury 
et al. 2002, p. 89). However, based on their presence in El Pinacate 
and the general lack of surveys in Mexico, the Sonoran desert tortoise 
may potentially be found in this habitat in northwestern Sonora in low 
densities. The extent of Sonoran desert tortoise distribution in 
northeastern Sonora, an area characterized as a transitional zone of 
foothills thornscrub, tropical deciduous forest, and Madrean oak 
woodland, is poorly understood (Bury et al. 2002, p. 89).
Burrow Use
    Adequate shelter, often in the form of constructed burrows, is one 
of the most important habitat features for the Sonoran desert tortoise. 
Burrows are constructed under rocks and boulders, beneath vegetation, 
on semi-open slopes, within the sidewalls of washes, or by using rocky 
crevices which may or may not be altered by the tortoise (Burge 1979, 
p. 44; 1980, pp. 44-45; Barrett 1990, p. 205; Averill-Murray et al. 
2002a, pp. 136-137, Grandmaison et al. in press, p. 14). Sonoran desert 
tortoises construct burrows in a variety of soil types including silt, 
silt with loose gravel, diatomite (a light-colored porous rock composed 
of the shells of diatoms) and diatomaceous marl (a crumbly mixture of 
clays, calcium and magnesium carbonates, with remnants of shells), and 
well-lithified (process whereby loose particles are converted into 
rock) volcanic ash, as observed in the lower San Pedro River Valley of 
Arizona (Bailey et al. 1995, pp. 363-364). Burrows are used for 
thermoregulation, nesting, and protection from predators, and the lack 
of suitable conditions for constructing burrows may be a limiting 
factor in Sonoran desert tortoise populations (Barrett and Humphrey 
1986, p. 262; Bailey et al. 1995, p. 366; Zylstra and Steidl 2008, p. 
752). In fact, Sonoran desert tortoise population densities appear to 
be highly correlated with available burrows, or potential burrow sites 
(Averill-Murray and Klug 2000, p. 69; Averill-Murray et al. 2002b, p. 
126). Sonoran desert tortoises often use a group of relatively closely-
located burrows as focal areas of activity in their home range. In 
doing so, they establish circular or slightly linear movement patterns, 
and may temporarily move on to another such cluster of burrows within 
the same active season (Bulova 1994, p. 140; Averill-Murray and Klug 
2000, p. 62; Lutz et al. 2005, p. 21).
    Burrows influence a variety of Sonoran desert tortoise behaviors 
and physiological characteristics. During the winter dormancy period 
(colder, winter months of inactivity), female Sonoran desert tortoises 
typically use more shallow burrows that are more susceptible to 
variation in ambient temperatures and consequently females emerge 
earlier in the spring (as early as late February) than do males, who 
often remain dormant until the commencement of the summer monsoon 
(AIDTT 2000, p. 7; Ernst and Lovich 2009, p. 547). Averill-Murray and 
Klug (2000, p. 66) and Bailey et al. (1995, p. 367) suggest that 
shallow burrows may account for responsiveness of females to warming 
periods in early spring for additional foraging opportunities to 
increase energy reserves for egg development, as shallower burrows are 
more reflective of ground-surface temperatures. Alternatively, cool, 
less variable temperatures in deeper burrows selected by male Sonoran 
desert tortoises may enhance sperm development and viability, as cooler 
temperatures allow more sperm production (Bailey et al. 1995, p. 367).
    The season may influence the locations and dimensions of burrows 
used by Sonoran desert tortoises in order to meet their behavioral and 
physiological needs (Barrett 1990, p. 205; Bailey et al. 1995, pp. 363, 
366). Finally, particularly in hatchling and juvenile size classes, the 
burrow microclimate can affect the rate of water loss in desert 
tortoises, which results in behaviors (drinking pooled rain, 
withdrawing into their shell, seeking long, deep burrows) to avoid 
lethal dehydration in relatively hot, dry seasons (Wilson et al. 2001, 
p. 158; Bulova 2002, pp. 184-186).
    Other forms of shelter used by Sonoran desert tortoise include 
packrat middens, which are often shared with other native reptiles, 
including other tortoises (Averill-Murray et al. 2002a, pp. 136-137; 
Lutz et al. 2005, p. 22; Grandmaison et al. in press, p. 2). These 
shelter types provide less insulation than earthen burrows and are 
therefore used for shorter duration, especially during the months with 
extremely hot or cold temperatures. This was the most commonly used 
shelter site at Florence Military Reservation.
Seasonal Behavior and Long-Distance Movements
    The Sonoran desert tortoise is diurnal (active during daylight 
hours) but sometimes emerge at night in response to rainfall (Ernst and 
Lovich 2009, p. 544). Sonoran desert tortoises may be surface-active 
every month of the year, but in the winter, surface activity is likely 
a response to thermoregulatory needs or movements between burrows 
(Averill-Murray and Klug 2000, p. 66).

[[Page 78098]]

Temperature and precipitation are important predictors of Sonoran 
desert tortoise activity (Meyer et al. 2010, p. 11). Precipitation 
amounts and timing vary among the populations of desert tortoise. The 
lowest amount of rainfall (usually during the winter) occurs in the 
northwestern-most portion of the species' range, and gradually 
increases and becomes seasonally bimodal pattern (rains in winter and 
summer) to the south into the southern-most extent of the species range 
in northern Sinaloa, Mexico (Germano et al. 1994, p. 76). Sonoran 
desert tortoise surface activity largely mimics the warm-season 
precipitation pattern (Averill-Murray et al. 2002a, p. 139; Van 
Devender 2002a, p. 7). Like the Arizona populations, Sonoran desert 
tortoises in Mexico seem to be most active in late summer (Ernst and 
Lovich 2009, p. 544). Sonoran desert tortoises are approximately half 
as active during the spring as they are in the summer, with females 
typically becoming surface active to forage in late March, while males 
typically emerge (but are not necessarily active) in late April 
(Averill-Murray et al. 2002a, p. 138).
    The summer monsoon (occurring typically from late June through 
September), characterized by both excessive heat and frequent 
thunderstorms, is the peak activity season for the Sonoran desert 
tortoise (Averill-Murray et al. 2002a, pp. 139-140). During this 
period, new growth of perennial plants is initiated and annual plants 
germinate, providing forage for tortoises (Averill-Murray et al. 2002a, 
p. 140). The onset of the summer monsoon triggers Sonoran desert 
tortoises to drink, flush their bladders, and rehydrate, establishing a 
positive water and energy balance, and spurring reproductive behaviors 
(AIDTT 2000, p. 7). Sonoran desert tortoises have been observed to seek 
out rocks with surface depressions during summer months to drink 
puddled water from monsoon storm events (Oftedal 2007, p. 23). Surface 
activity in Sonoran desert tortoises begins to wane as early as late 
September and ends by mid-December as they prepare for hibernation. 
Temperature and photoperiod (the duration of daylight) are likely the 
cues used by Sonoran desert tortoises to commence hibernation (Bailey 
et al. 1995, p. 367; Averill-Murray et al. 2002a, p. 147). Periods of 
hibernation (typically from mid-November through mid-February) in 
Sonoran desert tortoises appear to vary greatly among populations and 
among years but appear to correlate with seasonal temperatures (Bailey 
et al. 1995, p. 367; Averill-Murray and Klug 2000, p. 66).
    The behavior and ecology of hatchling Sonoran desert tortoises is 
poorly understood because their small size makes them very difficult to 
observe in the wild. Their scat is small, inconspicuous, and ephemeral, 
and burrows used by individuals in this size class resemble those of 
other terrestrial vertebrates in Sonoran desert tortoise habitat 
(Germano et al. 2002, pp. 271-272). This size class is thought to be 
the most vulnerable, experiencing the highest mortality rates (Morafka 
1994, p. 161).
    Home range sizes of Sonoran desert tortoises vary with 
precipitation levels, contracting during wet years and expanding during 
dry years in response to the availability of forage plants (Averill-
Murray and Klug 2000, p. 67). The home range of Sonoran desert 
tortoises may be as small as 6.4 ac (2.6 ha) but can vary widely, with 
males having larger home ranges than females (Barrett 1990, p. 203; 
Averill-Murray and Klug 2000, pp. 55-61; Averill-Murray et al. 2002a, 
pp. 150-151). In the lower San Pedro River Valley, Meyer (1993, p. 99) 
found Sonoran desert tortoise home ranges varied between 45 and 640 ac 
(18 and 258 ha) in size. Sonoran desert tortoises are known to exhibit 
high fidelity to their home ranges, with exception to dispersal 
movements when they move to new areas (Zylstra and Swann 2009, p. vi). 
They likely habituate to specific attributes of their home range, 
including the location of mates, water catchments, mineral licks, and 
burrow sites (Berry 1986a, p. 113).
    Sonoran desert tortoises are known to make long-distance movements 
between populations in adjacent mountain ranges. In an extreme example, 
Edwards et al. (2004, p. 494) tracked an adult female Sonoran desert 
tortoise moving 20 mi (32 km) between the Rincon and Santa Rita 
mountains of southern Arizona (also see Zylstra and Swann 2009, p. 10). 
During this long-distance movement, this tortoise encountered several 
barriers to movement that required human intervention to overcome such 
as fence lines, railroad tracks, an interstate highway, and several 
captures (including a temporary adoption) by humans (Edwards et al. 
2004, p. 494). In another example, in the San Pedro Valley of southern 
Arizona, a sub-adult Sonoran desert tortoise was captured and marked in 
1992. It was recaptured in 2005 approximately 14 mi (23 km) from its 
original point of capture (Meyer et al. 2010, p. 18). Dispersal 
distances of hatchling Sonoran desert tortoises are not well 
understood, but are likely shorter than those of adults because of the 
complex habitat of boulders and vegetation (where they occur) may 
inhibit long-distance movements (Van Devender 2002a, p. 14).
    Gibbons (1986, p. 104) suspected that long-distance movements by 
turtles can be explained by: (1) Nest site selection; (2) seasonal 
migration; (3) departure from unfavorable habitat conditions; or (4) 
movement by males in search of females. Averill-Murray and Klug (2000, 
p. 68) suggested that long-distance movements may be interpreted as 
random wanderings, infrequent travels to known sources of biological 
needs, explorations, adaptations for genetic exchange, or for dispersal 
to other suitable areas. Precipitation may influence the likelihood of 
long-distance movements, especially in individuals approaching 
reproductive age in populations that experience above-average 
precipitation for a 2- to 3-year period (AIDTT 2000, p. 8). Averill-
Murray and Klug (2000, p. ii) stated, ``A large cohort of young 
tortoises that experiences a relatively wet and productive environment, 
with high survival, may provide the stock for dispersal between 
populations as they approach sexual maturity, in addition to replacing 
aging adults within the local population.'' Long-distance movements by 
Sonoran desert tortoises observed by Averill-Murray and Klug (2000, p. 
69) suggest the potential for metapopulation (interrelated population 
dynamics between regionally proximal populations) relationships between 
local populations inhabiting regional hillsides. Habitat features may 
also influence the Sonoran desert tortoises' ability to make long-
distance movements. Dispersal of Sonoran desert tortoises between 
populations might be less likely through sparse desertscrub in very 
hot, dry river valleys in the Lower Colorado River subdivision of 
Sonoran desertscrub. Van Devender (2002a, p. 16) suggested that 
populations occurring in the Eagletail, Maricopa, Sand Tank, and 
similarly situated mountain ranges might have existed in isolation for 
decades, if not centuries.
    There are no data to evaluate long-distance movements in 
populations that occur in Mexico. Although Sonoran desert tortoises in 
Mexico are known to occupy slopes, arroyos, and bajadas, they are 
infrequently observed using valley bottoms (Fritts and Jennings 1994, 
p. 52). Sonoran desert tortoise populations in Mexico have been poorly 
studied, but we presume individuals make similar long-distance 
movements between populations.

[[Page 78099]]

Longevity
    Estimates of longevity in wild Sonoran desert tortoises vary 
considerably from 30 years to over 100 years (Germano 1992, pp. 369-
370; 1994, p. 176; Zylstra and Swann 2009, p. vii). Using a growth 
equation to extrapolate longevity in Sonoran desert tortoises, Germano 
et al. (2002, p. 271) estimated that the average oldest ages attained 
for Sonoran desert tortoises is 62.2 years in females and 64.4 years in 
males; however, they admitted that correlating age with size is 
problematic in turtles. Zylstra and Swann (2009, p. vii) suspected that 
Sonoran desert tortoises may reach 80 to 100 years of age in the wild. 
Sonoran desert tortoises have been shown to live longer in the wild 
than those from the Mojave population.
Bladder Physiology
    The bladder in the Sonoran desert tortoise is unique and serves an 
important function in its survival. Sonoran desert tortoises are 
capable of drinking large amounts of water when it is available, and 
may even construct water catchments by digging earthen depressions, 
likely as an adaptation to the infrequent and unpredictable nature of 
rainfall events throughout their range (Ernst and Lovich 2009, p. 546). 
The bladder of Sonoran desert tortoises is a large and bilobed (divided 
into two lobes) organ critical for withstanding the effects of seasonal 
and short-term drought because of its ability to store water, dilute 
excess dietary salts and metabolic wastes, and reabsorb water into the 
bloodstream (Averill-Murray et al. 2002a, p. 146; Ernst and Lovich 
2009, p. 545). In seasonal or short-term drought conditions, the 
concentration of urine in Sonoran desert tortoises allows them to 
forage on dried vegetation by reducing the dehydration effects of such 
forage types (Averill-Murray et al. 2002a, p. 146; Ernst and Lovich 
2009, p. 545). Water serves an important role in flushing salts from 
the body of Sonoran desert tortoises and resetting the electrolytic 
balance, preparing the Sonoran desert tortoise for the next dry period 
(Averill-Murray et al. 2002a, pp. 140, 146).
Diet, Foraging Behavior, and Potassium Excretion Potential
    The Sonoran desert tortoise is an herbivore, and has been 
documented to eat 199 different species of plants, including herbs 
(55.3 percent), grasses (17.6 percent), woody plants (22.1 percent), 
and succulents (5 percent) (Ogden 1993, pp. 1-8; Van Devender et al. 
2002; pp. 175-176; Brennan and Holycross 2006, p. 54; Oftedal 2007, p. 
21; Ernst and Lovich 2009, p. 562; Meyer et al. 2010, pp. 28-29, 44-
48). Of the numerous nonnative plant species that have become 
established throughout the range of the Sonoran desert tortoise, only 
red brome (Bromus rubens) and redstem filaree (Erodium cicutarium) are 
frequently eaten and considered relatively important nonnative species 
in the diets of Sonoran desert tortoises (Van Devender et al. 2002, p. 
183). However, physical injury to Mojave desert tortoises resulting 
from consuming nonnative grass species (i.e., red brome and cheatgrass 
(Bromus tectorum)) has been documented, and sharp seeds have been found 
lodged between the tortoises' upper and lower jaw. This injury may 
adversely affect their foraging ability or become a source for 
infection (Medica and Eckert 2007, p. 447). Though this study focused 
on Mojave desert tortoises, this may affect all desert tortoises 
wherever these plant species occur (i.e., within the Sonoran Desert in 
Arizona).
    Significant differences in the nutritional quality of native versus 
nonnative forage for desert tortoises were not found by Hazard et al. 
(2010, pp. 139-145). Nagy et al. (1998, pp. 260, 263) compared the 
nutritional values of native and nonnative grasses (native: Indian 
ricegrass (Achnatherum (Oryzopsis) hymenoides); nonnative: Mediterrean 
grass (Schismus barbatus)) and forbs (native: desert dandilion 
(Malacothrix glabrata); nonnative: redstem filaree), finding that the 
two grasses possessed similar nutritional value. The dry matter and 
energy digestibility of the two grasses were much lower than those of 
the forbs, providing little nitrogen, and tortoises lost more water 
than they gained while processing grasses. The native forb was more 
readily digestible than the nonnative forb as dried mass, but the 
inverse was true as fresh mass (Nagy et al. 1998, p. 263). However, the 
native forbs provide significantly more nitrogen and water than the 
nonnative forbs, which is important in maintaining a positive water 
balance. Results of these feeding trials suggest that the proliferation 
of nonnative grasses leading to the exclusion of forbs places desert 
tortoises at a nutritional disadvantage. If, instead of eating to 
obtain a given volume of food, tortoises consume just enough food to 
satisfy their energy needs (as commonly noted in other vertebrate 
groups), then the native forbs provide the best nutrition. Nagy et al. 
(1998, p. 260) concluded that the life stage of the plant and the plant 
type (forb or grass) were important predictors of nutritional quality 
versus a plant being native or nonnative to a particular region. In 
summary, research has shown that forbs are more valuable to Sonoran 
desert tortoise nutrition than grasses, and that native forbs are more 
valuable than nonnative forbs in a dried state, which may be important 
in periods of drought.
    Diets of Sonoran desert tortoises vary among populations in 
response to seasonal availability of plant species and in response to 
precipitation amounts (Martin and Van Devender 2002, p. 31). In years 
of low winter rainfall, Sonoran desert tortoises are less selective in 
plant species consumed because there are fewer options, but in years of 
high winter rainfall, Sonoran desert tortoises have exhibited highly 
selective foraging habits (Oftedal 2002, pp. 205-206). During years 
when monsoon rains are light or irregular, Sonoran desert tortoises 
consume dried plant material (Averill-Murray et al. 2002a, p. 140). 
Within Saguaro National Park in southern Arizona, Sonoran desert 
tortoises frequently ate annual legumes in the spring (high in water 
content, low in potassium), and annual and perennial grasses 
(supplemented by prickly pear fruit (Opuntia engelmannii)) during the 
monsoon when ponding water can replenish water reserves (Oftedal 2007, 
p. 17). In most years, Sonoran desert tortoises consume enough calories 
during the summer monsoon to fuel growth and store fat for the next 
year (Van Devender 2002a, p. 10).
    Desert tortoises are uniquely vulnerable to changes in their 
potassium levels (Oftedal 2002, p. 208). Because potassium cannot be 
easily stored in the body, excess potassium must be excreted to avoid 
toxicological effects (Oftedal 2002, p. 208). Therefore, Sonoran desert 
tortoises that must forage on plants with high potassium content must 
also flush their bladders more frequently and therefore risk a net loss 
in metabolic water levels and subsequent dehydration (Oftedal 2002, p. 
209).
    The potassium excretion potential (PEP) is an index of water, 
nitrogen, and potassium levels in a plant that relates to a desert 
tortoise's ability to efficiently excrete potassium. PEP is a critical 
consideration for determining the value or risk of particular forage 
species during times of drought or major perturbations to habitat, and 
for comparing potential effects of forage competition between tortoises 
and livestock. A positive PEP value for a plant species (preferred by 
tortoises) means there is more water and nitrogen

[[Page 78100]]

in the food than is needed to excrete potassium, and vice-versa for a 
negative PEP value (Oftedal 2002, p. 215; Ernst and Lovich 2009, p. 
545). Sonoran desert tortoises have been documented to selectively 
forage on high PEP plant species to minimize water loss associated with 
metabolizing potassium (Oftedal 2002, p. 214; Ernst and Lovich 2009, p. 
545). High PEP values can be found in certain species of primroses, 
filaree, legumes, mustards, and spurges (Ernst and Lovich 2009, p. 
545). Sonoran desert tortoises have been found to be seasonally 
selective for high PEP forage species, based on the abundance and 
diversity of plants and precipitation (Oftedal 2002, p. 223; 2007, pp. 
3, 22).
    In addition to herbivory, Sonoran desert tortoises are also 
geophagous; in other words, they consume bones, stones, and soil for 
additional nutrient and mineral supplements, for mechanical assistance 
in grinding plant matter in the stomach, or to expel parasites in the 
intestinal tract (Sokol 1971, p. 70; Marlow and Tollestrup 1982, p. 
475; Esque and Peters 1994, pp. 108-109; Stitt and Davis 2003, p. 57; 
Walde et al. 2007b, p. 148). Sonoran desert tortoises are highly 
attracted to sites with exposed calcium carbonate and have been 
observed congregating at these sites year after year eating these soils 
(Meyer et al. 2010, p. 11). Soil condition and quality are important to 
the Sonoran desert tortoise, not only for nutrients derived from eating 
soil, but also production and maintenance of vegetation that is 
consumed by tortoises (Avery and Neibergs 1997, p. 13).
    Desert tortoises have been observed eating scat from black-tailed 
jack rabbits, wood rats, collared peccaries, and even desert tortoises. 
This behavior could possibly aid in the transfer of gut microflora such 
as bacteria or fungi or it could be used as a source of additional 
nutrients (Walde et al. 2005, p. 77-78). Bostick (1990, p. 149) 
asserted that desert tortoises feed ``primarily on dung'' although this 
claim was refuted in the literature (Boarman 2002, pp. 27, 35, 38). 
Infrequent observations of sand, bird feathers, arthropod parts, and 
snake and lizard skins have also been made during fecal analyses of 
desert tortoises (Ernst and Lovich 2009, p. 560).
Reproduction
    The Sonoran desert tortoise breeding season begins with the summer 
monsoon when male-male combat over receptive females can be observed, 
such as at sites with exposed calcium carbonate soils, where tortoise 
densities may be higher (discussed above) (Meyer et al. 2010, p. 11). 
Sexual maturity and first reproduction in female Sonoran desert 
tortoises occurs from 12 to 22 years of age, or at 8.7 in (22 cm) in 
midline carapace length, and reproductive activity is highly influenced 
by winter and spring precipitation (Averill-Murray and Klug 2000, p. 
69; Averill-Murray et al. 2002b, p. 119; Bury et al. 2002, p. 100; 
Germano et al. 2002, p. 265). Females may store sperm for up to two 
years, meaning that one season's mating produces the following season's 
clutch of eggs (Palmer et al. 1998, pp. 704-705; Averill-Murray et al. 
2002a, p. 141). Female Sonoran desert tortoises may lay one clutch of 
1-12 eggs per year, usually around the onset of the summer rainy 
season, although they may not produce a clutch every year (Averill-
Murray 2002b, p. 295). Eggs hatch in September and October (Van 
Devender 2002a, pp. 10-11; Averill-Murray 2002b, p. 295). The average 
clutch size is 3.8 to 5.7 eggs, and in contrast to Mojave Desert 
tortoises, clutch size is not positively correlated with female body 
size (Mueller et al. 1998, p. 313; Averill-Murray 2002b, p. 299; 
Averill-Murray et al. 2002b, p. 119). Late oviposition (deposition of 
eggs) dates recorded on the Sugarloaf study site in central Arizona in 
1998 and 1999 suggest that eggs and hatchlings may occasionally 
overwinter in nests (Averill-Murray 2002b, p. 299). Female desert 
tortoises have been known to urinate on their nest sites before and 
after nesting; this may be to aid in digging the nest, and might make 
it more difficult to dig up the nest after the soil dries, or possibly 
to hydrate soils in contact with eggs as the rigid-shelled eggs of 
desert tortoises have been shown to uptake moisture from the soil 
faster than it evaporates from the shell exposed to air (Patterson 
1971, p. 199; Spotila et al. 1994, p. 112). Female Sonoran desert 
tortoises that survive to reproductive age are believed to produce as 
many as 85 eggs over the course of their lives, with perhaps two or 
three of those hatchlings surviving to reproductive age (Van Devender 
2002a, p. 11).
    Desert tortoises exhibit environmental sex determination, which 
means that incubation temperatures during embryonic development 
determine the sex of the tortoises. Higher incubation temperatures 
produce more females and lower temperatures produce more males (Spotila 
et al. 1994, pp. 109-111; Rostal et al. 2002, p. 313). Incubation 
temperatures at or below 86.9 degrees Fahrenheit ([deg] F) (30.5 
degrees Celsius ([deg] C)) result in the production of all male desert 
tortoises, whereas temperatures of 90.5 [deg]F (32.5 [deg]C) result in 
all females, and eggs incubated at the ``pivotal'' temperature of 88.3 
[deg]F (31.3 [deg] C) develop a 1:1 sex ratio (Rostal et al. 2002, p. 
313).
Predation
    As adults, Sonoran desert tortoises are relatively protected from 
natural predation because of their hard shells. Mountain lions (Felis 
concolor) appear to be the only natural predator in the Sonoran Desert 
with the jaw strength required to puncture or crack the shells of adult 
Sonoran desert tortoises. However, mountain lion predation is not known 
to contribute to elevated mortality rates within monitored Sonoran 
desert tortoise populations (AIDTT 2000, p. 8; Meyer et al. 2010, p. 
18; Riedle et al. 2010, p. 165). Dickenson et al. (2001, p. 254) 
recorded 14 Sonoran desert tortoise mortalities in the Little Shipp 
Wash and Harcuvar monitoring plots from 1990-1994, five of which were 
attributed to mountain lion predation. Javelina (Tayassu tajacu) 
predation on Sonoran desert tortoises was suspected in the San Pedro 
Valley of southern Arizona (Meyer et al. 2010, p. 18). Other mammalian 
predators may include badgers (Taxidea taxus), ring-tailed cats 
(Bassiriscus astutus), bobcats (Felis rufus), skunks (Spilogale 
gracilis, Mephitis mephitis, M. macroura, Conepatus mesoleucus), kit 
foxes (Vulpes macrotis), gray foxes (Urocyon cinereoargenteus), coyotes 
(Canis latrans), and domestic dogs (Canis familiaris) (Boarman 2002, p. 
17; Ernst and Lovich 2009, p. 563).
    Both golden eagles (Aquila chrysaetos) and common ravens (Corvus 
corvax) have been documented to prey upon all size classes of Mojave 
desert tortoises in California (Berry 1985, pp. 1, 6-10). Such 
predation might also occur on Sonoran desert tortoises. The greater 
roadrunner (Geococcyx californianus) is also a suspected predator on 
juvenile Mojave desert tortoises, based upon one field observation of 
roadrunner tracks next to a freshly killed individual (Berry 1985, p. 
11); such predation might also occur on Sonoran desert tortoises. 
However, because avian predators rely exclusively on their vision to 
detect prey, we expect lower rates of avian predation on Sonoran desert 
tortoises occupying Arizona upland Sonoran desertscrub because the 
dense, complex habitat structure likely limits birds' ability to detect 
tortoises. Habitat-associated protection from avian predation may be 
less pronounced where Sonoran desert tortoises occur in the sparser 
vegetation of the Lower Colorado River subdivision of Sonoran 
desertscrub.

[[Page 78101]]

    Sonoran desert tortoises are most vulnerable to predation while in 
their eggs or as hatchlings and juveniles predominantly because of 
their size and undeveloped, softened shells (which do not adequately 
harden until approximately 7 years of age) which provide little 
protection and are easily compromised. Higher mortality rates in the 
hatchling and juvenile age classes may also be partially due to their 
higher metabolic rates, which necessitates longer periods of surface 
activity to obtain suitable amounts of forage. Longer surface activity 
may cause greater risk of detection by predators (Morafka 1994, p. 
163). Nest predation levels may be high in some populations. Seventy-
five percent of Sonoran desert tortoise nests suffered predation over a 
two-year period at the Sugarloaf study plot in Maricopa County, Arizona 
(Averill-Murray 2002b, p. 298). Gila monsters (Heloderma suspectum) are 
a primary predator on tortoise eggs, and female Sonoran desert 
tortoises in the process of oviposition will actively defend the burrow 
and aggressively pursue Gila monsters in attempting to drive them away 
(Barrett and Humphrey 1986, p. 262). Coachwhips (Coluber flagellum) and 
gophersnakes (Pituophis catenifer) have been reported consuming 
juvenile Sonoran desert tortoises (Amarello et al. 2004, p. 178; Ernst 
and Lovich 2009, p. 563). Presumably, other snake species such as 
common kingsnakes (Lampropeltis getula) with generalized prey 
preferences consume eggs or hatchling Sonoran desert tortoises, but we 
did not find other examples in the literature.
    For more detailed information on all aspects of Sonoran desert 
tortoise biology, see Barrett and Johnson (1990, pp. 1-95) and Bury and 
Germano (1994, pp. 1-212).

Monitoring and Population Status

Monitoring and Statistical Analyses
    We are unaware of any structured, long-term monitoring program for 
Sonoran desert tortoises in Mexico; therefore, we are unable to assess 
the current status or population trends in that part of the range. 
Therefore, we discuss only Arizona studies in this section.
    Twenty-eight individual Sonoran desert tortoise populations in 
Arizona have been studied since the mid-1970s but few populations have 
been studied for more than a few years (Averill-Murray 2000, p. 1; 
Averill-Murray et al. 2002b, p. 109). Monitoring plots (also referred 
to as ``plots'') have varied from 0.2 to 1.5 sq mi (0.3 to 2.4 sq km) 
in size (Averill-Murray 2000, p. 4). Beginning in 1987, AGFD and the 
U.S. Bureau of Land Management (BLM) have established and maintained 17 
plots in Arizona as long-term monitoring plots and have surveyed them 
in a somewhat irregular, but repeated fashion. Each plot has been 
surveyed between two and nine times during this timeframe, with 11 to 
86 person-days (cumulative days spent by researchers working on plots) 
spent during each survey (AGFD 2010, p. 1). These long-term monitoring 
plots are located in six counties within Arizona, and their locations 
were chosen to represent Sonoran desert tortoise distribution in the 
State.
    General monitoring objectives for the 17 plots are to document 
abundance, density, and changes of Sonoran desert tortoise populations 
across the State using capture-recapture methods (Averill-Murray 2000, 
p. 3). Records of demographic characteristics of each population, 
including sex ratios and age/size structure as well as individual 
health and signs of disease within each population were also recorded 
during monitoring activities (Averill-Murray 2000, p. 3). Monitoring 
protocols used from 1987 to 2000 are summarized in Averill-Murray 
(2000, pp. 3-7).
    The Sonoran desert tortoise is a difficult species to monitor in 
the wild because of its slow movement and camouflaged appearance, 
especially in the smaller hatchling and juvenile age classes. These 
factors can significantly hamper a surveyor's ability to detect them in 
the field (Zylstra et al. 2010, p. 1311). In addition, Arizona Upland 
subdivision of Sonoran desertscrub (where Sonoran desert tortoise 
population densities are the highest) is complex, often with many large 
boulders, somewhat dense vegetation, and challenging topographic 
relief. Drought and emigration also affect the reliability of data from 
Sonoran desert tortoise population monitoring because the tortoises may 
be inactive (in their burrows) or have left the population (dispersed). 
In these cases the absence of observations might be mistaken as 
mortality. Also, Sonoran desert tortoises can occur in low densities 
with little surface activity both seasonally and daily (Zylstra et al. 
2010, p. 1311). Alone or in combination, these factors, in addition to 
a relatively short sampling period for such a long-lived species, make 
subtle population trends difficult to distinguish and overall 
population trend analysis problematic.
    Low detectability may have been responsible for long periods 
between recaptures of marked desert tortoises in an 18-year desert 
tortoise study from 1980 to 1997 in the San Pedro Valley, Arizona. For 
example, a sub-adult Sonoran desert tortoise was captured and marked in 
1992, and was not encountered again until 2005, when it was 
incidentally observed approximately 14 mi (22.5 km) from its original 
point of capture, 8 years after the conclusion of the study (Meyer et 
al. 2010, p. 18). Within the entire duration of this study, 
approximately 30 percent of 577 marked Sonoran desert tortoises were 
never recaptured, with only 15 total carcasses found, indicating 
potential emigration, long-term burrow use, or difficulties in 
detecting individuals in complex landscapes (Meyer et al. 2010, p. 20). 
The amount of time between recaptures of Sonoran desert tortoises can 
be significant; durations between recaptures of some individuals in the 
San Pedro Valley study were as high as 18 years (Meyer et al. 2010, p. 
20).
    Several authors have investigated how detectability may bias 
results of Mojave desert tortoise monitoring. For example, Anderson et 
al. (2001, p. 583) studied the degree to which field observers can meet 
the assumptions underlying line-transect sampling to monitor 
populations of desert tortoises in Mojave desertscrub. They found that 
when all Mojave desert tortoises are not detected along the centerline 
of the transect route (which routinely occurs), biases in sampling data 
result (Anderson et al. 2001, p. 583). Anderson et al. (2001, p. 593-
596) noted that surveyor numbers and level of experience contribute to 
the reliability of line transect methods. Freilich and LaRue (1998, p. 
594) experimentally tested the effect of personnel experience on Mojave 
desert tortoise survey outcomes in Mojave desertscrub. They found that 
observers consistently overestimated the number of desert tortoise 
burrows (falsely assigning other animal burrows as those made by desert 
tortoises), and found fewer desert tortoises and scat than were 
actually placed on test plots. Their results indicated that experience 
played a relatively small role in detecting Mojave desert tortoises 
(Freilich and LaRue 1998, pp. 593-594). In an effort to increase 
detections, some investigators have tested the use of tortoise 
detection dogs in Mojave desert tortoise monitoring projects (Cablk and 
Heaton 2006, p. 1926; Heaton et al. 2008, pp. 476-477; Nussear et al. 
2008, pp. 109-111). Because Sonoran desertscrub is more dense and 
complex than Mojave desertscrub, detection is even more difficult in 
Sonoran desert tortoise monitoring. Zylstra and Steidl (2009, p. 16) 
found that line transect methods are

[[Page 78102]]

not an efficient means with which to monitor Sonoran desert tortoises.
    The seasonal timing of surveys and fluctuating influence of 
precipitation on Sonoran desert tortoise surface activity also create 
problems with monitoring populations and interpreting results. Sonoran 
desert tortoises often become inactive, residing in their burrows, 
during periods of seasonal or short-term drought. For example, in a 
multi-year mark and recapture study of Mojave desert tortoises in 
Joshua Tree National Park, Freilich et al. (2000, pp. 1487-1488) found 
that in years of below-normal precipitation, desert tortoise home 
ranges decreased, individual captures decreased, and the effort 
required to find each tortoise nearly doubled; indicating the 
significant influence of precipitation on the possible discrepancy 
between the number of tortoises that can be observed versus the number 
of tortoises that actually occur within a monitoring plot.
    In an attempt to improve monitoring protocols to account for such 
complicating factors described above, Averill-Murray (2000, pp. 7-13) 
critiqued the original protocols used for long-term monitoring plots of 
Sonoran desert tortoise populations in Arizona. This work became the 
basis for several changes in monitoring protocols, beginning in 2000. 
Although line transect methods have not been implemented on Arizona's 
Sonoran desert tortoise long-term monitoring plots, the capture-
recapture methods currently used likely violate assumptions about equal 
detection probability (all animals having the same probability of being 
captured during every sampling occasion) (Zylstra and Steidl 2009, p. 
9).
    While monitoring of Sonoran desert tortoise populations in Arizona 
has been ongoing for several decades, attempts to quantify temporal 
trends in abundance have been hampered by the data limitations 
discussed above (Zylstra and Steidl 2009, p. 5; Zylstra et al. 2010, 
pp. 1311-1317). Effective monitoring is largely dictated by the 
objective of the monitoring, whether that objective is to detect 
changes in distribution, abundance, density, or survival. In addition, 
using existing plot data to establish rangewide trends in Sonoran 
desert tortoise populations is generally problematic because the 
current set of monitoring plots does not represent a random sample from 
the species' entire range in Arizona (Averill-Murray and Klug 2000, p. 
25). Despite the history and effort dedicated to monitoring Sonoran 
desert tortoise populations in Arizona since 1987, there are 
limitations of these data with respect to interpreting rangewide trends 
of the Sonoran desert tortoise. Averill-Murray (2000, pp. 12-13) 
identified problems with extrapolating the results of the plot 
monitoring data to making range-wide assessments outside of the plots. 
We elaborate on these problems in our assessment of Boarman and Kristan 
(2008) below.
    Boarman and Kristan (2008, pp. 3-12) analyzed mark and recapture 
data from the 17 Sonoran desert tortoise long-term monitoring plots 
throughout Arizona that were surveyed on the average of once every 4 
years from 1987 to 2006. Boarman and Kristan (2008, p. ii) concluded 
that the Sonoran population of the desert tortoise in Arizona 
experienced statistically significant declines, at an annual rate of 
3.52 percent over the 20-year period; equating to a cumulative 51 
percent decline in overall numbers during this timeframe.
    We received several comments from the public in response to our 90-
day finding that addressed the Boarman and Kristan (2008) report (AGFD 
2010, pp. 4-6; Carothers et al. 2010, pp. 5, 8-12; Ogden 2009, pp. 3-
12, Smith 2010, pp. 4-5). Commenters criticized the method and manner 
with which Boarman and Kristan (2008) used statistical tests, as well 
as the conclusions they made. Significant concerns were noted with 
respect to the type of statistical tests used by Boarman and Kristan 
(2008) because data were extrapolated beyond the statistical tests' 
ability to avoid inherent biases (AGFD 2010, p. 4). Problems associated 
with the statistical confidence intervals for monitoring plot data used 
by Boarman and Kristan (2008) were also identified (Ogden 2009, pp. 2-
3). Also, monitoring plot data used in Boarman and Kristan (2008, p. 
20) were not designed to compare population trends among individual 
plots (Ogden 2009, p. 2). Carothers et al. (2010, pp. 8-12) identified 
numerous additional problems with the statistical analysis provided by 
Boarman and Kristan (2008). Collectively, based upon comments received 
from the public as well as our internal review, the number and 
magnitude of potential problems associated with Boarman and Kristan's 
(2008) statistical analysis call into question the validity of their 
conclusions. After careful review of the report and the questions 
raised by reviewers of the report, we decided that the conclusions 
pertaining to overall Sonoran desert tortoise population trends do not 
represent the best available information and, therefore, we did not use 
the report in this finding. However, other information in the Boarman 
and Kristan (2008) report was used in our analysis of the status of and 
threats to the Sonoran desert tortoise and is cited in this finding. 
For a more detailed analysis of the Boarman and Kristan (2008) report, 
see our ``Review of Boarman and Kristan (2008)'' provided at http://www.regulations.gov (Docket Number FWS-R2-ES-2009-0032).
Survivorship and Population Densities in Arizona
    Viable populations in turtles usually require that both juvenile 
and adult size classes have high survivorship (Averill-Murray and Klug 
2000, p. 70). Data on the recruitment of juveniles into Sonoran desert 
tortoise populations, and their survivorship, are generally lacking due 
to the difficulty detecting juveniles in the field (AGFD 2010, p. 3). 
Data on juvenile and adult survivorship in Sonoran desert tortoises 
require long-term, repeated population monitoring, which in turn, 
requires long-term, reliable funding sources. Consequently, these data 
are conspicuously rare or absent for most Sonoran desert tortoise 
monitoring plots making population viability estimates for Sonoran 
desert tortoise populations within Arizona problematic at best. As 
expected for a long-lived species, survivorship in Sonoran desert 
tortoises (using data generated from a few long-term monitoring plots 
in Arizona) is generally high for adults but potentially lower for 
juveniles and hatchlings (Zylstra and Steidl 2009, p. 7). Where enough 
data from long-term monitoring plots or independent studies exist, 
survivorship has been calculated for adults in the following plots or 
study areas: Sugarloaf Mountain (96-98 percent), Florence Military 
Reservation (88-97 percent), Little Shipp Wash (94-97 percent), Granite 
Hills (94-97 percent), and Eagletail Mountains (94-97 percent) (AGFD 
2010, p. 2; Riedle et al. 2010, p. 165).
    Densities of Sonoran desert tortoises among populations vary 
considerably. In 2000, the density of Sonoran desert tortoises, as 
determined by surveys on long-term monitoring plots and other 
monitoring plots during the 1990s, varied from 15 to 150 individuals 
per square mile (2.6 sq km) (AIDTT 2000, pp. 5-6; Averill-Murray and 
Klug 2000, p. i). In the San Pedro Valley of southern Arizona, the 
average density of the Sonoran desert tortoise population was 38 
individuals per square mile (Meyer et al. 2010, p. 17). Stager et al. 
(2010, p. 37) suspect that Sonoran desert tortoise populations in 
Mohave County, Arizona may be naturally lower due to limited burrowing 
habitat available to them to survive cold winters and hot summers.

