[Federal Register Volume 76, Number 50 (Tuesday, March 15, 2011)]
[Proposed Rules]
[Pages 14209-14268]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 2011-5411]



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Vol. 76

Tuesday,

No. 50

March 15, 2011

Part III





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; Withdrawal of Proposed 
Rule To List the Flat-Tailed Horned Lizard as Threatened; Proposed Rule

Federal Register / Vol. 76 , No. 50 / Tuesday, March 15, 2011 / 
Proposed Rules

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DEPARTMENT OF THE INTERIOR

Fish and Wildlife Service

50 CFR Part 17

[Docket No. FWS-R8-ES-2010-0008; MO 92210-0-0008]
RIN 1018-AX07


Endangered and Threatened Wildlife and Plants; Withdrawal of 
Proposed Rule To List the Flat-Tailed Horned Lizard as Threatened

AGENCY: Fish and Wildlife Service, Interior.

ACTION: Proposed rule; withdrawal.

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SUMMARY: We, the U.S. Fish and Wildlife Service (Service), determine 
that the listing of the flat-tailed horned lizard (Phrynosoma mcallii) 
as a threatened species under the Endangered Species Act of 1973, as 
amended (Act), is not warranted, and we therefore withdraw our November 
29, 1993, proposed rule to list it under the Act. We made this 
determination in this withdrawal because threats to the species as 
identified in the 1993 proposed rule are not as significant as earlier 
believed, and available data do not indicate that the threats to the 
species and its habitat, as analyzed under the five listing factors 
described in section 4(a)(1) of the Act, are likely to endanger the 
species in the foreseeable future throughout all or a significant 
portion of its range.

DATES: The November 29, 1993 (58 FR 62624), proposal to list the flat-
tailed horned lizard as a threatened species is withdrawn as of March 
15, 2011.

ADDRESSES: This withdrawal of the proposed rule is available on the 
Internet at http://www.regulations.gov. Comments and materials 
received, as well as supporting documentation for this rulemaking is 
available for public inspection, by appointment, during normal business 
hours at the U.S. Fish and Wildlife Service, Carlsbad Fish and Wildlife 
Office, 6010 Hidden Valley Road, Suite 101, Carlsbad, CA 92011; 
telephone 760-431-9440; facsimile 760-431-9624.

FOR FURTHER INFORMATION CONTACT: Jim Bartel, Field Supervisor, Carlsbad 
Fish and Wildlife Office (see ADDRESSES section). If you use a 
telecommunications device for the deaf (TDD), call the Federal 
Information Relay Service (FIRS) at 800-877-8339.

SUPPLEMENTARY INFORMATION:

Background

    The flat-tailed horned lizard (Phrynosoma mcallii) is a small, 
spiny lizard found in the Sonoran Desert of the southwestern United 
States and northwestern Mexico. All of the species of lizards in the 
genus Phrynosoma--the horned lizards--have dorso-ventrally flattened, 
``pancake-like'' bodies; spiny scales; head spines or ``horns''; 
cryptic coloration; and certain similar behavioral traits (Sherbrooke 
2003, pp. 4-17; Stebbins 2003, p. 299; Leach[eacute] and McGuire 2006, 
p. 629).
    Among horned lizard species, the flat-tailed horned lizard has 
particularly long and sharp horns (Funk 1981, p. 281.1; Sherbrooke 
2003, p. 40; Young et al. 2004a, p. 65). Other characteristics that 
help distinguish flat-tailed horned lizards from other members of the 
genus include a dark line down the middle of the back (vertebral 
stripe), lack of external ear openings, two rows of fringe scales, an 
unspotted vent, and--as indicated by its common name--a long, broad, 
flattened tail (Funk 1981, p. 281.1; Sherbrooke 2003, p. 40). The flat-
tailed horned lizard is average in size when compared to other horned 
lizard species. Flat-tailed horned lizards become adults when about 60 
to 64 millimeters (mm) (2.4 to 2.5 inches (in)) long, not including the 
tail (snout-to-vent length), and may grow to be about 87 mm (3.4 in) 
long (Young and Young 2000, p. 34; Rorabaugh and Young 2009, p. 182). 
The dorsal coloration of flat-tailed horned lizards varies and closely 
matches the colors of the desert soils on which they live, ranging from 
pale gray to light rust-brown, while their ventral coloration is white 
or cream-colored (Funk 1981, p. 281.1; Flat-tailed Horned Lizard 
Interagency Coordinating Committee [FTHLICC] 2003, p. 1; Stebbins 2003, 
p. 304). First described by Hallowell in 1852, no subspecies have been 
described or are recognized for the flat-tailed horned lizard (Crother 
et al. 2008, p. 35).
    The flat-tailed horned lizard occurs within the range of the desert 
horned lizard (Phrynosoma platyrhinos). Additionally, Goode's horned 
lizard (P. [platyrhinos] goodie), which Klauber (1935, p. 179) 
considered to be a subspecies of the desert horned lizard (Klauber 
1935, p. 179), also occurs within the range of the flat-tailed horned 
lizard in the portion southeast of the confluence of the Gila and 
Colorado Rivers (Mulcahy et al. 2006, p. 1823). Recent genetic analyses 
support Goode's horned lizard as a differentiable evolutionary species 
(Mulcahy et al. 2006, pp. 1807-1826). Hybrids between flat-tailed and 
Goode's horned lizards, exhibiting a mix of morphological and genetic 
characters, have been observed southeast of Yuma, Arizona (Mulcahy et 
al. 2006, p. 1810), while apparent hybrids between flat-tailed and 
desert horned lizards have been observed in the vicinity of Ocotillo, 
California (Stebbins 2003, p. 302). Additionally, the regal horned 
lizard (P. solare) also occurs in northwestern Sonora, Mexico 
(Rorabaugh 2008, p. 39); we are not aware of hybridization with this 
species.