[[Page 78103]]

Periodic, Localized Declines in Arizona Populations
    There are no records of actual extirpations of Sonoran desert 
tortoises from any of the monitored populations. However, periodic, 
localized, and sometimes substantial declines have been documented in 
at least five of 17 monitored populations (Hart et al. 1992, p. 60; 
Averill-Murray et al. 2002b, p. 124; AGFD 2010, p. 4). Because of their 
life history, Sonoran desert tortoise populations may be slow to 
rebound from declines (Howland and Rorabaugh 2002, p. 340). The AGFD 
(2010, p. 4) suggested that observed declines in certain plots 
demonstrate localized, stochastic events and are not indicative of 
population trends as a whole across the distribution of the Sonoran 
desert tortoise. Sonoran desert tortoise populations are particularly 
vulnerable to elevated mortality of adults. Sustaining the adult, 
reproductive age class within Sonoran desert tortoise populations is 
important because mortality rates of juveniles are high and because it 
takes a long time for a Sonoran desert tortoise to reach sexual 
maturity (Howland and Rorabaugh 2002, p. 339). The relatively higher 
visibility of adult Sonoran desert tortoises leaves them more 
vulnerable to human impacts like collecting or shooting, and their 
tendency to move longer distances make them more susceptible to road 
mortality (Howland and Rorabaugh 2002, p. 340).
    The largest population decline noted at any Sonoran desert tortoise 
monitoring plot was observed on the Maricopa Mountains plot, where 
substantially more tortoise carcasses were found than live tortoises in 
successive years from 1987 through 1991 (Hart et al. 1992, p. 54; 
Averill-Murray et al. 2002b, p. 124). Regional drought from 1984-1992 
was a suspected cause of the die-off of Sonoran desert tortoises in the 
Maricopa Mountains (Hart et al. 1992, p. 60; Averill-Murray et al. 
2002b, p. 124). However, in 1987, the estimated density of Sonoran 
desert tortoises on the Maricopa Mountains plot was 
uncharacteristically high at 146 tortoises per square mile (2.6 sq km), 
suggesting that the population may have been in the process of 
naturally correcting to carrying capacity (the state at which a 
population level is commensurate with available resources) (AGFD 2010, 
p. 3). Since 1991, the Sonoran desert tortoise population on the 
Maricopa Mountains plot has experienced relatively high survivorship 
and shown evidence of reproduction. No additional carcasses have been 
documented, indicating the population may be stable, if not returning 
to the previous 1987 level (AGFD 2010, p. 3).
    The AGFD (2010, p. 3) and Hart et al. (1992, p. 120) confirm 
Sonoran desert tortoise populations declined from initial population 
estimates (as demonstrated by density estimates and relative carcass 
numbers) on three additional plots (Hualapai Foothills, San Pedro 
Valley, and East Bajada), suspecting that drought conditions may have 
played a role in the observed declines on these plots (Ogden 2009, pp. 
12-13). An observed decline on the Tortilla Mountains plot in 2001 may 
have been an artifact of low surface activity in response to below-
average precipitation, because an increase in carcasses was not 
detected (AGFD 2010, p. 3).
    For detailed information on monitoring and survey results from the 
previous three decades for the Sonoran desert tortoise in Arizona, see 
the following reports: Schneider (1981), Shields and Woodman (1987), 
Wirt (1988), Woodman and Shields (1988), Holm (1989), Shields et al. 
(1990), SWCA (1990a; 1990b; 1990c), Hart et al. (1992), Murray and 
Schwalbe (1993; 1997), Woodman et al. (1993; 1994; 1995; 1996; 1998; 
1999a; 1999b; 2000; 2001; 2002; 2003; 2004; 2005; 2006; 2007; 2008; 
2009), AIDTT (2000, pp. 5-6), Averill-Murray (2000, pp. 3-7), Averill-
Murray and Klug (2000, pp. 3-25), Averill-Murray et al. (2002b, pp. 
110-112), Walker and Wood (2002), Young et al. (2002), and Zylstra and 
Swann (2009).
    It should be noted that an average generation time for a Sonoran 
desert tortoise is 12-15 years and that monitoring of Sonoran desert 
tortoise populations has only occurred for about 30 years, representing 
approximately two generations. Many threats described below have been 
potentially acting on Sonoran desert tortoise populations for many 
decades, longer than populations have been studied. Below, we discuss 
the effects of various threats to individual Sonoran desert tortoises. 
However, due to limitations in monitoring data, we are unable to 
discern how Sonoran desert tortoise populations may have responded to 
these threats over time, or identify any long-term, historical trends 
in tortoise populations. We have not observed any extirpations among 
monitored populations.

Distinct Population Segment

    We consider a species for listing under the Act if available 
information indicates such an action might be warranted. ``Species'' is 
defined by the Act as including any subspecies of fish or wildlife or 
plants, and any distinct population segment (DPS) of any species of 
vertebrate fish or wildlife that interbreeds when mature (16 U.S.C. 
1532(16)). We, along with the National Marine Fisheries Service (now 
the National Oceanic and Atmospheric Administration--Fisheries), 
developed the Policy Regarding the Recognition of Distinct Vertebrate 
Population Segments (61 FR 4722; February 7, 1996), to help us in 
determining what constitutes a DPS. The policy identifies three 
elements that are to be considered regarding the status of a possible 
DPS. These elements include: (1) The discreteness of the population 
segment in relation to the remainder of the taxon (group of similar 
biological organisms); (2) the significance of the population segment 
to the taxon to which it belongs; and (3) the population segment's 
conservation status in relation to the Act's standards for listing 
(i.e., whether the population segment, when treated as if it were a 
species, is endangered or threatened) (61 FR 4722, February 7, 1996). 
The first two elements are used to determine if a population segment 
constitutes a valid DPS. If it does, then the third element is used to 
consider whether such DPS warrants listing. In this section, we will 
consider the first two criteria (discreteness and significance) to 
determine if the Sonoran desert tortoise is a valid DPS (i.e., a valid 
listable entity). Our policy further recognizes it may be appropriate 
to assign different classifications (i.e., threatened or endangered) to 
different DPSs of the same vertebrate taxon (61 FR 4722).

Discreteness

    Under the DPS policy, a population segment of a vertebrate species 
may be considered discrete if it satisfies either one of the following 
two conditions:
    (1) It is markedly separated from other populations of the same 
taxon as a consequence of physical, physiological, ecological, or 
behavioral factors. Quantitative measures of genetic or morphological 
discontinuity (separation based on genetic or morphological characters) 
may provide evidence of this separation.
    (2) It is delimited by international governmental boundaries within 
which significant differences in control of exploitation, management of 
habitat, conservation status, or regulatory mechanisms exist that are 
significant in light of section 4(a)(1)(D) of the Act.
    Based upon available information, the international boundary 
between Mexico and the United States is not considered for delineation 
of discreteness because

[[Page 78104]]

the edge of the DPS is not located at the International Border and, 
therefore, will not be addressed further.
    The Colorado River and R[iacute]o Yaqui are two perennial rivers 
that form biogeographical barriers (a natural barrier that prevents the 
migration of species) to movement of tortoises between the Mojave and 
Sonoran desert tortoise populations, and between the Sonoran and 
Sinaloan desert tortoise populations, respectively. The Colorado River, 
separating California and Arizona, comprises the northern and western 
boundaries of the Sonoran desert tortoise population as identified in 
the April 2, 1990, final rule designating the Mojave population of the 
desert tortoise (occurring north and west of the Colorado River) as a 
threatened species under the Act (55 FR 12178; see final rule for a 
summary of previous actions regarding the Mojave population of the 
desert tortoise). The eastern boundary is the extent of the range of 
the Sonoran desert tortoise where desert habitats end and grassland, 
chaparral, and mountain habitats begin, which are areas that do not 
contain desert tortoises. The southern boundary of the Sonoran desert 
tortoise DPS, as considered in this finding, is the R[iacute]o Yaqui in 
southern Sonora, Mexico; south and east of there, desert tortoises are 
considered Sinaloan populations. Potential threats to the Sinoloan 
desert tortoise are not evaluated as part of this finding.
    In view of this biogeographical isolation, significant ecological 
divergence has occurred between the Mojave and Sonoran populations of 
desert tortoise, largely due to significant differences in geology, 
vegetation types, and precipitation cycles where the populations are 
distributed. Desert tortoises in the Mojave population are most dense 
in the intermountain valleys that have soil types favorable to the 
construction of large, deep burrows (Bury et al. 1994, pp. 66-70). 
However, Sonoran desert tortoises reach maximum densities in the rocky 
bajadas and hillsides of higher slopes, with reduced densities in the 
intermountain valleys (Berry 1984, p. 434; AIDTT 2000; p. 4; Van 
Devender 2002a, p. 7; Brennan and Holycross 2006, p. 54; Zylstra and 
Steidl 2008, p. 747). At the southern end of the DPS, Edwards et al. 
(2009, pp. 7-8) suggested that Sinaloan population of desert tortoise 
uses Sinaloan thornscrub and tropical deciduous forest habitats. These 
different habitat types with differing soils and vegetation communities 
are created by higher precipitation levels. However, some level of 
gradation may occur in the vegetative transition zone between Plains of 
Sonora subdivision of Sonoran desertscrub and Sinaloan thornscrub 
habitats of central Sonora such as in the vicinity of the R[iacute]o 
Yaqui (Edwards et al. 2009, p. 8).
    In addition to habitat differences, morphological differences have 
also been documented among the three populations of desert tortoise. 
Several morphological differences in carapace size and shape have been 
documented between the Mojave, Sonoran, and Sinaloan populations of 
desert tortoise: The carapace of the Mojave desert tortoise is the 
widest and tallest of the three, the Sinaloan desert tortoise carapace 
is the most narrow and least domed, and the carapace of the Sonoran 
desert tortoise is intermediate between the two in those dimensions 
(Germano 1993, pp. 324-325; AGFD 2001, p. 1). Using eight independent 
shell measurements, Weinstein and Berry (1987, pp. 26-28) documented 
three distinct phenotypes (physical appearances) in desert tortoise 
populations within the United States based on morphometric (body 
measurement) analyses: The ``California'' phenotype (Mojave 
population), ``Beaver Dam Slope'' phenotype (Mojave form in Arizona), 
and the ``Sonoran type'' (Sonoran population). Desert tortoises from 
southern Sonora and northern Sinaloa in Mexico were not studied as part 
of this effort.
    Differences in reproduction strategies between the Sonoran and 
Mojave populations of desert tortoises also occur. Mojave desert 
tortoises lay up to three clutches of eggs per year with larger clutch 
sizes (more eggs), earlier in the year (April to mid-July) (Wallis et 
al. 1999, p. 405) while those in the Sonoran population lay one clutch 
per year of smaller size, later in the year (June through August) 
(Averill-Murray et al. 2002a, p. 141). These differences led Averill-
Murray (2002b, pp. 119-122) to the conclusion that Sonoran desert 
tortoises invest all reproductive effort into a single clutch which 
hatches at the peak of forage and water availability and abundance 
owing to late-summer rainfall. Whereas desert tortoises in the Mojave 
population (maturing at smaller body sizes) (Berry et al. 2002a, p. 
259) have higher clutch numbers to offset higher mortality from greater 
variability in environmental conditions.
    The Mojave, Sonoran, and Sinaloan populations of the desert 
tortoise have been found to have significantly differentiated genotypes 
(genetic characteristics) (Lamb and McLuckie 2002, p. 74; Van Devender 
2002a, p. 24). Genetic distances, expressed as percent sequence 
divergence (an estimate of percent difference in the genetic code), are 
substantial among the three populations of desert tortoise. Divergence 
is 5.1-5.6 percent between the Sonoran and Mojave populations, 4.2 
percent between the Sonoran and Sinaloan populations, and 5.1 percent 
between the Sinaloan and Mojave populations (Lamb and McLuckie 2002, 
pp. 74, 77). Considering geographic distribution, genealogical depth, 
and a suite of other characteristics, the Mojave, Sonoran, and Sinaloan 
populations of desert tortoise are considered to be ecologically 
significant units (populations or groups of populations historically 
isolated from one another, and thus representing deep phylogenetic 
(evolutionary development of species over time) subdivisions within 
species) (Lamb and McLuckie 2002, pp. 81-82). According to 
mitochondrial DNA markers, the Sonoran and Mojave populations appear to 
have diverged some 5 million years ago (Lamb et al. 1989, p. 83; Lamb 
and McLuckie 2002, p. 76).
    McCord (2002, p. 62) presented three possible causes of the 
significant genetic differentiation between Sonoran and Mojave desert 
tortoises. First, genetic differentiation between Sonoran and Mojave 
desert tortoises may have been the result of differences in rainfall 
patterns between the winter-dominated rainfall pattern of the Mojave 
Desert and the summer-dominated rainfall pattern of the Sonoran desert. 
Second, genetic differentiation between Sonoran and Mojave desert 
tortoises may have occurred because the Sonoran desert tortoises may be 
represented as a relict population (remnant survivor from the past) of 
the tropical deciduous forest-evolved population of the Sinaloan 
population (based upon their general absence in valley bottoms due to 
heavy flooding during summer rains, a phenomenon generally absent in 
the Mojave Desert). Last, genetic differences between Sonoran and 
Mojave desert tortoises may have resulted from their mutual competition 
with the Bolson tortoise (Gopherus flavomarginatus), another desert 
tortoise species which was widely distributed throughout Arizona in the 
Pleistocene, but which never occurred in California. The competing 
Bolson tortoise population may have acted as a wedge between the 
Sonoran and Mojave populations, driving them even farther apart, in a 
process known as competitive displacement.
    To explore the evolutionary track the three desert tortoise 
populations may have taken and the extent of their current genetic 
differentiation on the landscape, Edwards et al. (2009, p. 8) collected 
genetic samples from desert

[[Page 78105]]

tortoises within three regions of Sonora, Mexico: Twenty-two samples 
from near Alamos, Sonora (tropical deciduous forest in extreme southern 
Sonora), 19 samples from near Ciudad Obreg[oacute]n (foothill 
thornscrub in south-central Sonora, south of the R[iacute]o Yaqui), and 
14 samples from two sites north of Hermosillo (Sonoran desertscrub in 
central Sonora). When they compared genetic data with previously 
collected samples from Arizona, they found a ``continuum of genetic 
similarity'' in genetic samples taken from desert tortoises from the 
Hermosillo area of Sonora, Mexico, 528 mi (850 km) northwest to the 
Kingman, Arizona area when they compared genetic data with previously 
collected samples from Arizona (Edwards et al. 2009, p. 8). This 
confirms the similar genetic relationships of Sonoran desert tortoises 
throughout the DPS. Genetic samples from the Ciudad Obreg[oacute]n 
region, southward, showed clear genetic distinction and supported prior 
evidence for a third distinct population of desert tortoise, referred 
to as the Sinaloan population (Edwards et al. 2009, p. 8). The southern 
limits of desert tortoise distribution in northern Sinaloa are likely 
influenced by the growth of disease-causing bacteria and fungi present 
in the soil of burrows, exacerbated by the hot, humid, and wet 
conditions during tropical summer rainy seasons (Van Devender 2002b, p. 
43).
Evaluation of Discreteness
    Some biological similarities do exist among the three populations 
of desert tortoise (Mojave, Sonoran, and Sinaloan). For example, some 
overlap in habitat use occurs. It is well known that Sonoran desert 
tortoises generally occur on steep, rocky slopes and bajadas in 
contrast to the Mojave desert tortoise, which occurs primarily along 
the valley bottoms. But to a lesser extent, Sonoran desert tortoises 
also use valley bottoms and Mojave desert tortoises also use steep 
slopes and mountain bajadas (Gardner and Brodie 2000, p. 51; Averill-
Murray and Averill-Murray 2002, p. 16; Lutz et al. 2005, p. 22; 
Grandmaison et al. in press, p. 4; Riedle et al. 2008, p. 418). 
However, there are many more numerous and convincing data in the 
scientific literature to support the discreteness of the three 
recognized populations of Gopherus agassizii, including differences in 
their ecology, behavior, morphology, physiology, and genetics 
(Weinstein and Berry 1987, pp. 26-28; Germano 1993, pp. 324-325; 
Germano et al. 1994, p. 82; AGFD 2001, p. 1; Averill-Murray 2002b, pp. 
299-300; Berry et al. 2002a, p. 259; Lamb and McLuckie 2002, pp. 74, 
77; McCord 2002, p. 62; Van Devender 2002a, pp. 24-25; Van Devender 
2002b, p. 45; Zylstra and Steidl 2008, p. 747; Edwards et al. 2009, p. 
8).
    We have reviewed the best available commercial and scientific 
information and find that the Sonoran population of the desert tortoise 
as it occurs east and south of the Colorado River, south to the 
R[iacute]o Yaqui, in Sonora, Mexico, is discrete, under the Service's 
DPS policy, from the Mojave and Sinaloan desert tortoise populations. 
We base this conclusion on ecological (habitat use), physiological 
(reproductive characteristics), morphological (shell dimensions), and 
behavioral (seasonal activity patterns) differences that are further 
supported by analysis of genetic differences that concluded significant 
divergence has occurred among the three populations.

Significance

    If a population segment is considered discrete under one or more of 
the conditions described in the Service's DPS policy, its biological 
and ecological significance will be considered in light of 
Congressional guidance that the authority to list DPSs be used 
``sparingly'' while encouraging the conservation of genetic diversity. 
In making this determination, we consider available scientific evidence 
of the discrete population segment's importance to the taxon to which 
it belongs. Since precise circumstances are likely to vary considerably 
from case to case, the DPS policy does not describe all the classes of 
information that might be used in determining the biological and 
ecological importance of a discrete population. However, the DPS policy 
describes four possible classes of information that provide evidence of 
a population segment's biological and ecological importance to the 
taxon to which it belongs. As specified in the DPS policy (61 FR 4722), 
this consideration of the population segment's significance may 
include, but is not limited to, the following:
    (1) Persistence of the discrete population segment in an ecological 
setting unusual or unique to the taxon;
    (2) Evidence that loss of the discrete population segment would 
result in a significant gap in the range of a taxon;
    (3) Evidence that the discrete population segment represents the 
only surviving natural occurrence of a taxon that may be more abundant 
elsewhere as an introduced population outside its historic range; or
    (4) Evidence that the discrete population segment differs markedly 
from other populations of the species in its genetic characteristics.
    A population segment needs to satisfy only one of these conditions 
to be considered significant. Furthermore, other information may be 
used as appropriate to provide evidence for significance.
    The current range of the Sonoran desert tortoise, as described in 
the discussion above pertaining to discreteness, represents several 
hundred miles of occupied habitat spanning across an international 
border. This population segment is confined by two large perennial 
rivers: The Colorado River in its northern periphery (separating the 
Mojave and Sonoran populations), and the R[iacute]o Yaqui at its 
southern periphery (separating the Sonoran and Sinaloan populations). 
These two rivers represent significant biogeographical barriers to 
genetic exchange between adjacent population segments and, therefore, 
preclude recolonization of this expanse of habitat from adjacent 
populations, should the Sonoran population of the desert tortoise 
become extirpated. Thus, the loss of the Sonoran desert tortoise would 
constitute a significant gap of several hundred miles in the range 
between the Mojave and Sinaloan populations of desert tortoises, and 
may constitute as much as 40 percent of the total range occupied by 
desert tortoises as a whole, rangewide, which affirms its significance 
to the entire species.
    In addition, our evaluation of discreetness above found extensive 
scientific support concluding that the Sonoran desert tortoise differs 
significantly in its behavior (reproduction, seasonal activity), 
ecology (habitat use and burrow construction), morphology (physical 
characteristics), and genetics from either the Sinaloan or the Mojave 
populations. Because of these distinctions, the loss of the Sonoran 
desert tortoise population would result in the permanent loss of a 
unique biological entity and would diminish the natural variation 
within the species as a whole.
Evaluation of Significance
    We have reviewed the best available commercial and scientific data, 
and based on that review, we find that the Sonoran desert tortoise is 
significant to the continued existence of the taxon. We base this 
conclusion on: (1) The large geographic range of the Sonoran 
population, which is significant (approximately 40 percent) to the 
taxon as a whole; (2) a gap of several hundred miles that would result 
from the loss of the Sonoran population, which would effectively bisect 
the species' range; and

[[Page 78106]]

(3) the behavioral, ecological, physical, and genetic distinctions 
among the three desert tortoise populations.

Determination of Distinct Population Segment

    Based on our review of the best commercial and scientific 
information available, the Sonoran population of desert tortoise is 
discrete from the Mojave and Sinaloan populations and significant to 
the species as a whole. As a result, we have determined that the 
Sonoran population of desert tortoise qualifies as a DPS and a listable 
entity under the Act.
    In the August 23, 2009, 90-day finding (74 FR 44335), we discussed 
a local population of Mojave-genotype (genotype: genetic code) desert 
tortoises (that also share Mojave phenotype (the physically-expressed 
genetic code) and habitat-use characteristics with the Mojave desert 
tortoise population) occurring within the delineated Sonoran population 
in the Black Mountains area of western Mohave County, Arizona. This 
population is isolated from the threatened Mojave DPS that occurs north 
and west of the Colorado River. The exact geographic extent of this 
Mojave-genotype in Arizona is currently undefined and we expect there 
is interbreeding between desert tortoises with the Mojave and Sonoran 
genotype along the periphery of this population in the Black Mountains. 
Therefore, we include this population of desert tortoises as part of 
our status assessment for the Sonoran desert tortoise in this finding.

Distinct Population Segment Five-Factor Analysis

    Section 4 of the Act (16 U.S.C. 1533) and implementing regulations 
(50 CFR part 424) set forth procedures for adding species to, removing 
species from, or reclassifying species on the Federal Lists of 
Endangered and Threatened Wildlife and Plants. Under section 4(a)(1) of 
the Act, a species may be determined to be endangered or threatened 
based on any of the following five factors:
    (A) The present or threatened destruction, modification, or 
curtailment of its habitat or range;
    (B) Overutilization for commercial, recreational, scientific, or 
educational purposes;
    (C) Disease or predation;
    (D) The inadequacy of existing regulatory mechanisms; or
    (E) Other natural or manmade factors affecting its continued 
existence.
    In making this finding, information pertaining to the Sonoran 
desert tortoise in relation to the five factors provided in section 
4(a)(1) of the Act is discussed below.
    In considering what factors might constitute threats to a species, 
we must look beyond the exposure of the species to a particular factor 
to evaluate whether the species may respond to that factor in a way 
that causes actual impacts to the species. If there is exposure to a 
factor and the species responds negatively, the factor may be a threat 
and, during the status review, we attempt to determine how significant 
a threat it is. The threat is significant if it drives, or contributes 
to, the risk of extinction of the species such that the species 
warrants listing as endangered or threatened as those terms are defined 
in the Act. However, the identification of factors that could impact a 
species negatively may not be sufficient to compel a finding that the 
species warrants listing. The information must include evidence 
sufficient to suggest that these factors are operative threats that act 
on the species to the point that the species may meet the definition of 
endangered or threatened under the Act.
    In our review of the best scientific and commercial data available, 
we found numerous threats are impacting Sonoran desert tortoises or 
their habitat throughout their range. Some of these threats occurred 
historically, some are current, and some will continue into the 
foreseeable future. As described in detail below, these threats include 
nonnative plant species and altered fire regimes, urban and 
agricultural development, barriers to dispersal and genetic exchange, 
off-highway vehicles, roads and highways, ironwood and mesquite tree 
harvest, improper livestock grazing, undocumented human immigration, 
illegal collection, effects from field research and manipulation, 
predation from feral dogs, human depredation and vandalism, drought, 
and climate change. The effect of habitat disturbances on Sonoran 
desert tortoises may differ among age classes, but may be most 
significant to hatchlings or juveniles (Tracy et al. 2006b, pp. 271-
272).

Factor A. The Present or Threatened Destruction, Modification, or 
Curtailment of Its Habitat or Range.

Nonnative Plant Species and Altered Fire Regimes
    The most significant modification to Sonoran desert tortoise 
habitat is associated with the ongoing invasion of nonnative plants in 
Mojave and Sonoran desertscrub habitats, permanently altering these 
ecosystems and causing a change in the frequency, duration, intensity, 
and magnitude of wildfires in a region that largely evolved in the 
absence of invasive nonnative plants. These ecosystem-level changes 
cause both direct and indirect effects on the Sonoran desert tortoise 
and its habitat.
    Much of the available research on the effects of nonnative plant 
species invasions and wildfire used in our analysis has focused on 
Mojave desertscrub habitats, largely due to the presence of the Mojave 
desert tortoise, which is already listed as endangered. However, Brooks 
and Matchett (2006, p. 158) suggest that research from the Mojave 
Desert is applicable to the Sonoran Desert when stating, ``Both (Mojave 
and Sonoran deserts) occur at elevations above the hyperarid 
shrublands, are often positioned on the lower slopes of mountain 
ranges, and possess moderate woody plant cover.'' Therefore, we used 
the information available from research on Mojave Desert habitats in 
our assessment of the effects of nonnative plants in the Sonoran 
Desert.
    Nonnative perennial plants like buffelgrass, fountain grass, and 
Lehmann lovegrass were historically introduced to the Sonoran Desert of 
Arizona as livestock forage and to prevent soil erosion. For example, 
buffelgrass was included in the nonnative plant species recommended for 
release by the Tucson Plant Materials Center of the Soil Conservation 
Service until at least 1987 (Bahr 1991, p. 156). These nonnative plant 
species subsequently became common and widespread in Sonoran 
desertscrub in Arizona (Brooks and Pyke 2001, p. 5). They have since 
colonized new areas, often taking advantage of disturbed soils, such as 
those resulting from construction associated with roadways, power 
lines, and railroad tracks (Bahre 1991, p. 155; D'Antonio and Vitousek 
1992, p. 65). Construction and maintenance of roads and highways can 
also significantly enhance the likelihood of nonnative plant invasions 
by increasing nitrogen deposition in the soil, the dispersal potential 
of nonnative seeds, and adjacent soil moisture (Brooks 2007, pp. 153-
154). Roadside ditches along highways are particularly important 
dispersal corridors for nonnative plant species such as red brome and 
buffelgrass (Esque et al. 2002, p. 313).
    Mechanisms that allow the spread of nonnative species generally 
pertain to ground disturbance, but the plants may also be spread by 
other mechanisms. For example, Smith et al. (2000, pp. 79-80), and 
Brooks and Esque (2002, p. 337) both found that elevated atmospheric 
carbon dioxide levels, predicted as a result of climate change 
(discussed in

[[Page 78107]]

Factor E below), are likely to favor nonnative plant species, such as 
red brome, over native species in desertscrub habitats. Increases in 
atmospheric nitrogen deposition may also be advantageous to nonnative 
plant species. Brooks (2003, pp. 344-345) suspected that increasing 
human populations will lead to increased levels of atmospheric 
pollution and nitrogen deposition and stated, ``Increased levels of 
soil nitrogen caused by atmospheric nitrogen deposition may increase 
the dominance of invasive alien plants and decrease the diversity of 
(native) plant communities in desert regions, as it has in other 
ecosystems.'' Sonoran desert tortoise habitat may be particularly 
vulnerable to even minor increases in soil nitrogen levels, because the 
ratio of increased nitrogen to plant biomass is higher compared with 
that of most other ecosystems (Brooks 2003, p. 344). This suggests that 
even small changes in nitrogen levels could result in substantial 
changes in the plant community that supports Sonoran desert tortoise 
habitat.
    The prevalence of nonnative grasses in many areas of Sonoran 
desertscrub habitats has resulted in high amounts of flammable fuels in 
interspaces between native plants that would otherwise be free of 
vegetation. This situation serves to promote the ignition and carrying 
of wildfire (Brooks 1999, p. 13). In our review of the best scientific 
data available, red brome, splitgrass (or Mediterranean grass, Schismus 
spp.), and buffelgrass were considered the nonnative plant species that 
pose the greatest concern to the Sonoran desert tortoise and its 
habitat, because they are thoroughly integrated into some areas of the 
desertscrub communities, and serve to promote and carry wildfire (Bahre 
1991, p. 155; D'Antonio and Vitousek 1992, pp. 65, 75; Brooks 1999, p. 
13; Brooks and Pyke 2001, p. 5; Brooks and Esque 2002, p. 337; Esque et 
al. 2002, p. 313; Van Devender 2002a, p. 16; Brooks and Matchett 2006, 
p. 148; DeFalco 2007a, p. 1; Zouhar et al. 2008, p. 157; Abella 2010, 
p. 1249; AGFD 2010, p. 13). Red brome is known to carry wildfire in 
Sonoran desertscrub habitat north of Tucson, natal grass is known to 
carry wildfire in desert grassland habitat south of Tucson to Nogales, 
Arizona, and buffelgrass is known to carry wildfire in Sonoran 
desertscrub and foothills thornscrub south of the international border 
to central Sonora (Esque et al. 2002, p. 316). Other nonnative plant 
species identified in the literature as present in Sonoran and Mojave 
desertscrub communities include Saharan (or Asian) mustard (Brassica 
tournefortii), thistles (genera Centaurea and Cirsium), crimson 
fountaingrass (Pennisetum setaceum), natal grass (Melinus repens), and 
Lehmann lovegrass (Eragrostis lehmanniana) (Brooks 2001, p. 4; Brooks 
and Pyke 2001, pp. 3, 5).
    We are not aware of any good estimates of the number of acres of 
desertscrub that have been invaded by nonnative plant species, but 
Thomas and Guertin (2007, Appendices I and II) calculated the number of 
records by county for many known invasive, nonnative plants in Arizona 
that are harmful to Sonoran desert tortoise habitat. These data 
illustrate general locations where certain nonnative species are most 
common and describe which nonnative species are the most reported in 
each area. Thomas and Guertin (2007, Appendices I and II) reported the 
following for Arizona as of 2007 (relative number of reports of 
densities being ``extremely high,'' ``high,'' ``moderate,'' and 
``occurs,'' all within the distribution of the Sonoran desert 
tortoise):
    (1) Buffelgrass is the most-reported nonnative plant species in 
Arizona, at 16.3 percent of total reports with 6,287 reports (p. 3); it 
reaches extremely high densities in Maricopa and Pima Counties, with 
high densities in Pinal and Yuma Counties and moderate densities in 
Santa Cruz and La Paz Counties, but it also occurs in Yavapai, Gila, 
and Cochise Counties (A-I, p. 60);
    (2) Schismus spp. is one of the top 20 invasive plant species, at 
2.4 percent of total reports, with 919 reports (p. 3); it reaches high 
densities in Maricopa, Pinal, and Pima Counties, with moderate 
densities in Mohave, Yavapai, Gila, La Paz, and Yuma Counties, but it 
also occurs in Santa Cruz County (A-I, p. 69);
    (3) Red brome is one of the top 20 invasive plant species, at 3 
percent of total reports, with 1,152 reports (p. 3); it reaches high 
densities in Yavapai, Gila, Pinal, and Pima Counties, with moderate 
densities in Mohave and Maricopa Counties, but it also occurs in La Paz 
and Yuma Counties (A-I, p. 24);
    (4) Saharan mustard is one of the top 20 invasive plant species, at 
3.3 percent of total reports, with 1,261 reports (p. 3); it reaches 
high densities in Maricopa, Pinal, Pima, La Paz, and Yuma Counties, 
with moderate densities in Mohave, Yavapai, and Gila Counties, but it 
also occurs in Cochise County (A-I, p. 21);
    (5) Centaurea spp. had a total of 3-318 reports (depending on 
species) (p. 9) and reaches high densities in Pima County, with 
moderate densities in Mohave, Yavapai, Gila, Pinal, and Cochise 
Counties (A-I, pp. 15, 28-30);
    (6) Bull thistle (Cirsium vulgare) is one of the top 20 invasive 
plant species, at 3.1 percent of total reports, with 1,195 reports (p. 
3); it reaches moderate densities in Yavapai and Gila Counties (A-I, p. 
35);
    (7) Crimson fountaingrass is one of the top 20 invasive plant 
species, at 2.6 percent of total reports, with 999 reports (p. 3); it 
reaches high densities in Pima County, with moderate densities in 
Yavapai, Gila, La Paz, Santa Cruz, and Maricopa Counties (A-I, p. 61); 
and
    (8) Lehman lovegrass is one of the top 20 invasive plant species, 
at 2.5 percent of total reports, with 980 reports (p. 3); it reaches 
high densities in Pima and Cochise Counties, with moderate densities in 
Yavapai, Gila, Santa Cruz, Maricopa, and Pinal Counties, but also 
occurs in La Paz County (A-I, p. 45).
    No spatial data were provided for natal grass, but there were 191 
observations (Thomas and Guertin 2007, p. 10).
    Buffelgrass has widely invaded Arizona and northern Mexico since 
its introduction in 1939 (Stevens and Fehmi 2009, p. 379). While 
buffelgrass invasions are occurring and are poised to seriously impact 
the southwestern United States, the species has already exacted 
significant tolls on Sonoran desertscrub communities in Sonora, Mexico, 
because its expansion continues to be facilitated through intentional 
plantings and cultivation. Consequently, the clearing of Sonoran 
desertscrub and Sinaloan thornscrub in Sonora to plant pastures of 
buffelgrass for livestock grazing creates a near monoculture (area 
covered by a single plant species) that is highly prone to wildfires, 
and therefore represents a substantial threat to the Sonoran desert 
tortoise in Mexico (Bury et al. 2002, p. 104; Walker and Pavlakovich-
Kochi 2003, p. 14; Van Devender and Reina 2005, pp. 160-161; University 
of Arizona 2010, p. 2). Buffelgrass has been planted in Sonora's 
desertscrub lands since the 1950s and at least 5.5 million ac (2.2 
million ha) of potential Sonoran desert tortoise habitat has already 
been converted into a near monoculture of buffelgrass (Stoleson et al. 
2005, p. 62). Buffelgrass has become established in both the lower 
valley habitats and into the granite boulder-strewn areas of adjacent 
foothills, and has altered historical fire regimes, regionally 
converting large areas of Sonoran desertscrub into habitat resembling 
the African savannah (Bury et al. 2002, p. 104).
    In Arizona, the Southern Arizona Buffelgrass Coordination Center

[[Page 78108]]

(SABCC, a coalition of non-profit organizations, Federal, State, and 
local governments, conservation organizations, private businesses, and 
individual citizens) reports dense stands of buffelgrass on public 
reserves, State and local lands, and private property, including 
Saguaro National Park, Coronado National Forest, Bureau of Land 
Management's (BLM) Ironwood Forest National Monument, neighborhoods of 
Tucson, Sahuarita, Marana and Oro Valley, and along roadsides 
throughout this region of Arizona (SABCC 2010, p. 1) These areas are 
all within the distribution of the Sonoran desert tortoise in Arizona.
    Brooks and Minnich (2006, p. 9) stated that southwestern desert 
ecosystems likely evolved in a fire regime best described by ``low 
intensity, patchy burns and long fire return intervals.'' Wildfire 
capable of carrying itself in Sonoran desertscrub is a recent 
phenomenon in evolutionary and geological contexts and only became 
apparent recently in the Sonoran Desert (Brooks and Pyke 2001, p. 5; 
Esque et al. 2002, p. 312; Zouhar et al. 2008, pp. 155, 160). From 1937 
to 1986, only 1 percent of all lightning-caused fires in the Rincon 
Mountains area of southern Arizona occurred in desertscrub habitat; 5.6 
percent occurred in desert grassland habitat (Bahre 1991, p. 126). 
While historical wildfires in desertscrub habitat were exceptionally 
rare, after successive years of above-average levels of precipitation, 
enough native fuels can develop to carry wildfire in desertscrub 
communities, such as happened south of Florence, Arizona in 1979 (Bahre 
1991, p. 141; Brooks and Esque 2002, p. 336; Brooks and Minnich 2006, 
p. 9). While increased precipitation enhances plant growth and 
subsequently increases the likelihood for wildfire starts in 
desertscrub habitat, drought can have an inverse effect with respect to 
certain nonnative plant species. Red brome, for example, is sensitive 
to drought conditions and, therefore, might contribute to reduced fuel 
loads and decreased fire frequency during long-term drought (Brooks and 
Esque 2002, p. 337), which might help to minimize the likelihood of 
wildfires in areas where red brome has formed a monoculture. Smith et 
al. (2000, p. 79) noted, ``This shift in species composition in favor 
of exotic annual grasses, driven by global [climate] change, has the 
potential to accelerate the fire cycle, reduce biodiversity and alter 
ecosystem function in the deserts of western North America.''
    Wildfire ignitions in the Sonoran Desert region historically 
resulted from lightning but ignitions are now more common from human 
sources such as burning trash, parking vehicles over dry vegetation, 
fireworks, discarded cigarettes, and accidental starts from backcountry 
recreationists (Esque et al. 2002, p. 313). Human-caused wildfires in 
desertscrub habitat are most common near urban developments, major 
roadways, and in areas where off-highway vehicle use is unregulated, 
while lightning-caused wildfire in desertscrub is typically located in 
more remote wilderness areas (Brooks 1999, p. 13). In central Sonora, 
ranchers intentionally set fires to maintain the vigor of buffelgrass 
for livestock forage (Esque et al. 2002, p. 313).
    Numerous wildfires, varying in size, have occurred in recent times 
in many areas throughout the Sonoran Desert including the: (1) Pusch 
Ridge Fire of 1987 on the southern slopes of the Santa Catalina 
Mountains; (2) Skyline (1992) and Rock Peak (1993) fires in the San Tan 
Mountains; (3) Mother's Day Fire of 1994 on the eastern slope of the 
Rincon Mountains (Esque et al. 2002, p. 323; 2003, p. 104); and (4) 
Cave Creek Complex fire of 2005 northeast of Cave Creek, Arizona, which 
burned 248,310 ac (100,487 ha) of Sonoran desert tortoise habitat; the 
largest wildfire ever recorded in Sonoran desertscrub in the United 
States.
    The BLM has kept records of wildfire in Sonoran desert tortoise 
habitat. From 1990 to 2008, there have been 61 wildfires, affecting 
21,977 ac (8,894 ha) in Category I Sonoran desert tortoise habitat; 285 
wildfires, affecting 33,364 ac (13,502 ha) in Category II Sonoran 
desert tortoise habitat; and 508 wildfires, affecting 109,460 ac (44, 
297 ha) in Category III Sonoran desert tortoise habitat (USBLM 2010, p. 
9). In total, during the 1990-2008 period, 164,801 ac (66,693 ha) of 
categorized and uncategorized Sonoran desert tortoise habitat has 
burned on BLM lands (USBLM 2010, p. 9). Combining the known area of 
habitat affected by fire on both BLM and other lands, an estimated 1.5 
percent of habitat in Arizona has been adversely affected due to 
wildfire in recent years; rangewide this is estimated to be 0.8 
percent, although total acreage data on wildfires in Mexico are unknown 
and the total percentage of affected habitat is likely higher because 
of the higher incidence of buffelgrass and lessened capacity to fight 
wildfire in Sonora, Mexico. The total area reported as burned is a 
relatively small proportion of BLM lands and has not likely been a 
significant impact to most Sonoran desert tortoise populations in 
Arizona so far. As the invasion of nonnative plants continues to 
expand, the high number of fire starts has a greater potential of 
creating larger and more destructive wildfires, especially where they 
occur in remote, inaccessible areas as a result of lightning strikes.
    Indirect effects of wildfires on Sonoran desert tortoises are 
variable and can be significant, including habitat changes such as 
altered nutrient availability and quality, loss of perennial plant 
species that are important as temporary cover from predators, loss of 
thermal refugia, altered tortoise behavior, shifts in biotic community, 
pronounced desert tortoise emigration from burned habitat, and lower 
growth and reproductive output (Esque et al. 2003, p. 107; DeFalco 
2006, p. 5; McLuckie et al. 2007, p. 8). While a single fire in an area 
may or may not produce long-term reductions in plant cover or biomass, 
repeated wildfires in a given area are capable of ecosystem type-
conversion from native desertscrub to nonnative annual grassland, and 
render the area unsuitable for desert tortoises (Brooks and Esque 2002, 
p. 336). Increased frequency in wildfires caused by nonnative plant 
species invasion increases light intensity at ground level and soil 
nutrient availability, and reduces competition from native perennial 
plants. These changes further promote dominance by nonnative plant 
species (Brooks and D'Antonio 2003, p. 29). Wildfire in desertscrub 
habitats can reduce native and nonnative seed banks (Brooks and Draper 
2006, p. 2). In Mojave desertscrub, the effects of fire are most 
pronounced under shrubs, where fire can kill seed banks and reduce 
annual grass diversity, due to higher burn intensity (Brooks 2002a, p. 
1; 2002b, p. 1088). Microhabitat associated with shrubs in Sonoran 
desert tortoise habitat is an important source of temporary shelter and 
provides foraging opportunities while tortoises are thermoregulating.
    Fires associated with nonnative plant species have already affected 
Sonoran desert tortoise populations in Arizona. The AGFD (2010, p. 13) 
reported results from an unpublished study after the Edge Complex Fire 
of 2005 in the Four Peaks area on the Tonto National Forest, which 
indicated higher numbers of Sonoran desert tortoises (or their scat 
were observed in unburned versus burned habitat), but they acknowledged 
that the study was preliminary and very limited in scope (AGFD 2010, p. 
13).
    In Sonora, Mexico, 5.5 million ac (2.2 million ha), representing an 
estimated 22 percent of Sonoran desert habitat in Mexico, or 11 percent 
rangewide, has been planted to bufflegrass. This figure still does not 
account for the land area

[[Page 78109]]

where buffelgrass has become naturally established or the 11.9 million 
ac (4.8 million ha) (or one-third of the land area of the state of 
Sonora) that are suitable for future natural establishment of 
buffelgrass (Stoleson et al. 2005, p. 62). Combining the current and 
predicted number of acres converted to buffelgrass in Mexico, 34 
percent of the Sonoran desert tortoises' habitat is lost or at risk 
across its range. In the area of El Batamote, 29 mi (47 km) north of 
Hermosillo, Sonora, buffelgrass has invaded Sonoran desert tortoise 
habitat in the adjacent foothills, which has led to wildfires that 
burned so hot that the soil was scorched and the bedrock cracked (Esque 
et al. 2002, p. 321).
    In addition to impacts from fire, Franklin and Molina-Freaner (in 
press, p. 1) found that these large-scale conversions from desertscrub 
to grasslands in Sonora have reduced plant species richness by half, 
and reduced tree and shrub cover by 78 percent, vastly affecting the 
ability of Sonoran desert habitat to meet the species' thermoregulatory 
needs (that is, using vegetation as cover to regulate body 
temperature). These changes have resulted in substantial changes in 
primary productivity (creation of organic nutrients and the lowest 
level of the food chain, the plant community) and vegetation structure 
(the physical structure of plant sizes and shapes as a mosaic on the 
landscape) which can affect the forage base and habitat suitability for 
Sonoran desert tortoises, as well as lessened the feasibility of 
restoring native plant communities in Sonora without aggressive land 
management (Franklin and Molina-Freaner, in press, p. 1). Dense stands 
of buffelgrass have also been shown to physically disrupt tortoise 
movements in the closely related Texas tortoises (Gopherus berlandieri) 
(Fujii and Forstner 2010, p. 61), so this may also be true for Sonoran 
desert tortoises. The grass can become so thick that the tortoises 
cannot walk through it, and the grass may be too tall for the tortoises 
to walk on top of it.
    In addition to damaging Mojave and Sonoran desertscrub habitat, 
wildfires can directly injure and kill Sonoran desert tortoises. 
Wildfire may kill a desert tortoise by incineration, by elevating body 
temperature, by poisoning from smoke inhalation, or by asphyxiation 
(Brooks et al. 1999, p. 40; Brooks and Esque 2002, p. 335; McLuckie et 
al. 2007, p. 7). Survival rates of Sonoran desert tortoises may be 
contingent upon several factors, including soil type, substrate, 
vegetation, tortoise activity during fire, whether tortoises are active 
and above ground or in shelter during a fire, weather, fire behavior, 
and shelter depth (McLuckie et al. 2007, p. 8). The desert tortoise is 
most vulnerable to the direct effects of wildfire when they are surface 
active and away from primary cover sites such as burrows, caliche 
caves, and rock shelters, because these structures reduce direct 
exposure to heat and smoke (Brooks and Esque 2002, p. 335). Gravid 
(with fertilized eggs) female Sonoran desert tortoises may be more 
likely to perish from wildfire than other tortoises because peak 
wildfire season in Sonoran desertscrub occurs during the months of May 
and June. This is when reproductive females are actively foraging on 
spring growth to compensate for energy used in egg development; (Esque 
et al. 2002, pp. 323-324; 2003, p. 106).
    Sonoran desert tortoises that survive the wildfire itself may 
struggle to survive in post-burned Sonoran desertscrub habitat due to: 
(1) A reduction in forage and shade structure, such as packrat (Neotoma 
sp.) middens and shrubs; and (2) increased visibility to predators 
(which may be further increased in intermountain valleys where 
temporary shade, predator avoidance, and available forage are 
particularly important in long-distance movements in these dispersal 
corridors) (Esque et al. 2002, pp. 325-326).
    The effects on Sonoran desert tortoises of one particular fire were 
studied in some detail. Within Saguaro National Park, the Mother's Day 
Fire of 1994 burned 340 ac (138 ha) of Arizona Upland Sonoran 
desertscrub habitat that was occupied by Sonoran desert tortoises, 
killing an estimated 11 percent of the tortoise population (Esque et 
al. 2003, p. 105). To assess how Sonoran desert tortoises used burned 
versus unburned habitat following this fire, transmitters were attached 
to 12 tortoises, 6 each in burned and unburned habitat within or 
adjacent to the Mother's Day Fire footprint. Surprisingly, no 
differences were observed in movement or activity patterns between 
tortoises in burned and unburned areas, nor were long-term effects of 
the fire on surviving tortoises noted over the 6-year study period 
(Zylstra and Swann 2009, p. 7). These results indicate that different 
tortoise populations may respond differently to wildfires and that 
numerous variables and factors are at work.
    One of the principal reasons that nonnative plants pose a 
significant impact to Sonoran desert tortoise habitat is because few, 
if any, reasonable methods currently exist to control the ongoing 
invasion of these plants or to remediate areas where they have become 
established. Mechanical removal is one option that has been implemented 
on a small scale in some areas, but is extremely labor intensive and 
not practical for treating large areas. Prescribed fire has been 
proposed as an alternative means to control nonnative plant species 
invasions, but also carries obvious inherent risks to habitat and to 
Sonoran desert tortoises (Brooks 2006, p. 31).
    It is also important to note the limitations of Sonoran desert 
habitat with respect to post-disturbance (for example, after fires) 
regeneration (ability for native vegetation to recover). Desertscrub 
regions receive low annual precipitation totals, and the plant 
communities have correspondingly low growth rates. Based on the type of 
disturbance, recovery time estimates range from 40 years to centuries 
(Abella 2010, pp. 1271, 1273). Combined, these factors result in slow, 
post-disturbance recovery periods and it may take a long time before 
any area becomes suitable for Sonoran desert tortoises to recolonize, 
if at all. The presence of nonnative species such as buffelgrass, 
cheatgrass, or red brome in disturbed Mojave or Sonoran desertscrub may 
further limit post-disturbance recovery, delay recovery, or prevent 
recovery altogether (Brown and Minnich 1986, p. 411; Brooks 1999, p. 
18).
    In our review of the best available information, we have documented 
that nonnative plant species pose a significant threat to the Sonoran 
desert tortoise and its habitat, both in Arizona and Sonora, by 
promoting and carrying wildfire in an ecosystem that evolved in its 
absence. Wildfires that are facilitated by nonnative plant species 
invasions may have direct and indirect adverse effects on tortoises and 
tortoise populations. The threat from nonnative plant species to the 
Sonoran desert tortoise occurs throughout the species' range and is 
expected to increase over time with the expansion of nonnative plants. 
There is currently no viable solution to curbing this continued 
expansion across the landscape. This threat also acts synergistically 
with other threats discussed in this finding.
Urban Development and Agriculture
    Human population growth results in the disturbance or loss of 
Sonoran desertscrub or the conversion of land for urban and 
agricultural development. Arizona increased its population by 394 
percent from 1960 to 2000, and was second only to Nevada as the fastest 
growing State during this timeframe (Social Science Data Analysis 
Network (SSDAN) 2000, p. 1). Since 1990, Arizona's population has grown 
by 44

[[Page 78110]]

percent. From 1960 to 2000, population growth rates in Arizona counties 
where the Sonoran desert tortoise occurs have varied by county but are 
no less remarkable, and all are increasing: Maricopa (463 percent); 
Pima (318 percent); Pinal (54 percent); Santa Cruz (355 percent); 
Cochise (214 percent); Yavapai (579 percent); Gila (199 percent); 
Graham (238 percent); Yuma (346 percent); LaPaz (142 percent); and 
Mohave (2,004 percent) (see SSDAN 2000). The population of Phoenix, 
Arizona, grew 67 percent from 1980 to 2000 (Berry et al. 2006, p. 7).
    Urban expansion and human population growth trends in Arizona are 
expected to continue into the future. Maricopa-Pima-Pinal county areas 
of Arizona are expected to grow by as much as 71 percent in the next 15 
years, creating rural-urban edge effects across millions of acres of 
public lands currently supporting Sonoran desert tortoise populations 
(AIDTT 2000, p. 10; BLM files--Lands Livability Initiative). In another 
projection, the population in Arizona is expected to more than double 
within the next 20 years compared to the 2000 population estimate (U.S. 
Census Bureau 2005, p. 1). Many cities and towns within the 
distribution of the Sonoran desert tortoise have already experienced 
substantial growth during the 8-year time span, 2000-2008: City of 
Avondale (118.3 percent); City of Buckeye (392.5 percent); Bullhead 
City (20.3 percent), Town of Carefree (30.5 percent); Casa Grande (56 
percent); Town of Cave Creek (44.2 percent); City of Chandler (37.5 
percent); City of Coolidge (24.9 percent); City of El Mirage (195.6 
percent); City of Eloy (22.3 percent); City of Florence (20.3 percent); 
Town of Fountain Hills (23.2 percent); City of Gilbert (84.5 percent); 
City of Goodyear (203 percent); City of Kingman (32.2 percent); Lake 
Havasu City (33.3 percent); City of Litchfield Park (34.2 percent); 
City of Mammoth (45 percent); Town of Marana (139.9 percent); City of 
Maricopa (2,508 percent); Town of Oro Valley (32.5 percent); Town of 
Queen Creek (544.5 percent); Town of Saguarita (507.3 percent); City of 
San Luis (58.5 percent); City of Somerton (63.2 percent); City of 
Surprise (187.3 percent); City of Tolleson (43.2 percent); and, Town of 
Youngtown (62.2 percent) (U.S. Census Bureau 2008, pp. 1-4).
    This population growth has spurred a significant increase in 
urbanization and development in these areas. Regional development is 
predicted to be extreme in certain areas within the distribution of the 
Sonoran desert tortoise in Arizona. In particular, a wide swath from 
the international border in Nogales, through Tucson, Phoenix, and north 
into Yavapai County (called the Sun Corridor ``Megapolitan'') is 
predicted to have 8 million people by 2030, an 82.5 percent increase 
from 2000 (Gammage et al. 2008, pp. 15, 22-23). If build-out occurs as 
expected, it will encompass a significant proportion of the Sonoran 
desert tortoise distribution in Arizona, and will in effect permanently 
isolate Sonoran desert tortoise populations that occur on either side 
of the Interstate 19, Interstate 10, and Interstate 17 corridors.
    The land area permanently altered by human activities from urban 
development and agriculture has grown to 13 percent of all land in the 
western United States, Lue et al. (2008, p. 1130). Lue et al. (2008, p. 
1133) concluded that in low-productivity habitat, such as desertscrub 
habitats, slight human disturbances can have pronounced effects. 
Significant urban development occurs within intermountain valleys, 
within or adjacent to occupied Sonoran desert tortoise habitat, which 
increases the likelihood of effects along the rural-urban interface, 
and may also inhibit movement of individuals between populations on 
nearby hillsides or mountain ranges. Disturbances to Sonoran desert 
tortoise habitat on the landscape can take many forms and cover extreme 
distances. Roads, canals, pipelines, and railroad tracks are examples 
of linear habitat destruction. We discuss the potential effects of 
linear disturbances below in the section titled, ``Development as a 
Barrier.''
    Development pressure across Arizona has slowed due to the recent 
economic downturn and decline in the housing market. However, 
development will likely continue in the future, although perhaps at a 
slower pace than in the earlier part of this century. We also recognize 
that economic trends are difficult to predict into the future. The most 
recent draft Pinal County Comprehensive Plan (February 2009) 
acknowledges that the county is in the middle of the Sun Corridor 
Megapolitan and proposes four shorter-term growth areas in defining 
where development will likely occur, or be encouraged to develop, over 
the next decade, but does not discourage growth outside of these areas 
(Pinal County Comprehensive Plan 2009, p. 109). These four growth areas 
(Gateway/Superstition Vistas, West Pinal, Red Rock, and Tri-
Communities) fall completely within the range of the Sonoran desert 
tortoise. The Gateway/Superstition Vistas growth area alone encompasses 
176,000 ac (71,225 ha), or 275 sq mi (712 sq km), of State Trust land, 
and it is anticipated that 800,000 to more than 1 million people will 
one day live in this development (Pinal County Comprehensive Plan 2009, 
p. 115). The loss of 176,000 ac (71,225 ha) constitutes a loss of 0.7 
percent of Sonoran desert tortoise habitat in Arizona; rangewide, 0.34 
percent. The Pinal County Comprehensive Plan (2009, p. 117) identifies 
many miles of new freeways and principal arterials in the analysis area 
at build-out, which the plan acknowledges may take over a half century 
to realize (Pinal County Comprehensive Plan 2009, p. 115). The effect 
of roads on Sonoran desert tortoises is discussed below.
    Additionally, the Maricopa County Comprehensive Plan calls for 
growth areas to the south and east of Chandler and Mesa, Arizona, which 
are within the range of the Sonoran desert tortoise (Maricopa County 
Comprehensive Plan 2002 (revised), p. 92). City comprehensive plans 
within the range of the Sonoran desert tortoise also call for future 
growth areas. For example, the City of Eloy has designated six such 
areas encompassing 15,520 ac (6,281 ha), mostly along the Interstate 10 
corridor (City of Eloy General Plan 2004, pp. 7-6 through 7-10). The 
loss of 15,520 ac (6,281 ha) constitutes a loss of 0.06 percent of 
their habitat in Arizona; rangewide, 0.03 percent. While much of this 
area has already been impacted by development or irrigated agriculture, 
any remaining dispersal habitat for the Sonoran desert tortoise will 
likely be negatively affected as development and its associated 
infrastructure progress into these areas.
    Much of the past and projected development within the range of the 
Sonoran desert tortoise in central and southwestern Arizona has 
occurred and is expected to continue as a conversion from agricultural 
uses to municipal uses. Land traditionally used for agriculture is not 
occupied by Sonoran desert tortoises, but has a comparatively minor 
effect on adjacent Sonoran desert tortoises. When these lands are 
converted to municipal uses, the effect to adjacent Sonoran desert 
tortoise populations increases human access, and use of adjacent 
undeveloped land increases as a result of development of these former 
agricultural areas.
    The human population of Sonora, Mexico, doubled in size from 1970 
(1.1 million) to 2000 (2.2 million) (Stoleson et al. 2005, p. 54). The 
population of Sonora is expected to increase by 23 percent, to 2.7 
million people, in 2020 (Stoleson et al. 2005, p. 54). In discussing 
threats to Sonoran desert tortoise populations adjacent to, and 
stemming from, urbanization in Sonora, Mexico, Fritts and Jennings 
(1994, p. 53)

[[Page 78111]]

stated, ``Tortoise populations adjacent to large population centers 
such as Hermosillo, Guaymas, and Caborca probably have experienced 
long-term harm, including direct human exploitation, habitat 
degradation, road kills, predation by domestic dogs, and use as pets. 
However, we found evidence of tortoise populations on hillsides and 
mountain slopes near each of these cities, which suggests that some 
tortoise populations have survived despite perturbations by humans.'' 
Therefore, Sonoran desert tortoises may persist as depressed 
populations adjacent to urban development, but without long-term 
population trend data for these areas, we are unable to know for how 
long.
    Urban development has been identified as a concern for Sonoran 
desert tortoise conservation in several areas within Arizona because of 
the associated increase in human-based threats to populations in close 
proximity. Averill-Murray and Swann (2002, p. 1) stated that urban 
development adjacent to the Saguaro National Park in Pima County 
threatens the Sonoran desert tortoise via several mechanisms including 
harassment and predation by feral or off-leash domestic dogs, illegal 
releases of captive Sonoran desert tortoises and exotic species that 
may transmit diseases to wild Sonoran desert tortoises, elevated 
mortality on roads, and illegal collection for pets. Averill-Murray and 
Swann (2002, p. 7) stated that mid- to large-scale development projects 
on the bajadas and foothills of the Rincon, Santa Rita, Santa Catalina, 
Tortolita, and Tucson Mountains has likely led to area-wide decreases 
in Sonoran desert tortoise populations. However, no population 
estimates for Sonoran desert tortoises before development of these 
areas exist, and, therefore, population responses to development of 
these areas cannot be ascertained.
    In addition to the Tucson metropolitan area, urban encroachment on 
Sonoran desert tortoise habitat occurs adjacent to the greater Phoenix 
metropolitan area, in the area around South Mountain and adjacent to 
the Superstition Mountains (AGFD 2010, p. 7). Sonoran desert tortoises 
are known or suspected to still occur in 12 of the 16 Maricopa County 
and City of Phoenix urban mountain parks and reserves. The four parks 
where no tortoise sign has been found in recent years are completely 
surrounded by urban development (AGFD 2010, p. 7). Urban development 
has occurred adjacent to five monitoring plots, but only the Hualapai 
Foothills plot is completely surrounded by developed lands (AGFD 2010, 
p. 7). A development consisting of 48,000 single family homes, south of 
the Colorado River in western Mohave County, is also currently being 
planned (THS 2009, p. 4; Mardian 2010, p. 1).
    Because less area is being used currently for agriculture in the 
United States, habitat loss due to agricultural development is more of 
a historical issue. However, impacts to Sonoran desert tortoise 
dispersal habitat within valley floors from historical agricultural use 
and wood harvesting are still evident. The vegetation and soils of many 
valleys in the Sonoran Desert were shaped by the periodic flooding of 
dynamic wash systems, which partially recharged a shallow, fluctuating 
groundwater table. Because of agricultural development, these valleys 
no longer experience these defining processes and there has been a 
permanent loss of meso- and xeroriparian habitat which are known to be 
corridors for movement by Sonoran desert tortoises (Jackson and Comus 
1999, pp. 233, 249; Lutz et al. 2005, p. 22; Riedle et al. 2008, p. 
418).
    Agriculture in Sonora, Mexico, has shifted from small-scale, local 
markets toward large-scale agro-industry, with Sonora producing 40 
percent of the country's total wheat crop (Stoleson et al. 2005, p. 
59). While agriculture in Sonora is largely constrained to valleys 
(along the Rio Sonora), many types of habitat used by Sonoran desert 
tortoises have been cleared for agriculture, including Sonoran 
desertscrub, thornscrub, and tropical deciduous forest (Stoleson et al. 
2005, p. 60). In 1994, the total irrigated acreage in Sonora was 
128,000 ac; in 2004 that figure rose to 530,509 ac (214,689 ha), an 
increase of 314 percent (AQUASTAT 2007, p. 2). This constitutes an 
estimated loss of 2 percent of Sonoran desert tortoise habitat in 
Mexico; rangewide, 1 percent.
    The projected growth of the human population in Arizona and 
northern Mexico and subsequent urbanization discussed above is expected 
to place onerous demands on lands where the Sonoran desert tortoise 
occurs, increasing the need for infrastructure associated with 
development, such as power lines, power plants, pipelines, landfills, 
roads, sand and gravel mines, and removal of boulders for landscaping 
(AIDTT 2000, p. 10). In addition, these growth projections will 
increase human visitation to formerly remote Sonoran desert tortoise 
habitat as urban-rural interface expands, whereby increasing human-
associated threats discussed in detail below (AIDTT 2000, p. 10). The 
AGFD (2010, p. 7) concluded that ``* * * as urbanization continues to 
expand, (Sonoran desert tortoise) habitat will continue to be lost.'' 
In a Global Information System exercise, we calculated that currently, 
75 percent of potentially occupied Sonoran desert tortoise habitat 
within Arizona occurs within 30 mi (48 km) (a reasonable distance a 
person might travel to recreate outdoors on public land) or less of a 
city or town with a population of 1,000 or more. As the human 
population of Arizona grows and development expands as expected, we 
assume that 100 percent of Sonoran desert tortoise populations will 
occur within 30 mi (48 km) or less of a city or town with a population 
of 1,000 or more, in the foreseeable future. Tortoise populations are 
being increasingly exposed to humans and human activities, and 
therefore to numerous threats that would otherwise be minimized or 
nonexistent. We discuss these types of threats and how they affect 
Sonoran desert tortoises and their habitat below in Factors B, C, D, 
and E.
    Some forms of development are likely to increase. The interest in 
renewable energy projects is expected to increase significantly in the 
future. Solar radiation levels in the southwestern United States, 
including Arizona, are some of the highest in the world, and interest 
in tapping into this source of potential energy is growing. Potentially 
significant tracts of BLM lands in southwestern Arizona have been 
identified for possible solar energy development, encompassing large 
percentages of Arizona's valley bottomland in La Paz and Yuma Counties 
and adjacent to or within the foothills of the Black Mountains of 
western Mohave County, which could isolate Sonoran desert tortoise 
populations and affect genetic exchange among regional populations in 
those areas (USDOE 2009, p. 1). Since most solar projects are in the 
early planning stages and have yet to be officially approved by the 
BLM, we are unable to ascertain the amount of Sonoran desert tortoise 
habitat likely to be impacted. However, we acknowledge that large areas 
within the distribution of the Sonoran desert tortoise in Arizona are 
being considered for solar projects.
    In one example, 12,100-15,100 ac (4,897-6,110 ha) of BLM, State, 
and private land containing Sonoran desert tortoise habitat along the 
southern bajada of the Black Mountains in western Mohave County, 
Arizona, has been identified for development of the Sterling Solar 
Generating Facility within the next 4 to 6 years (Needle Mountain 
Power, LLC 2010, pp. 4, 8, 11). At build-out, the Sterling Solar 
Generating

[[Page 78112]]

Facility will consist of solar fields, power blocks, buildings, 
retention ponds, rainwater catch basins, evaporation ponds, wastewater 
and water treatment facilities, water storage tanks, on-site housing, a 
substation, a visitors center, a substation and switching station 
interconnection with the Western Area Power Administration power lines, 
and septic tanks (Needle Mountain Power, LLC 2010, p. 11). We expect 
the construction of this facility to render at least 13,100 ac (5,300 
ha) of Sonoran desert tortoise habitat as unusable because this type of 
construction requires the complete grading (removal of vegetation) of 
the project footprint. It could, therefore, significantly affect the 
Black Mountains desert tortoise population, especially in consideration 
of other effects acting in combination with those poised from the 
proposed housing development and highway construction in the immediate 
area (THS 2009, p. 4; ADOT 2010, p. 3; Mardian 2010, p. 1). The 
estimated loss of 13,100 ac (5,300 ha) constitutes an estimated loss of 
0.05 percent of their habitat in Arizona; rangewide, 0.025 percent.
    Other solar energy development and transmission corridors pose 
similar threats to the Sonoran desert tortoise as development and 
roadway projects (see discussion below). An average utility-scale solar 
facility to generate 250 megawatts of electricity would occupy about 
1,250 ac (500 ha) of land (BLM 2009a, p. 1), and would involve removal 
of all vegetation within its footprint. Additionally, concentrating 
solar power facilities requires liquids such as oils or molten salts to 
create steam to power conventional turbines and generators, as well as 
various industrial fluids, such as hydraulic fluids, coolants, and 
lubricants, all of which may present a contaminant risk should these 
fluids leak onto the ground (Scott 2009, p. 12). New transmission lines 
would need to be built for these facilities, as well as roads to 
maintain the facilities, posing additional threats to the Sonoran 
desert tortoise through the destruction or contamination of remaining 
habitat and increased potential for road-kill mortality.
    In conclusion, the literature documents that urban development and 
population growth in Arizona and Sonora has been remarkable, and no 
information is available to suggest these trends will not continue into 
the foreseeable future. Sonoran desert tortoise habitat is permanently 
lost where urban development occurs. Sonoran desert tortoises and their 
habitats that occur adjacent to developed areas are also threatened by 
the increased incidence of an array of human activities or influences 
such as off-highway vehicle use, facilitation of the spread of 
nonnative plant species via soil disturbances, and increased wildfire 
ignitions. These threats act in combination with other threats 
discussed elsewhere in this finding, including ironwood and mesquite 
tree harvest, livestock grazing, nonnative plants and altered fire 
regimes, roads and highways, and undocumented human immigration and 
interdiction.
Development as a Barrier
    Urban development, canals, and transportation infrastructure, such 
as roads and railroads, disrupt ecological processes, increase 
mortality in animals, promote the degradation, loss, and isolation of 
wildlife habitat, and cause fragmentation of populations (Spang et al. 
1988, p. 9; Saunders et al. 1991, pp. 23-24; Averill-Murray and Klug 
2000, p. 68; Seiler 2001, p. 3; Howland and Rorabaugh 2002, p. 335; 
Edwards et al. 2004, p. 496). Sonoran desert tortoise populations are 
island-like in their distribution, meaning they are generally 
concentrated on the bajadas and hillsides of mountains, and less-
distributed within the valleys between these areas. As a result, they 
may be particularly vulnerable to large-scale disturbances that affect 
the suitability of intervening habitat (Spang et al. 1988, p. 9). 
Factors that affect inter-population dynamics in Sonoran desert 
tortoises include distance between populations, physical size of 
habitat areas, sizes of source populations, and the ease of which 
intervening areas can be crossed by dispersing individuals (Howland and 
Rorabaugh 2002, p. 335).
    The effect of potential barriers to inter-population movements of 
Sonoran desert tortoises (discussed above in the Species Information 
section) is not equal across their range. The ability for the Sonoran 
desert tortoise to move among populations is also important for 
allowing shifts in their range in response to climate change, and to 
promote recolonization after fire or other regional disturbances (Beier 
and Majka 2006, p. 2). Dispersal of Sonoran desert tortoises between 
populations through sparse desertscrub is less likely in very hot, dry 
valleys in the Lower Colorado subdivision of Sonoran desertscrub and 
populations in mountain ranges, such as the Eagletails, Maricopas, and 
Sand Tanks, have likely been existing in isolation for a long time (Van 
Devender 2002a, p. 16).
    Genetic analysis of blood samples collected from Sonoran desert 
tortoises in Saguaro National Park in Pima County, Arizona, suggest 
that intermediate gene flow still occurs, or occurred recently, among 
isolated populations at the rate of at least 1 migrant per generation 
(12-15 years) (Edwards et al. 2004, p. 485). However, thousands of 
acres of tortoise habitat have been recently lost to large residential 
developments in the foothills of the Santa Catalina, Tortolita, Rincon, 
and Tucson Mountains in the greater Tucson metropolitan area (Edwards 
et al. 2004, p. 485).
    The importance of allowing movement of individual tortoises between 
populations is observable by evaluating historical gene flow. Edwards 
et al. (2004, p. 485) used seven microsatellite DNA markers to examine 
the genetic relationships of tortoises in eight populations in southern 
and central Arizona, in the vicinity of Tucson and Phoenix. They also 
calculated migration rates among these populations to estimate 
historical rates of gene flow, and, therefore, the importance of 
individuals moving between populations (Edwards et al. 2004, p. 485). 
Edwards et al. (2004, p. 496) found no evidence of recent loss of 
genetic diversity that would indicate genetic bottlenecking that could 
occur from lack of mixing among Sonoran desert tortoise populations in 
southern Arizona. However, the authors acknowledged that a small sample 
size and small number of genetic markers (alleles) used in their 
analyses would likely not detect this genetic effect. Despite reduced 
mixing among populations, Sonoran desert tortoises may be capable of 
maintaining small effective population sizes (still viable populations, 
despite small size), even with a low degree of genetic diversity 
(Edwards et al. 2004, p. 496). However, Edwards et al. (2004, p. 496) 
also stated, ``Because effective population sizes of Sonoran desert 
tortoises are small, dispersal events probably play an important role 
in the long-term maintenance of these populations.'' This suggests that 
while dispersal and movement of tortoises may be rare, they may be 
important events. Therefore, barriers that prevent this movement could 
result in significant genetic impacts, by preventing mixing of 
populations over the long term.
    The effect of urban barriers limits inter-population movements of 
Sonoran desert tortoises resulting in ``closed'' populations. Experts 
believe that an isolated population of Sonoran desert tortoises that 
experiences significant declines in population size could not overcome 
losses simply through an increase in reproduction, based on evidence of 
past gene flow (Edwards et al. 2004, p. 496). Therefore, if a

[[Page 78113]]

population were to experience a catastrophic decline as a result of a 
stochastic event such as drought, the immigration of new tortoises from 
adjacent populations would be necessary for population recovery 
(Edwards et al. 2004, p. 496). Urban barriers effectively prevent this 
immigration of new tortoises, resulting in closed, or isolated, Sonoran 
desert tortoise populations, which are now evident within the 
metropolitan areas of Phoenix and Tucson. Mountains and associated 
foothills with Sonoran desertscrub habitat occur in these urban areas, 
and although development within this habitat has been restricted by 
zoning laws, development is still allowed to virtually surround the 
bases of the mountains, isolating tortoise populations. Examples of 
this development include the Union Hills, White Tank Mountains, 
McDowell Mountains, Black Mountains, and South Mountain Park in the 
Phoenix metropolitan area and Tumamoc Hill, Tucson Mountains, and 
Saguaro National Park West in the Tucson metropolitan area (Edwards et 
al. 2004, p. 496). Zylstra and Swann (2009, pp. 10-11) remarked that 
the increasing negative effect of human-made barriers on Sonoran desert 
tortoise movements between populations may require translocation 
(moving animals out of harm's way into more secured areas of suitable 
habitat), or occasional augmentation of populations with tortoises from 
other populations, to remain viable.
    Translocation has been considered an option, and implemented to 
some degree for Mojave desert tortoise conservation and recovery. In 
assessing the viability of translocation as a recovery and conservation 
tool for the Mojave population, concern has been expressed for 
potentially moving tortoises into areas where threats to desert 
tortoise populations remain, which could negate any conservation value 
associated with the action. Our (Mojave) Desert Tortoise Recovery 
Office stresses that translocation of tortoises should not occur under 
such circumstances, emphasizing the need to address threats which 
impact all tortoises regardless of origin.
    Translocation of desert tortoises has received mixed reviews in the 
scientific literature and, as noted, may not be a viable option for the 
Sonoran desert tortoise. There are several factors that must be 
considered in deciding whether or not to translocate tortoises into new 
areas, including temporary or longer-term holding conditions of 
tortoises; the propensity for post-release, long-distance movements; 
drought; the status of receiving population; and disease screening, 
among other factors (Berry 1986a, p. 113; Field et al. 2007, pp. 232, 
237, 240, 242; Martel et al. 2009, p. 218). Translocated Mojave desert 
tortoises have been shown to settle at release sites, travel in 
straight lines for substantial distances, or disperse up to 
approximately 4 miles (6.4 km) (Berry 1986a, p. 113). Translocated 
desert tortoises may disrupt social hierarchies in receiving 
populations by displacing residents or they may be displaced themselves 
(Berry 1986a, p. 113). Howland and Rorabaugh (2002, p. 341) suggest 
that translocation of Sonoran desert tortoises may not be a viable tool 
for conservation because most intact Sonoran desert tortoise 
populations in Arizona are currently considered relatively healthy, and 
likely occur at or near carrying capacity. Mullen and Ross (1997, pp. 
145-146) found that translocated Mojave desert tortoises have a lower 
survivorship than resident individuals (especially when moved during 
the summer versus during the spring), but that negative effects 
commonly associated with translocations are generally short-lived (1-2 
years).
    A 2004 population viability analysis for the Mojave desert tortoise 
recommended that a minimum of 50,000 individuals are required for a 50 
percent chance of persistence for 500 years, yet extrapolation of 
Sonoran desert tortoise population data from southern Arizona suggest 
that most populations number less than 20,000 individuals, with some as 
low as several hundred (Edwards et al. 2004, p. 496). Because the 
average generation time of a Sonoran desert tortoise is approximately 
12-15 years and much of the urban development is relatively recent, the 
full effect of developments as barriers to genetic exchange among 
Sonoran desert tortoise populations cannot be fully assessed at this 
time (Edwards et al. 2004, p. 486). Edwards et al. (2004, p. 495) 
further cautioned that their estimates of gene flow are contingent on 
what occurred pre-settlement, and should not be taken as evidence that 
natural immigration or emigration still occurs.
    In conclusion, the literature documents that urban development and 
population growth, roads and highways, canals, railroad tracks, and 
other types of development threaten the Sonoran desert tortoise by 
creating barriers to movement in Arizona and, perhaps to a lesser 
extent, in Sonora, Mexico. The creation of barriers affects the 
tortoises' genetic exchange capacity within and between populations, 
which in turn affects their ability to recolonize habitat in the event 
of population declines or extirpations, and may lead to isolation and 
eventual genetic bottlenecking. This threat acts synergistically with 
other factors as discussed above.
Off-Highway Vehicles
    Off-highway vehicle use may pose a variety of threats to the 
suitability of habitat within the range of the Sonoran desert tortoise. 
Off-highway vehicle use in Sonoran desert tortoise habitat can result 
in damage to soil, riparian areas, wetlands, water quality, and air 
quality. This damage occurs due to reduced vegetation cover and growth 
rates, soil compaction, diminished water infiltration, diminished 
presence and impaired function of soil stabilizers (biotic and abiotic 
soil crusts), noise, wildlife habitat fragmentation, spread of invasive 
plant species, and accelerated erosion rates (Boarman 2002, pp. 43-51; 
Ouren et al. 2007, pp. 5, 11; USGAO 2009, pp. 10, 13; Vega 2010, p. 3). 
Off-highway vehicle use in Sonoran desert tortoise habitat can also 
potentially affect Sonoran desert tortoises directly by crushing 
individuals or their burrows (Boarman 2002, pp. 43-51).
    Off-highway vehicle use has grown considerably in Arizona. Between 
21 and 56 percent of Arizona residents (depending on the county in 
Arizona) consider themselves off-highway vehicle users as of 1999, and 
projected increases in population growth are expected to increase 
recreation on public lands, in particular off-highway vehicle use 
(AIDTT 2000, p. 10). As of 2007, 385,000 off-highway vehicles were 
registered in Arizona (a 350 percent increase since 1998), and 1.7 
million people (29 percent of the Arizona's public) engaged in off-road 
activity from 2005-2007 (Sacco, pers. comm., 2007). Over half of off-
highway vehicle users reported that merely driving off-road was their 
primary activity, versus using the off-highway vehicle for the purpose 
of hunting, fishing, or hiking (Sacco, pers. comm., 2007). The BLM 
(USBLM 2001, p. 1) stated that interest in off-highway vehicle use has 
increased substantially in recent years and cited several reasons, such 
as urban growth in the west, improved capabilities of off-highway 
vehicles in accessing previously inaccessible areas, and greater public 
interest in unconfined outdoor recreational opportunities.
    The Forest Service stated that ``the number of off-highway vehicle 
users has climbed sevenfold in the past 28 years, from approximately 5 
million in 1972 to 36 million in 2000'' (USFS 2009, p. 2). The Tonto 
National Forest, which encompasses a considerable amount of

[[Page 78114]]

Sonoran desert tortoise habitat, receives the highest off-highway 
vehicle use of any national forest nationwide, partially due to its 
close proximity to the Phoenix metropolitan area. The Arizona State 
Land Department recently closed to off-highway vehicle use many of 
their lands in Maricopa County (which includes Phoenix), to control 
dust pollution, which appears to have shifted off-highway vehicle 
access to the nearby Tonto National Forest (USFS 2009, p. 2; USGAO 
2009, p. 11). The Tonto National Forest has indicated that soil erosion 
appears to be the most significant result from off-highway vehicle use 
on their lands and identified ``unmanaged recreation'' (off-highway 
vehicle use) as one of four key threats to soil, water, and wildlife 
habitat (USFS 2009, p. 1; USGAO 2009, pp. 10, 13).
    Off-highway vehicle use is widespread across Arizona, occurring on 
Forest Service, BLM, private, tribal, and State Trust lands, and has 
been documented on all 17 Sonoran desert tortoise monitoring plots. 
Pronounced effects are found on the Four Peaks and Wickenburg Mountains 
plots, which are near urbanized areas (greater Phoenix and Wickenburg, 
respectively) (AGFD 2010, p. 13).
    The Tonto National Forest has proposed to designate approximately 
800 mi (1,287 km) of roads as open for use, and close 280 mi (451 km) 
of roads which are currently open (due to significant resource damage). 
This is a net increase of 520 mi (837 km) of off-highway vehicle trails 
and roads on the Tonto National Forest (USFS 2009, p. 3). In addition, 
the Tonto National Forest has proposed the designation of five more 
off-highway vehicle areas (representing 2,799 ac (1,132 ha) 
collectively, or 0.01 percent of its habitat in Arizona) within Sonoran 
desert tortoise habitat on the Mesa and Globe Ranger Districts (USFS 
2009, p. 3). All other motorized travel not specifically designated 
will be prohibited by the Tonto National Forest except as authorized 
for dispersed camping access and big game retrieval (USFS 2009, p. 4). 
Because of the increase in off-highway vehicle access and subsequent 
use anticipated to occur on the Tonto National Forest, associated 
threats to the Sonoran desert tortoise and its habitat on the Forest 
are expected to increase in scope and magnitude in the immediate 
future.
    BLM regulations require their lands be designated as open, limited, 
or closed to off-highway vehicle use (USGAO 2009, p. 7). As of March 
2009, the BLM has nationally designated approximately 32 percent of its 
lands as open to off-highway vehicle use, 48 percent as limited-use, 4 
percent as closed, and 16 percent of lands have yet to be designated 
(USGAO 2009, p. 7). These figures indicate that at least 80 percent of 
BLM lands allow for off-highway vehicle use in some capacity. However, 
we do not have specific information for BLM off-highway vehicle use in 
Arizona. The BLM is taking actions to help manage off-highway vehicle 
use on their lands.
    Historically, competitive off-highway vehicle racing events have 
occurred on a comparatively infrequent basis in Arizona. On BLM lands 
in Arizona, these activities are generally restricted from March 31 to 
October 15, in consideration of potential surface activity of Sonoran 
desert tortoises (USBLM 2010, p. 4). However, similar considerations 
may not occur with respect to these events on lands managed by other 
agencies, thus making their lands more desirable for planning such 
events. For example, a Special Land Use Permit application was recently 
submitted to the Arizona State Land Department for the establishment of 
a semiannual competitive off-highway vehicle race within Sonoran desert 
tortoise habitat, slightly north of Tucson near Mammoth, Arizona (Vega 
2010, pp. 1-16).
    Competitive off-highway vehicle events can have a variety of 
detrimental effects on Sonoran desert tortoises or their habitat. Event 
courses have been found to create new destinations for increased, year-
long use, and correspondingly greater impacts to local Sonoran desert 
tortoise habitats and higher incidence of illegal route proliferation 
(Vega 2010, p. 3). The high rates of speed associated with competitive 
off-highway vehicle events significantly increase the likelihood for 
damage to burrows or other habitat features (Vega 2010, p. 4). Lastly, 
event spectators seeking good views have been found to park their 
vehicles indiscriminately along the race course without regard to 
vegetation and may crush Sonoran desert tortoises and their burrows, or 
start wildfires if parked over dry vegetation (Vega 2010, p. 5).
    In his literature review, Boarman (2002a, p. 50) found that, as of 
2002, most research on the effect of off-highway vehicles had been 
performed in areas of high off-highway vehicle use within the Mojave 
desert tortoise distribution. As a result, there are fewer available 
data for lightly-traveled areas (Boarman 2002, p. 50).
    On the Florence Military Reservation, Grandmaison et al. (in prep., 
p. 16) found that Sonoran desert tortoises use infrequently traveled 
gravel roads as movement corridors within their home ranges, placing 
individuals at greater risk of mortality from collisions with off-
highway vehicles. Populations that occur in similar areas throughout 
their distribution may also be vulnerable to mortality associated with 
collisions, or previously discussed indirect effects to their habitat 
from off-highway vehicle use.
    Effects of off-highway vehicle use on Sonoran desert tortoises are 
likely to be more significant within washes that separate steep slopes 
and rocky bajadas used by Sonoran desert tortoises, where tortoises are 
known to frequent and off-highway vehicle use often occurs (AGFD 2010, 
p. 13). For example, ``rock crawling'' (technical off-roading usually 
with highly-modified, high clearance, four-wheel drive vehicles), 
generally occurs in boulder-strewn washes where Sonoran desert 
tortoises are most likely to inhabit. This activity may be uniquely 
destructive to Sonoran desert tortoise habitat because: (1) It occurs 
on steep slopes and rocky bajadas within Arizona Upland Sonoran 
desertscrub where populations reach their highest densities; and, (2) 
the intent of rock crawling is to aggressively challenge aspects of a 
given landscape that would otherwise clearly represent barriers to 
overland travel, which places habitat and tortoises at greater risk. 
However, rock crawling activity is presumed to be less popular an 
activity than more conventional off-highway vehicle use and, therefore, 
likely affects a much smaller percentage of Sonoran desert tortoise 
habitat.
    Bury (1987, p. 1) studied the effects of off-highway vehicle use on 
Mojave desert tortoises in Mojave desertscrub habitat. Some of his 
findings included a 60 percent reduction in perennial plant cover, 1.3 
desert tortoises per hectare (2.47 ac) in a control plot in which off-
highway vehicles were excluded, versus 0.3 desert tortoises in an area 
used by off-highway vehicles, and four times the number of active 
burrows in the control plot versus the off-highway vehicle area (Bury 
1987, p. 1). Bury and Luckenbach (2002, p. 257) found that there were 
1.3 times more live plants, 3.9 times more plant cover, 3.9 times the 
number of Mojave desert tortoises, and four times the number of active 
burrows in undisturbed Mojave desertscrub as compared to areas where 
off-highway vehicles were used. We are not certain whether the areas 
studied by Bury (1987, p. 1) and Bury and Luckenbach (2002, p. 257) 
were unregulated, or regulated areas with designated routes, but 
similar effects to Sonoran desert tortoises and their habitat can be 
expected in areas of high off-road

[[Page 78115]]

vehicle use in Sonoran and Mojave desertscrub habitat within Arizona, 
particularly in areas of higher accessibility (such as valley bottoms 
and lower foothills), such as the Florence Military Reservation in 
Pinal County (AIDTT 2000, p. 34; Lutz et al. 2005; p. 22; AGFD 2010, p. 
7; Grandmaison et al. in press, p. 4).
    Brooks and Lair (2005, pp. 7-8) found that, in Mojave desertscrub, 
off-highway vehicle routes can cause a myriad of effects including: (1) 
Altering precipitation runoff patterns which promote increased erosion; 
(2) producing air-borne pollutants laden with heavy metals that affect 
habitat at distances ranging from 65 to 650 feet (20 to 200 m) from the 
road; (3) increasing nitrogen deposition in soils, thereby favoring 
nonnative plant invasions; and (4) providing a pathway for nonnative 
plant species invasions. These impacts degrade Sonoran desert tortoise 
habitat as well as their forage base.
    Soil disturbance from off-highway vehicle use, development 
projects, and other activities can facilitate the invasion of nonnative 
plant species by eliminating competition and creating a rougher soil 
surface for seeds to lodge and germinate (Hobbs and Huenneke 1992, pp. 
329-330). Motorized and mechanical vehicles aid in the dispersal of 
plants by transporting seeds of both native and nonnative plant 
species. Rew and Pollnac (2010, p. 2) found that trucks and sport 
utility vehicles driven off road in dry conditions can pick up as many 
as 176 seeds from 50 mi (80 km) of driving, and recreational off-
highway vehicles can pick up as many as 200,000 seeds in 48 mi (77 km) 
of off-road driving. Off-highway vehicles are generally transported via 
trailer from site to site and may spread nonnative plant species in 
subsequent uses. Off-highway vehicle use has also been shown to create 
edge effects along trails that generate dust, blanketing adjacent 
vegetation, and inhibiting plant growth rates, size, and survivorship, 
all of which affect the forage base and available cover for Sonoran 
desert tortoises (Ouren et al. 2007, p. 11).
    We have documented that off-highway vehicle use poses a threat to 
the Sonoran desert tortoise and its habitat in Arizona because it 
damages soil, reduces vegetation cover and growth rates, leads to soil 
compaction, diminishes water infiltration, diminishes the presence and 
impairs the function of soil stabilizers (biotic and abiotic soil 
crusts), fragments habitat, facilitates the spread of nonnative plant 
species, ignites wildfire, accelerates soil erosion, enhances the 
potential for illegal collection (discussed below), and may crush or 
injure Sonoran desert tortoises (also discussed below). In addition, we 
have documented the tremendous growth in popularity of off-highway 
vehicle use in Arizona, as well as compliance deficiencies in off-
highway vehicle licensing programs (and therefore deficient fees 
collected that are intended to fund enforcement and environmental 
mitigation) and enforcement programs (discussed above and below). This 
threat acts synergistically with other threats discussed herein. 
Considering the population growth estimates we have documented above 
for Arizona, we believe that the popularity of off-highway vehicle use 
will continue to grow, leading to an increase in severity and 
geographic extent of impacts across the distribution of the Sonoran 
desert tortoise in Arizona over time.
Roads and Highways
    Foreman (2002, p. 35) estimated that at least 20 percent of land in 
the United States has been ecologically affected by roads. Roads and 
highways might also adversely affect Sonoran desert tortoises as they 
do Mojave desert tortoises. Studies of Mojave desert tortoises suggest 
that effects include providing human access to occupied habitat, 
facilitating the spread of nonnative plant species, altering movement 
patterns, enhancing the genetic fragmentation effect between 
populations of Sonoran desert tortoises by acting as barriers, and 
contaminating adjacent habitat (Boarman and Sazaki 1996, p. 1; Forman 
and Alexander 1998, p. 207; Boarman 2002, pp. 54-55; Edwards et al. 
2004, pp. 495, 497; Boarman and Sazaki 2006, p. 95; Andrews et al. 
2008, pp. 127, 129-130; Rew and Pollnac 2010, p. 2). Roads that act as 
barriers to genetic exchange between Sonoran desert tortoise 
populations may increase the risk of inbreeding depression and 
population extirpation (Boarman and Sazaki 2006, p. 95). In one 
example, biological connectivity between Sonoran desert tortoise 
populations of the Harquahala and Wickenburg Mountains is significantly 
limited due to several barriers to tortoise movement including highways 
U.S. 60 and U.S. 93, the Burlington Northern Santa Fe Railroad, and 
urban development, and would be further limited by the proposed 
Wickenburg bypass highways which are in the planning phase (Beier et 
al. 2006d, p. vi).
    The use of dirt or gravel roads by vehicles generates dust which 
may adversely affect physiological processes of adjacent plants and 
reduce overall primary productivity, whereby affecting the amount and 
quality of available forage vegetation for Sonoran desert tortoises 
(Sharifi et al. 1997, pp. 844-845).
    Construction of major highways planned in Arizona has the potential 
to greatly affect certain Sonoran desert tortoise populations. For 
example, the Arizona Department of Transportation (ADOT) has proposed 
rerouting State Route 95 through the southern and eastern bajada of the 
Black Mountains in Mohave County, Arizona (Jacobs Engineering Group, 
Inc. 2009, pp. 24, 33; ADOT 2010, p. 3; Goodman 2010, pp. 3-4). The 
proposed realignment of State Route 95 is expected to pass directly 
through 30 mi (48 km) of a Sonoran desert tortoise population (THS 
2009, p. 4; Goodman 2010, pp. 3-4). We expect this new four-lane 
highway to eliminate considerable amounts of Sonoran desert tortoise 
habitat, become a significant source of mortality, and threaten the 
continued viability of the Black Mountains habitat to support the 
population of the Sonoran desert tortoise there, if appropriate 
mitigation measures are not enacted or are ineffective.
    Both the ADOT and the Federal Highways Administration participate 
in the BLM's tortoise mitigation program and provide funding for the 
acquisition of Sonoran desert tortoise habitat using compensation rates 
prescribed for in the BLM's mitigation policy (ADOT 2010, p. 3). 
Compensation rates for disturbances in Category I or II habitat are 3-
6:1 and 2-5:1, respectively (USBLM 2009, p. 18). To date, 584 ac (236 
ha) of Sonoran desert tortoise habitat have been acquired through this 
program with ADOT and Federal Highways Administration. Another 98 ac 
(40 ha) are scheduled to be acquired as a result of the proposed 
rerouting of U.S. Highway 95 through the Black Mountains of Mohave 
County (ADOT 2010, p. 3).
    Considerable planning efforts for future road and highway 
development in Arizona have been afforded to the preservation of 
wildlife corridors, or ``linkages.'' Linkage design plans have been 
completed for several biological corridor areas in Arizona where 
Sonoran desert tortoises may be threatened by construction and 
development activities that could become barriers to movement between 
populations (Beier and Majka 2006, pp. 1-81; Beier et al. 2006a, pp. 1-
189; 2006b, pp. 1-151; 2006c, pp. 1-88; 2006d, pp. 1-97; 2006e, pp. 1-
135). These linkage design plans are specific to both individual 
corridors that may be affected throughout Arizona, and to species 
(including the Sonoran desert

[[Page 78116]]

tortoise) chosen as representative ``focal species'' in each individual 
assessment (Beier and Majka 2006, pp. 1-81; Beier et al. 2006a, pp. 1-
189; 2006b, pp. 1-151; 2006c, pp. 1-88; 2006d, pp. 1-97; 2006e, pp. 1-
135).
    In one example, a series of voluntary conservation recommendations 
were proposed in Beier et al. (2006c, pp. 15-16; 2006e, pp. 14-15) to 
mitigate effects of major roadways, such as U.S. Highway 60 which 
traverses Sonoran desert tortoise habitat in Pinal and Gila Counties, 
Arizona. However, the Sonoran desert tortoise was not afforded 
consideration in all projects. For example, Sonoran desert tortoise 
populations in Rincon and Santa Rita mountains in eastern Pima County, 
Arizona, are adversely affected by Interstate 10 and State Highway 83 
(known barriers to tortoise movement), yet were not addressed in the 
Rincon-Santa Rita-Whetstone linkage design plan (Beier et al. 2006a, 
pp. i-ii). In another example, the Sonoran desert tortoise was not 
afforded any consideration in the Santa Rita-Tumacacori linkage design 
plan, despite the likely adverse effects by Interstate 19, a known 
barrier to movement between populations located in the Santa Rita and 
the Atascosa-Pajarito-Tumacacori mountains complex in southern Santa 
Cruz County, Arizona (Beier et al. 2006b, pp. i-ii). While some 
highways have associated structures that prevent or funnel tortoises to 
underground crossings, several populations are still affected by 
barriers to movement from major roads and highways that have no such 
structures.
    In our review of the literature, we have documented that roads and 
highways pose a threat to Sonoran desert tortoises in Arizona because 
they form barriers to movement, whether through direct mortality from 
vehicles or from avoidance of roads by tortoises. The effects 
associated with barriers are described in detail in the ``Development 
as a Barrier'' section above. While several roads or highways have 
associated tortoise fencing and or culverts to prevent road-kill of 
tortoises and facilitate safe movement, studies have shown that these 
devices are often not maintained and, therefore, become ineffective 
over time in achieving their desired goal. This threat also acts 
synergistically with other influences discussed herein.
Ironwood and Mesquite Harvest
    The harvest of mesquite and ironwood trees for charcoal production 
and use in wood carvings adversely affects Sonoran desertscrub habitat 
in Mexico, both historically and more recently (Bahre 1991, pp. 143-
146). The harvest of mature mesquites from Mexico's Sonoran desertscrub 
habitat permanently alters desert ecosystems because these leguminous 
(bearing seed pods similar to pea or bean plants) trees are important 
anchors for these systems and their associated flora and fauna (Taylor 
2006, p. 8). More than 200 plant and animal species depend on mesquite 
trees in northern Mexico for survival and reproduction (American 
University Database 2010, p. 1). Mesquite and ironwood trees are 
ecologically important to Sonoran desert habitat as they serve as 
nursery plants (i.e., aiding in dispersal, germination, seedling 
development, and survival) for other plant species used as forage for 
desert tortoises, and provide valuable shade for temporary shelter 
sites for Sonoran desert tortoises (American University Database 2010, 
p. 2). In areas where harvest has been concentrated, the loss of 
mesquite trees results in the loss of organic matter, fixed nitrogen, 
and sulfur and soluble salts, affecting overall habitat quality and 
quantity (Rodriguez Franco and Maldonado Aguirre 1996, p. 47).
    The demand for mesquite wood, used for cooking, has increased in 
the Sonoran Desert region of northern Mexico; one million ac (400,000 
ha) have been cleared of mesquite to meet these growing demands 
(American University Database 2010, p. 1). The modification of one 
million ac contributes to the degradation or possible loss of 4 percent 
of tortoise habitat in Mexico; rangewide, 2 percent. Ironwood trees are 
also being harvested in the Sonoran desert of northern Mexico, where it 
is cherished for its hardness and carving potential in Seri Indian 
artwork (American University Database 2010, p. 2). The accelerated rate 
of legume tree depletion for charcoal and carvings in Sonora has 
affected the health of ironwood populations and associated communities 
(Suzan et al. 1997, p. 955). This is evidenced by an increased number 
of damaged and dying trees, as well as generally small size classes for 
sampled areas (Suzan et al. 1997, pp. 950-955). In the Sonoyta region 
of northern Sonora, more than 478,000 ac (193,000 ha) have been 
affected by deforestation related to charcoal production, brick 
foundries, tourist crafts, and pasture conversion (Nabhan and Suzan 
1994, p. 64). The modification of 478,000 ac (193,000 ha) contributes 
to the degradation or possible loss of an estimated 2 percent of their 
habitat in Mexico; rangewide, 1 percent.
    Pressure for fuel wood and crafts materials has been so intense in 
Mexico south of Organ Pipe Cactus National Monument that wood harvest, 
especially ironwood, has been detected more than a third of a mile 
inside the boundary of the Monument, as supplies have been decimated 
south of the border (Suzan et al. 1999, p. 1499). The structure of 
Sonoran desert tortoise habitat in both washes and upland habitats in 
the Monument boundary has been affected by this harvest (Suzan et al. 
1999, p. 1499).
    In conclusion, the literature documents that harvest of ironwood 
and mesquite trees has degraded Sonoran desert tortoise habitat in 
Mexico, primarily, by the loss of organic matter, fixed nitrogen, and 
sulfur and soluble salts, affecting overall habitat quality and 
quantity, which collectively and indirectly affect the forage base and 
protective cover for Sonoran desert tortoises in as much as 4 percent 
of its range in Mexico. This threat acts in combination with other 
threats that affect Sonoran desert tortoise populations in Mexico 
discussed in this finding.
Livestock Grazing
    Sonoran desert tortoises, livestock, and wild burros potentially 
share habitat throughout their distribution in Arizona, with the 
exception of lands managed by the U.S. Fish and Wildlife Service or 
National Park Service. Wild burro herds range across millions of acres 
of Sonoran desert tortoise habitat in Arizona, predominantly on BLM 
lands northwest of Phoenix, although the literature is generally 
lacking in analysis of potential effects of wild burros on Sonoran 
desert tortoise populations or habitat (AIDTT 2000, p. 21).
    The Mexican government has designated over 5 million ac (2 million 
ha) of Sonoran desertscrub for conversion into grasslands for livestock 
production (American University Database 2010, p. 1). Sonoran desert 
tortoises are not found in grasslands, and this habitat type is not 
considered suitable for the species. The loss of 5 million ac (2 
million ha) would constitute an estimated loss of 20 percent of their 
habitat in Mexico; rangewide, 10 percent. Livestock grazing began to 
expand and modernize in its extent and distribution in Sonora, Mexico, 
in 1950, when land considered unsuitable for agriculture was 
subsequently used for livestock grazing (Hawks 2003, p. 3). During this 
time, new bulls were introduced throughout ranching operations to 
improve herd genetics, and artificial seeding of

[[Page 78117]]

pastures also commenced at this time (Hawks 2003, p. 3). By 1970, 
buffelgrass was the chosen seed for artificial range supplementation 
for a growing rural livestock industry, and pastures were seeded with 
the species throughout Sonora, Mexico. In Sonora, buffelgrass has 
trended towards a monoculture in many areas, and changed the fire 
regime to the detriment of native vegetation (Hawks 2003, p. 4). We 
discuss the threat of nonnative plant species such as buffelgrass in 
the ``Nonnative Plant Species and Altered Fire Regimes'' section above.
    Livestock stocking rates in Sonora have been documented at 2-5 
times the recommended rate for resource sustainability (Walker and 
Pavlakovich-Kochi 2003, p. 14; University of Arizona 2010, p. 2). 
Rorabaugh (2008, p. 25) found that livestock grazing ``* * * is 
probably the most widespread human use of Sonora's landscapes'' and 
that rangelands in Sonora are often heavily grazed, with effects most 
apparent during periods of drought. Livestock production in Mexico is 
concentrated in the northern states, and the numbers of livestock have 
grown from 10 million in 1940, to 37.5 million in 1983, largely due to 
the proximity to the United States, the major importer of Mexican 
cattle and beef (Stoleson et al. 2005, p. 60). In Sonora, 79 percent of 
agricultural and rangelands are devoted to livestock production 
(Stoleson et al. 2005, p. 60). Effects of poorly-managed livestock 
grazing observed in Sonora include changes in plant species composition 
and vegetation cover and structure, soil compaction, erosion, altered 
fire regimes, and nonnative plant species introductions and invasions 
(Stoleson et al. 2005, pp. 61-62).
    In the United States, however, permitted levels of livestock 
grazing have been reduced to 10 percent of historical levels (Bostick 
1990, p. 149). Potential effects of livestock grazing in desertscrub 
habitat received significant treatment in the literature, with varied 
scientific conclusions. Fleischner (1994, p. 631) listed specific 
attributes of ecosystems, such as composition, function, and structure, 
as vulnerable to the effects of livestock management through a variety 
of mechanisms including: (1) Decreasing the density and biomass of 
individual species, reducing species richness, and changing biological 
community organization; (2) interfering with nutrient cycling and 
ecological succession; and (3) changing vegetation stratification, 
contributing to soil erosion, and decreasing availability of water to 
biotic communities (Waser and Price 1981, pp. 409-410). In Mojave 
desertscrub, livestock grazing can increase soil compaction and 
decrease water absorption, thereby reducing water availability to 
potential Sonoran desert tortoise forage species and subsequently 
reducing available forage (Boarman 2002, p. 30). Oldemeyer (1994, pp. 
100-101) commented that there remains much uncertainty on the exact 
effects of livestock grazing on desert tortoises. Meyer et al. (2010, 
p. 42) suggested that the effects of livestock grazing on Sonoran 
desert tortoises should be placed in the context of a grazing regime, 
effective precipitation, habitat type, topography, Sonoran desert 
tortoise behavior, and habitat requirements. Loeser et al. (2007, pp. 
93-96) suggested that climatic variation is key in determining the 
ecological effects of grazing practices in arid rangelands.
    The effects of soil compaction on desertscrub vegetation have been 
analyzed. In Mojave desertscrub where Sonoran desert tortoises also 
occur, Adams et al. (1982, p. 167) found that soil strength of drying 
compacted soils increased at a greater rate than non-compacted soils, 
and that even minor compaction produced similar effects to soil 
strength. Soil strength was found to be inversely proportionate to 
production of summer annual grass species (Adams et al. 1982, p. 167). 
Plant species with taproots appeared more vulnerable to the effects of 
soil compaction whereas fibrous root systems common in nonnative 
species such as Schismus spp. appeared less vulnerable, which indicates 
that root structure affects the response of plant species and that 
plant species respond differently to soil compaction, potentially 
favoring nonnative species in compacted soils (Adams et al. 1982, p. 
174).
    While the Mojave and Sonoran desert tortoises differ to some degree 
in their biology and behavior, research on livestock grazing effects on 
Mojave desert tortoises or their habitat does have applicability to 
Sonoran desert tortoises (especially where Sonoran desert tortoises 
occupy Mojave desertscrub habitat and by virtue of the arid-land 
commonality), representing the best scientific information available. 
However, because Mojave desert tortoises typically occur in flat or 
gently-sloped terrain and construct earthen burrows in soil, they may 
be more susceptible to direct effects from livestock grazing. In 
comparison, Sonoran desert tortoises typically occur on steeper slopes 
and often construct burrows that are reinforced by boulders and, 
consequently, less susceptible to direct effects from livestock 
grazing.
    Observed effects of livestock grazing within Mojave desert tortoise 
habitat include dietary overlap and competition for food resources, 
destruction of vegetation structure used as temporary shelter sites, 
trampling of tortoises, collapsing of tortoise burrows, altering plant 
species composition by facilitating the invasion of nonnative plant 
species, and compaction of soil which may inhibit the construction of 
burrows (Avery and Neibergs 1997, p. 13). Boarman (2002a, p. 32) as 
well as Hobbs and Huenneke (1992, p. 329) found that livestock grazing 
can import nonnative plant propagules (seeds and other plant parts that 
may propagate) into native vegetation and subsequent physical 
alterations in vegetation structure and soil disturbance, such as 
trampling by livestock hoof-action, may increase germination rates of 
seeds through burying and compaction and provide microsites for 
establishment of nonnative plant species.
    Avery and Neibergs (1997, p. 13) compared Mojave desert tortoise 
habitat in both grazed and ungrazed areas (where buffelgrass was not 
intentionally planted), and found no significant differences in annual 
plant cover, biomass, or density between study areas. The densities and 
individual volumes of big galleta (Hilaria rigida), a perennial grass 
species, were greater in grazed habitat than within the grazing 
exclosure (Avery and Neibergs 1997, p. 13). There was no significant 
difference in total cover of perennial plant species within study plots 
(Avery and Neibergs 1997, p. 13). Avery and Neibergs (1997, p. 13) 
documented livestock nudging and rubbing Mojave desert tortoises, 
collapsing (potentially occupied) desert tortoise burrows, and 
destroying vegetation shading actively used burrows. The number of 
damaged and undamaged burrows in grazed habitat was equal, whereas the 
number of undamaged burrows in ungrazed habitat was significantly 
higher (Avery and Neibergs 1997, p. 18). Winter grazing appears to 
affect a higher proportion of actively used Mojave desert tortoise 
burrows. Indirect effects from burrow damage include increased risk of 
tortoise mortality, increased energy costs, and altered activity time 
budgets as a result of the need to construct new burrows (Avery and 
Neibergs 1997, p. 19). The potential for livestock to damage Sonoran 
desert tortoise burrows on lower slopes not reinforced with granite 
boulders may be similar to the findings of Avery and Neibergs (1997, p. 
18), as almost 200 Sonoran desert tortoise burrows were recorded as 
trampled during a survey of the East Bajada plot in the Black Mountains 
of

[[Page 78118]]

Arizona in 1997 (Woodman et al. 1998, pp. 74-75).
    Some degree of overlap was observed in the forage plant preferences 
between Mojave desert tortoises and livestock, with both preferring 
green annual species when available, and most overlap occurring during 
the spring (Avery and Neibergs 1997, pp. 18-19). However, preferences 
began to diverge as spring and summer ensued, with Mojave desert 
tortoises preferring dried annuals, beavertail cactus (Opuntia 
basilaris), and stems and dried flowers of silver cholla (Opuntia 
echinocarpa), and livestock preferring California jointfir (Ephedra 
californica) and big galleta grass (Avery and Neibergs 1997, p. 18). We 
presume similar relationships between preferred forage species of 
livestock and Sonoran desert tortoises exist, because of their highly 
varied, and often opportunistic, foraging behavior as they take 
advantage of both summer and winter rainy seasons characteristic of the 
Sonoran desert. This precipitation pattern affords Sonoran desert 
tortoises greater access to standing water and, therefore, the ability 
to forage on a more varied forage base, compared to the Mojave desert 
tortoise.
    Studies have shown that livestock grazing may result in varying 
effects on plant species richness, composition, and density of the 
Sonoran desert tortoise forage base. Blydenstein et al. (1957, pp. 523, 
525) found that vegetation density in some perennial species can be 
affected by livestock grazing in Sonoran desertscrub, while species 
composition and annual plant species density were unaffected. Sixteen 
years of rest from livestock grazing in the desert grassland and oak 
woodlands in southeastern Pima County in Arizona (at the extreme 
periphery of the Sonoran desert tortoise range) showed increases in 
plant species richness and significant increases in canopy cover for 
midgrass, shortgrass, shrubs, and forbs (Brady et al. 1989, pp. 285-
287). However, there was no statistical difference in total vegetation 
cover between grazed land and rested land (Brady et al. 1989, pp. 285-
287).
    Features that attract livestock to certain locations within an 
allotment may have pronounced effects on desert tortoises and their 
habitat. Livestock watering, supplemental feeding, or salt-lick sites 
in desertscrub attract higher use by greater densities of livestock in 
arid environments. Effects to desertscrub habitat are commensurate with 
livestock use of these areas and decrease with increasing distance from 
these sources (Avery and Neibergs 1997, p. 19; Boarman 2002, p. 34). 
The density of certain nonnative plant species, such as Schismus spp., 
has also been positively correlated to distance to watering sites, 
while others, such as red brome, are negatively correlated (Brooks et 
al. 2006, p. 139). Native plant species cover and richness has been 
shown to decrease with increasing proximity to livestock waters (Brooks 
et al. 2006, pp. 140-141). Brooks et al. (2006, p. 138) state that 
these effects can be anticipated from 164 to 656 ft (50 to 200 m) from 
the edge of the watering site. Juvenile and adult Sonoran desert 
tortoises were frequently observed by Meyer (1993, pp. 101-102) using 
salt licks provided for livestock. Frequenting salt licks may benefit 
desert tortoises (especially hatchlings and small juveniles), but 
likely increases risk of being trampled by livestock because the salt 
licks can attract higher concentrations of both livestock and tortoises 
in actively grazed pastures. Based on the results of a study conducted 
by Balph and Malecheck (1985, p. 227), cattle avoid stepping on uneven 
surfaces. Desert tortoises will likely be perceived as an uneven ground 
surface, therefore, cattle may intentionally avoid stepping on them.
    Neff et al. (2005, p. 87) compared the effects to soil geology, 
geomorphology, and geochemical characteristics of biological soil 
crusts that had been disturbed, and the subsequent wind erosion due to 
livestock grazing, to an ungrazed area in arid lands of southeastern 
Utah. They found that ``* * * despite almost 30 years without livestock 
grazing, surface soils in the historically grazed sites have 38-43 
percent less silt, as well as 14-51 percent less total elemental soil 
magnesium, sodium, phosphorus, and magnesium content relative to soils 
never exposed to livestock disturbances'' and 60-70 percent declines in 
surface soil carbon and nitrogen reserves (Neff et al. 2005, p. 87). We 
are not certain to what extent the loss of these surface soil nutrients 
may affect the forage quality or quantity for Sonoran desert tortoises 
in arid habitat. Approximately 46 livestock grazing allotments on the 
Tonto National Forest partially or wholly overlap the potential range 
of the Sonoran desert tortoise, with several rated as having impaired 
or unsatisfactory soil conditions (AIDTT 2000, p. 37).
    We observed several instances in the literature that discussed an 
inherent partitioning of land used by livestock and that used by 
Sonoran desert tortoises. Livestock often take the paths of least 
resistance and are unlikely to venture great distances from water. 
These behavioral traits of domestic livestock limit, to some degree, 
the potential effects from livestock grazing in Sonoran desert habitat, 
as livestock are less likely to travel into rough, steep terrain, 
instead favoring valley bottoms and water sources (AIDTT 2000, pp. 9, 
21). Effects from livestock grazing are expected to be attenuated due 
to the relatively steep slopes and rugged terrain often preferred by 
Sonoran desert tortoises, but quantitative studies have not been 
conducted to confirm this assumption (AIDTT 2000, p. 9; Oftedal 2007, 
p. 26). Because of the generalized differences in habitat usage by 
livestock (flats, ridge tops, and drainage bottoms) and Sonoran desert 
tortoises (steep slopes and rocky bajadas), ecological and dietary 
overlap is uncommon, but does occur to some degree (AGFD 2010, p. 6). 
Where such overlap is significant, in particular in periods of drought, 
the effect of livestock use on Sonoran desert tortoise habitat may be 
considerable (AGFD 2010, p. 7). Sonoran desert tortoises may also 
selectively avoid grazed areas. While Sonoran desert tortoises are 
generally known to use steep rocky slopes and bajadas as their primary 
habitat areas, they occasionally occur in more flat terrain, such as 
the Florence Military Reservation, where they are 35 percent less 
likely to use habitat where livestock grazing occurs (AGFD 2010, p. 7). 
Grandmaison et al. (in press, p. 2) examined microhabitat selection by 
the Sonoran desert tortoise on the Florence Military Reservation in 
south-central Arizona, and found that tortoises most strongly selected 
for canopy cover, followed by an absence of cattle activity and 
proximity to roads and washes.
    Of the 17 long-term monitoring plots, evidence of some degree of 
habitat usage overlap with livestock has been observed on 12 plots. On 
several plots (Arrastra Mountains, Bonanza Wash, West Silverbell 
Mountain, and Tortilla Mountains) extensive overlap with livestock use 
has been documented in each year they were surveyed (AGFD 2010, p. 7). 
Heavy trampling and destruction of Sonoran desert tortoise burrows has 
been documented on the Bonanza Wash plot. One Sonoran desert tortoise 
was crushed by livestock trampling on the West Silverbell Mountain 
plot, although such extreme reports of livestock-related direct effects 
on Sonoran desert tortoises are uncommon in the literature (AGFD 2010, 
p. 7).
    Sonoran desert tortoises might compete with livestock for high-PEP 
plants (for review, see discussion of diet in the Species Information 
section above) and therefore may place unique competitive pressure on 
Sonoran desert tortoise populations (Oftedal 2002, pp. 235-236). Many 
high-PEP plant species

[[Page 78119]]

are found primarily in the transition zone between areas where 
livestock and Sonoran desert tortoises compete directly for these plant 
species, as noted in several Arizona long-term monitoring plots (East 
Bajada of the Black Mountains, Hualapai Foothills, Little Shipp Wash, 
New Water Mountains, San Pedro Valley), in addition to similar 
observations from studies performed at Ragged Top, Saguaro National 
Park, and Sugarloaf Mountain (Oftedal 2007, p. 26). However, Oftedal 
(2007, p. 25) hypothesized that in situations where winter 
precipitation is modest, high-PEP plant species are in low abundance, 
and nonnative annual grass species are in high abundance, ``the 
immediate effect of grazing (forage competition with Sonoran desert 
tortoise) would be [a] reduction of overall forage biomass, not [a] 
change in the quality of tortoise diets. This suggests that cattle 
grazing may be less damaging to tortoises in years of modest 
rainfall.'' In conclusion, Oftedal (2007, p. 26) found that ``the high 
degree of diet selection that occurs during spring leaves (Sonoran) 
desert tortoises susceptible to influences that may alter the abundance 
of the somewhat scarce high-PEP plants, and thus that may reduce the 
overall quality of the diet. Tortoises foraging in summer appear less 
susceptible to the impacts of livestock grazing.'' Thus, seasonality 
and precipitation levels appear to affect the likelihood of grazing to 
adversely affect the forage base of Sonoran desert tortoises, with 
spring being a period of elevated sensitivity of Sonoran desert 
tortoises to livestock grazing where tortoises and livestock spatially 
overlap.
    Livestock grazing can influence the microclimate at the ground 
surface. Grazing may positively affect soil temperature and, therefore, 
benefit desert tortoise burrow temperatures where burrows are not 
associated with boulders, but instead constructed in more open habitat 
such as underneath shrubs (Boarman 2002, p. 31). Field research in 
Mojave desertscrub indicates that when the undergrowth beneath shrubs 
is grazed, and the shrub itself is minimally browsed or unaffected by 
grazing, underlying soils may cool from effects from wind and shade. 
Heavily vegetated undergrowth traps heat and increases soil temperature 
(Boarman 2002, p. 31). Alternately, heavily browsed shrubs can increase 
soil temperatures (Boarman 2002, p. 31). Lower vegetative ground cover 
in northern Sonora, as a response to livestock overgrazing, was found 
to increase soil and air temperatures above the levels found in 
adjacent grazed lands within the United States (Bryant et al. 1990, p. 
243). Increased soil temperatures may impact the Sonoran desert 
tortoise in a variety of ways, such as influencing changes in behavior, 
lowering survivorship, and skewing the sex ratios of hatchlings (which 
are determined by incubation temperatures; see Species Information, 
above).
    Bostick (1990, pp. 150-151) suggested that high desert tortoise 
densities are correlated with high livestock use, citing health 
examinations of Mojave desert tortoises that existed in grazing 
exclosures in northwestern Arizona. Bostick (1990, p. 149) also 
asserted that desert tortoises feed ``primarily on dung,'' inferring 
that with more livestock, there would be an abundance of available 
tortoise forage. Bostick (1990, p. 151) summarized his conclusions on 
the relationship between livestock grazing and desert tortoises with 
the following: (1) Desert tortoises have coexisted with cattle for 300 
years in California and Mexico and at least 100 years elsewhere; (2) 
the highest tortoise densities known occurred at a time when 
overgrazing by livestock was the most severe ever known; (3) the fewer 
the cattle on a range, the fewer the number of tortoises; and, (4) 
excluding cattle for many years endangers the tortoise population. 
Boarman (2002, pp. 27, 35, 38) refuted the conclusions made by Bostick 
(1990, pp. 149-151) that grazing benefits the desert tortoise. In 
addition, we found no information in the scientific literature that 
supported the findings of Bostick (1990, pp. 149-151).
    Some research has examined the effects of various livestock grazing 
regimes to Sonoran desert tortoise populations. Meyer et al. (2010, pp. 
20-26) compared the number and density of Sonoran desert tortoises in 
study plots exposed to four different livestock grazing regimes: 
Yearlong light grazing (plot size 2,279 ac (922 ha)), yearlong moderate 
grazing (plot size 3,254 ac (1,317 ha)), yearlong heavy grazing (plot 
size 4,634 ac (1,875 ha)), and rest-rotation (plot size 4,758 ac (1,925 
ha)). They found that the highest number and density of Sonoran desert 
tortoises (266 total individuals; 36.89 individuals per square mile) 
was observed in the pastures with yearlong heavy grazing as compared to 
rest-rotation (215 total individuals; 28.94 individuals per square 
mile), yearlong light grazing (52 total individuals; 14.61 individuals 
per square mile), and yearlong moderate grazing (47 total individuals; 
9.23 individuals per square mile) (Meyer et al. 2010, p. 23). The study 
plots used for this comparison between the number and density of 
Sonoran desert tortoises and various livestock grazing regimes were of 
unequal size, with the yearlong light and moderate plots being the 
smallest. This could affect the number of tortoises observed but not 
likely the density of tortoises. Other variables that likely affected 
the analysis of Sonoran desert tortoise densities were differences in 
vegetation, topography, soil types, and the location of tortoise 
populations among study plots (Meyer et al. 2010, p. 38). In addition, 
the ability to detect Sonoran desert tortoises is likely to increase 
with intensity of livestock use and a subsequent decrease in ground 
cover, which could have further biased the number of observations in 
the yearlong moderate and heavy grazing study plots. Given the results 
of these analyses, Meyer et al. (2010, p. 42) surmised that ``tortoise 
densities were affected by soil, topography and vegetation and had 
little or no relationship to livestock grazing or grazing systems.''
    Additional research examined effects of grazing regimes on fire 
behavior and wildlife and vegetation communities, citing beneficial 
effects. Bahre (1991, p. 141) compared the relative frequency of 
wildfires that occurred in the mid-1900s (carried by nonnative plants), 
to fires in more recent times, and suggested that mechanical fuel 
reduction by livestock grazing might assist in reducing the propensity 
of wildfires in Sonoran desertscrub habitat. Loeser et al. (2007, p. 
97) found that in Arizona grasslands ``* * * some intermediate level of 
cattle grazing may maintain greater levels of native plant diversity 
than the alternatives of cattle removal or high-density, short-duration 
grazing practices.''
    In an unpublished review of livestock grazing literature, Holecheck 
(undated, p. 2) found that ``* * * controlled livestock grazing may 
enhance rangeland vegetation by accelerating plant succession, 
increasing plant diversity, increasing plant productivity, and reducing 
plant mortality during drought. These positive impacts of livestock 
grazing are most likely to occur when grazing intensities are light to 
conservative.'' Holecheck (undated, p. 2) countered the unanimous 
findings of over 30 independent livestock grazing impact studies that 
documented that controlled grazing increases compaction, reduces 
infiltration, and increases erosion by claiming that ``these impacts 
are generally of small magnitude and are ameliorated by natural 
processes that cause soil formation, soil deposition, and soil 
loosening.''
    Some local land management organizations are currently working on 
proactive conservations efforts to reduce

[[Page 78120]]

potential impacts of ranching and other activities on the Sonoran 
desert tortoise. For example, the Winkelman Natural Resource 
Conservation District (WNRCD, a coalition of local livestock ranchers 
and grazing lease permittees in the Winkelman area of the lower San 
Pedro River in Arizona) has prepared a draft conservation plan for the 
desert tortoise within their area (WNRCD 2010, pp. 1-13). This draft 
plan proposes conservation and land management prescriptions for land 
managers in their area as recommended by the Arizona Interagency Desert 
Tortoise Team. However, presently the draft plan has not secured 
specific agreements with land managers responsible for Sonoran desert 
tortoise habitat, and it lacks financial commitments to carry out the 
recommended conservation actions. For example, Pinal County was 
identified as having responsibilities for conservation actions but has 
since indicated that they are unable to participate in the draft plan 
(Pinal County 2010, p. 1). While this draft conservation plan could 
further Sonoran desert tortoise conservation in this area once all the 
necessary management and financial agreements are in place and the plan 
is finalized, it currently provides limited conservation benefit to the 
Sonoran desert tortoise.
    In consideration of the literature presented above, we conclude 
that grazing effects to the Sonoran desert tortoise may occur but are 
likely limited in severity and scope in Arizona, because habitat shared 
by livestock and Sonoran desert tortoises is not a significant 
proportion in most areas in Arizona, and because livestock grazing in 
Arizona is actively managed by land management agencies (see Factor D). 
We also acknowledge that data generated from research on grazing 
effects to tortoises and their habitat are variable, making it 
difficult to accurately assess the risk of livestock grazing to the 
Sonoran desert tortoise. However, due to limited regulations affecting 
livestock management in Mexico, and the information we have examined on 
its extent in Sonora, we conclude that livestock grazing likely poses a 
threat to the Sonoran desert tortoise in Mexico. We also acknowledge 
the potential for livestock grazing effects to act synergistically with 
other influences discussed herein.
Undocumented Human Immigration
    United States border-enforcement efforts have significantly 
increased along the United States-Mexico international border in 
Arizona in recent years. Sonoran desert tortoise habitat occurs along 
approximately 140 mi (225 km) of the border, from approximately Nogales 
west to the California State line. International border fencing 
structures and barriers (especially the impenetrable pedestrian 
fencing) along the Arizona-Sonoran border pose population-connectivity 
problems for the Sonoran desert tortoise, which depends on emigration 
and immigration for genetic fitness of regional populations. However, 
along most of the border, just vehicle barriers occur, which allow 
tortoises to pass through them, and do not pose a barrier to movement 
(Cohn 2007, p. 96; Flesch et al. 2010, p. 179; Audsley 2010, p. 5; 
Sferra 2010, pers. comm.). The two primary types of barrier devices 
that have been constructed, or are planned for construction, are 
vehicle barriers and pedestrian fences, the latter of which may be 
impenetrable to Sonoran desert tortoises where the fence is buried into 
the ground (Audsley 2010, p. 5; Sferra 2010, pers. comm.). Where 
pedestrian fences are not buried completely and bollard fences 
(barriers formed by a series of vertical posts) are installed, Sonoran 
desert tortoises less than 4 in (10 cm) in width may be able to get 
through (Audsley 2010, p. 5; Sferra 2010, pers. comm.).
    Undocumented immigrants affect Sonoran desert tortoise habitat by 
trampling vegetation along well-used routes and cutting wood for 
campfires, which affects the quality and amount of forage and also 
reduces the number of temporary shelter sites for Sonoran desert 
tortoises (Averill-Murray and Averill-Murray 2002, p. 29). Other human 
activities along the international border (off-road driving, high-speed 
driving, accidentally setting fires from cooking or purposefully for 
distraction of law enforcement personnel, and interdiction activities 
by the U.S. Border Patrol, U.S. Immigration and Customs Enforcement, 
and other enforcement agencies) also impact Sonoran desert tortoises 
and their habitat (AIDTT 2000, p. 27; Marris 2006, pp. 338-339; Sayre 
and Knight 2010, p. 347).
    Historically, border enforcement policies and associated structures 
have indirectly channeled undocumented immigration pressure onto the 
Cabeza Prieta National Wildlife Refuge (Marris 2006, pp. 338-339; Cohn 
2007, p. 96). Analysis has shown there are about 8,000 mi (12,875 km) 
of unauthorized routes on the approximate 1,000 sq mi (2,600 sq km) 
refuge, mostly in designated wilderness (McCasland 2010, pers. comm.). 
These routes are most likely attributable to illegal cross-border 
traffic and associated law enforcement response by Border Patrol 
(McCasland 2010, pers. comm.). Recently, 33.5 mi (54 km) of permanent 
vehicle barriers were installed along the international border within 
the Cabeza Prieta National Wildlife Refuge, which has likely reduced 
illegal vehicular access to the Refuge (SBBI Incorporated 2010, p. 1).
    Along the entire southern boundary of the Buenos Aires National 
Wildlife Refuge, a 7-mi- (11.3-km-) long pedestrian barrier has been 
constructed (USDHS 2007, pp. 4, Figure 2-1). Because pedestrian 
barriers on the border are generally well-fortified, complete barriers 
to terrestrial movement, we assume that Sonoran desert tortoises in the 
larger juvenile and adult size classes are now prevented from making 
trans-border dispersal movements as a result of the barrier 
construction in this area.
    The border region associated with the Tohono O'odham Nation in Pima 
County, Arizona, was recently considered to have one of the highest 
rates of attempted crossings, because it is relatively remote (Sferra 
2010, pers. comm.). Currently, all but 3 mi (4.8 km) of the 70-mi (113-
km) section of border between the Tohono O'odham Nation and Mexico is 
reinforced with a vehicle barrier (Lackner 2010b, pers. comm.). Vehicle 
barriers are not constructed where terrain is too steep or rocky, or 
where vehicular access is considered impossible (Lackner 2010b, pers. 
comm.). The lands of the Tohono O'odham Nation are predominantly 
classified as Arizona Upland Sonoran desertscrub. The lands presumably 
have significant numbers of Sonoran desert tortoises, although survey 
data are generally scarce from that area.
    Along the Organ Pipe Cactus National Monument border with Mexico, 
vehicle barriers exist across most of the monument, and a potentially 
impenetrable pedestrian fence has been erected in Arizona Upland 
Sonoran desertscrub on Monument Hill and along 4 mi (6.4 km) of the 
border at the Lukeville Port of Entry (Sferra 2010, pers. comm.).
    The comparison of 2009 and 2010 apprehension rates of undocumented 
immigrants reflects both the number of attempted illegal crossings and 
the intensity of enforcement activities within various regions of the 
Arizona-Mexico border, as well as areas north of the border (Lackner 
2010a, pers. comm.). Within Sonoran desert tortoise habitat, 
significant increases in apprehension rates have occurred in the 
following areas (percentage denotes change from 2009 to June 2010): 
Tohono O'odham Nation (18.37 percent); Organ Pipe Cactus National 
Monument (63.8 percent), and the Sonoran Desert

[[Page 78121]]

National Monument (70.69 percent) (U.S. Border Patrol 2010, pers. 
comm.). In other areas, the apprehension rates have substantially 
decreased over the same time period: Ironwood Forest National Monument 
(-47.18 percent), Barry M. Goldwater Air Force Range (-32.02 percent), 
and the Cabeza Prieta National Wildlife Refuge (-13.19 percent) (U.S. 
Border Patrol 2010, pers. comm.). Over the same time period, and in 
total, there have been 79,307 apprehensions made, compared to 71,775 
apprehensions in 2009, which represents a 10 percent increase (Lackner 
2010a, pers. comm.).
    New border- and access-road construction has connected previously 
remote and undisturbed habitat to the existing network of Arizona 
roads, providing vehicular access to areas previously only accessible 
by foot or on horseback (Sayre and Knight 2010, pp. 346-347; Sferra 
2010, pers. comm.). An unintended consequence of these new roads is 
that they are used not only by U.S. Border Patrol, but by the public 
and illegal traffic, increasing the risk of wildfires, invasions of 
nonnative plant species, alteration of erosion and water movement 
patterns (affecting infiltration and soil stability), and mechanical 
damage to vegetation (Sayre and Knight 2010, p. 347; Sferra 2010, pers. 
comm.). Many new roads along the border have included cattle guards 
built with enclosed concrete pits that have the unintended consequence 
of acting as lethal pit-fall traps for reptiles, such as smaller size 
class Sonoran desert tortoises (Sayre and Knight 2010, p. 347).
    Based on our review of the literature and communications with 
resource experts and enforcement personnel, we conclude that Sonoran 
desert tortoises and their habitat, both near the international border 
and within corridors of heavy undocumented immigrant travel and 
enforcement interdiction, are threatened by these activities. 
Specifically, off-road route proliferation, high-speed driving, road 
construction (providing new access to formerly inaccessible areas), 
human depredation of tortoises as food sources, and barriers to 
tortoise movement created by pedestrian fencing are recognized as 
having serious impacts to Sonoran desert tortoise habitat. The 
geographic scope of these threats is relatively small on the landscape, 
restricted to the immediate border region, and to undocumented 
immigrant migration corridors, such as that recognized through the 
Tohono O'odham Nation, extending through Ironwood Forest National 
Monument. However, these impacts are significant where they occur.
Summary of Factor A
    Our analysis under Factor A identified an array of threats to 
Sonoran desert tortoise habitat. The documented invasion and purposeful 
cultivation of nonnative plant species within the distribution of the 
Sonoran desert tortoise in the United States and Mexico significantly 
increases the threat of wildfire in an ecosystem that evolved in the 
absence of wildfire. This threat is widespread and, although currently 
and comparatively less significant in Arizona, is substantial in 
Mexico, and is expected to increase in the future. When including the 
total land area adversely modified by ironwood and mesquite harvesting, 
an estimated 98 percent of the Sonoran desert tortoises' habitat will 
be lost or adversely modified in Mexico in the near future, or 47 
percent of the Sonoran desert tortoise's habitat rangewide. It is 
important to recognize that while nonnative plant species are expanding 
their distribution on the landscape, Sonoran desert tortoise 
populations have persisted in affected areas that remain unburned, for 
decades. The effect of nonnative plants on Sonoran desert tortoise 
populations is most significant after a wildfire has occurred; 
effectively giving nonnative species a distinct competitive advantage 
over native vegetation, and threatening a type-conversion in habitat. 
While we have found evidence of numerous wildfires in occupied 
desertscrub, the majority of occupied habitat that has been invaded by 
nonnative plants has not yet burned and remains suitable habitat for 
the tortoise.
    In addition, projections for human population growth and urban 
development throughout the species' range are likely to both pose 
significant problems for genetic exchange among Sonoran desert tortoise 
populations as well as increase the degree and scope of human 
interactions with tortoises and occupied habitat, which threatens the 
tortoise in a variety of ways. Currently in Arizona, 75 percent of 
potentially occupied Sonoran desert tortoise habitat occurs within 30 
mi or less of a city or town with a population of 1,000 or more, and 
considering future growth projections, it is likely that 100 percent of 
occupied tortoise habitat will be affected in the future. Livestock 
grazing in Mexico poses significant threats to the Sonoran desert 
tortoise habitat there due to ineffective livestock management and 
continued overgrazing. Lastly, desertscrub habitat that has been 
disturbed takes a very long time to recover, on the order of decades or 
centuries, which hinders remediation projects with respect to their 
ability to prevent population declines in Sonoran desert tortoises in 
the short- or medium-term. Each of these impacts results in significant 
cumulative threats to the species' habitat and, based upon our review 
of the best commercial and scientific data available, we conclude that 
the present or threatened destruction, modification, or curtailment of 
its habitat or range is an immediate threat of high magnitude to the 
Sonoran desert tortoise, both now and in the foreseeable future.

Factor B. Overutilization for Commercial, Recreational, Scientific, or 
Educational Purposes

Illegal Collection
    In urban areas of Sonora, Mexico, such as Hermosillo, desert 
tortoises have become increasingly common as household pets. They have 
been mostly obtained from the wild in adjacent areas (Bury et al. 2002, 
p. 103). The sale of desert tortoises in Mexican pet stores ended when 
the tortoise was listed as threatened in that country in 1994 (Bury et 
al. 2002, p. 103).
    Sonoran desert tortoises are a closed season species in Arizona 
(Commission Order 43), and therefore cannot be legally taken from the 
wild or possessed without special license. In Arizona, the current 
possession limit for Sonoran desert tortoises legally held in 
captivity, i.e., either obtained prior to season closure or obtained 
through the tortoise adoption program, is one per person per household 
(AGFD 2010, p. 12). The AGFD allows for disposition of lawfully 
possessed tortoises by gift to another person in Arizona, or as 
directed by the AGFD (AIDTT 2000, p. 14). Despite collection 
prohibitions in Arizona, the Sonoran desert tortoise is a very common 
reptile pet in Arizona households and has been so for decades. The 
actual number of Sonoran desert tortoises in captivity is unclear 
because there are no special licenses or permits required to possess 
Sonoran desert tortoises, or laws that prohibit their propagation in 
captivity (Jarchow et al. 2002, p. 289; Jones 2008, p. 69). Jarchow et 
al. (2002, p. 289) state that the number of captive Sonoran desert 
tortoises in Arizona is so large that an outright prohibition of their 
possession is both impossible and impractical.
    The popularity of Sonoran desert tortoises in captivity, as well as 
the various adoption programs around the State, may unintentionally 
mislead the public into thinking that Sonoran desert tortoises are not 
protected, and may, therefore, be collected from the wild

[[Page 78122]]

(Grandmaison in press, p. 6). For example, the area surrounding the 
Hualapai Foothills plot experienced increased development in 2001, 
which may have increased human-tortoise interactions and possibly 
illegal collection. Declines in tortoise encounters at this plot in 
2001 and 2005 may have, in part, resulted from illegal collection due 
to that plot's proximity to developed land (AGFD 2010, p. 7).
    Arizona's regulations have no provisions requiring permits for 
possession of Sonoran desert tortoises, which would aid in 
identification of those tortoises that were in lawful possession before 
January 1, 1988. In addition, there may be incentive created for the 
illegal release of captive tortoises into the wild because of the 
number of tortoises breeding in captivity, and the difficulty 
associated with finding recipients of offspring within the legal 24-
month window (under Arizona's Commission Order 42). This could result 
in a higher number of illegal and indiscriminant releases into the wild 
(AIDTT 2000, p. 14). Edwards et al. (2010, pp. 801-807) conducted 
genetic testing of 180 captive tortoises from Arizona to discern their 
genetic origin (as Sonoran, Mojave, or a hybrid). They found that 45 
percent of sampled captive tortoises were not of strictly Sonoran 
origin, but rather either pure Mojave, Sonoran-Mojave cross, or Texas 
tortoise (Gopherus berlandieri)--Sonoran desert tortoise hybrids 
(Edwards et al. 2010, p. 804). These data indicate there may be a risk 
of genetic contamination of wild populations when captives are 
released. Genetic contamination can weaken the genetic fitness of a 
population and render it vulnerable to extirpation. In addition, as 
documented in Factor C below, captive Sonoran desert tortoises have 
been shown to have a higher incidence of disease, and their release can 
place wild populations at risk.
    Opportunities to collect Sonoran desert tortoises often result from 
incidental observations by motorists while using dirt, gravel, or paved 
roads. In a recent study, out of a total of 561 opportunities for 
motorist-Sonoran desert tortoise interaction, 1.43 percent resulted in 
attempted collection of a live decoy, and 7.4 percent attempted the 
collection of an artificial Sonoran desert tortoise decoy (Grandmaison 
in press, pp. 8-9). Combining the data, Grandmaison (in press, p. 11-
12) found that collection attempts varied with road type and 
approximately 1 in 12 (8 percent) motorists that detect a Sonoran 
desert tortoise in the wild may attempt to illegally collect it. Adult 
tortoises are the most conspicuous and are likely the most-frequently 
collected age class, which could be detrimental to populations, 
especially when reproductive females are collected. Grandmaison (2010a, 
pers. comm.) stated, ``Illegal collection of desert tortoises is a form 
of additive mortality resulting from the impacts of roadways in 
tortoise habitat. Given that adult tortoises are the most likely 
demographic to be collected (i.e., they are easier to detect than 
juveniles or hatchlings), and the sensitivity of tortoise population 
growth rates to even small increases in adult mortality, illegal 
collection really needs to be considered when discussing the cumulative 
impacts of roads.''
    While the actual collection of Sonoran desert tortoises detected on 
roadways is one form of interaction, a higher percentage of motorists 
attempt to move Sonoran desert tortoises off the roadway when they are 
detected. Grandmaison (2010a, pers. comm.) found that 28 percent of all 
motorists passing a desert tortoise will move the tortoise off of the 
road. While moving a Sonoran desert tortoise off the roadway may be 
considered well-intended, the stress to a Sonoran desert tortoise that 
is created when it is handled may result in intestinal torsion (which 
can cause intestinal obstructions), or lead to the tortoise voiding its 
bladder. As discussed below, bladder voiding has serious implications, 
potentially resulting in decreased survival, especially during late 
spring and early summer in the Sonoran Desert, when precipitation is 
usually rare or non-existent (Grandmaison 2010a, pers. comm.; in press, 
p. 11).
    Although removal of Sonoran desert tortoises from the wild has 
clear negative effects on wild populations, their popularity as 
household pets may provide some educational benefits to the public. 
Jarchow et al. (2002, p. 310) provided evidence for potential 
conservation benefits from Sonoran desert tortoises that are already in 
captivity by stating, ``The captive population of desert tortoises 
provides not only enjoyment to their custodians but, more importantly, 
opportunities for education of the public and increased awareness of 
the species among those who may never see a desert tortoise in nature. 
Thus, the captive population may play an important role in mustering 
public support for conservation of their wild relatives.''
    In conclusion, research suggests that about 1 in 12 motorists in 
Arizona who detect a Sonoran desert tortoise will attempt to collect 
it, and that the highest incidence of collection is within the adult 
age class. The removal of an adult Sonoran desert tortoise from a 
population poses a higher threat to that population, because the 
survivorship of tortoises in this size class is the highest, and the 
odds of a given Sonoran desert tortoise reaching this size class is 
believed to be comparatively low, further adding importance to the 
maintenance of adults within a population. The removal of an adult 
female from a population also removes the opportunity for numerous 
clutches of eggs. In addition, nearly one-third of all motorists who 
encounter a Sonoran desert tortoise will attempt to move it off the 
roadway, which increases the risk of bladder-voiding, which may place 
additional physiological stress on moved tortoises and may decrease 
their survivorship. We also found data on collection and sale of 
Sonoran desert tortoises in Mexico, which is likely less of a threat in 
current times, due to the prohibition of commercial sale and to the 
demographic trend associated with more people moving to urban areas, 
reducing the number of wild encounters with tortoises in Mexico.
Field Research and Physical Manipulation
    Field research and monitoring of wild Sonoran desert tortoise 
populations has been ongoing since the 1970s, producing invaluable 
information for wildlife and habitat managers to make reasoned 
decisions with respect to conservation planning. However, some level of 
harassment or potential harm from disease transmission or dehydration 
is inherent to hands-on manipulation (such as collecting blood samples, 
affixing radio transmitters, and conducting health assessments).
    One of the more significant risks to Sonoran desert tortoises from 
the handling of wild tortoises by researchers is the increased 
potential for them to void water reserves stored in their bladder. As a 
defense mechanism when threatened, Sonoran desert tortoises may 
occasionally evacuate their bladders, releasing valuable water stores 
important for survival in their arid habitat, especially during drought 
years. Averill-Murray (2002a, p. 430) noted, ``This water loss could 
result in serious health threats or compromise normal behavior or 
physiology, especially during hot, dry summer months.'' Water loss in 
Sonoran desert tortoises can also result in reductions of reproductive 
output and survivorship (Averill-Murray 2002a, pp. 430, 433-434). 
Averill-Murray (2002a, pp. 430, 434) found that Sonoran desert 
tortoises that urinated during field research handling had a 5-13 
percent lower survival rate.

[[Page 78123]]

    Any kind of handling of tortoises during field research or 
monitoring of Sonoran desert tortoise populations during periods of 
excessive drought may be stressful to the tortoises (Berry et al. 
2002b, p. 436). Berry et al. (2006b, p. 436) recommended that 
scientists working with wild desert tortoises recognize abnormalities 
in behavior and laboratory data as early warning signs of stress to 
modify, delay, or terminate specific field protocols on stressed 
populations.
    Use of radio telemetry technology on desert tortoises may affect 
their behavior, survival, and reproductive success, but available 
literature is largely inconclusive (Boarman et al. 1998, p. 26). There 
is little doubt that radio telemetry studies have provided many 
insightful data on the biology and behavior of Sonoran desert 
tortoises, and are therefore more of a benefit than a potential threat.
    Jacobson et al. (1992, pp. 238-239) reviewed the recommended 
procedures for obtaining blood samples from desert tortoises, including 
collection from the heart, jugular vein, brachial vein, ventral 
coccygeal vein, orbital sinus, and trimmed toenails, and assessed the 
potential risks associated with each collection site. At a minimum, the 
collection of blood samples from desert tortoises is considered 
relatively invasive and is likely a source of temporary stress to the 
animal, potentially leading to bladder voiding and subsequent 
dehydration if fluid levels are not replenished before release. 
However, we believe the majority of field researchers exercise 
appropriate caution when collecting blood samples from Sonoran desert 
tortoises, and the literature does not indicate these procedures are an 
appreciable source of mortality for wild Sonoran desert tortoises.
    Over the years, field protocols have been developed and 
standardized to minimize risks to Sonoran desert tortoises while they 
are being physically handled. These protocols are outlined in Averill-
Murray (2000, p. 17) and Berry and Christopher (2001a, pp. 433-434). We 
believe these field protocols have minimized potential risks to 
individual tortoises posed by researchers during their field work.
Summary of Factor B
    We identified two possible mechanisms for which the potential 
overutilization of Sonoran desert tortoises for commercial, 
recreational, scientific, or educational purposes could occur: Illegal 
collection and field research. Many desert tortoises exist in 
captivity, and are generally available to those who want one as a 
household pet, through several channels within the captive population 
(discussed further in Factor D). In addition, efforts are being made to 
educate the public about the Sonoran desert tortoise, with an emphasis 
on leaving Sonoran desert tortoises in the wild when they are observed. 
We believe these factors may reduce the likelihood of illegal 
collection. However, a recent scientific study found that one in 12 
tortoises that is detected by a motorist (mostly adult tortoises) is 
illegally collected. We expect that in the foreseeable future, 
incidence of collection will likely increase as the human population 
grows and more people will use off-road trails, with higher frequency, 
within occupied tortoise habitat. Scientists who conduct field research 
on and monitoring of wild Sonoran desert populations have identified 
the potential risk for bladder voiding and disease transmission during 
field manipulation of tortoises, and have now built appropriate 
protocols in their field methodology to minimize these risks. Based on 
this information, we find that overutilization for commercial, 
recreational, scientific, or educational purposes, in the form of 
illegal collection, is likely to threaten the Sonoran desert tortoise 
now or in the foreseeable future.

Factor C. Disease or Predation

    Natural predation of Sonoran desert tortoises occurs as discussed 
previously in the Species Information section above. Unnatural sources 
of predation, such as from feral, or off-leash dogs, human depredation 
for recreation or as food, and as an indirect result of human land uses 
(referred to as subsidized predation) also occur. A subsidized predator 
is one whose survival in a particular area is facilitated by the 
availability of food, water, or other potentially limiting resources 
made available by the presence of human activities in that area 
(Boarman 1993, p. 192). Common examples of subsidized predators are 
coyotes and ravens. Human activity-related resources that provide basic 
biological needs for subsidized predators include such things as roads, 
landfills, sewage and septic ponds, open dumpsters, agricultural 
fields, feedlots, parks, picnic areas, livestock waters, utility poles, 
building sites, and overpasses (Boarman 1993, p. 193; Rosentstock et 
al. 2004, p. 3; Boarman et al. 2006, p. 259; Webb et al. 2009, p. 72).
    For example, Averill-Murray and Swann (2002, p. 1) stated that 
urban development adjacent to the Saguaro National Park in Pima County 
threatens the Sonoran desert tortoise via several mechanisms, including 
harassment and predation by feral or off-leash domestic dogs, and 
illegal releases of captive Sonoran desert tortoises and exotic species 
that may transmit diseases to wild Sonoran desert tortoises.
Predation by Ravens
    Ravens and coyotes are known predators on Mojave desert tortoises, 
and possibly on Sonoran desert tortoises, and are most likely to 
benefit from anthropogenic subsidization (Boarman 1993, p. 192; Boarman 
et al. 2006, p. 259). Ravens turn over hatchling desert tortoises and 
pierce through their soft plastrons, or pierce directly through their 
carapace, to access their meat and organs. Ravens are often less likely 
to emigrate long distances to colonize would-be suitable areas, but 
subsidization from human activities on the landscape create 
opportunities for rapid population growth of ravens where they formerly 
did not occur (Boarman et al. 1995, p. 1; Fleischner et al. 2008, p. 
472). Ravens, in particular, have been identified as subsidized 
predators on juvenile Mojave desert tortoises, and possibly on juvenile 
Sonoran desert tortoises (Boarman 1993, p. 192). Roads and power line 
rights of way attract potential avian predators of Sonoran desert 
tortoises, such as ravens and red-tailed hawks that use power lines as 
nesting and perching sites, and roads can serve as sources of carrion 
(Knight and Kawashima 1993, p. 266). Raven populations, and potential 
risk of predation of Sonoran desert tortoises by ravens, are both 
higher with increasing proximity to human development (Kristan and 
Boarman 2003, p. 2432).
    Documented reports of raven predation on Sonoran desert tortoises 
are rare in the literature, however. One local rancher in southeastern 
Mohave County, Arizona, reported an observation of raven predation on a 
Sonoran desert tortoise (Dieringer 2010, p. 1). Ravens have also been 
observed on the Four Peak monitoring plot on several occasions, but 
their predation on Sonoran desert tortoises within this plot has never 
been documented (Murray and Schwalbe 1997, p. 33). Mojave desert 
tortoises are most commonly associated with valley bottomlands 
characterized by relatively open, sparse vegetation communities which 
may be advantageous to a purely visual-based predator such as the 
raven. In Arizona Upland Sonoran desertscrub, where Sonoran desert 
tortoises reach their peak population densities, habitat is a more 
complex mosaic of boulders and denser vegetation, which would hamper 
the ability of such predators to locate

[[Page 78124]]

prey, in particular, small hatchlings. Some exceptions include habitat 
within sparsely vegetated valley bottoms that are used for dispersal 
between populations on adjacent mountains or foothills, or similar, 
uncharacteristic areas that maintain Sonoran desert tortoise 
populations, such as the Florence Military Reservation. The best 
scientific and commercial data available indicates that predation by 
ravens is significantly less of a concern for Sonoran desert tortoises 
than it is for Mojave desert tortoises.
    In conclusion, although raven predation has been identified as a 
substantial threat to the Mojave desert tortoise, largely because of 
the relatively open, valley bottomland where they occur, the risk to 
Sonoran desert tortoise populations is relatively low. Very few 
observations of raven predation of Sonoran desert tortoises in Arizona 
or Sonora have been documented in the literature, leading us to 
conclude that raven predation on the Sonoran desert tortoise is not a 
concern.
Predation From Feral or Off-Leash Dogs
    Feral dogs are known to interact with numerous species of animals, 
including desert tortoises and related species, and they may force 
Sonoran desert tortoises to use their habitat in an unnatural manner 
(Causey and Cude 1978, pp. 94-95; Lenth et al. 2008, pp. 222-223). The 
risk of feral or off-leash dog predation on Sonoran desert tortoises is 
expected to be highest within the urban-rural interface (a likely 
source of domesticated, feral dogs).
    Jones (2008, p. 66) documented 35 separate incidences of harassment 
by wild or domestic dogs in surveys conducted in high-use public lands 
adjacent to the urban centers of Tucson, Phoenix, and Kingman, Arizona 
(Pima, Maricopa, and Mohave Counties, respectively), based upon 
observed shell damage. These incidences were positively correlated with 
increasing proximity to urban centers. Also, three to five packs of 
presumably feral dogs were observed in both the East Bajada monitoring 
plot in Mohave County and in Saguaro National Park West in Pima County 
(Jones 2008, p. 66). Researchers of Sonoran desert tortoises within the 
Tucson Mountain District of Saguaro National Park noted a high number 
of tortoises with injuries consistent with dog attacks, attributing 
these observations to the close proximity of this district to urban 
development (Zylstra and Swann 2009, pp. 14-15). The AGFD (2010, pp. 
11-12) reported that domestic dogs, their scat, and chew marks on, or 
trauma to, Sonoran desert tortoises have been reported in 47 percent of 
the monitoring plots. Three such plots occur within 1 mi (1.6 km) of 
developed areas. Domestic dogs have been observed attacking and chewing 
on Sonoran desert tortoises in the Hualapai Foothills and Bonanza Wash 
plots (AGFD 2010, p. 12). Domestic dogs appear to be a significant 
problem, which may be worsening, in the East Bajada plot, where in 
1997, 53 percent of live tortoises, and in 2002, 78 percent of live 
tortoises, exhibited injuries associated with domestic dogs (AGFD 2010, 
p. 12). One citizen commented that in 1997 a purebred Rottweiler was 
observed roaming freely on the Ironwood Forest National Monument with 
an adult Sonoran desert tortoise in its jaws. The tortoise was mortally 
wounded from a punctured carapace, suggesting that large, powerful 
domestic dog breeds may be able to penetrate the carapace of adult 
tortoises and kill them (Coping 2009, p. 7).
    Numerous signs of attempted predation (consistent with those from 
feral dogs), ranging from mild to severe, were observed in wild Sonoran 
desert tortoises examined in Sonora, Mexico (Brown et al. 2006, p. 6). 
We are unaware of the locations where these wild Sonoran desert 
tortoises were captured by Brown et al., but the proximity to human 
settlements, and free-ranging domestic dogs (a common sight in Mexico) 
may have been responsible.
    In conclusion, the threat of feral dog predation exists in both 
Arizona and Sonora, Mexico, and has been shown to be strongly 
correlated with distance to urbanized areas in most cases. We found 
numerous reports of observed or suspected feral dog predation in the 
literature, most in immediate proximity to urban areas. Feral dog 
predation has been documented in approximately half of the long-term 
monitoring plots in Arizona, and may be a significant cause of 
population decline in one plot. As urbanization and human population 
growth continues into the future, as described in Factor A, the 
incidence of feral dog predation of Sonoran desert tortoises is 
expected to also increase.
Human Depredation and Vandalism
    Human depredation (intentional killing) of Sonoran desert tortoises 
has been documented to occur either as a result of vandalism (most 
commonly via gunshot) or as a source of food. The intentional shooting 
of Mojave desert tortoises in southern California was reported to be 
relatively common, at least before the Mojave population was Federally 
listed. Berry (1986b, p. 127) found that 14 percent of 635 carcasses 
taken from 11 sites in the Mojave Desert over a 6-year time period 
exhibited signs of gunshots. Many of these observations occurred before 
the listing of the Mojave desert tortoise, indicating that tortoises 
may have been shot simply for misdirected recreational sport or 
entertainment, not from politically-driven motives (people disliking 
the protections of the Act). Bury and Marlow (1973, p. 11) described 
examples of Mojave desert tortoise mortalities in California as a 
result of shooting, including eight independent observations of shot 
Mojave desert tortoises along two miles (3.2 km) of dirt road; an 
individual's confession of using juvenile desert tortoises as skeet 
(aerial shotgun) targets; and a report of an individual lining up a 
total of 47 desert tortoises and shooting each of them with a shotgun.
    Recreational firearms target practice occurs in dispersed fashion 
throughout Federal and State lands in Arizona within the distribution 
of Sonoran desert tortoises. Some reports of gunshot deaths of Sonoran 
desert tortoises on these lands have been made (Hart et al. 1992, p. 
120; AGFD 2010, p. 9; Jones 2010, pers. comm.). In some locations, 
recreational firearms target practice is highly conspicuous (as 
evidenced by large amounts of debris used as targets and left behind) 
in densely occupied Sonoran desert tortoise habitat, most notably in 
areas near urban population centers, such as at Sugarloaf Mountain on 
the Cave Creek Ranger District of the Tonto National Forest. In this 
location, two incidences of shot Sonoran desert tortoises have been 
reported, although it could not be determined whether these wounds 
occurred pre- or post-mortem (Jones 2010, pers. comm.). Another 
incidence of shooting was reported in the Hualapai Foothills monitoring 
plot (Hart et al. 1992, p. 120). The AGFD (2010, p. 9) reported 13 
separate incidences of vandalism on Sonoran desert tortoises on or 
adjacent to 7 different monitoring plots; several of the Sonoran desert 
tortoises appeared to have been killed by gunshot.
    When studying Mojave desert tortoises, Berry (1986b, p. 129) found 
that the incidence of gunshot deaths is likely to be higher in areas of 
greater vehicular access and in proximity to urban areas. The potential 
effect of gunshot deaths on Sonoran desert tortoise populations is not 
entirely known, but is likely most significant on the adult size class, 
which is the most conspicuous, and this effect may act synergistically 
with other threats we have identified. Combined with the relatively low 
recruitment rate of juvenile desert tortoises into adult size

[[Page 78125]]

classes, adverse effects to survivorship of populations adjacent to 
urban areas might be expected (Berry 1986b, p. 130).
    Sonoran desert tortoises are sometimes used as a food source in 
Sonora, and likely experience population declines where they occur 
adjacent to moderately sized settlements (Fritts and Jennings 1994, p. 
52). Bury et al. (2002, p. 102) reported several historical incidences 
of Sonoran desert tortoises being used as a source of food by native 
peoples in Sonora, but less frequently in current times. According to 
12 interviews at 6 ranches in central Sonora, 67 percent of local 
people described Sonoran desert tortoises as declining. All but one 
interviewee stated they have eaten Sonoran desert tortoise meat at some 
point in their lives (Bury et al. 2002, p. 102). However, demographic 
trends in Sonora indicate the number of people living on ranches and 
ejidos (commonly owned lands used for agriculture and livestock 
grazing) have declined, while city populations have increased, 
potentially reducing the likelihood of Sonoran desert tortoises being 
used for food (Bury et al. 2002, pp. 102-103).
    Sonoran desert tortoises have also been documented as a food source 
for undocumented immigrants on their journey through the Sonoran Desert 
of Arizona, specifically in the Ironwood Forest National Monument. 
Coping (2009, p. 4) claims that by the time undocumented immigrants 
reach the Ironwood Forest National Monument, many have been abandoned 
by their guides and left without food, water, or a sense of direction, 
leaving them in intense desperation (Coping 2009, p. 4). In one 
instance on June 2, 1997, a small group of undocumented immigrants 
approached a resident living within the Ironwood Forest National 
Monument. The immigrants had a live Sonoran desert tortoise they had 
captured along the way that had a rope tethered to its front leg. They 
told this resident that if they did not receive food from him, they 
planned to eat the tortoise (Coping 2009, p. 5). In another reported 
observation, a livestock grazing permittee on the Ironwood Forest 
National Monument stated that he had seen immigrants carrying 
tortoises, ``presumably with the intent to consume'' (Averill-Murray 
and Averill-Murray 2002, p. 29). Indigenous communities of the Sonoran 
Desert historically used Sonoran desert tortoises for food and 
medicine, and their shells for ladles, dippers, bowls, and shovels 
(Nabhan 2002, p. 356). However, we have no information to suggest these 
uses have continued into modern times.
    In conclusion, direct human depredation on Sonoran desert tortoises 
is most likely to occur via vandalism (i.e., shooting) and utilization 
as a source of food. While the deliberate shooting of Sonoran desert 
tortoises has been documented in Arizona, reports are comparatively 
rare, especially considering the amount of monitoring and survey effort 
that has been afforded to wild populations over the past several 
decades. However, as the human population continues to grow and 
urbanization expands, we expect the incidence of human depredation to 
increase. Sonoran desert tortoises have been used for food in Mexico 
historically, but these occurrences are suspected to be comparatively 
rare in current times. Sonoran desert tortoises may also be captured by 
undocumented immigrants as they pass through remote areas of Arizona, 
but increasing border-enforcement activities are expected to reduce the 
number of undocumented immigrants entering Arizona in the foreseeable 
future, reducing this risk.
Upper Respiratory Tract Disease
    The threats of mycoplasmosis (or upper respiratory tract disease 
(URTD)), and cutaneous dyskeratosis (shell disease) were major factors 
in the listing of the Mojave desert tortoise (Berry 1997, p. 91). 
Genetic analyses were performed by Brown et al. (1994, p. 4580) on 
seven Mycoplasma organisms that were recovered from the upper 
respiratory tract of clinically ill desert tortoises. These laboratory 
tests led to the discovery and subsequent species description of 
Mycoplasma agassizii, the species of bacteria that causes upper 
respiratory tract disease in infected tortoises (Berry and Christopher 
2001b, p. 413). Although M. agassizii has been studied in Mojave and 
Sonoran desert tortoises, as well as gopher tortoises (G. polyphemus), 
since the 1980s, its origins are unknown. It may be a naturally 
occurring or an exotic pathogen. There are several potential routes of 
inoculation of vertebrates by microbiota such as Mycoplasma spp., 
including horizontal (transmission between individuals), vertical 
(passed down from parent to offspring), and environmental (passed from 
environment to individual) (Belden and Harris 2007, p. 536). Brown 
(2002, p. 1340) states that direct contact with infected individuals is 
the most likely route of transmission. Brown (2003, p. 1) stated that 
M. agassizii is not known to be transferred through the eggshell.
    Disease may be spread to wild populations as a result of the 
release of captive native or nonnative tortoise species, which can be 
carriers of diseases that could affect wild Sonoran desert tortoises 
(Howland and Rorabaugh 2002, p. 343). The release of any captive 
reptile or amphibian is strictly prohibited by the AGFD. In a study 
investigating the relationship between exposure to M. agassizii and an 
urban gradient of Greater Tucson, Arizona, Jones (2008, p. 36-37) found 
evidence to suggest a positive correlation between the likelihood of 
testing seropositive for antibodies to M. agassizii (meaning a tortoise 
has been exposed to URTD), and proximity to urban centers. These 
results suggest that there may be a relationship between urbanization 
and this pathogen. Tortoises from suburban sites are 2.3 times more 
likely to test seropositive for antibodies to M. agassizii than 
tortoises from other sites in the greater Tucson area. In fact, Sonoran 
desert tortoise populations in the Rincon Mountains (adjacent to 
Tucson, Arizona) had the highest prevalence of exposure to URTD of any 
sites tested in Arizona, with 72.7 percent of sampled Sonoran desert 
tortoises identified as seropositive (Jones 2008, p. 93).
    Jones (2008, p. 60) also explored the relationship between URTD and 
captive and wild desert tortoises from high-use public lands in 
Maricopa, Mohave and Pima counties, and found that captive desert 
tortoises are 1.8 times more likely to test seropositive for exposure 
to M. agassizii than wild tortoises (p. 65). Sonoran desert tortoises 
from Pima County (wild and captive) had the highest incidence of 
exposure to URTD and were 5.4 times more likely to be seropositive for 
antibodies to M. agassizii than those from Mohave or Maricopa Counties 
(Jones 2008, p. 65). While clinical signs of URTD are infrequently 
observed in wild Sonoran desert tortoises in Arizona, Jones (2008, pp. 
37, 74) found that M. agassizii is widespread among captive desert 
tortoises in Arizona, suggesting that the captive population may be an 
important reservoir of URTD-infected tortoises that can spread the 
disease to wild populations if unlawfully released or allowed to 
escape.
    Even though URTD appears to occur widely and has been documented in 
Sonoran desert tortoise populations, no die-offs have been attributed 
to URTD in Arizona. Currently, URTD does not appear to be a source of 
mortality for Sonoran desert tortoise populations (Hart et al. 1992, p. 
120; AIDTT 2000, p. 9; Averill-Murray and Klug 2000, p. 69; Dickinson 
et al. 2002, p. 256; Howland and Rorabaugh 2002, p. 343; Jones 2008, p. 
22; AGFD 2010, p. 9). Howland and Rorabaugh (2002, p. 343) hypothesized 
that if disease does

[[Page 78126]]

become a significant threat to Sonoran desert tortoise populations in 
the future, their patchy distribution may limit the spread of disease. 
However, because the captive population of desert tortoises may serve 
as a reservoir of disease and because captives are unlawfully released 
into the wild by the public, monitoring wild tortoise populations that 
occur near urban areas will continue to be important (Howland and 
Rorabaugh 2002, p. 343; Jones 2008, pp. 6-7, 41, and 72-73).
    An indirect effect of disease is that it may also subject 
individuals to increased predation. Sonoran desert tortoises that are 
exhibiting clinical signs of URTD may be more active during winter 
months, in order to increase their metabolism and elevate their body 
temperatures. This increase in surface activity might result in a 
greater chance of predation or human detection (Jones 2008; p. 105). 
Jones (2008, p.103) found that periods of surface activity may increase 
in clinically ill Sonoran desert tortoises; however, home range size 
did not differ between seropostive and seronegative tortoises (p. 103), 
so seropositive tortoises which are more active in winter months do not 
appear to be increasing the areas over which they move.
    Wild Sonoran desert tortoises in Sonora, Mexico, were tested for 
the presence of antibodies to two Mycoplasma species, M. agassizii and 
M. testudineum, and were found to be generally unexposed (Brown et al. 
2006, p. 5). Twenty-seven of 28 wild Sonoran desert tortoises were 
found to be seronegative, indicating they had not been exposed to 
Mycoplasma spp.; and one individual was serosuspect (a result 
indicating that the antibody level is intermediate between positive and 
negative, and is considered inconclusive) for M. testudineum (Brown et 
al. 2006, p. 5). However, 11 of 21 captive Sonoran desert tortoises in 
Sonora, Mexico, tested seropositive for antibodies, indicating exposure 
to M. agassizii; and four were serosuspect for exposure to M. 
testudineum. Ten captive desert tortoises had M. agassizii isolated 
from nasal flushes, indicating a current infection, suggesting that 
disease may be more prevalent in the Sonora captive population (Brown 
et al. 2006, pp. 5-6). Nearly all of the captive desert tortoises 
exhibited mild to severe clinical signs of URTD. Of the captive 
tortoises, six had swollen or draining chin glands and four had 
evidence of nasal discharge (Brown et al. 2006, p. 5-6). Once infected 
by URTD, tortoises may ultimately die from the disease.
Cutaneous Dyskeratosis
    Cutaneous dyskeratosis, a shell disease, was also a major factor 
considered in the listing of Mojave desert tortoises. In populations of 
Mojave desert tortoises exhibiting clinical signs of this disease, 
significant die-offs have been documented, some as high as 70 percent 
mortality rate (Jacobson et al. 1994, p. 69). Cutaneous dyskeratosis 
may appear on the carapace, plastron, and thickened scales of the 
forelimbs, but is most often apparent on the plastron (Jacobson et al. 
1994, pp. 70-74). Potential causes of cutaneous dyskeratosis have not 
been confirmed, but may be related to deficiency diseases and 
environmental contamination (Berry 1997, p. 91).
    Cutaneous dyskeratosis has been reported as more prevalent than 
URTD within Sonoran desert tortoise populations across Arizona. As of 
2000, Sonoran desert tortoises infected with cutaneous dyskeratosis had 
been observed in every monitored population, with the exception of the 
Wickenburg Mountains plot (AIDTT 2000, p. 9; Averill-Murray and Klug 
2000, p. 69). However, noticeable population-level effects have not 
been reported in any of the monitoring plots (AIDTT 2000, p. 9; 
Averill-Murray and Klug 2000, p. 69; AGFD 2010, p. 9). Of the 36 
individual Sonoran desert tortoises sampled from the Little Shipp Wash 
and the Harcuvar Mountains from 1990 to 1994, only 5 (all females 
presumed to be at least 30 years old) had signs of cutaneous 
dyskeratosis, and all lived through the end of the field study. This 
prompted Dickinson et al. (2002, p. 258) to suspect that Sonoran desert 
tortoises might not be affected by this disease, although they 
acknowledged that more research was necessary. As of 2000, the highest 
incidence of cutaneous dyskeratosis (62 percent of individuals) was 
reported from the East Bajada plot (AIDTT 2000, p. 9). In Sonora, 
Mexico, 14 of the 28 wild Sonoran desert tortoises examined exhibited 
clinical signs of cutaneous dyskeratosis (Brown et al. 2006, p. 6).
    In conclusion, disease has been documented as a serious threat to 
the Mojave desert tortoise, and was a primary cause for its listing 
under the Act. The two most prevalent diseases that could affect 
Sonoran desert tortoise populations are URTD and cutaneous 
dyskeratosis. Researchers have speculated that Sonoran desert tortoises 
may be able to clear infections of M. agassizii, and no wild Sonoran 
desert tortoises have been found to have died from URTD in Arizona, 
although it is nearly impossible to document the precise cause of death 
in many situations. The literature documents that Sonoran desert 
tortoise populations in proximity to urbanized areas are most at risk 
of disease (as a result of released captives), because the captive 
population (both in Arizona and Mexico) has a significantly higher 
percentage of seropositive tortoises and tortoises that have acquired 
URTD. Cutaneous dyskeratosis has been documented in virtually all 
Sonoran desert tortoise long-term monitoring plots in Arizona, although 
no Sonoran desert tortoises have been documented to have succumbed to 
this disease, and we conclude that cutaneous dyskeratosis is not a 
substantial threat to populations. Disease screening has been a regular 
component to field research and monitoring of wild Sonoran desert 
tortoise populations throughout their range for many years, and has not 
indicated that either URTD or cutaneous dyskeratosis pose a current 
threat to the Sonoran desert tortoise.
    For additional information on disease in desert tortoises, or 
specific disease data from monitored Sonoran desert tortoise 
populations, see Hart et al. (1992, p. 120); Berry (1997, p. 91); Brown 
et al. (1994, p. 4580; 1995, p. 350; 2002, p. 497; 2006, pp. 5-6); 
Jacobson et al. (1994, pp. 69, 70-74); Schumacher et al. (1999, pp. 
829-830); AIDTT (2000, p. 9); Averill-Murray and Klug (2000, p. 69); 
Berry and Christopher (2001b, p. 413); Averill-Murray and Averill-
Murray (2002, pp. 16, 19, 26); Brown (2002, pp. 1340, 1343; 2003, p. 
1); Dickinson et al. (2001, pp. 254-256; 2002, pp. 256, 258, 260-261; 
2005, p. 841); Howland and Rorabaugh (2002, p. 343); Tracy et al. 
(2006a, p. 1191); Belden and Harris (2007, pp. 536, 538); Wendland et 
al. (2007, p. 1190); Jones et al. (2005, p. 1); Boarman and Kristan 
(2008, p. 19); Jones (2008, pp. 6-7, 70, 93, 103, 105); Zylstra and 
Swann (2009, pp. ix-x); and AGFD (2010, p. 9).
Summary of Factor C
    In review of the information presented above, we conclude that 
predation from feral domestic dogs and, to a lesser extent, human 
depredation and vandalism, in combination with other threats, threaten 
Sonoran desert tortoise populations, most notably as a result of the 
expansion of urbanization and associated increases in human activity in 
remote areas. We conclude this threat to be of moderate magnitude. 
Based upon our review of the available literature, disease does not 
appear to be significantly affecting the status of wild Sonoran desert 
tortoise populations. Therefore, we conclude that disease

[[Page 78127]]

does not pose a significant threat to the Sonoran desert tortoise now 
or in the foreseeable future.

Factor D. The Inadequacy of Existing Regulatory Mechanisms

    Within its distribution in the United States, the Sonoran desert 
tortoise occurs on lands managed by a myriad of Federal and State 
agencies and Native American tribes, and on private lands. State 
agencies, such as the Arizona Game and Fish Department (AGFD) or the 
Arizona Department of Transportation (ADOT), have either direct 
management authority over the Sonoran desert tortoise, or could 
potentially impact Sonoran desert tortoise populations or habitat 
directly or indirectly in carrying out their intended missions. 
Internationally, the Sonoran desert tortoise is listed in Appendix I of 
the Convention on International Trade in Endangered Species of Wild 
Fauna and Flora (commonly referred as to CITES), which requires permits 
to transport individuals between member nations (Bury et al. 2002, p. 
86; Howland and Rorabaugh 2002, p. 348). Under the International Union 
for Conservation of Nature's ``Red List,'' the desert tortoise 
(rangewide) is considered ``vulnerable''--meaning it faces a high risk 
of extinction in the medium-term (Rorabaugh 2008, p. 27). In our 
review, we found that the Sonoran desert tortoise is commonly 
considered in conservation planning where it occurs on public or tribal 
lands in Arizona. Below we discuss how each agency or entity manages 
their land, or otherwise considers the Sonoran desert tortoise in their 
planning activities.
U.S. Bureau of Land Management
    BLM is very proactive in their conservation management, directly 
and indirectly, through three main mechanisms: (1) Sonoran desert 
tortoise habitat categorization and compensation (monies derived from 
adverse effects to Sonoran desert tortoise habitat for the acquisition 
of new habitat, funding research, etc.); (2) resource management 
planning; and (3) land designation. The BLM has developed numerous 
documents that outline how Sonoran desert tortoise habitat management 
goals and objectives are to be achieved and accounted for in their land 
use planning.
    The BLM developed the document titled ``Desert Tortoise Management 
on the Public Lands: A Rangewide Plan'' (authored by Spang et al. 
1988), and created the designation of three categories of desert 
tortoise habitat throughout the species' range, using four main 
criteria to indicate the importance of the habitat: (1) Maintaining 
viable populations, (2) resolvability of conflicts, (3) desert tortoise 
density, and (4) population status (stable, increasing, or decreasing) 
(AIDTT 2000, p. 16; USBLM 2010, p. 1). The BLM categorized habitat 
based upon its suitability for the desert tortoise, with Category I 
being the most suited, and Category III the least, with the goals of 
maintaining viable desert tortoise populations in Category I and II 
habitat, and limiting population declines in Category III habitat to 
the extent possible (AIDTT 2000, p. 16). However, not all Sonoran 
desert tortoise habitat was included in this categorization process.
    AIDTT (2000, p. 19) depicts the distribution of the categorized 
habitat included in Arizona. In Arizona, there are 723,769 ac (292,899 
ha) of Category I Sonoran desert tortoise habitat, 2.6 million ac (1.1 
million ha) of Category II habitat, and 3.8 million ac (1.5 million ha) 
of Category III habitat, totaling 7.1 million ac (2.9 million ha) of 
categorized habitat (AIDTT 2000, p. 18). The 1988 Rangewide Plan also 
indentified 14 different management objectives the BLM has defined 
specifically for desert tortoise management, each with its own itemized 
management action plan. These management objectives include the 
following categories: (1) Increased awareness; (2) inventory and 
monitoring; (3) cumulative impacts; (4) identification of endangered 
populations; (5) coordination and cooperation; (6) research and 
studies; (7) management of tortoise habitat; (8) regulation of lands 
and realty actions; (9) regulation of off-highway vehicles; (10) 
regulation of livestock use; (11) regulation of wild horses and burros; 
(12) wildlife habitat management; (13) predator control; and (14) 
management of energy and minerals research and extraction (Spang et al. 
1988, pp. 14-23; AIDTT 2000, p. 18).
    In 1990, BLM's Arizona State Office issued the policy titled 
Strategy for Desert Tortoise Habitat Management on Public Lands in 
Arizona, Instruction Memorandum No. AZ-91-16. It outlined objectives 
and management actions to be implemented, and also established the BLM 
Desert Tortoise Mitigation Policy, which was later reissued in 1999 
(USBLM 2010, p. 2). In 2009, the BLM finalized the Desert Tortoise 
Mitigation Policy, in order ``to articulate mitigation policy including 
off-site compensation for the Sonoran desert tortoise and its habitat 
on public lands managed by (BLM) in Arizona, in a consistent manner 
between District and Field Offices'' (USBLM 2009b, p. 1). The BLM's 
Desert Tortoise Mitigation Policy ``establishes policy to mitigate for 
impacts to desert tortoises and their habitats including compensation 
for residual impacts that cannot otherwise be mitigated. Mitigation, 
including compensation must be designed to meet the purposes of the 
Rangewide Plan, including maintaining viable populations as well as 
maintaining the quantity and quality of Category I and II desert 
tortoise habitat'' (USBLM 2009b, p. 1). Compensatory funds derived from 
BLM's compensation policy are then used for a variety of conservation 
activities to lessen impacts to Sonoran desert tortoises including 
protective tortoise fencing, culverts for crossing, land acquisition, 
and research (AIDTT 2000, p. 19). Details of this policy can be found 
in USBLM (2009b, pp. 1-45).
    The BLM implements various objectives and management actions 
through resource management plans unique to certain geographic regions 
of BLM-managed lands (USBLM 2010, p. 3). Currently, there are eight 
individual resource management plans, some recently issued and others 
up to 22 years old, representing the areas with potential Sonoran 
desert tortoise habitat (USBLM 2010, p. 3). The Phoenix Resource 
Management Plan, which directs the management of approximately 440,000 
ac (178,000 ha) of Sonoran desert tortoise habitat, does not contain 
district-specific management actions, but incorporates management 
actions described in the Strategy for Desert Tortoise Habitat 
Management on Public Lands in Arizona (USBLM 2010, p. 3). Approximately 
1.1 million ac (455,000 ha) in the Yuma, Lake Havasu, Bradshaw-
Harquahala, and Kingman resource management planning areas that were 
considered Sonoran desert tortoise habitat have been designated as 
``priority habitats,'' meaning that the BLM prioritizes management of 
wildlife habitat over other multiple-use activities (USBLM 2010, p. 3).
    The BLM can directly or indirectly manage for the Sonoran desert 
tortoise through the process of land designation, such as Areas of 
Critical Environmental Concern (ACEC) and Wilderness Areas. In the case 
of ACECs, those values may pertain to specific species or habitats, or 
cultural or scenic values (AIDTT 2000, p. 22). Sonoran desert tortoises 
were the impetus for the Poachie and McCracken ACECs, while other ACECs 
benefit the Sonoran desert tortoise through broad protections, such as 
in the Agua Fria and Ironwood Forest National Monuments (AIDTT 2000, p. 
22). Sixteen Arizona ACECs contain Sonoran

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desert tortoise habitat (AIDTT 2000, p. 22). ACEC designations 
facilitate the minimization of surface-disturbing activities, such as 
vehicular travel, camping, fire use, mineral extraction activities, and 
grazing (AIDTT 2000, p. 22). There are also 48 wilderness areas managed 
by the BLM in Arizona, including approximately 850,000 ac (344,000 ha) 
of Sonoran desert tortoise habitat, through ``reclaiming damaged areas, 
reclaiming old vehicle ways and routes, establishing campfire and 
camping policies to avoid resource impacts, establishing livestock 
grazing use objectives with respect to desired vegetation, setting 
objectives for wildlife habitat including the desert tortoise, and 
setting prescriptions for wildfire'' (AIDTT 2000, pp. 22-23). In 
addition, the BLM manages Sonoran desert tortoise habitat in Wilderness 
Areas and National Monuments with an emphasis on maintaining natural 
conditions and biological function of these areas (USBLM 2010, p. 10). 
Approximately 22 percent of categorized Sonoran desert tortoise habitat 
falls under these management prescriptions on BLM lands in Arizona 
(USBLM 2010, p. 10).
    Livestock grazing is the most widespread land-use activity 
permitted on BLM lands, with 273 individual allotments covering 
approximately 6 million ac (2.4 million ha), and 74 percent of Sonoran 
desert tortoise habitat in the U.S. on their lands (Rosmarino and 
Connor 2008, p. 49). A policy was developed by the BLM's Arizona State 
Office in 1994, addressing livestock use of upland vegetation growth in 
response to significant winter precipitation, ensuring adequate amounts 
of forage remained for the Sonoran desert tortoise (and other species) 
before and after livestock use. These ``ephemeral'' pastures or 
allotments are permitted for 30 days of livestock grazing, with 
additional 30-day extensions if monitoring concludes adequate forage 
capacity exists (AIDTT 2000, p. 22). AIDTT (2000, p. 22) viewed this 
grazing policy as a ``significant protective change that ensured forage 
for other animals, such as desert tortoises, and also ensured that 
perennial plants would not be damaged due to insufficient ephemeral 
growth.'' In 1997, the BLM (USBLM 1997, pp. 1-18) further developed 
standards and guidelines for livestock grazing and rangeland health. In 
upland sites, the BLM standard is ``Upland soils exhibit infiltration, 
permeability, and erosion rates that are appropriate to soil type, 
climate and landform (ecological site)'' (USBLM 1997, p. 5). To assess 
whether an allotment is meeting this standard, the BLM uses descriptive 
criteria that pertain to soil conditions, ground cover, and erosion 
rates (USBLM 1997, p. 5).
    The BLM generally prohibits mineral material sales (mining 
activities) in Category I and II Sonoran desert tortoise habitat, but 
requests are evaluated on a case-by-case basis (USBLM 2010, p. 3). For 
example, in the Phoenix District, the BLM has denied 11 such mineral 
material sales, while others have been denied in the Tucson District, 
to prevent potential impacts to Sonoran desert tortoises and their 
habitat (USBLM 2010, p. 4).
    In summary, the BLM considers the Sonoran desert tortoise in its 
land management planning and has denied or altered projects which could 
adversely affect the Sonoran desert tortoise or its habitat, 
specifically with respect to mining and livestock-grazing activities. 
However, we are not aware of specific actions the BLM is taking with 
respect to invading nonnative plant species and subsequent wildfire 
concerns, vandalism of tortoises, feral dog predation, or management to 
counter anticipated climate change. In addition and as discussed below, 
BLM management of off-highway vehicle use on their lands is not 
protective of Sonoran desert tortoise populations. Therefore, we 
conclude that BLM management of the Sonoran desert tortoise and its 
habitat is currently inadequate.
U.S. Forest Service
    The Sonoran desert tortoise is included on the U.S. Forest 
Service's Regional Forester's Sensitive Species List, which means it is 
evaluated in all biological evaluations for activities and projects 
proposed within its habitat (AIDTT 2000, p. 35). Sonoran desert 
tortoises occur on the Prescott (Bradshaw Ranger District), Coronado 
(Santa Catalina and Nogales Ranger Districts), and Tonto National 
Forests in Arizona (Murray and Schwalbe 1993, p. 39). The Tonto 
National Forest manages the most Sonoran desert tortoise habitat of the 
three National Forests in Arizona, where they occur in the Cave Creek, 
Mesa, Globe, and Tonto Basin Ranger Districts.
    Multiple land uses occur on these National Forests, including 
recreation, camping, livestock grazing, and off-highway vehicle use. 
Approximately 46 livestock grazing allotments on the Tonto National 
Forest partially or wholly overlap the potential range of the Sonoran 
desert tortoise, with several rated as having impaired or 
unsatisfactory soil conditions (AIDTT 2000, p. 37). We are not aware of 
the exact number of livestock grazing allotments that overlap Sonoran 
desert tortoise habitat on the Coronado or Prescott National Forests. 
With the exception of livestock grazing, the majority of land uses that 
have the highest potential to affect the Sonoran desert tortoise occur 
in districts adjacent to urbanized areas, such as the Santa Catalina 
Ranger District on the Coronado National Forest (adjacent to the Tucson 
metropolitan area) and the Cave Creek and Mesa Ranger Districts on the 
Tonto National Forest (adjacent to the Phoenix metropolitan area). 
While the Coronado National Forest does not have specific management 
policies for the Sonoran desert tortoise, two policies may serve its 
benefit: (1) ``Provide habitat for wildlife populations consistent with 
the goals outlined in the Arizona and New Mexico Department of Game and 
Fish Comprehensive Plans and consistent with other resource values;'' 
and, (2) ``Provide for ecosystem diversity by at least maintaining 
viable populations of all native and desirable nonnative wildlife, 
fish, and plant species through improved habitat management'' (AIDTT 
2000, p. 36).
    In September 2005, Region 3 of the U.S. Forest Service adopted a 
new policy for rangeland adaptive management (USFS 2007, pp. 1-34), 
called the Chapter 90 policy. Under this policy, limits on timing, 
intensity, frequency, and duration of livestock grazing are set in 
Allotment Management Plans. Monitoring and adaptive management are key 
attributes of the Chapter 90 policy and are intended to ensure 
livestock grazing outcomes meet desired resource conditions which 
include the needs of wildlife such as the Sonoran desert tortoise. The 
term ``conservative use'' in this policy is defined as forage 
utilization on key forage species between 30 and 40 percent or less of 
annual forage production by weight for herbaceous perennials, and 50 
percent or less on woody browse species (USFS 2007, pp. 26, 30). It is 
inherent in the term ``conservative use'' that watershed conditions and 
vegetative ground cover will be optimized as appropriate to various 
range sites. At no time is excessive use considered acceptable. The 
goal is to achieve conservative use in the uplands over successive 
years. This strategy recognizes the importance of adaptive management, 
and may include adjustments of timing, intensity, frequency, and 
duration of grazing to reach resource objectives (USFS 2007, pp. 13-
14).
    Implementation monitoring of livestock grazing under conservative 
use practices can be done using a variety of methods, and is designed 
to provide

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information that will enable decision-makers to practice adaptive 
management by making necessary changes needed for plant development and 
recovery, and to assess physical improvements to allotments (USFS 2007, 
pp. 16-17). Effectiveness monitoring of conservative use practices 
documents whether management actions are having the expected progress 
toward achieving resource-management objectives, and is used to track 
upland vegetative and soil condition over the long term (USFS 2007, pp. 
16-17). From a short-term (within-year) perspective, wildlife habitat 
and watershed conditions are gauged by monitoring seasonal utilization 
on key forage species during the grazing period. Due to a warmer 
climate, variable precipitation, and mild winters, seasonal-utilization 
monitoring is important because the end of a particular growing season 
is not well-defined for all plant communities in Sonoran desert 
tortoise habitat on Forest Service lands. In review of this policy, we 
conclude that implementation of the Forest Service's rangeland 
management strategy is likely to retain physical characteristics 
necessary to provide for the necessary forage and shelter requirements 
for Sonoran desert tortoise.
    In summary, the USFS considers the Sonoran desert tortoise in all 
biological evaluations for activities and projects proposed within its 
habitat. The USFS has developed a system of adaptive management for 
livestock grazing on their lands, using resource monitoring to indicate 
when changes in land conditions occur or prescribed use levels are 
unsustainable, preventing excessive harm to sensitive Sonoran desert 
tortoise habitat. However, we are not aware of specific actions the 
USFS is taking with respect to management of invasive, nonnative plant 
species and subsequent wildfire concerns, vandalism of tortoises, feral 
dog predation, or efforts to counter anticipated climate change. In 
addition, and as discussed below, USFS management of off-highway 
vehicle on their lands is not protective of Sonoran desert tortoise 
populations. Therefore, we conclude that USFS management of the Sonoran 
desert tortoise and its habitat is currently inadequate.
Off-Highway Vehicle Management and Enforcement on Public Lands
    While both the USFS and BLM have developed broad, strategic plans 
to manage off-highway vehicle use, these plans have been found to be 
missing some key elements that could improve off-highway vehicle 
management, such as results-oriented goals, strategies to achieve the 
goals, timeframes for implementing strategies, or performance measures 
to monitor incremental progress (USGAO 2009, p. 16). Limitations of the 
USFS's strategic plan have resulted from a general failure to address 
motorized travel designations on the ground, communicate with the 
public, monitor off-highway vehicle trail systems, or enforce off-
highway vehicle regulations (USGAO 2009, p. 16).
    In response to public concerns, the BLM developed the ``National 
Management Strategy for Motorized Off-Highway Vehicle Use on Public 
Lands'' (USBLM 2001, p. 9). This strategy outlines action items that 
are to be implemented ``as soon as practical'' (USBLM 2001, pp. 10-21). 
However, the U.S. Government Accountability Office (2009, pp. 17-18) 
found that ``[d]espite identifying numerous goals and strategies to 
achieve the goals, BLM's recreation plan does not identify any 
timeframes for implementing the strategies or any performance measures 
for monitoring incremental progress * * *. Without performance measures 
and timeframes, the BLM cannot ensure that it is making progress on 
achieving its goals in a timely manner.''
    The BLM generally prohibits competitive off-highway vehicle events 
that could adversely affect Sonoran desert tortoises, from March 31 
through October 15, but noncompetitive off-highway vehicle activities 
are evaluated on a case-by-case basis, and mitigation measures are 
implemented to reduce potential impacts to Sonoran desert tortoises 
(USBLM 2010, p. 4). Although requests to permit rock crawling events 
(defined in Factor A, above) have been denied where they were proposed 
in Sonoran desert tortoise habitat (USBLM 2010, p. 4), this activity 
still occurs outside of organized ``events.'' Rock crawling is allowed 
where it might adversely affect the Sonoran desert tortoise or its 
habitat (USBLM 2010, p. 4).
    Both the USFS and BLM acknowledge limited staff and financial 
resources for off-highway vehicle management (USGAO 2009, p. 37). Off-
highway vehicles that pass over undisturbed desertscrub habitat may 
leave tracks which are then noticed by others and subsequently used 
until the trail is mistakenly recognized as a designated route; this 
process is known as ``route proliferation'' (Brooks and Lair 2005, p. 
5). Illegal proliferation of roads and unauthorized use of off-highway 
vehicles has left persistent scars in the Sonoran Desert (Abella 2010, 
p. 1249). In the Kingman area, between 1994 to 1999, the BLM tracked an 
increase of greater than 20 percent of off-highway vehicle use within 
the range of the Sonoran desert tortoise, and reported 124 and 123 
violations of improper vehicle use Statewide in 1998 and 1999, 
respectively (AIDTT 2000, p. 10). The BLM has only 195 law enforcement 
officers nation-wide, which means that on average, each officer is 
responsible for overseeing approximately 1.2 million ac (490,000 ha) of 
land, or 1,875 sq mi (4,856 sq km) (USGAO 2009, p. 38). Law enforcement 
of off-highway vehicle use in the Arizona-Mexico border region is 
further complicated by increasing demands to address drug smuggling and 
other border-related issues (USGAO 2009, p. 39). To address an 
inadequate law enforcement presence, the BLM's Phoenix District has 
initiated an ``ambassador program'' which recruits volunteers to 
``educate users and promote safe, sustainable off-highway vehicle use 
in the area'' (USGAO 2009, p. 38). The use of signs is a common method 
to enforce off-highway vehicle regulations on Federal lands, but signs 
are often vandalized (sometimes within 48 hours of their installation), 
and must be frequently replaced (USGAO 2009, p. 40).
    In addition to wildlife management (described below), the AGFD also 
licenses, promulgates rules for, and assists with regulatory 
enforcement of off-highway vehicles use on public lands. In January 
2009, the AGFD created an off-highway vehicle decal program, designed 
to increase revenues for off-highway vehicle enforcement, education, 
and signage on public lands (AGFD 2009, p. 1). However, as of November 
2009, only 21 percent of all eligible off-highway vehicles and off-
highway vehicle owners in Arizona were participating in the off-highway 
vehicle decal program (AGFD 2009, p. 1).
    In review of off-highway vehicle management on USFS and BLM lands 
in Arizona, we conclude that the current status of law enforcement is 
inadequate to protect Sonoran desert tortoises and their habitat. We 
considered the following in making this conclusion: (1) The documented 
adverse effects of off-highway vehicle use on Sonoran desert tortoise 
habitat (see Factor A); (2) the propensity for off-highway vehicle 
users to illegally collect Sonoran desert tortoises in the wild 
(discussed in Factor B); (3) the significant, and growing, use of off-
highway vehicles in Arizona (discussed above in Factor A); and (4) the 
deficient level of law enforcement staff responsible for regulating the 
use of off-highway vehicles on these lands discussed above.

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In addition, we accept the U.S. Government Accountability Office 
finding that the USFS and BLM goals and objectives, intended to protect 
trust resources from damage associated with off-highway vehicle use, 
miss some key elements that could improve off-highway vehicle 
management.
Ironwood and Mesquite Harvest
    To address ecological problems stemming from wide-ranging mesquite 
and ironwood harvesting in northern Mexico (discussed above in Factor 
A), the Arizona-Mexico Commission, and state government in Sonora, 
Mexico, made it illegal to cut and export these species (American 
University Database 2010, p. 4). Additionally, Mexico's Federal 
government has protected the ironwood tree, adding additional 
monitoring and enforcement to protect remaining ironwood trees 
(American University Database 2010, p. 4). Finally, non-profit, bi-
national groups are raising awareness and funds to help stop these 
practices in Mexico (American University Database 2010, p. 4). We 
consider these regulations effective in reducing the harvest of 
ironwood and mesquite in the future, but the land area already 
adversely modified by ironwood and mesquite harvesting, as discussed in 
Factor A above, constitutes a current threat to Sonoran desert tortoise 
habitat.
U.S. Department of Defense
    Three prominent Department of Defense-administered lands maintain 
populations of Sonoran desert tortoise: The Yuma Proving Ground, Barry 
M. Goldwater Range, and Florence Military Reservation. The Yuma Proving 
Ground, administered by the Department of the Army, encompasses 840,000 
ac (340,000 ha) in LaPaz and Yuma Counties of southwestern Arizona 
(AIDTT 2000, p. 32). The majority of land on the Yuma Proving Ground is 
closed to public access year-round with the exception of 133,000 ac 
(54,000 ha) that are open to hunting access for 6 months per year. The 
relative inaccessibility of these lands results in little disturbance 
to the Sonoran desert tortoise and its habitat (AIDTT 2000, p. 33). In 
addition, the Yuma Proving Ground developed a management plan for the 
Sonoran desert tortoise in 1996 (AIDTT 2000, pp. 33-34). We are 
uncertain whether or not this management plan is effective in Sonoran 
desert tortoise conservation on the Yuma Proving Ground.
    The Barry M. Goldwater Range, used for aerial training exercises, 
is the largest contiguous portion of Department of Defense lands in 
Arizona (1.7 million ac, 690,000 ha), and is jointly administered by 
the Luke Air Force Base and Marine Corps Air Station--Yuma, and is 
located in portions of Maricopa, Yuma, and Pima Counties (AIDTT 2000, 
pp. 32-33). The majority of military training exercises occur over the 
valleys where Sonoran desert tortoise densities are low, leaving the 
majority of Sonoran desert tortoise populations unexposed to potential 
threats from these exercises (AIDTT 2000, p. 34). Outside of training 
exercises, the public may access the Barry M. Goldwater Range with a 
permit, via designated routes (AIDTT 2000, p. 34).
    The Florence Military Reservation encompasses 25,752 ac (10,421 
ha), and is jointly administered by the Arizona Army National Guard, 
the Arizona State Land Department, and the BLM (AIDTT 2000, p. 34). As 
stated previously, the Sonoran desert tortoise population on the 
Florence Military Reservation is unique among other populations across 
their range, because of the conspicuous absence of boulder outcrops and 
use by tortoises of broad alluvial fans and incised washes (Riedle et 
al. 2008, p. 418; Grandmaison et al. in press, p. 4). There is 
significant public access and multiple land uses allowed on the 
Florence Military Reservation, with no specific protections afforded to 
the Sonoran desert tortoise (AIDTT 2000, p. 34). Sonoran desert 
tortoise home ranges overlap with concentrated military training areas 
on the Florence Military Reservation (Grandmaison et al. in press, p. 
1). When not used for military training, these areas serve as 
recreational areas for camping, hunting, and off-highway vehicle use, 
which cumulatively have degraded Sonoran desert tortoise habitat by 
removing vegetative cover, which in turn may have led to reduced use of 
these areas by Sonoran desert tortoises (Grandmaison et al. in press, 
p. 4).
    There are few data on the potential effects of military operations 
to Sonoran desert tortoises on U.S. Department of Defense lands, 
specifically with respect to aircraft operations. However, Bowles et 
al. (1999, pp. 19-26) tested the response of Mojave desert tortoises to 
simulated aircraft sound and to sonic booms associated with aircraft, 
in an attempt to ascertain potential effects to wild desert tortoises 
that are exposed to such auditory stimuli within and adjacent to 
aircraft flight paths and military training areas. They found that 
Mojave desert tortoises could detect these sounds and had somewhat 
subdued reactions ranging from ``freezing'' all movements, to bladder 
voiding (Bowles et al. 1999, pp. xxii-xxiv). We are not certain whether 
Sonoran desert tortoise populations on U.S. Department of Defense lands 
are subjected to aircraft noise at similar sound pressure levels, but 
we presume they are, because aircraft training occurs on these lands in 
Arizona.
    In summary, the Barry M. Goldwater Range and Yuma Proving Ground 
provide for considerable protection of Sonoran desert tortoise habitat 
on their installations as a result of access restrictions or through a 
permitting program. The Barry M. Goldwater Range also created a 
management plan specifically for the Sonoran desert tortoise in 1996. 
In addition, since these lands are unlikely to be developed in the 
future, these areas will likely be important in future Sonoran desert 
tortoise conservation planning. However, the literature has documented 
that current management on the Florence Military Reservation is not 
adequate for protecting Sonoran desert tortoises or their habitat. In 
discussion under Factors A and B, we discussed several activities that 
occur in this area which adversely affect the Sonoran desert tortoise 
and its habitat.
U.S. Fish and Wildlife Service National Wildlife Refuges
    Sonoran desert tortoises occur on several National Wildlife Refuges 
in Arizona. Sonoran desert tortoise populations are highest on the 
Kofa, Buenos Aires, and Cabeza Prieta National Wildlife Refuges, 
although they also may occur in low densities within the Cibola, 
Imperial, and Lake Havasu National Wildlife Refuges along the Colorado 
River (AIDTT 2000, p. 31). The mission of the National Wildlife Refuge 
System is `` * * * to administer a national network of lands and waters 
for the conservation, management, and where appropriate, restoration of 
the fish, wildlife, and plant resources and their habitats within the 
United States for the benefit of present and future generations of 
Americans'' (AIDTT 2000, p. 31). Management on these National Wildlife 
Refuges is largely protective of Sonoran desert tortoises, as multiple 
use activities such as livestock grazing and off-highway vehicle use 
are prohibited (AIDTT 2000, p. 31). However, the U.S. Border Patrol 
uses administrative roads, which are closed to public use in these 
areas, along the border region of the Buenos Aires and Cabeza Prieta 
National Wildlife Refuges, which may affect Sonoran desert tortoises or 
their habitat in these areas. For further discussion of the effect of 
U.S. Border Patrol operations on Sonoran desert tortoises or their 
habitat, see the section on Undocumented Immigration in Factor A of 
this finding.

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    In summary, we conclude that the regulations establishing the 
mission and management of the National Wildlife Refuge system are 
consistent with Sonoran desert tortoise habitat management, and are 
therefore adequate to protect the tortoise where it occurs on our 
lands.
National Park Service
    Sonoran desert tortoise habitat occurs on Organ Pipe Cactus 
National Monument, Saguaro National Park, and the Lake Mead National 
Recreation Area (AIDTT 2000, p. 27). The National Park Service is 
mandated by law to ``conserve the scenery and the natural and historic 
objects and the wildlife therein and to provide for the enjoyment of 
the same in such manner and by such means as will leave them unimpaired 
for the enjoyment of future generations'' (AIDTT 2000, p. 26). The 
resource-management goals on National Park Service lands are broad in 
scope, and include reducing ground disturbance, developing and 
implementing inventory and monitoring programs, assessing and 
mitigating resource disturbance, and developing environmental 
restoration and research programs (AIDTT 2000, p. 26). Livestock 
grazing and off-highway vehicle use are not permitted on National Park 
Service lands. While the National Park Service has no specific 
provision for Sonoran desert tortoise conservation on their lands, all 
wildlife inhabiting National Park Service lands in Arizona, including 
the Sonoran desert tortoise, are protected, and possession or removal 
of wildlife is prohibited (AIDTT 2000, p. 26).
    However, where National Park Service lands are adjacent to urban 
areas, such as Saguaro National Park outside of the Tucson metropolitan 
area, threats to Sonoran desert tortoises have been documented. 
Averill-Murray and Swann (2002, p. 1) and Jones (2008, p. 66) 
documented threats such as harassment and predation by feral domestic 
dogs, releases of captive Sonoran desert tortoises and exotic species 
(that may transmit diseases), road mortality, and illegal collection of 
tortoises, as affecting the Sonoran desert tortoise population on 
Saguaro National Park land.
    In summary, we acknowledge that the mission and management of the 
National Park Service and their lands is consistent with Sonoran desert 
tortoise habitat management, but where Park Service land is affected by 
adjacent urbanized areas, adequate regulatory protections for the 
tortoise have not been realized.
Arizona State Land Department
    Arizona State Trust Land, managed to derive revenues for trust 
beneficiaries including educational, health, and penal institutions, 
comprises 13 percent of all land in Arizona, much of which contains 
Sonoran desert tortoise habitat (AIDTT 2000, p. 15). In general, the 
mission of the Arizona State Land Department is to maximize economic 
return (AIDTT 2000, p. 16). The Arizona State Land Department has no 
broad management practices, policies, or directives that pertain to 
Sonoran desert tortoise management, but does coordinate with the AGFD 
on some projects to reduce potential impacts to the Sonoran desert 
tortoise (AIDTT 2000, p. 16). Four Sonoran desert tortoise monitoring 
sites occur partially or fully on Arizona State Trust Lands: Granite 
Hills, Little Shipp Wash, Tortolita Mountains, and Picacho Mountains; 
two of these sites, Granite Hills (Pinal County) and Little Shipp Wash 
(Yavapai County) are long-term monitoring plots (AIDTT 2000, pp. 5-6, 
15). Other blocks of Sonoran desert tortoise habitat on Arizona State 
Trust Lands occur west of the Upper Burro Creek, Arrastra Mountain, and 
Tres Alamos wilderness areas in Yavapai County and from the Tortolita 
to the Tortilla Mountains in Pinal County (AIDTT 2000, p. 15). 
Recreation on State Trust Lands is generally not monitored and 
therefore may not be protective of Sonoran desert tortoises or their 
habitat.
    The Arizona State Land Department is considering restricting access 
to its lands for purposes of conducting wildlife studies. These access 
restrictions may prohibit further research due to numerous permit 
requirements. These new policies are not yet in place and could be 
changed prior to final issuance (Jody Latimer, ASLD, 2010, pers. 
comm.). If implemented as described by Latimer (ASLD, 2010, pers. 
comm.), these proposed procedures and fees have the potential to limit 
Sonoran desert tortoise monitoring and research on Arizona State Trust 
lands in the future through new monetary and procedural requirements. 
While these new policies and regulations are not yet in effect, even if 
they are implemented it appears they will not address conservation and 
management of the Sonoran desert tortoise and its habitat, and further, 
may have a negative effect by potentially restricting important 
research needed for conservation of the tortoise. Furthermore, we are 
not aware of specific actions the Arizona State Land Department is 
taking with respect to management of invasive, nonnative plant species 
and subsequent wildfire concerns, vandalism of tortoises, feral dog 
predation, or efforts to counter anticipated climate change. Therefore, 
we conclude that Arizona State Land Department management of the 
Sonoran desert tortoise and its habitat is currently inadequate.
Arizona Game and Fish Department
    The Arizona Game and Fish Department (AGFD) currently classifies 
the Sonoran desert tortoise as a Tier 1b ``Species of Greatest 
Conservation Need'' AGFD (2006, p. 485). A Tier 1b species is one that 
requires immediate conservation actions aimed at improving conditions 
through intervention at the population or habitat level. Before April 
28, 1989, the AGFD allowed the collection and possession of one 
lawfully captured Sonoran desert tortoise per person (AIDTT 2000, p. 
14). After this date, under Commission Order 43, the AGFD closed the 
season on Sonoran desert tortoises, which prohibited the take of desert 
tortoises from the wild, except under special permit (for example, 
scientific or educational) (AIDTT 2000, p. 14). Unless otherwise 
prescribed in title 17, it is unlawful to [t]ake, possess, transport, 
buy, sell or offer or expose for sale wildlife except as expressly 
permitted by this title'' (ARS 17-309). It is also unlawful to release 
wildlife into the wild except as authorized by the Arizona Game and 
Fish Commission or as defined in title 3 (see ARS 17-306). As a closed-
season species, the desert tortoise cannot be taken from the wild or 
possessed without special permit (Commission Order 43). As restricted 
live wildlife (R12-4-406), they cannot be imported, exported, or 
possessed without special license or lawful exemption.
    Enforcement of the State closure on collection of Sonoran desert 
tortoises occurs when directly observed by law enforcement personnel, 
but the remoteness of many Sonoran desert tortoise populations makes 
enforcement strategies and techniques problematic (AIDTT 2000, p. 14). 
Furthermore, regulations regarding the collection or possession of 
Sonoran desert tortoises are poorly known to the public, emphasizing 
the importance of education efforts (AIDTT 2000, p. 14). The effect of 
illegal collection of Sonoran desert tortoises on wild populations in 
Mexico is largely unknown (see Factor B).
    The AGFD has led Sonoran desert tortoise conservation in Arizona 
through research, guidance provided to the public and other agencies, 
and cooperative conservation management

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on public lands. For example, the AGFD (2007a, p. 1) provides 
construction and development contractors with guidance, should a 
Sonoran desert tortoise be encountered within an area of a development. 
In addition, the AGFD (2007b, p. 1) also provides environmental 
consultants guidance on proper survey techniques and considerations 
when surveying for Sonoran desert tortoises. AGFD (2006, pp. 485-487) 
described numerous management priorities with respect to mitigating 
potential threats facing the tortoise in Arizona. The recommendations 
outlined in these documents are recommended guidance, voluntary in 
nature, and no reporting requirements are mandated. Therefore, we are 
uncertain whether project proponents implement these recommendations.
Arizona Interagency Desert Tortoise Team
    As part of a multi-agency collaborative project, the Arizona 
Interagency Desert Tortoise Team (AIDTT) was formed in 1985 to 
coordinate research and management of Sonoran desert tortoise 
populations in Arizona. Participating agencies in the AIDTT manage 
habitat, manage the species, or conduct research, and include the AGFD, 
Arizona State Lands Department, U.S. Forest Service, BLM, U.S. Bureau 
of Reclamation, U.S. Bureau of Indian Affairs, U.S. Fish and Wildlife 
Service, National Park Service, U.S. Geological Survey, and several 
U.S. Department of Defense military reservations (AIDTT 1996, Preface; 
AIDTT 2000, p. 2). The AIDTT is co-chaired by representatives from the 
U.S. Fish and Wildlife Service (Arizona Ecological Services Office) and 
the AGFD. Since its inception, the AIDTT has collaborated in the 
development of numerous documents addressing conservation of the 
Sonoran desert tortoise including ``Survey Protocol for Sonoran Desert 
Tortoise Monitoring Plots: Reviewed and Revised'' (Averill-Murray 
2000a), ``Status of the Sonoran Population of the Desert Tortoise in 
Arizona: An Update'' (Averill-Murray 2000b), ``Guidelines for Handling 
Sonoran Desert Tortoises Encountered on Development Projects'' (AGFD 
2007a), ``Desert Tortoise Survey Guidelines for Environmental 
Consultants'' (AGFD 2007b), and ``Recommended Standard Mitigation 
Measures for Projects in Sonoran Desert Tortoise Habitat'' (AIDTT 
2008). Available online, the AIDTT (2008, pp. 1-7) offers guidance on 
standard types of mitigation for projects that may affect Sonoran 
desert tortoises; these measures are voluntary.
    The AIDTT's Memorandum of Understanding, signed in 1995, 
established specific objectives for the team including: (1) Ensuring 
the survival of the species; (2) preventing loss of the species; and 
(3) improving the quality of Sonoran desert tortoise habitat in 
Arizona, with the team to function as an advocate for the Sonoran 
desert tortoise (AIDTT 1996, Preface; AIDTT 2000, p. 2). A management 
plan for the Sonoran desert tortoise completed in 1996 called for 
improved monitoring protocols, the implementation of threat-
minimization activities, and the creation of Sonoran Desert Management 
Areas (AIDTT 1996, pp. 20-26). However, common criticisms of the 1996 
plan include: (1) Lack of meaningful goals and objectives; (2) lack of 
political willpower without legal protection for the Sonoran desert 
tortoise; (3) failure to designate Sonoran Desert Management Areas; and 
(4) poor funding (AIDTT 2000, p. 2). Collectively, these recognized 
shortcomings hampered the implementation of threat-minimization 
activities. In recognition of these shortcomings, the AIDTT is 
currently in the process of developing a State Conservation Agreement, 
Assessment and Strategy with the goal of identifying reasonable, 
obtainable conservation goals and objectives that will contribute to 
Sonoran desert tortoise conservation on public lands in a meaningful 
capacity.
Mexican Government (Secretaria de Medio Ambiente y Recursos Naturales)
    Throughout Mexico, the desert tortoise is listed as ``Amenazadas,'' 
or Threatened, by the Secretaria de Medio Ambiente y Recursos Naturales 
(SEMARNAT) (Bury et al. 2002, p. 86; Howland and Rorabaugh 2002, p. 
348; SEDESOL 2008, p. 99). Threatened species are ``those species, or 
populations of the same, likely to be in danger of disappearing in a 
short or medium timeframe, if the factors that negatively impact their 
viability, cause the deterioration or modification of their habitat or 
directly diminish the size of their populations continue to operate'' 
(SEDESOL 2008 (NOM-059-ECOL-2008), p. 5). This designation prohibits 
taking of the species, unless specifically permitted, and also 
prohibits any activity that intentionally destroys or adversely 
modifies its habitat (SEDESOL 2000 and 2001 (NOM-059-ECOL-2001). 
However, activities that unintentionally destroy or adversely modify 
their habitat do not appear to be specifically prohibited (e.g., 
cultivation of buffelgrass for livestock grazing). In 1988, the Mexican 
Government passed a regulation that is similar to the National 
Environmental Policy Act of the United States (42 U.S.C. 4321 et seq.). 
This Mexican regulation requires an environmental assessment of private 
or government actions that may affect wildlife or their habitat 
(SEDESOL 1988 (LGEEPA)).
    The Mexican Federal agency known as the Instituto Nacional de 
Ecolog[iacute]a (INE) is generally considered the Mexican counterpart 
to the U.S. Fish and Wildlife Service. INE is responsible for the 
analysis of the status and threats that pertain to species that are 
proposed for listing in the Norma Oficial Mexicana NOM-059 (the Mexican 
equivalent to a threatened and endangered species list), and if 
appropriate, the nomination of species to the list. INE developed the 
Method of Evaluation of the Risk of Extinction of the Wild Species in 
Mexico (MER), which unifies the criteria of decisions on the categories 
of risk, and permits the use of specific information fundamental to 
listing decisions. The MER is based on four independent, quantitative 
criteria: (1) Size of the distribution of the taxon in Mexico, (2) 
state (quality) of the habitat with respect to natural development of 
the taxon, (3) intrinsic biological vulnerability of the taxon, and (4) 
impacts of human activity on the taxon. INE implemented use of the MER 
in 2006; therefore, all species previously listed in the NOM-059 were, 
in many cases, based solely on expert review and opinion. Specifically, 
until 2006, the listing process under INE consisted of a panel of 
scientific experts who convened as necessary for the purpose of 
defining and assessing the status and threats that affect Mexico's 
native species that are considered to be at risk, and for applying 
those factors to the definitions of the various listing categories.
    In summary, while the desert tortoise is federally listed in 
Mexico, we have documented significant threats to its persistence in 
that country (see Factors A and C) that are not controlled by the 
listing, and therefore conclude that regulations establishing 
management of the Sonoran desert tortoise in Mexico do not provide 
adequate assurances of its continued existence in that country.
Summary of Factor D
    Numerous State and Federal entities have regulations or policies 
which implement management of either the Sonoran desert tortoise or its 
habitat throughout the species' range in Arizona. In Mexico, the 
species is currently listed as threatened. In our

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review of the available information on each entity's management 
policies and regulations, we found numerous examples where the Sonoran 
desert tortoise is considered in management actions and tortoise-
specific mitigation measures are mandated, or where land activities 
that could appreciably threaten Sonoran desert tortoise populations are 
prohibited. While several land managers and agencies in Arizona 
actively consider the Sonoran desert tortoise in their resource 
planning, we found deficiencies in management of off-highway vehicle 
use, policies and procedures inconsistent with Sonoran desert tortoise 
conservation, and some threats such as invasive, nonnative plant 
species and subsequent wildfire concerns, vandalism of tortoises, feral 
dog predation, or efforts to counter anticipated climate change were 
not addressed by land management control. Lastly, significant threats 
we discuss above in Factors A and C are not being adequately addressed 
by land managers, including invasive, nonnative plant species and 
associated wildfire concerns, vandalism of tortoises, feral dog 
predation, and management to counter anticipated climate change.
    Although the Sonoran desert tortoise is considered a threatened 
species in Mexico, we are not aware of conservation planning or 
enforcement of regulations that has occurred because of this status. 
Based upon our review of the information pertaining to threats in 
Mexico, it is unlikely that protections afforded to the Sonoran desert 
tortoise are adequate to ensure conservation for the foreseeable future 
in Mexico. As a result, we conclude that the Sonoran desert tortoise is 
threatened due the inadequacy of existing regulatory mechanisms, in 
combination with the other threats identified in this finding, both now 
and in the foreseeable future.

Factor E. Other Natural or Manmade Factors Affecting Its Continued 
Existence

Environmental Contaminants
    Many sources of potential contamination presently occur throughout 
the distribution of the Sonoran desert tortoise. Copper mining in the 
Sonoran Desert has occurred in Arizona and adjacent Mexico for 
centuries, and many of these sites have smelters (now decommissioned), 
which are former sources of airborne contaminants. In Arizona, 
historical or current large-scale copper mining operations exist in 
Pima, Pinal, Yavapai, Gila, and Mohave Counties, which are sources of 
low-level, persistent contaminants in surrounding areas as a result of 
fugitive dust, contaminated surface runoff, and other mechanisms 
consistent with contaminant fate and transport. Soil contamination 
within ephemeral washes from leaching operations associated with mining 
activities has occurred throughout the Sonoran Desert, and will likely 
continue to occur where these activities take place. Sonoran desert 
tortoises that forage in contaminated ephemeral washes may ingest toxic 
constituents through soil or contaminated plant matter, but we are not 
aware of any specific reports of tortoises that became sick or deceased 
from this risk. The mining industry in Mexico is largely concentrated 
in the northern tier of that country, with Sonora as the leader for 
generating copper, gold, graphite, molybdenum, and wollastonite, as 
well as the leader among Mexican States with the most surface area 
dedicated to mining (Stoleson et al. 2005, p. 56). The three largest 
mines (all copper) are found in Sonora (Stoleson et al. 2005, p. 57). 
The sizes of mines in Sonora vary considerably, as do the known 
environmental effects from mining-related activities (from exploration 
to long after closure), which include contamination and drawdown of 
groundwater aquifers, erosion, acid mine drainage, fugitive dust, 
pollution from smelter emissions, and landscape clearing (Stoleson et 
al. 2005, p. 57).
    Rowe (2008, p. 623) investigated potential effects of persistent, 
low-level contaminants (e.g., heavy metals, polychlorinated biphenols, 
organochlorides) on long-lived vertebrates (such as the Sonoran desert 
tortoise). Cadmium and lead are of special concern due to their 
toxicity, and because they are persistent, common environmental 
contaminants (Mart[iacute]nez-L[oacute]pez et al. 2010, p. 671). 
Cadmium may affect turtle gonadal development, and lead may affect an 
individual tortoise's susceptibility to infections and disease, because 
it may suppress its immune capacity. The latter can potentially affect 
the spread of known diseases such as herpesvirus, cutaneous 
dyskeratosis, and URTD within and among affected populations 
(Mart[iacute]nez-L[oacute]pez et al. 2010, p. 671). As stated 
previously, cutaneous dyskeratosis is prevalent within most populations 
of Sonoran desert tortoise throughout their distribution in Arizona, 
but this disease has not been determined to currently be a significant 
threat to Sonoran desert tortoise populations. Another common 
environmental contaminant is the heavy metal arsenic, which is 
carcinogenic (cancer-causing) and may also already occur in naturally-
high levels in some areas of the American Southwest (Seltzer and Berry 
2005, p. 263).
    Because the Sonoran desert tortoise is characterized as having a 
delayed sexual maturation and a long generation time, potential effects 
from persistent, low-level contaminants in the environment include: (1) 
Mortality before reproduction, (2) chronic accumulation of contaminants 
that may be transferred to offspring upon maturation, (3) reduced size 
at maturity reducing offspring quantity or quality, (4) delayed 
expression of fitness effects at the population level, and (5) delayed 
recovery of populations following abatement of fitness effects (Rowe 
2008, p. 626). In several areas of the Sonoran Desert in Arizona and 
Sonora, Mexico, mining operations and other human-related activities 
can result in remobilization and concentration of elemental toxicants 
in the air, on the soil surface, and on the surfaces of forage plants, 
both from ground disturbance and from long-range atmospheric deposition 
associated with old copper smelter sites, coal-fired power plants, and 
fugitive dust from abandoned and active mining sites (Seltzer and Berry 
2005, p. 263; Rowe 2008, p. 628). The most likely routes for exposure 
of Sonoran desert tortoises to these types of contaminants are through 
ingestion of contaminated soil or plant matter, or through inhalation 
of contaminated dust or particles, especially when a tortoise 
constructs or modifies a burrow (Seltzer and Berry 2005, p. 263; Hinck 
et al. 2010, p. 287). We have no specific records of Sonoran desert 
tortoises becoming sick or dying from this type of contamination; 
effects from these contaminants can be significantly delayed and slow 
to manifest. Also, few field researchers are sampling wild tortoises to 
test for contaminant exposure.
    Conversion of habitat to large-scale agriculture has been 
concentrated in Sonora, Mexico, which has provided sources of surface 
and groundwater pollution such as salt intrusion due to agricultural 
water use extraction; municipal and agricultural discharges; and solid 
waste, including cast-off agrochemical containers, winery residues, and 
hog farm muck (Nauman 2007, p. 1). The extent to which Sonoran desert 
tortoises drink freely from perennial or intermittent streams is not 
known, but since tortoises are opportunistic drinkers, we presume they 
use streams as a source of water in addition to ephemeral pools 
generated by precipitation events, and that they may subsequently 
ingest such toxins.

[[Page 78134]]

    In conclusion and based upon our review of the best available 
scientific or commercial data, little is known of the potential effect 
of low-level environmental contamination on Sonoran desert tortoises. 
We did ascertain that the risk of environmental contaminants affecting 
Sonoran desert tortoise populations is most likely from the presence of 
persistent, low-level toxicants such as heavy metals, polychlorinated 
biphenols, and organochlorides. However, potential effects of this type 
of environmental contamination are often delayed and difficult to 
observe in long-lived species such as the Sonoran desert tortoise, 
largely because of delayed sexual maturation and long generation times. 
We did not find documentation of population-level effects in Sonoran 
desert tortoises as a result of environmental contamination. Therefore, 
we conclude that environmental contamination of Sonoran desert tortoise 
habitat is not currently threatening populations; however, we 
acknowledge that further study is warranted to identify whether there 
is a risk for population-level impacts, and we recommend that land 
managers consider collecting baseline soil data in areas that may be 
vulnerable.
Vehicle Strike Mortalities
    We expect that the increased use of off-highway vehicles within 
Sonoran desert tortoise habitat will increase the likelihood of 
encounters with Sonoran desert tortoises which can result in a variety 
of potential outcomes for tortoises. According to the Arizona 
Interagency Desert Tortoise Team (AIDTT 2000, p. 10), ``[a]n abundance 
of anecdotal knowledge indicates that contacts between people and wild 
tortoises usually end to the detriment of tortoises (e.g., collection, 
handling, vandalism, crushing under vehicle tires, and shooting).''
    Averill-Murray and Swann (2002, p. 1) stated that urban development 
adjacent to the Saguaro National Park in Pima County threatens the 
Sonoran desert tortoise via several mechanisms, including elevated 
mortality on roads. The high rates of speed associated with competitive 
off-highway vehicle events significantly increase the risk of direct 
mortality of Sonoran desert tortoises from vehicle collisions (Vega 
2010, p. 4).
    Reptiles, including the Sonoran desert tortoise, may be 
particularly vulnerable to roads due to the higher risk of mortality as 
a result of vehicle strikes (Boarman and Sazaki 1996, p. 1; Boarman et 
al. 1997, p. 57; Forman and Alexander 1998, p. 213; Boarman 2002, pp. 
54-55; Boarman and Sazaki 2006, p. 98; Dieringer 2010, p. 1). 
Anticipated adverse effects of roads on Sonoran desert tortoise 
populations are likely related to the level of their use. For example, 
Hoff and Marlow (2002, pp. 451-454) found that the impact of roads on 
the prevalence of Mojave desert tortoise signs (tracks, scat, etc.) was 
commensurate with traffic volume--with the impacts more significant 
adjacent to heavily traveled roads. Mojave desert tortoise populations 
showed depressed numbers within 1,300 feet (400 m) of highways in the 
Mojave Desert (Boarman and Sazaki 2006, p. 98). Similar effects to 
Sonoran desert tortoise populations might be expected when heavily used 
roads are adjacent to, or are routed through, core Sonoran desert 
tortoise habitat such as steep, boulder-strewn slopes within Arizona 
Upland Sonoran desertscrub (Dieringer 2010, p. 1; Grandmaison 2010b, p. 
3).
    Sonoran desert tortoises move slowly and take a relatively long 
time to cross roads and highways, which may place them at elevated risk 
(Andrews et al. 2008, p. 124). However, we suspect that, due to their 
size and shape (particularly in the sub-adult and adult size classes), 
drivers may instinctively avoid striking a crossing tortoise because of 
their similarity to rocks, and the subsequent damage that hitting a 
``rock'' could do to a vehicle. However, intentional vehicle strikes of 
Mojave desert tortoises have been reported (Bury and Marlow 1973, p. 
11). While unpaved roads traverse 16 of the 17 Sonoran desert tortoise 
monitoring plots, the AGFD is only aware of one instance of direct 
mortality of a Sonoran desert tortoise from a vehicle on a long-term 
monitoring plot, on the East Bajada Plot (AGFD 2010, p. 14).
    Increased vegetation adjacent to paved or heavily compacted roads 
resulting from increased water runoff may be beneficial to Sonoran 
desert tortoises, serving as a means to rehydrate them, but it may also 
attract them to these areas, indirectly increasing the likelihood of 
adverse interactions from: (1) Tortoises wandering onto the road, (2) 
vehicles pulling onto the vegetated shoulder of the road and crushing 
tortoises, (3) injury from grading or mowing activities, (4) exposure 
to herbicides applied to control growth of weeds along the road 
shoulder, and (5) increased potential for observation and collection by 
passers-by (Boarman 2002, p. 55). As stated previously, Sonoran desert 
tortoises may use infrequently traveled gravel roads as travel routes 
within their home ranges (Grandmaison et al. in press, p. 16). This 
suggests that low density Sonoran desert tortoise populations observed 
adjacent to heavily traveled roads may be the result of mortality from 
vehicle collisions and illegal collection rather than road avoidance 
behavior (Grandmaison et al. in press, p. 16).
    There appears to be a concerted effort to mitigate the potential 
effect of several roads and highways on Sonoran desert tortoise 
populations and their habitat. Barrier fencing (or tortoise fencing) 
and culverts along roads and highways are recognized methods employed 
throughout Arizona to reduce potential mortality through vehicle 
strikes of Sonoran desert tortoises. Installing tortoise fencing along 
roads and highways minimizes the risk of road mortality of tortoises 
but may also enhance the barrier effect between populations by 
restricting long-distance movements (Boarman and Sazaki 1996, p. 3). 
Culverts that pass under roads and highways may provide opportunities 
for Sonoran desert tortoises to safely cross roads and highways 
(Boarman and Sazaki 1996, pp. 3-4).
    The ADOT constructs and maintains roads and highways that comprise 
Arizona's transportation system. It routinely implements varied 
conservation and mitigation actions with respect to Sonoran desert 
tortoise populations that may be affected by these activities. The ADOT 
(ADOT 2010, pp. 2-5) listed numerous conservation measures including 
those which address standard (voluntary and involuntary) mitigation 
measures, education, new construction design, habitat acquisition, 
native plant restoration, nonnative plant control, establishment of 
wildlife corridors, and research that have been integrated into their 
road system planning, construction, and improvement activities. 
Tortoise-proof fencing adjacent to highways has been installed along 
numerous routes throughout Arizona including 27.6 mi (44.4 km) along 
U.S. Highway 93 and 10.8 mi (17.4 km) along State Route 85 (ADOT 2010, 
p. 3). Numerous, additional structures that assist Sonoran desert 
tortoises to cross roads safely, such as pathways, ramps, and culverts, 
have been installed along the U.S. Highway 93 corridor and along a 
segment of the U.S. Highway 60 through the Tonto National Forest (ADOT 
2010, p. 3).
    The ability of tortoise fencing to prevent road mortality of 
Sonoran desert tortoises is highly contingent on inspections and 
maintenance. Sonoran desert tortoise fencing along 10 mi (16 km) of 
U.S. Highway 93 in Mohave and

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Yavapai Counties in Arizona, between mile markers 144 and 155, was 
shown to have major deficiencies, including 567 individual fencing 
breaches and instances of culvert undercutting, which diminish the 
effectiveness of these mitigation techniques (Grandmaison 2010b, p. 3). 
Five Sonoran desert tortoise road-mortalities were documented in 2008 
in this stretch of highway, though none was documented in 2009 
(Grandmaison 2010b, p. 5). A rancher in southeastern Mohave County, 
Arizona, reported observations of Sonoran desert tortoises being killed 
on U.S. Highway 93, particularly after heavy rains, when adjacent 
tortoise barrier fencing along the highway gets washed out, allowing 
access of tortoises to the highway surface (Dieringer 2010, p. 1). 
Using radio-telemetry, Grandmaison (2010b, p. 6) found that Sonoran 
desert tortoises with home ranges within 0.62 mi (1 km) adjacent to 
this stretch of Highway 93 did not cross the highway. However, 
additional instances of Sonoran desert tortoise mortality on this and 
other major routes within the distribution of Sonoran desert tortoises 
undoubtedly occurs but is rarely reported.
    Many activities undertaken by the ADOT minimize the effect of roads 
and highways on tortoise populations. However, we have concern 
regarding the lack of ongoing maintenance of protection structures such 
as tortoise barrier fencing. Therefore, we conclude that maintenance of 
tortoise protection structures is not adequate to meet the desired 
objective of these structures in many areas, or to protect Sonoran 
desert tortoise populations affected by heavily used roads and highways 
in Arizona.
Balloons and Trash
    Helium-filled balloons are capable of dispersing great distances 
(greater than 164 mi (264 km)) from their release points, and have been 
shown to make up the largest percentage of litter types encountered in 
desert tortoise field studies (Walde et al. 2007a, p. 148). Desert 
tortoises are known to eat trash, such as balloons, plastic, and other 
garbage, which may kill them by becoming lodged in the gastrointestinal 
tract or by entangling the tortoise (Averill-Murray and Averill-Murray 
2002, p. 27; Walde et al. 2007a, p. 148). Balloons and balloon string 
can also entangle the tortoise, sometimes leading to induced amputation 
of an appendage (Burge 1989, p. 7). Averill-Murray and Averill-Murray 
(2002, p. 27) reported 36 balloons found on Ironwood Forest National 
Monument in Pima County, Arizona, indicating that opportunities for a 
Sonoran desert tortoise to consume, or become entangled with balloons, 
exist. However, Averill-Murray and Averill-Murray (2002, p. 29) posited 
that while balloons may affect individuals, they are unlikely to cause 
population-level impacts to Sonoran desert tortoises.
    Illegal dumping in Arizona is ubiquitous throughout the Sonoran 
Desert, but most concentrated in areas adjacent to human settlements. 
These relatively small but widely dispersed piles of solid and 
potentially hazardous waste may also serve as sources of toxicological 
contamination of Sonoran desert tortoises in areas where ingestion of 
contaminated soils or plant matter can occur.
    In conclusion, balloons and trash occur throughout the range of the 
desert tortoise. Trash piles are most concentrated adjacent to human 
settlements but helium-filled balloons can travel many miles away from 
cities or towns and be deposited in remote habitat as they fall from 
the sky. We have documented that balloons in particular may pose health 
risks to Sonoran desert tortoises and are encountered in monitoring 
plots although specific reports of tortoises directly affected by 
balloons are rare in the literature. While effects can occur to 
individual tortoises, the literature did not indicate that population-
level effects can be expected from such exposure.
Climate Change
    There is unequivocal evidence that the earth's climate is warming 
based on observations of increases in average global air and ocean 
temperatures, widespread melting of glaciers and polar ice caps, and 
rising sea levels (IPCC 2007, p. 4). Furthermore, the Intergovernmental 
Panel on Climate Change (IPCC 2007, p. 7) summarized the likelihood of 
general future trends in several climatic variables, predicting: (1) 
Warmer and fewer cold days and nights over most land areas, (2) warmer 
and more frequent hot days and nights over most land areas, (3) more 
frequent warm spells/heat waves over most land areas, (4) changes in 
precipitation patterns favoring an increased frequency of heavy 
precipitation events (or proportion of total rainfall from heavy falls) 
over most areas, and (5) an increase in the area affected by droughts. 
All of these changes are caused by alterations in the energy balance 
within the atmosphere and the Earth's surface. The primary factors that 
affect this balance are concentrations of greenhouse gases (mainly 
carbon dioxide), aerosols, land surface properties, and solar 
radiation. These global climate changes will influence climatic 
patterns at regional and local scales.
    At a regional scale, there is a broad consensus among climate 
models that the area encompassing the southwestern United States and 
northern Mexico will get drier in the twenty-first century and that the 
trend towards a more arid climate is already under way (Seager et al. 
2007). Evidence to support such changes in temperature and rainfall in 
the southwest deserts is abundant. For example, maximum summer 
temperatures in the southwestern United States are expected to increase 
over time in response to changes in the climate system (Christensen et 
al. 2007, p. 887). Weiss and Overpeck (2005, p. 2075) examined low-
temperature data over a 40-year timeframe from numerous weather 
stations in the Sonoran Desert ecoregion of Arizona and California, as 
well as the Mexican States of Baja California, Baja California Sur, and 
Sonora. They found: (1) Widespread warming trends in winter and spring, 
(2) decreased frequency of freezing temperatures, (3) lengthening of 
the freeze-free season, and (4) increased minimum temperatures per 
winter year. Such changes are likely to have widespread impacts on 
Southwestern ecosystems.
    While temperatures in the Southwest are predicted to increase, 
rainfall patterns will also be affected. The current, multi-year 
drought in the western United States, including most of the Southwest, 
is the most severe drought recorded since 1900 (Overpeck and Udall, 
2010, p. 1642). Numerous models predict a decrease in annual 
precipitation in the southwestern United States and northern Mexico. 
Solomon et al. (2009, p. 1707) predict precipitation amounts in the 
southwestern United States and northern Mexico will decrease by as much 
as 9 to 12 percent (measured as percentage of change in precipitation 
per degree of warming, relative to 1900 to 1950 as the baseline 
period). Christensen et al. (2007, p. 888) state, ``The projection of 
smaller warming over the Pacific Ocean than over the continent, * * * 
is likely to induce a decrease in annual precipitation in the 
southwestern USA and northern Mexico.'' In addition, Seager et al. 
(2007, pp. 1181-1184) analyzed 19 models of differing variables to 
estimate the future climate of the southwestern United States and 
northern Mexico in response to predictions of changing climatic 
patterns. All but one of the 19 models predicted a drying trend within 
the southwest (Seager et al. 2007, p. 1181). A total of 49 projections 
were created using the 19 models and all but 3

[[Page 78136]]

predicted a shift to increasing aridity (dryness) in the southwest as 
early as 2021 to 2040 (Seager et al. 2007, p. 1181). While most climate 
change models predict less precipitation in the southwestern United 
States, a model produced by the Hadley Centre for Climate Prediction 
and Research (HadCM2) predicted increased precipitation throughout most 
of the United States, and particularly in the southwest (Weltzin et al. 
2003, p. 942). While there may be some uncertainty associated with the 
predictions of decreased rainfall in the arid deserts, there is broad 
agreement that the overall trend will be reduced precipitation.
    In addition to increasing trends in aridity, the timing of 
precipitation may also be altered as a result of climate change, which 
would result in important changes in the vegetation community within 
habitat of the Sonoran desert tortoise. The IPCC (2007, p. 20) found 
that winter precipitation in the southwestern United States is 
predicted to decline by as much as 20 percent as a result of climate 
change, while summer precipitation may increase slightly. Precipitation 
in Mojave desertscrub occurs predominantly during the cool-season 
(winter) months but, depending on location, it may also occur during 
the warm-summer months (Hereford et al. 2006, p. 29). Perennial plant 
species in Mojave desertscrub are most affected by changes in winter 
precipitation, as increases in winter precipitation increases 
germination and the establishment of new plants (Hereford et al. 2006, 
p. 25). In contrast, decreases in winter precipitation substantially 
increase mortality in perennial plants, most notably in short-lived 
species (Hereford et al. 2006, p. 25). In addition, decreasing winter 
precipitation has been linked with a high mortality of drought-
resistant shrubs in parts of the Sonoran and Mojave deserts (McAuliffe 
and Hamerlynck 2010, p. 885). A reduction in winter precipitation could 
significantly alter the plant communities of the Sonoran and Mojave 
deserts.
    Arid environments are especially sensitive to climate change, 
because the plants and animals that inhabit these areas are near their 
physical tolerances for temperature and water stress. Slight changes in 
temperature and rainfall, along with increases in the magnitude and 
frequency of extreme climatic events, can significantly alter species 
distributions and abundance (Archer and Predick 2008, p. 23). In fact, 
warming effects may be particularly severe for reptiles and amphibians. 
For instance, Walther et al. (2002, pp. 393-394) found that because of 
their physiology, reptiles and amphibians are sensitive to climatic 
changes, which may result in effects to their development, spatial 
distribution, and interactions with other species. Specifically, egg 
development, sperm development, and sex ratios may be affected by 
climatic changes in temperatures. Increased temperatures may influence 
sex ratios within clutches to favor females over males, which may 
benefit populations as one male can fertilize several females. However, 
if temperatures rise too much, the effect could strongly select for 
female-only clutches, significantly skewing the sex ratio within 
populations, and posing long-term problems for reptiles such as Sonoran 
desert tortoise populations (Walther et al. 2002, pp. 393-394). But as 
stated earlier, Sonoran desert tortoises build their nests in burrows 
underground, thereby tempering the effects of rising surface 
temperatures.
    Sonoran desert tortoises may be affected directly by regional 
climate change. For example, increasing temperatures may cause desert 
tortoises to overheat (Ernst and Lovich 2009, p. 544). Sonoran desert 
tortoises are vulnerable to overheating because they heat up 10 times 
faster than they can cool down, making them potentially sensitive to 
temperature extremes associated with anticipated climate change (Ernst 
and Lovich 2009, p. 544). While climate change may directly affect the 
Sonoran desert tortoise, most of the impacts of climate change are 
anticipated to be indirect effects to the tortoise caused by other 
changes in the ecosystem that supports them. The following discussion 
describes anticipated indirect effects to the tortoise in response to 
predicted climate change effects.
    Changes in atmospheric carbon dioxide and soil nitrogen levels are 
anticipated to affect the Sonoran desert tortoise through responses 
observed in their forage base. The desert ecosystems inhabited by the 
Sonoran desert tortoise are also expected to be sensitive to increased 
levels of carbon dioxide in the atmosphere. Desert shrub cover may 
increase with increasing carbon dioxide, but nonnative species may also 
respond positively, out-competing native vegetation (Smith et al. 2000, 
p. 79; Loubimsteva and Adams 2004, p. 401), thereby increasing the risk 
of fire. In addition, water and nitrogen are the biggest constraints 
that influence biological productivity in desert ecosystems (Ramanujan 
2009, p. 1). Predicted higher temperatures are expected to cause higher 
levels of nitrogen to escape as a gas from desert soils, leading to a 
decrease in soil fertility (Ramanujan 2009, p. 1). Murphy et al. (in 
prep., p. ii) expect these responses in the vegetation community to 
adversely affect the quality of forage for Sonoran desert tortoises, 
leading to dietary nitrogen deficiencies.
    Desert tortoises are likely to be affected by decreases in 
precipitation due to climate change. Rain is the single most important 
climatic factor that drives desert ecosystems because it ultimately 
determines recruitment rates, growth and reproduction rates, nutrient 
cycling, and net ecosystem productivity, resulting in these ecosystems 
being the most vulnerable to changes in precipitation levels (Weltzin 
et al. 2003, p. 944; Huxman et al. 2004, p. 254; Hereford et al. 2006, 
p. 25). Peterson (1996a, p. 1831) highlights the importance of rain for 
desert tortoises: ``Energy acquisition and expenditure in desert 
tortoises are strongly constrained by the contingencies of rainfall, 
both indirectly through effects on availability and quality of food, 
and directly through reliance on freestanding water for drinking, which 
is apparently necessary for achieving a net annual energy profit.'' 
Desert tortoises evolved in arid conditions, and possess numerous 
physiological and behavioral adaptations to survive some degree of 
drought (Schmidt-Nelson and Bently 1966, p. 911; Peterson 1996b, p. 
1325; Christopher 1999, p. 365; Duda et al. 1999, p. 1188; AIDTT 2000, 
p. 4; Berry et al. 2002b, pp. 443-446; Dickinson et al. 2002, pp. 251-
252). Peterson (1996a, p. 1831) found desert tortoises have a very low 
field metabolic rate when compared to other desert reptiles, which may 
provide them an advantage in drought conditions. However, a decrease in 
winter precipitation may disproportionately affect reproductive females 
because they are highly dependent upon springtime forage. A decrease in 
winter precipitation is expected to adversely affect the quantity and 
quality of their forage. This, in turn, is likely to directly affect 
reproductive output of Sonoran desert tortoise populations (Hereford et 
al. 2006, p. 25). Persistent drought, and subsequent changes in the 
tortoise forage base, can affect blood chemistry and water metabolism, 
reduce or eliminate the thymus and fat stores, and result in skeletal 
muscle and liver atrophy in desert tortoises (Berry et al. 2002b, pp. 
443-446; Dickinson et al. 2002, pp. 251-252).
    Seasonal changes in rainfall may contribute to the spread of 
invasive species, such as Sahara mustard and exotic grasses, which are 
capable of explosive growth, and able to quickly

[[Page 78137]]

out-compete native species (Barrows et al. 2009, p. 673). As explained 
in Factor A, invasive species displace the native vegetation, reducing 
forage for tortoises, and increasing the threat of wildfires in desert 
ecosystems, resulting in further reduction of forage plants for the 
tortoise.
    Droughts, which are likely to be more frequent and severe as a 
result of climate change, have been suggested to have caused in 
declines in local Sonoran desert tortoise populations. Periodic times 
of drought are not uncommon in the Southwest, and tortoises have 
evolved with drought. However, future drought conditions may be more 
severe and long-lasting than previously recorded droughts (Cook et al. 
2004, p. 1016). The effects of drought have been shown to have 
significant population-level impacts on Mojave desert tortoises, as 
exhibited by the observed declines in their populations during years of 
drought-induced reductions in annual plants (Longshore et al. 2003, p. 
169). As stated previously, Sonoran desert tortoises strongly benefit 
from the bimodal precipitation pattern characteristic of the Sonoran 
Desert region, specifically from precipitation received during the 
summer monsoon. However, the monsoon is characterized by highly-
localized rainfall events of short duration and high magnitude, and can 
be spatially unpredictable. Therefore, while some Sonoran desert 
tortoise populations may receive satisfactory amounts of summer 
precipitation, others may be exposed to reduced monsoon precipitation 
totals, and potentially zero precipitation in a given year. This seems 
to have been the case during the late 1980s in the Maricopa Mountains 
near Phoenix, Arizona. The precipitous loss of 226 Sonoran desert 
tortoises in the Maricopa Mountains plot, which occurred between 1987 
and 1990, is believed to have resulted from severe, localized drought, 
when no measurable rainfall occurred in that area in 1989. This 
indicates that even Sonoran desert tortoises may succumb to excessive 
drought conditions (Schwalbe 2010, p. 2). Subsequent surveys have shown 
that survivorship within this population has improved, and there is 
evidence that reproduction has resumed in this population. Also, a lack 
of additional carcasses found on the plot indicates that population 
declines have stabilized, and the population might be rebounding (AGFD 
2010, p. 4). Drought conditions also apparently played a significant 
role in a decline of new Sonoran desert tortoise captures between 1988 
and 1990 in the San Pedro Valley (Meyer et al. 2010, p. 11). Localized 
cases of population declines as a result of drought could be more 
common in the future, due to decreasing rainfall caused by climate 
change.
    Another way to evaluate the threats to a species is the use of 
vulnerability assessments. The results of one assessment, conducted by 
Galbraith and Price (2009, p. ii) concluded that the desert tortoise 
within the United States was ``highly vulnerable'' to extinction as a 
result of climate change. The framework used by Galbraith and Price 
(2009, pp. 80-82) considered numerous factors including: (1) Current 
population size and trends, (2) range trends, (3) likely future 
stressor trends, (4) individual replacement time, (5) likely future 
vulnerability to stochastic events, (6) future vulnerability to policy/
management change, (7) likely future vulnerability to natural 
stressors, (7) physiological sensitivity to temperature and 
precipitation change and to extreme weather events, (8) dispersive 
capability and potential rate of increase, (9) habitat specialization, 
(10) likely event of future habitat loss due to climate change, (11) 
ability of habitats to shift in response to climate change, and (12) 
dependence on temporal inter-relations and other species. They 
summarized: ``Over the last three or four decades, these populations 
(Mohave and Sonoran) have come under high degrees of stress due largely 
to human activity (particularly urbanization and recreational 
intrusion) * * * Climate change may be a significant new stressor, 
causing even more habitat loss and exacerbating an already difficult 
situation. Together, existing stressors and the direct and indirect 
effects of climate change could result in desert tortoises being put at 
even greater risk of population reduction and extinction in their U.S. 
range.''
    Galbraith and Price (2009, pp. 79-80) estimate that at least 20 to 
50 percent of habitat today will not be available to desert tortoises 
by 2020 as a result of climate change and, to a much lesser extent, 
anticipated development. However, in their analysis, Galbraith and 
Price (2009, pp. 74-84) largely disregarded the fact that the Sonoran 
desert tortoise ranges into Mexico (which represents approximately half 
of its total distribution), which should be factored into their 
vulnerability analysis. They also often misapplied or gave 
disproportionate influence to specific research on the Mojave desert 
tortoise in addressing the desert tortoise in the U.S. as a whole. 
While we found certain attributes of Galbraith and Price (2009, pp. 74-
84) to be accurate, these identified shortcomings provide an incomplete 
picture of the status of the desert tortoise and its vulnerability to 
the effects of climate change.
    Weiss and Overpeck (2005, p. 2074) disagreed with Galbraith and 
Price (2009, pp. 74-84). Accelerated increases in temperature projected 
as a result of climate change will potentially result in changes to the 
current geographical boundaries of the Sonoran Desert, as well as the 
distribution of associated plant species (Weiss and Overpeck 2005, p. 
2074). Specifically, Weiss and Overpeck (2005, p. 2074) predicted that 
the current geographic boundary of the Sonoran Desert will contract in 
its southeast portion and expand in distribution and rise in elevation 
in the eastern and northern portions, thus potentially expanding areas 
of suitable habitat for the Sonoran desert tortoise. Weiss and Overpeck 
(2005, p. 2075) and Galbraith and Price (2009, p. 80) agreed that 
observed changes to the fire regime of the Sonoran Desert favor 
nonnative plant species, and may impede the trajectory or degree of 
potential expansion of the Sonoran Desert.
    With the differences in predicted climate change under different 
scenarios, and the uncertainty of those effects on the tortoise, it is 
difficult to come to a definitive conclusion as to the potential 
impacts of climate change on the Sonoran desert tortoise. All, none, or 
a combination of these predictions may actually be realized in the 
future within the distribution of the Sonoran desert tortoise, which 
adds uncertainty to how the tortoise may respond to any given 
combination of these predictions. For example, warmer average 
temperatures may affect the Sonoran desert tortoise positively by 
lengthening annual surface-activity periods which may enhance 
reproduction potential and survivorship. Increased frequencies in heavy 
precipitation may provide more opportunities for rehydration of Sonoran 
desert tortoises and promote the production of forage species, whereby 
reducing daily foraging periods to both avoid excessive high 
temperatures and, as a consequence, lessen predation risks. However, 
higher temperatures coupled with drought conditions could also 
negatively affect the Sonoran desert tortoise by increasing metabolism 
rates, foraging needs, and associated foraging time, therefore 
increasing predation risk. Higher temperatures coupled with drought 
conditions could also reduce forage availability of plant species that 
depend on higher frequencies of precipitation events for growth (annual 
plant species that respond to monsoon storms).

[[Page 78138]]

    The temporal aspect of anticipated changes in climate and their 
effects on the Sonoran desert tortoise and its habitat must be 
considered in context with the rate of evolutionary adaptation of the 
species. Skelly et al. (2007, pp. 1353-1355) examined preferred 
temperature ranges and thermal maxima, and suggested that some species 
with short generation times might evolve to meet the demands of a 
changing climate. The Sonoran desert tortoise has much longer 
generation times (approximately 12 to 15 years) and may therefore be 
more vulnerable to the effects of climate change, because they are 
unlikely to be able to rapidly adapt to environmental changes. 
Specifically, we do not expect their evolutionary processes to keep 
pace with the relatively fast-paced changes predicted as a result of 
climate change in the near- or mid-term.
    Perhaps the most important aspect of projected changes in climate 
is the relative irreversibility of these changes into the future. 
Solomon et al. (2009, p. 1704) state that the effects of climate change 
will be irreversible for approximately 1,000 years, even if carbon 
emissions dropped to zero in current times, as a result of the 
longevity of atmospheric carbon dioxide and feedbacks associated with 
ocean warming (Solomon et al. 2009, p. 1709).
Summary of Factor E
    Our review of the best scientific and commercial data available 
indicated that Sonoran desert tortoises may be vulnerable to the 
effects of environmental contamination: Ingestion of trash, including 
balloons; and substances from illegal solid waste dumps. However the 
literature did not indicate these threats were currently affecting 
populations and specific reports of affected individual tortoises were 
rare. Vehicle strike mortalities have been documented, and may have 
some local sub-population effects in close proximity to more heavily 
traveled roads and highways, but again, these effects are more 
localized and not rangewide, and thus do not appear to have overall 
population-level effects. Further, while management and mitigation 
actions are being implemented, such as the construction of barrier 
fences and culverts, these devices are generally not maintained and 
appear to be ineffective in helping to reduce these individual 
mortalities.
    Climate change may also affect Sonoran desert tortoises. The 
combined effects of global and regional climate change, along with the 
effects of long-term drought, will play a role in the long-term 
persistence of the species. However, we are not able to quantify, with 
certainty, how the direct and indirect effects of climate change will 
affect Sonoran desert tortoise populations. Tortoise habitat may shift, 
native vegetation may change depending on rainfall patterns, increasing 
temperatures may affect the growth of native vegetation, the quality 
and quantity of desert tortoise forage may be affected, precipitation 
patterns will likely affect desert vegetation, and tortoises may 
experience physiological effects that could result in changes in 
reproduction and overall survival. We conclude that climate change may 
be a significant stressor that exacerbates current threats, both 
directly (physiological effects to the tortoise) and indirectly 
(habitat loss and fragmentation). As such, climate change, in and of 
itself, may affect Sonoran desert tortoise populations, but the 
magnitude of the impacts to the Sonoran desert tortoise remains 
uncertain. Climate change is not currently a threat to the Sonoran 
desert tortoise, but it has the potential to be a threat in the 
foreseeable future. Impacts from climate change in the future will 
likely exacerbate the current and ongoing threat of habitat loss caused 
by other factors, as discussed above.

Finding

    As required by the Act, we conducted a review of the status of the 
Sonoran desert tortoise DPS and considered the five factors in 
assessing whether the DPS is threatened or endangered throughout all or 
a significant portion of its range. We examined the best scientific and 
commercial information available regarding the past, present, and 
future threats faced by the Sonoran desert tortoise. We reviewed the 
petition, information available in our files, and other available 
published and unpublished information, and we consulted with species 
experts, land managers, and numerous stakeholders including Federal, 
State, and Tribal agencies.
    In considering what factors might constitute threats, we must look 
beyond the mere exposure of the species to the factor to determine 
whether the species responds to the factor in a way that causes actual 
impacts to the species. If there is exposure to a factor, but no 
response, or only a positive response, that factor is not a threat. If 
there is exposure and the species responds negatively, the factor may 
be a threat and we then attempt to determine how significant a threat 
it is. If the threat is significant, it may drive or contribute to the 
risk of extinction of the species such that the species warrants 
listing as threatened or endangered as those terms are defined by the 
Act. This does not necessarily require empirical proof of a threat; 
however, reasonably strong data-based inferences are the minimum 
standard for considering a threat significant. The mere identification 
of factors that could impact a species negatively is not sufficient to 
compel a finding that listing is appropriate; we require evidence that 
these factors are operative threats that act on the species to the 
point that the species meets the definition of threatened or endangered 
under the Act.
    Despite the history of conservation and management efforts afforded 
the Sonoran desert tortoise in Arizona, our review of the literature 
identified threats to the Sonoran desert tortoise attributable to all 
Threat Factors (A-E). The primary threats to the Sonoran desert 
tortoise from habitat modification and destruction (Factor A) include 
the: (1) Current and ongoing invasion of nonnative plant species 
resulting in an unnatural, destructive wildfire regime in portions of 
the species' distribution; (2) cumulative, anticipated indirect effects 
to habitat and individual tortoises from increased human activity tied 
to urbanization and human population growth; (3) current and 
anticipated creation of barriers to genetic exchange among populations 
from urbanization and associated infrastructure; (4) high and growing 
use and popularity of OHV use in Sonoran desert tortoise habitat; (5) 
mesquite and ironwood tree harvest in Mexico; (6) improper livestock 
grazing in Mexico; and (7) undocumented human immigration and 
interdiction activities. The primary threat to the Sonoran desert 
tortoise from overutilization for commercial, recreational, scientific, 
or educational purposes (Factor B) is illegal collection. The primary 
threat to the Sonoran desert tortoise from predation (Factor C) is the 
increase in feral or off-leash domestic dog predation and human 
depredation associated with anticipated increases in urbanization and 
human population growth. The Sonoran desert tortoise is also threatened 
by the inadequacy of regulatory mechanisms (Factor D). In our review of 
the available information, we found numerous examples where the Sonoran 
desert tortoise is considered in management actions and tortoise-
specific mitigation measures are mandated, or where land activities 
that could appreciably threaten Sonoran desert tortoise populations are 
prohibited. However, significant threats we have identified in Factors 
A, C, and E (primarily invading nonnative plant

[[Page 78139]]

species and subsequent wildfire concerns, vandalism of tortoises, feral 
dog predation, and climate change) are not being adequately addressed 
by land managers or other regulatory mechanisms. The primary threats to 
the Sonoran desert tortoise from other natural or manmade factors 
affecting its continued existence (Factor E) include the threats from 
vehicle strike mortality due to unmaintained structures intended to 
prevent tortoise mortality along heavily traveled routes through core 
Sonoran desert tortoise populations. In addition, anticipated effects 
from climate change are likely to exacerbate the ongoing threat of 
habitat loss and degradation by other factors, but we were unable to 
conclude that climate change, by itself, currently threatens the 
Sonoran desert tortoise. We have documented adverse effects of many of 
these threats on existing Sonoran desert tortoise populations, both 
historically and currently, and note that many threats act in 
synergistic combination in their effects to the tortoise. The factors 
that are the primary drivers of these threats, such as urbanization, 
human population growth, and drought, are predicted to increase in the 
foreseeable future.
    As a result of the numerous threats to the Sonoran desert tortoise 
identified above--which have occurred historically, continue today, and 
are predicted to continue in the foreseeable future--the tortoise has 
lost appreciable amounts of habitat to the collective footprint of 
urban development, agriculture, and infrastructure on the landscape. 
Collectively, these land changes have not only destroyed former Sonoran 
desert tortoise habitat, but have fragmented remaining populations, 
threatening long-term genetic fitness of the tortoise and precluding 
their recolonization ability in the event of population extirpations. 
In Mexico, significant areas of former Sonoran desert habitat have been 
significantly altered by the cultivation and natural colonization of 
invasive, nonnative plant species, and in combination with other 
threats, have likely greatly affected the viability of the Sonoran 
desert tortoise in that country.
    Available monitoring data are not adequate to accurately determine 
how the Sonoran desert tortoise historically responded to the loss of 
habitat or how populations have individually responded to threats, but 
we are reasonably certain that there are fewer Sonoran desert tortoises 
currently than historically, and that populations have become 
significantly fragmented over time. Currently within Arizona, 
approximately 75 percent of potential Sonoran desert tortoise habitat 
is within 30 mi (48 km) or less of human populations of 1,000 people or 
more. The factors that have resulted in the loss or degradation of 
habitat, or threaten the tortoise directly, are predicted to worsen in 
the foreseeable future as the footprint of development and 
infrastructure grows and human population growth ensues. Some 
populations may disappear altogether, while others become smaller and 
more contracted; each of these scenarios exacerbates isolation and 
genetic and demographic exchange. Therefore, we reasonably anticipate 
that the Sonoran desert tortoise DPS is in danger of extinction in the 
foreseeable future throughout all or a significant portion of its 
range.
    On the basis of the best scientific and commercial information 
available, we find that the petitioned action, to list the Sonoran 
desert tortoise is warranted. In making this finding, we gave 
significant deference to the irreversible effect of threats as they are 
anticipated to occur in the foreseeable future. We will make a 
determination on the status of the species as threatened or endangered 
when we do a proposed listing determination. However, as explained in 
more detail below, an immediate proposal of a regulation implementing 
this action is precluded by higher priority listing actions, and 
progress is being made to add or remove qualified species from the 
Lists of Endangered and Threatened Wildlife and Plants.
    We reviewed the available information to determine if the existing 
and foreseeable threats render the species at risk of extinction at 
this time such that issuing an emergency regulation temporarily listing 
the DPS under section 4(b)(7) of the Act is warranted. We determined 
that issuing an emergency regulation temporarily listing the species is 
not warranted for this species at this time because we have not 
documented any significant population extirpations. However, if at any 
time we determine that issuing an emergency regulation temporarily 
listing the Sonoran desert tortoise is warranted, we will initiate this 
action at that time.

Listing Priority Number

    The Service adopted guidelines on September 21, 1983 (48 FR 43098) 
to establish a rational system for utilizing available resources for 
the highest priority species when adding species to the Lists of 
Endangered and Threatened Wildlife and Plants or reclassifying species 
listed as threatened to endangered status. These guidelines, titled 
``Endangered and Threatened Species Listing and Recovery Priority 
Guidelines'' address the immediacy and magnitude of threats, and the 
level of taxonomic distinctiveness. The system places greatest 
importance on the immediacy and magnitude of threats, but also factors 
in the level of taxonomic distinctiveness by assigning priority in 
descending order to monotypic genera (genus with one species), full 
species, and subspecies (or equivalently, distinct population segments 
of vertebrates). As a result of our analysis of the best available 
scientific and commercial information, we assigned the Sonoran desert 
tortoise a Listing Priority Number of 6, based on the high magnitude 
and non-imminence of threats. One or more of the threats discussed 
above are occurring in virtually every known population throughout its 
range. These threats are ongoing, and will continue to occur into the 
foreseeable future and, in some cases (such as nonnative plant species 
invasions and climate change effects), are considered irreversible. Our 
rationale for assigning the Sonoran desert tortoise an LPN of 6 is 
outlined below.
    Under the Service's LPN Guidance, the magnitude of threat is the 
first criterion we look at when establishing a listing priority. The 
guidance indicates that species with the highest magnitude of threat 
are those species facing the greatest threats to their continued 
existence. These species receive the highest listing priority. Threats 
to the Sonoran desert tortoise vary in their magnitude. We found the 
most significant threats to the Sonoran desert tortoise to be the 
expansion of range and increase in number of nonnative plant species, 
urban development and associated human population growth in Arizona, 
and the highly popular and growing use of OHVs in Arizona. These 
threats have both direct and indirect effects to the Sonoran desert 
tortoise and its habitat. The area of land affected by nonnative 
species is widespread and, although currently and comparatively less 
significant in Arizona, it is substantial in Mexico. It is also 
expected to increase in the foreseeable future in both countries. When 
including the total land area adversely modified by ironwood and 
mesquite harvesting, it is projected that an estimated 98 percent of 
the Sonoran desert tortoises' habitat in Mexico (47 percent of habitat 
rangewide) will be lost or adversely modified in the foreseeable 
future. Additionally, there is currently no viable solution to the 
threat posed by the increase in nonnative plants on this landscape. The 
projected human population growth and urban development throughout this 
DPS are

[[Page 78140]]

likely to both pose significant problems for genetic exchange among 
Sonoran desert tortoise populations. This will increase the degree and 
scope of human interactions with tortoises and occupied habitat, which 
threatens the tortoise in a variety of ways that we discuss in detail 
above. Currently in Arizona, 75 percent of potentially occupied Sonoran 
desert tortoise habitat occurs within 30 mi (48 km) or less of a city 
or town with a human population of 1,000 or more, and, considering 
future growth projections, it is likely that 100 percent of occupied 
tortoise habitat will be affected in the future. The ever-expanding 
human population in Arizona is also likely to lead to commensurate 
increases in OHV use. As of 2007, 385,000 off-highway vehicles were 
registered in Arizona (a 350 percent increase since 1998), and 1.7 
million people (29 percent of the Arizona's public) engaged in off-road 
activity from 2005 to 2007. We identified significant threats from OHV 
use in Sonoran desert tortoise habitat, including habitat destruction, 
increased illegal collection of tortoises, and significant problems 
with law enforcement of OHV users. Despite problems associated with OHV 
management, several land management agencies responsible for Sonoran 
desert tortoise habitat have plans to expand OHV use on their lands. 
These three major threats operate in combination with other threats 
which, by themselves, might not be as serious, but acting together, 
cause a more serious cumulative impact. These threats include improper 
livestock management in Mexico, illegal collection and release of 
tortoises, undocumented human immigration and associated interdiction 
activities, predation from feral or off-leash dogs, vehicle strike 
mortality from unmaintained, roadside mitigation devices, and 
anticipated possible effects from climate change. In their totality, 
these threats are high in magnitude because of the amount of habitat 
that is likely to be affected and the irreversible nature of the effect 
of these threats in sensitive habitats that are slow to rebound.
    Under our LPN Guidance, the second criterion we consider in 
assigning a listing priority is the immediacy of threats. This 
criterion is intended to ensure that the species that face actual, 
identifiable threats are given priority over those species for which 
threats are only potential or that are intrinsically vulnerable but are 
not known to be presently facing such threats. The threats are non-
imminent because they are not ubiquitous throughout the range of the 
Sonoran desert tortoise where they occur. Some are acting currently in 
some areas, but not the whole DPS; some threats are likely to expand 
geographically over time; some are stabilized or even reducing in 
impact. Although we reviewed and discussed the numerous ways that 
individual Sonoran desert tortoises are affected by various threats, 
there is currently no evidence that any existing population is 
threatened with extirpation in the near future. So while some of the 
threats are happening now, impacts to tortoise populations are not 
likely to be evident in the immediate future.
    For example, we have documented that the invasion of nonnative 
plants is most significant in Sonora, Mexico, because of active 
planting for livestock grazing purposes. However, while there were 
historic practices of planting nonnative plant species as forage for 
livestock in the United States, these activities have ceased, leaving 
only slower, natural mechanisms to facilitate the expansion of 
nonnative plant species in this country. Thus, comparatively less 
habitat area is significantly altered by nonnative plant distribution 
and abundance in Arizona, representing approximately half of the 
Sonoran desert tortoises' range. Additionally, monitoring data indicate 
that Sonoran desert tortoise populations persist in habitat that is 
unburned, but where nonnative species have become established. As 
stated in Factor A, wildfire is an important trigger, capable of making 
nonnative-invaded habitat unsuitable for Sonoran desert tortoises. The 
majority of nonnative-invaded Sonoran desert tortoise habitat remains 
unburned in the United States; however we are less certain about the 
occurrence of wildfire in nonnative-invaded habitat in Mexico. In both 
cases in Arizona and Mexico the ongoing conversion of habitats to 
nonnative grasses are not expected to impact tortoise populations in 
the very immediate future. Therefore, the actual impacts on tortoise 
populations from these and similar threats, such as climate change, are 
more likely to occur in the mid- to long-term future and are not 
considered imminent.
    Also, many of the threats we discuss above are linked to 
urbanization and human population growth. In Arizona, we have observed 
significant development and human population growth over the past 
several decades, but a weakened economy has slowed growth in recent 
years. We documented that the Sun Corridor Megapolitan is expected to 
nearly double the human population of southern and central Arizona by 
2030. However, much of the urbanization that has already occurred 
replaced agricultural land that was not usable Sonoran desert tortoise 
habitat. Additionally, our evaluation of Sonoran desert tortoise 
population monitoring data has not indicated that any monitored 
population has been extirpated and less than one-third of monitored 
populations have shown declines, indicating that impacts on Sonoran 
desert tortoise populations are not currently imminent. These actual, 
identifiable threats are covered in detail under the discussion of 
Factors A through E of this finding and currently include habitat 
destruction, modification, and fragmentation, overutilization, 
predation from unnatural sources, inadequate regulatory mechanisms, and 
other natural and manmade factors.
    The third criterion in our LPN guidance is intended to devote 
resources to those species representing highly distinctive or isolated 
gene pools as reflected by taxonomy. The Sonoran desert tortoise is a 
valid taxon at the DPS level, and therefore receives a lower priority 
than species in a monotypic genus. The Sonoran desert tortoise faces 
high magnitude, non-imminent threats, and is a valid taxon at the DPS 
level. Thus, in accordance with our LPN guidance, we have assigned the 
Sonoran desert tortoise an LPN of 6.
    We will continue to monitor the threats to the Sonoran desert 
tortoise, and the species' status on an annual basis, and should the 
magnitude or the imminence of the threats change, we will revisit our 
assessment of the LPN.
    Work on a proposed listing determination for the Sonoran desert 
tortoise is precluded by work on higher priority listing actions with 
absolute statutory, court-ordered, or court-approved deadlines and 
final listing determinations for those species that were proposed for 
listing with funds from Fiscal Year 2011. This work includes all the 
actions listed in the tables below under expeditious progress.

Preclusion and Expeditious Progress

    Preclusion is a function of the listing priority of a species in 
relation to the resources that are available and the cost and relative 
priority of competing demands for those resources. Thus, in any given 
fiscal year (FY), multiple factors dictate whether it will be possible 
to undertake work on a listing proposal regulation or whether 
promulgation of such a proposal is precluded by higher-priority listing 
actions.

[[Page 78141]]

    The resources available for listing actions are determined through 
the annual Congressional appropriations process. The appropriation for 
the Listing Program is available to support work involving the 
following listing actions: Proposed and final listing rules; 90-day and 
12-month findings on petitions to add species to the Lists of 
Endangered and Threatened Wildlife and Plants (Lists) or to change the 
status of a species from threatened to endangered; annual 
``resubmitted'' petition findings on prior warranted-but-precluded 
petition findings as required under section 4(b)(3)(C)(i) of the Act; 
critical habitat petition findings; proposed and final rules 
designating critical habitat; and litigation-related, administrative, 
and program-management functions (including preparing and allocating 
budgets, responding to Congressional and public inquiries, and 
conducting public outreach regarding listing and critical habitat). The 
work involved in preparing various listing documents can be extensive 
and may include, but is not limited to: gathering and assessing the 
best scientific and commercial data available and conducting analyses 
used as the basis for our decisions; writing and publishing documents; 
and obtaining, reviewing, and evaluating public comments and peer 
review comments on proposed rules and incorporating relevant 
information into final rules. The number of listing actions that we can 
undertake in a given year also is influenced by the complexity of those 
listing actions; that is, more complex actions generally are more 
costly. The median cost for preparing and publishing a 90-day finding 
is $39,276; for a 12-month finding, $100,690; for a proposed rule with 
critical habitat, $345,000; and for a final listing rule with critical 
habitat, the median cost is $305,000.
    We cannot spend more than is appropriated for the Listing Program 
without violating the Anti-Deficiency Act (see 31 U.S.C. 
1341(a)(1)(A)). In addition, in FY 1998 and for each fiscal year since 
then, Congress has placed a statutory cap on funds which may be 
expended for the Listing Program, equal to the amount expressly 
appropriated for that purpose in that fiscal year. This cap was 
designed to prevent funds appropriated for other functions under the 
Act (for example, recovery funds for removing species from the Lists), 
or for other Service programs, from being used for Listing Program 
actions (see House Report 105-163, 105th Congress, 1st Session, July 1, 
1997).
    Since FY 2002, the Service's budget has included a critical habitat 
subcap to ensure that some funds are available for other work in the 
Listing Program (``The critical habitat designation subcap will ensure 
that some funding is available to address other listing activities'' 
(House Report No. 107-103, 107th Congress, 1st Session, June 19, 
2001)). In FY 2002 and each year until FY 2006, the Service has had to 
use virtually the entire critical habitat subcap to address court-
mandated designations of critical habitat, and consequently none of the 
critical habitat subcap funds have been available for other listing 
activities. In some FYs since 2006, we have been able to use some of 
the critical habitat subcap funds to fund proposed listing 
determinations for high-priority candidate species. In other FYs, while 
we were unable to use any of the critical habitat subcap funds to fund 
proposed listing determinations, we did use some of this money to fund 
the critical habitat portion of some proposed listing determinations so 
that the proposed listing determination and proposed critical habitat 
designation could be combined into one rule, thereby being more 
efficient in our work. In FY 2011 we anticipate that we will be unable 
to use any of the critical habitat subcap funds to fund proposed 
listing determinations.
    We make our determinations of preclusion on a nationwide basis to 
ensure that the species most in need of listing will be addressed first 
and also because we allocate our listing budget on a nationwide basis. 
Through the listing cap, the critical habitat subcap, and the amount of 
funds needed to address court-mandated critical habitat designations, 
Congress and the courts have, in effect, determined the amount of money 
available for other listing activities nationwide. Therefore, the funds 
in the listing cap, other than those needed to address court-mandated 
critical habitat for already listed species, set the limits on our 
determinations of preclusion and expeditious progress.
    Congress identified the availability of resources as the only basis 
for deferring the initiation of a rulemaking that is warranted. The 
Conference Report accompanying P.L. 97-304, which established the 
current statutory deadlines and the warranted-but-precluded finding, 
states that the amendments were ``not intended to allow the Secretary 
to delay commencing the rulemaking process for any reason other than 
that the existence of pending or imminent proposals to list species 
subject to a greater degree of threat would make allocation of 
resources to such a petition [that is, for a lower-ranking species] 
unwise.'' Although that statement appeared to refer specifically to the 
``to the maximum extent practicable'' limitation on the 90-day deadline 
for making a ``substantial information'' finding, that finding is made 
at the point when the Service is deciding whether or not to commence a 
status review that will determine the degree of threats facing the 
species, and therefore the analysis underlying the statement is more 
relevant to the use of the warranted-but-precluded finding, which is 
made when the Service has already determined the degree of threats 
facing the species and is deciding whether or not to commence a 
rulemaking.
    In FY 2010, $10,471,000 is the amount of money that Congress 
appropriated for the Listing Program (that is, the portion of the 
Listing Program funding not related to critical habitat designations 
for species that are already listed). Therefore, a proposed listing is 
precluded if pending proposals with higher priority will require 
expenditure of at least $10,471,000, and expeditious progress is the 
amount of work that can be achieved with $10,471,000. Since court 
orders requiring critical habitat work will not require use of all of 
the funds within the critical habitat subcap, we used $1,114,417 of our 
critical habitat subcap funds in order to work on as many of our 
required petition findings and listing determinations as possible. This 
brings the total amount of funds we had for listing actions in FY 2010 
to $11,585,417.
    The $11,585,417 was used to fund work in the following categories: 
compliance with court orders and court-approved settlement agreements 
requiring that petition findings or listing determinations be completed 
by a specific date; section 4 (of the Act) listing actions with 
absolute statutory deadlines; essential litigation-related, 
administrative, and listing program-management functions; and high-
priority listing actions for some of our candidate species. For FY 
2011, on September 29, 2010, Congress passed a continuing resolution 
which provides funding at the FY 2010 enacted level. In 2009, the 
responsibility for listing foreign species under the Act was 
transferred from the Division of Scientific Authority, International 
Affairs Program, to the Endangered Species Program. Therefore, starting 
in FY 2010, we use a portion of our funding to work on the actions 
described above as they apply to listing actions for foreign species. 
This has the potential to further reduce funding available for domestic 
listing actions. Although there are currently no foreign species issues 
included in our high-

[[Page 78142]]

priority listing actions at this time, many actions have statutory or 
court-approved settlement deadlines, thus increasing their priority. 
The budget allocations for each specific listing action are identified 
in the Service's FY 2011 Allocation Table (part of our administrative 
record).
    Based on our September 21, 1983, guidance for assigning an LPN for 
each candidate species (48 FR 43098), we have a significant number of 
species with an LPN of 2. Using this guidance, we assign each candidate 
an LPN of 1 to 12, depending on the magnitude of threats (high or 
moderate to low), immediacy of threats (imminent or nonimminent), and 
taxonomic status of the species (in order of priority: monotypic genus 
(a species that is the sole member of a genus); species, or part of a 
species (subspecies, distinct population segment, or significant 
portion of the range)). The lower the listing priority number, the 
higher the listing priority (that is, a species with an LPN of 1 would 
have the highest listing priority).
    Because of the large number of high-priority species, we have 
further ranked the candidate species with an LPN of 2 by using the 
following extinction-risk type criteria: International Union for the 
Conservation of Nature and Natural Resources (IUCN) Red list status/
rank, Heritage rank (provided by NatureServe), Heritage threat rank 
(provided by NatureServe), and species currently with fewer than 50 
individuals, or 4 or fewer populations. Those species with the highest 
IUCN rank (critically endangered), the highest Heritage rank (G1), the 
highest Heritage threat rank (substantial, imminent threats), and 
currently with fewer than 50 individuals, or fewer than 4 populations, 
originally comprised a group of approximately 40 candidate species 
(``Top 40''). These 40 candidate species have had the highest priority 
to receive funding to work on a proposed listing determination. As we 
work on proposed and final listing rules for those 40 candidates, we 
apply the ranking criteria to the next group of candidates with an LPN 
of 2 and 3 to determine the next set of highest-priority candidate 
species. Finally, proposed rules for reclassification of threatened 
species to endangered are lower priority, since as listed species, they 
are already afforded the protection of the Act and implementing 
regulations. However, for efficiency reasons, we may choose to work on 
a proposed rule to reclassify a species to endangered if we can combine 
this with work that is subject to a court-determined deadline.
    With our workload so much bigger than the amount of funds we have 
to accomplish it, it is important that we be as efficient as possible 
in our listing process. Therefore, as we work on proposed rules for the 
highest priority species in the next several years, we are preparing 
multi-species proposals when appropriate, and these may include species 
with lower priority if they overlap geographically or have the same 
threats as a species with an LPN of 2. In addition, we take into 
consideration the availability of staff resources when we determine 
which high-priority species will receive funding to minimize the amount 
of time and resources required to complete each listing action.
    As explained above, a determination that listing is warranted but 
precluded must also demonstrate that expeditious progress is being made 
to add and remove qualified species to and from the Lists of Endangered 
and Threatened Wildlife and Plants. As with our ``precluded'' finding, 
the evaluation of whether progress in adding qualified species to the 
Lists has been expeditious is a function of the resources available for 
listing and the competing demands for those funds. Although we do not 
discuss it in detail here, we are also making expeditious progress in 
removing species from the list under the Recovery program in light of 
the resource available for delisting, which is funded by a separate 
line item in the budget of the Endangered Species Program. During FY 
2010, we have completed two proposed delisting rules and two final 
delisting rules. Given the limited resources available for listing, we 
find that we made expeditious progress in FY 2010 in the Listing 
Program. This progress included preparing and publishing the following 
determinations:

                                  FY 2010 and FY 2011 Completed Listing Actions
----------------------------------------------------------------------------------------------------------------
         Publication date                    Title                 Actions                   FR pages
----------------------------------------------------------------------------------------------------------------
10/08/2009.......................  Listing Lepidium          Final Listing        74 FR 52013-52064.
                                    papilliferum (Slickspot   Threatened.
                                    Peppergrass) as a
                                    Threatened Species
                                    Throughout Its Range.
10/27/2009.......................  90-day Finding on a       Notice of 90-day     74 FR 55177-55180.
                                    Petition To List the      Petition Finding,
                                    American Dipper in the    Not substantial.
                                    Black Hills of South
                                    Dakota as Threatened or
                                    Endangered.
10/28/2009.......................  Status Review of Arctic   Notice of Intent to  74 FR 55524-55525.
                                    Grayling (Thymallus       Conduct Status
                                    arcticus) in the Upper    Review for Listing
                                    Missouri River System.    Decision.
11/03/2009.......................  Listing the British       Proposed Listing     74 FR 56757-56770.
                                    Columbia Distinct         Threatened.
                                    Population Segment of
                                    the Queen Charlotte
                                    Goshawk Under the
                                    Endangered Species Act:
                                    Proposed rule.
11/03/2009.......................  Listing the Salmon-       Proposed Listing     74 FR 56770-56791.
                                    Crested Cockatoo as       Threatened.
                                    Threatened Throughout
                                    Its Range with Special
                                    Rule.
11/23/2009.......................  Status Review of          Notice of Intent to  74 FR 61100-61102.
                                    Gunnison sage-grouse      Conduct Status
                                    (Centrocercus minimus).   Review for Listing
                                                              Decision.
12/03/2009.......................  12-Month Finding on a     Notice of 12-month   74 FR 63343-63366.
                                    Petition to List the      petition finding,
                                    Black-tailed Prairie      Not warranted.
                                    Dog as Threatened or
                                    Endangered.
12/03/2009.......................  90-Day Finding on a       Notice of 90-day     74 FR 63337-63343.
                                    Petition to List          Petition Finding,
                                    Sprague's Pipit as        Substantial.
                                    Threatened or
                                    Endangered.
12/15/2009.......................  90-Day Finding on         Notice of 90-day     74 FR 66260-66271.
                                    Petitions To List Nine    Petition Finding,
                                    Species of Mussels From   Substantial.
                                    Texas as Threatened or
                                    Endangered With
                                    Critical Habitat.
12/16/2009.......................  Partial 90-Day Finding    Notice of 90-day     74 FR 66865-66905.
                                    on a Petition to List     Petition Finding,
                                    475 Species in the        Not substantial
                                    Southwestern United       and Substantial.
                                    States as Threatened or
                                    Endangered With
                                    Critical Habitat.
12/17/2009.......................  12-month Finding on a     Notice of 12-month   74 FR 66937-66950.
                                    Petition To Change the    petition finding,
                                    Final Listing of the      Warranted but
                                    Distinct Population       precluded.
                                    Segment of the Canada
                                    Lynx To Include New
                                    Mexico.

[[Page 78143]]

 
1/05/2010........................  Listing Foreign Bird      Proposed Listing     75 FR 605-649.
                                    Species in Peru and       Endangered.
                                    Bolivia as Endangered
                                    Throughout Their Range.
1/05/2010........................  Listing Six Foreign       Proposed Listing     75 FR 286-310.
                                    Birds as Endangered       Endangered.
                                    Throughout Their Range.
1/05/2010........................  Withdrawal of Proposed    Proposed rule,       75 FR 310-316.
                                    Rule to List Cook's       withdrawal.
                                    Petrel.
1/05/2010........................  Final Rule to List the    Final Listing        75 FR 235-250.
                                    Galapagos Petrel and      Threatened.
                                    Heinroth's Shearwater
                                    as Threatened
                                    Throughout Their Ranges.
1/20/2010........................  Initiation of Status      Notice of Intent to  75 FR 3190-3191.
                                    Review for Agave          Conduct Status
                                    eggersiana and Solanum    Review for Listing
                                    conocarpum.               Decision.
2/09/2010........................  12-month Finding on a     Notice of 12-month   75 FR 6437-6471.
                                    Petition to List the      petition finding,
                                    American Pika as          Not warranted.
                                    Threatened or
                                    Endangered.
2/25/2010........................  12-Month Finding on a     Notice of 12-month   75 FR 8601-8621.
                                    Petition To List the      petition finding,
                                    Sonoran Desert            Not warranted.
                                    Population of the Bald
                                    Eagle as a Threatened
                                    or Endangered Distinct
                                    Population Segment.
2/25/2010........................  Withdrawal of Proposed    Withdrawal of        75 FR 8621-8644.
                                    Rule To List the          Proposed Rule to
                                    Southwestern Washington/  List.
                                    Columbia River Distinct
                                    Population Segment of
                                    Coastal Cutthroat Trout
                                    (Oncorhynchus clarki
                                    clarki) as Threatened.
3/18/2010........................  90-Day Finding on a       Notice of 90-day     75 FR 13068-13071.
                                    Petition to List the      Petition Finding,
                                    Berry Cave salamander     Substantial.
                                    as Endangered.
3/23/2010........................  90-Day Finding on a       Notice of 90-day     75 FR 13717-13720.
                                    Petition to List the      Petition Finding,
                                    Southern Hickorynut       Not substantial.
                                    Mussel (Obovaria
                                    jacksoniana) as
                                    Endangered or
                                    Threatened.
3/23/2010........................  90-Day Finding on a       Notice of 90-day     75 FR 13720-13726.
                                    Petition to List the      Petition Finding,
                                    Striped Newt as           Substantial.
                                    Threatened.
3/23/2010........................  12-Month Findings for     Notice of 12-month   75 FR 13910-14014.
                                    Petitions to List the     petition finding,
                                    Greater Sage-Grouse       Warranted but
                                    (Centrocercus             precluded.
                                    urophasianus) as
                                    Threatened or
                                    Endangered.
3/31/2010........................  12-Month Finding on a     Notice of 12-month   75 FR 16050-16065.
                                    Petition to List the      petition finding,
                                    Tucson Shovel-Nosed       Warranted but
                                    Snake (Chionactis         precluded.
                                    occipitalis klauberi)
                                    as Threatened or
                                    Endangered with
                                    Critical Habitat.
4/5/2010.........................  90-Day Finding on a       Notice of 90-day     75 FR 17062-17070.
                                    Petition To List          Petition Finding,
                                    Thorne's Hairstreak       Substantial.
                                    Butterfly as Endangered.
4/6/2010.........................  12-month Finding on a     Notice of 12-month   75 FR 17352-17363.
                                    Petition To List the      petition finding,
                                    Mountain Whitefish in     Not warranted.
                                    the Big Lost River,
                                    Idaho, as Endangered or
                                    Threatened.
4/6/2010.........................  90-Day Finding on a       Notice of 90-day     75 FR 17363-17367.
                                    Petition to List a        Petition Finding,
                                    Stonefly (Isoperla        Not substantial.
                                    jewetti) and a Mayfly
                                    (Fallceon eatoni) as
                                    Threatened or
                                    Endangered with
                                    Critical Habitat.
4/7/2010.........................  12-Month Finding on a     Notice of 12-month   75 FR 17667-17680.
                                    Petition to Reclassify    petition finding,
                                    the Delta Smelt From      Warranted but
                                    Threatened to             precluded.
                                    Endangered Throughout
                                    Its Range.
4/13/2010........................  Determination of          Final Listing        75 FR 18959-19165.
                                    Endangered Status for     Endangered.
                                    48 Species on Kauai and
                                    Designation of Critical
                                    Habitat.
4/15/2010........................  Initiation of Status      Notice of            75 FR 19591-19592.
                                    Review of the North       Initiation of
                                    American Wolverine in     Status Review for
                                    the Contiguous United     Listing Decision.
                                    States.
4/15/2010........................  12-Month Finding on a     Notice of 12-month   75 FR 19592-19607.
                                    Petition to List the      petition finding,
                                    Wyoming Pocket Gopher     Not warranted.
                                    as Endangered or
                                    Threatened with
                                    Critical Habitat.
4/16/2010........................  90-Day Finding on a       Notice of 90-day     75 FR 19925-19935.
                                    Petition to List a        Petition Finding,
                                    Distinct Population       Substantial.
                                    Segment of the Fisher
                                    in Its United States
                                    Northern Rocky Mountain
                                    Range as Endangered or
                                    Threatened with
                                    Critical Habitat.
4/20/2010........................  Initiation of Status      Notice of            75 FR 20547-20548.
                                    Review for Sacramento     Initiation of
                                    splittail (Pogonichthys   Status Review for
                                    macrolepidotus).          Listing Decision.
4/26/2010........................  90-Day Finding on a       Notice of 90-day     75 FR 21568-21571.
                                    Petition to List the      Petition Finding,
                                    Harlequin Butterfly as    Substantial.
                                    Endangered.
4/27/2010........................  12-Month Finding on a     Notice of 12-month   75 FR 22012-22025.
                                    Petition to List          petition finding,
                                    Susan's Purse-making      Not warranted.
                                    Caddisfly (Ochrotrichia
                                    susanae) as Threatened
                                    or Endangered.
4/27/2010........................  90-day Finding on a       Notice of 90-day     75 FR 22063-22070.
                                    Petition to List the      Petition Finding,
                                    Mohave Ground Squirrel    Substantial.
                                    as Endangered with
                                    Critical Habitat.
5/4/2010.........................  90-Day Finding on a       Notice of 90-day     75 FR 23654-23663.
                                    Petition to List Hermes   Petition Finding,
                                    Copper Butterfly as       Substantial.
                                    Threatened or
                                    Endangered.
6/1/2010.........................  90-Day Finding on a       Notice of 90-day     75 FR 30313-30318.
                                    Petition To List          Petition Finding,
                                    Castanea pumila var.      Substantial.
                                    ozarkensis.
6/1/2010.........................  12-month Finding on a     Notice of 12-month   75 FR 30338-30363.
                                    Petition to List the      petition finding,
                                    White-tailed Prairie      Not warranted.
                                    Dog as Endangered or
                                    Threatened.
6/9/2010.........................  90-Day Finding on a       Notice of 90-day     75 FR 32728-32734.
                                    Petition To List van      Petition Finding,
                                    Rossem's Gull-billed      Substantial.
                                    Tern as Endangered or
                                    Threatened.
6/16/2010........................  90-Day Finding on Five    Notice of 90-day     75 FR 34077-34088.
                                    Petitions to List Seven   Petition Finding,
                                    Species of Hawaiian       Substantial.
                                    Yellow-faced Bees as
                                    Endangered.
6/22/2010........................  12-Month Finding on a     Notice of 12-month   75 FR 35398-35424.
                                    Petition to List the      petition finding,
                                    Least Chub as             Warranted but
                                    Threatened or             precluded.
                                    Endangered.
6/23/2010........................  90-Day Finding on a       Notice of 90-day     75 FR 35746-35751.
                                    Petition to List the      Petition Finding,
                                    Honduran Emerald          Substantial.
                                    Hummingbird as
                                    Endangered.
6/23/2010........................  Listing Ipomopsis         Proposed Listing     75 FR 35721-35746.
                                    polyantha (Pagosa         Endangered
                                    Skyrocket) as             Proposed Listing
                                    Endangered Throughout     Threatened.
                                    Its Range, and Listing
                                    Penstemon debilis
                                    (Parachute Beardtongue)
                                    and Phacelia submutica
                                    (DeBeque Phacelia) as
                                    Threatened Throughout
                                    Their Range.

[[Page 78144]]

 
6/24/2010........................  Listing the Flying        Final Listing        75 FR 35990-36012.
                                    Earwig Hawaiian           Endangered.
                                    Damselfly and Pacific
                                    Hawaiian Damselfly As
                                    Endangered Throughout
                                    Their Ranges.
6/24/2010........................  Listing the Cumberland    Proposed Listing     75 FR 36035-36057.
                                    Darter, Rush Darter,      Endangered.
                                    Yellowcheek Darter,
                                    Chucky Madtom, and
                                    Laurel Dace as
                                    Endangered Throughout
                                    Their Ranges.
6/29/2010........................  Listing the Mountain      Reinstatement of     75 FR 37353-37358.
                                    Plover as Threatened.     Proposed Listing
                                                              Threatened.
7/20/2010........................  90-Day Finding on a       Notice of 90-day     75 FR 42033-42040.
                                    Petition to List Pinus    Petition Finding,
                                    albicaulis (Whitebark     Substantial.
                                    Pine) as Endangered or
                                    Threatened with
                                    Critical Habitat.
7/20/2010........................  12-Month Finding on a     Notice of 12-month   75 FR 42040-42054.
                                    Petition to List the      petition finding,
                                    Amargosa Toad as          Not warranted.
                                    Threatened or
                                    Endangered.
7/20/2010........................  90-Day Finding on a       Notice of 90-day     75 FR 42059-42066.
                                    Petition to List the      Petition Finding,
                                    Giant Palouse Earthworm   Substantial.
                                    (Driloleirus
                                    americanus) as
                                    Threatened or
                                    Endangered.
7/27/2010........................  Determination on Listing  Final Listing        75 FR 43844-43853.
                                    the Black-Breasted        Endangered.
                                    Puffleg as Endangered
                                    Throughout its Range;
                                    Final Rule.
7/27/2010........................  Final Rule to List the    Final Listing        75 FR 43853-43864.
                                    Medium Tree-Finch         Endangered.
                                    (Camarhynchus pauper)
                                    as Endangered
                                    Throughout Its Range.
8/3/2010.........................  Determination of          Final Listing        75 FR 45497-45527.
                                    Threatened Status for     Threatened.
                                    Five Penguin Species.
8/4/2010.........................  90-Day Finding on a       Notice of 90-day     75 FR 46894-46898.
                                    Petition To List the      Petition Finding,
                                    Mexican Gray Wolf as an   Substantial.
                                    Endangered Subspecies
                                    With Critical Habitat.
8/10/2010........................  90-Day Finding on a       Notice of 90-day     75 FR 48294-48298.
                                    Petition to List          Petition Finding,
                                    Arctostaphylos            Substantial.
                                    franciscana as
                                    Endangered with
                                    Critical Habitat.
8/17/2010........................  Listing Three Foreign     Final Listing        75 FR 50813-50842.
                                    Bird Species from Latin   Endangered.
                                    America and the
                                    Caribbean as Endangered
                                    Throughout Their Range.
8/17/2010........................  90-Day Finding on a       Notice of 90-day     75 FR 50739-50742.
                                    Petition to List Brian    Petition Finding,
                                    Head Mountainsnail as     Not substantial.
                                    Endangered or
                                    Threatened with
                                    Critical Habitat.
8/24/2010........................  90-Day Finding on a       Notice of 90-day     75 FR 51969-51974.
                                    Petition to List the      Petition Finding,
                                    Oklahoma Grass Pink       Substantial.
                                    Orchid as Endangered or
                                    Threatened.
9/1/2010.........................  12-Month Finding on a     Notice of 12-month   75 FR 53615-53629.
                                    Petition to List the      petition finding,
                                    White-Sided Jackrabbit    Not warranted.
                                    as Threatened or
                                    Endangered.
9/8/2010.........................  Proposed Rule To List     Proposed Listing     75 FR 54561-54579.
                                    the Ozark Hellbender      Endangered.
                                    Salamander as
                                    Endangered.
9/8/2010.........................  Revised 12-Month Finding  Notice of 12-month   75 FR 54707-54753.
                                    to List the Upper         petition finding,
                                    Missouri River Distinct   Warranted but
                                    Population Segment of     precluded.
                                    Arctic Grayling as
                                    Endangered or
                                    Threatened.
9/9/2010.........................  12-Month Finding on a     Notice of 12-month   75 FR 54822-54845.
                                    Petition to List the      petition finding,
                                    Jemez Mountains           Warranted but
                                    Salamander (Plethodon     precluded.
                                    neomexicanus) as
                                    Endangered or
                                    Threatened with
                                    Critical Habitat.
9/15/2010........................  12-Month Finding on a     Notice of 12-month   75 FR 56028-56050.
                                    Petition to List          petition finding,
                                    Sprague's Pipit as        Warranted but
                                    Endangered or             precluded.
                                    Threatened Throughout
                                    Its Range.
9/22/2010........................  12-Month Finding on a     Notice of 12-month   75 FR 57720-57734.
                                    Petition to List Agave    petition finding,
                                    eggersiana (no common     Warranted but
                                    name) as Endangered.      precluded.
9/28/2010........................  Determination of          Final Listing        75 FR 59645-59656.
                                    Endangered Status for     Endangered.
                                    the African Penguin.
9/28/2010........................  Determination for the     Notice of 12-month   75 FR 59803-59863.
                                    Gunnison                  petition finding,
                                    Sage[dash]grouse as a     Warranted but
                                    Threatened or             precluded.
                                    Endangered Species.
9/30/2010........................  12-Month Finding on a     Notice of 12-month   75 FR 60515-60561.
                                    Petition to List the      petition finding,
                                    Pygmy Rabbit as           Not warranted.
                                    Endangered or
                                    Threatened.
10/6/2010........................  Endangered Status for     Proposed Listing     75 FR 61664-61690.
                                    the Altamaha              Endangered.
                                    Spinymussel and
                                    Designation of Critical
                                    Habitat.
10/7/2010........................  12-month Finding on a     Notice of 12-month   75 FR 62070-62095.
                                    Petition to list the      petition finding,
                                    Sacramento Splittail as   Not warranted.
                                    Endangered or
                                    Threatened.
----------------------------------------------------------------------------------------------------------------

    Our expeditious progress also includes work on listing actions that 
we funded in FY 2010 and FY 2011, but have not yet been completed to 
date. These actions are listed below. Actions in the top section of the 
table are being conducted under a deadline set by a court. Actions in 
the middle section of the table are being conducted to meet statutory 
timelines, that is, timelines required under the Act. Actions in the 
bottom section of the table are high-priority listing actions. These 
actions include work primarily on species with an LPN of 2, and, as 
discussed above, selection of these species is partially based on 
available staff resources, and when appropriate, include species with a 
lower priority if they overlap geographically or have the same threats 
as the species with the high priority. Including these species together 
in the same proposed rule results in considerable savings in time and 
funding compared to preparing separate proposed rules for each of them 
in the future.

       Actions Funded in FY 2010 and FY 2011 But Not Yet Completed
------------------------------------------------------------------------
           Species                               Action
------------------------------------------------------------------------
           Actions Subject to Court Order/Settlement Agreement
------------------------------------------------------------------------
6 Birds from Eurasia.........  Final listing determination.

[[Page 78145]]

 
Flat-tailed horned lizard....  Final listing determination.
Mountain plover \4\..........  Final listing determination.
6 Birds from Peru............  Proposed listing determination.
Pacific walrus...............  12-month petition finding.
Wolverine....................  12-month petition finding.
Solanum conocarpum...........  12-month petition finding.
Desert tortoise--Sonoran       12-month petition finding.
 population.
Thorne's Hairstreak butterfly  12-month petition finding.
 \3\.
Hermes copper butterfly \3\..  12-month petition finding.
------------------------------------------------------------------------
                    Actions With Statutory Deadlines
------------------------------------------------------------------------
Casey's june beetle..........  Final listing determination.
Georgia pigtoe, interrupted    Final listing determination.
 rocksnail, and rough
 hornsnail.
7 Bird species from Brazil...  Final listing determination.
Southern rockhopper penguin--  Final listing determination.
 Campbell Plateau population.
5 Bird species from Colombia   Final listing determination.
 and Ecuador.
Queen Charlotte goshawk......  Final listing determination.
5 species southeast fish       Final listing determination.
 (Cumberland darter, rush
 darter, yellowcheek darter,
 chucky madtom, and laurel
 dace) \4\.
Altamaha spinymussel.........  Final listing determination.
Salmon crested cockatoo......  Proposed listing determination.
CA golden trout..............  12-month petition finding.
Black-footed albatross.......  12-month petition finding.
Mount Charleston blue          12-month petition finding.
 butterfly.
Mojave fringe-toed lizard \1\  12-month petition finding.
Kokanee--Lake Sammamish        12-month petition finding.
 population \1\.
Cactus ferruginous pygmy-owl   12-month petition finding.
 \1\.
Northern leopard frog........  12-month petition finding.
Tehachapi slender salamander.  12-month petition finding.
Coqui Llanero................  12-month petition finding.
Dusky tree vole..............  12-month petition finding.
3 MT invertebrates (mist       12-month petition finding.
 forestfly(Lednia tumana),
 Oreohelix sp.3, Oreohelix
 sp. 31) from 206 species
 petition.
5 UT plants (Astragalus        12-month petition finding.
 hamiltonii, Eriogonum
 soredium, Lepidium ostleri,
 Penstemon flowersii,
 Trifolium friscanum) from
 206 species petition.
2 CO plants (Astragalus        12-month petition finding.
 microcymbus, Astragalus
 schmolliae) from 206 species
 petition.
5 WY plants (Abronia           12-month petition finding.
 ammophila, Agrostis rossiae,
 Astragalus proimanthus,
 Boechere (Arabis) pusilla,
 Penstemon gibbensii) from
 206 species petition.
Leatherside chub (from 206     12-month petition finding.
 species petition).
Frigid ambersnail (from 206    12-month petition finding.
 species petition).
Gopher tortoise--eastern       12-month petition finding.
 population.
Wrights marsh thistle........  12-month petition finding.
67 of 475 southwest species..  12-month petition finding.
Grand Canyon scorpion (from    12-month petition finding.
 475 species petition).
Anacroneuria wipukupa (a       12-month petition finding.
 stonefly from 475 species
 petition).
Rattlesnake-master borer moth  12-month petition finding.
 (from 475 species petition).
3 Texas moths (Ursia furtiva,  12-month petition finding.
 Sphingicampa blanchardi,
 Agapema galbina) (from 475
 species petition).
2 Texas shiners (Cyprinella    12-month petition finding.
 sp., Cyprinella lepida)
 (from 475 species petition).
3 South Arizona plants         12-month petition finding.
 (Erigeron piscaticus,
 Astragalus hypoxylus,
 Amoreuxia gonzalezii) (from
 475 species petition).
5 Central Texas mussel         12-month petition finding.
 species (3 from 475 species
 petition).
14 parrots (foreign species).  12-month petition finding.
Berry Cave salamander \1\....  12-month petition finding.
Striped Newt \1\.............  12-month petition finding.
Fisher--Northern Rocky         12-month petition finding.
 Mountain Range \1\.
Mohave Ground Squirrel \1\...  12-month petition finding.
Puerto Rico Harlequin          12-month petition finding.
 Butterfly.
Western gull-billed tern.....  12-month petition finding.
Ozark chinquapin (Castanea     12-month petition finding.
 pumila var. ozarkensis).
HI yellow-faced bees.........  12-month petition finding.
Giant Palouse earthworm......  12-month petition finding.
Whitebark pine...............  12-month petition finding.
OK grass pink (Calopogon       12-month petition finding.
 oklahomensis) \1\.
Southeastern pop snowy plover  90-day petition finding.
 & wintering pop. of piping
 plover \1\.
Eagle Lake trout \1\.........  90-day petition finding.
Smooth-billed ani \1\........  90-day petition finding.
Bay Springs salamander \1\...  90-day petition finding.
32 species of snails and       90-day petition finding.
 slugs \1\.
42 snail species (Nevada &     90-day petition finding.
 Utah).
Red knot roselaari subspecies  90-day petition finding.
Peary caribou................  90-day petition finding.

[[Page 78146]]

 
Plains bison.................  90-day petition finding.
Spring Mountains checkerspot   90-day petition finding.
 butterfly.
Spring pygmy sunfish.........  90-day petition finding.
Bay skipper..................  90-day petition finding.
Unsilvered fritillary........  90-day petition finding.
Texas kangaroo rat...........  90-day petition finding.
Spot-tailed earless lizard...  90-day petition finding.
Eastern small-footed bat.....  90-day petition finding.
Northern long-eared bat......  90-day petition finding.
Prairie chub.................  90-day petition finding.
10 species of Great Basin      90-day petition finding.
 butterfly.
6 sand dune (scarab) beetles.  90-day petition finding.
Golden-winged warbler \4\....  90-day petition finding.
Sand-verbena moth............  90-day petition finding.
404 Southeast species........  90-day petition finding.
Franklin's bumble bee \4\....  90-day petition finding.
2 Idaho snowflies (straight    90-day petition finding.
 snowfly & Idaho snowfly) \4\.
American eel \4\.............  90-day petition finding.
Gila monster (Utah             90-day petition finding.
 population) \4\.
Arapahoe snowfly \4\.........  90-day petition finding.
Leona's little blue \4\......  90-day petition finding.
------------------------------------------------------------------------
                    High-Priority Listing Actions \3\
------------------------------------------------------------------------
19 Oahu candidate species \2\  Proposed listing.
 (16 plants, 3 damselflies)
 (15 with LPN = 2, 3 with LPN
 = 3, 1 with LPN = 9).
19 Maui-Nui candidate species  Proposed listing.
 \2\ (16 plants, 3 tree
 snails) (14 with LPN = 2, 2
 with LPN = 3, 3 with LPN =
 8).
Dune sagebrush lizard          Proposed listing.
 (formerly Sand dune lizard)
 \3\ (LPN = 2).
2 Arizona springsnails \2\     Proposed listing.
 (Pyrgulopsis bernadina (LPN
 = 2), Pyrgulopsis trivialis
 (LPN = 2)).
New Mexico springsnail \2\     Proposed listing.
 (Pyrgulopsis chupaderae (LPN
 = 2).
2 mussels \2\ (rayed bean      Proposed listing.
 (LPN = 2), snuffbox No LPN).
2 mussels \2\ (sheepnose (LPN  Proposed listing.
 = 2), spectaclecase (LPN =
 4),).
8 Gulf Coast mussels           Proposed listing.
 (southern kidneyshell (LPN =
 2), round ebonyshell (LPN =
 2), Alabama pearlshell (LPN
 = 2), southern sandshell
 (LPN = 5), fuzzy pigtoe (LPN
 = 5), Choctaw bean (LPN =
 5), narrow pigtoe (LPN = 5),
 and tapered pigtoe (LPN =
 11)).
Umtanum buckwheat (LPN = 2)    Proposed listing.
 \4\.
Grotto sculpin (LPN = 2) \4\.  Proposed listing.
2 Arkansas mussels (Neosho     Proposed listing.
 mucket (LPN =2) &
 Rabbitsfoot (LPN = 9)) \4\.
Diamond darter (LPN = 2) \4\.  Proposed listing.
Gunnison sage-grouse (LPN =    Proposed listing.
 2) \4\.
------------------------------------------------------------------------
\1\ Funds for listing actions for these species were provided in
  previous FYs.
\2\ Although funds for these high-priority listing actions were provided
  in FY 2008 or 2009, due to the complexity of these actions and
  competing priorities, these actions are still being developed.
\3\ Partially funded with FY 2010 funds and FY 2011 funds.
\4\ Funded with FY 2010 funds.
\5\ Funded with FY 2011 funds.

    We have endeavored to make our listing actions as efficient and 
timely as possible, given the requirements of the relevant law and 
regulations, and constraints relating to workload and personnel. We are 
continually considering ways to streamline processes or achieve 
economies of scale, such as by batching related actions together. Given 
our limited budget for implementing section 4 of the Act, these actions 
described above collectively constitute expeditious progress.
    The Sonoran desert tortoise will be added to the list of candidate 
species upon publication of this 12-month finding. We will continue to 
monitor the status of this DPS as new information becomes available. 
This review will determine if a change in status is warranted, 
including the need to make prompt use of emergency listing procedures.
    We intend that any proposed listing determination for the Sonoran 
desert tortoise will be as accurate as possible. Therefore, we will 
continue to accept additional information and comments from all 
concerned governmental agencies, the scientific community, industry, or 
any other interested party concerning this finding.

References Cited

    A complete list of references cited is available on the Internet at 
http://www.regulations.gov and upon request from the Arizona Ecological 
Services Office (see ADDRESSES section).

Author(s)

    The primary authors of this notice are the staff members of the 
Arizona Ecological Services Office.

Authority

    The authority for this section is section 4 of the Endangered 
Species Act of 1973, as amended (16 U.S.C. 1531 et seq.).

    Dated: November 23, 2010.
Rowan W. Gould,
Acting Director, Fish and Wildlife Service.
[FR Doc. 2010-31000 Filed 12-13-10; 8:45 am]
BILLING CODE 4310-55-P