Life History

    Flat-tailed horned lizards are oviparous (egg-laying), are early 
maturing, and may produce multiple clutches within a breeding season 
(Howard 1974, p. 111; Turner and Medica 1982, p. 819), which, when it 
occurs, results in two groups of individuals in a single year that are 
all generally the same age (that is, two cohorts). However, some 
authors question whether the observed two cohorts is the result of 
individual females producing two clutches in a year or whether 
different groups of females lay eggs at different times (Muth and 
Fisher 1992, p. 46; Young and Young 2000, p. 11). Flat-tailed horned 
lizards produce relatively small clutches of eggs (mean clutch size = 
4.7; range = 3 to 7) (Howard 1974, p. 111) compared to most other 
horned lizards (Sherbrook 2003, p. 139). The first cohort hatches in 
July to August (Muth and Fisher 1992, p. 19; Young and Young 2000, p. 
13), and when it occurs, the second cohort may be produced in September 
(Howard 1974, p. 111; Muth and Fisher 1992, p. 19). Hatchlings from the 
first cohort may reach sexual maturity after their first winter season, 
whereas individuals that hatch later may require an additional growing 
season to mature (Howard 1974, p. 111). Flat-tailed horned lizards 
typically live for 4 years, or rarely even 6 years, in the wild 
(FTHLICC 2003a, p. 10).
    A home range is the area in which an animal (as an individual) 
typically lives. Flat-tailed horned lizards can have relatively large 
home ranges compared to other species of lizards of similar size 
(FTHLICC 2003a, p. 9). Muth and Fisher (1992, p. 34) found the mean 
home range size was 2.7 hectares (ha) (6.7 acres (ac)) on the West 
Mesa, California. In the Yuma Desert of Arizona, Young and Young (2000, 
p. 54) found mean home ranges for males differed between drought and 
wet years, while those of females did not. The mean home range size for 
males was 2.5 ha (6.2 ac) during a dry year versus 10.3 ha (25.5 ac) 
during a wet year. Female mean home ranges were smaller at 1.3 ha (3.2 
ac) and 1.9 ha (4.7 ac) in dry and wet years, respectively (Young and 
Young 2000, p. 54). Young and Young (2000, p. 55) noted a wide 
variation in movement

[[Page 14211]]

patterns, with a few home ranges estimated at greater than 34.4 ha (85 
ac).
    Flat-tailed horned lizards are not known to drink standing water 
(FTHLICC 2003a, p. 8), but they apparently do rain-harvest (Grant 2005, 
pp. 66-67), which is a behavior that some horned lizard species use to 
channel precipitation or condensation collected on the lizard's body to 
its mouth for consumption (Sherbrook 2003, p. 104). Thus, nearly all of 
the water consumed by flat-tailed horned lizards is from the food they 
eat (preformed water) (FTHLICC 2003a, p. 8; Grant 2005, pp. 66-67). 
Most horned lizard species, including the flat-tailed horned lizard, 
are ant-foraging specialists (Pianka and Parker 1975, pp. 141-162; 
Sherbrooke and Schwenk 2008, pp. 447-459). More than 95 percent of the 
diet of flat-tailed horned lizards is composed of ants, with species of 
harvester ants (genera Messor and Pogonomyrmex) predominating in most 
areas of the lizard's range, but species of Dorymyrmex, Pheidole, and 
Myrmecocystus are also consumed (Pianka and Parker 1975, p. 148; Turner 
and Medica 1982, p. 820; Young and Young 2000, p. 38; FTHLICC 2003a, p. 
8).
    Flat-tailed horned lizards, typical of reptiles, obtain their body 
heat from the surrounding environment (ectothermic) (Mayhew 1965, p. 
104; Sherbrooke 2003, pp. 75-81). To gain body heat, they bask in the 
sun, often on rocks or other substrates that are warmed by insolation. 
During the heat of the day, to escape extreme surface temperatures, 
flat-tailed horned lizards may bury themselves just below the surface 
(Norris 1949, pp. 178-179) or retreat to a burrow made by other 
organisms (Young and Young 2000, p. 12). Adult flat-tailed horned 
lizards are reported to be obligatory hibernators (i.e., an organism 
that must enter a dormant period regardless of environmental 
conditions) (Mayhew 1965, p. 103). Hibernation may begin as early as 
October and end as late as March (Muth and Fisher 1992, p. 33), 
although individuals have been noted on the surface during January and 
February (FTHLICC 2003a, p. 9). Hibernation burrows appear to be self-
constructed (as opposed to using burrows constructed by other animals) 
and are typically within 10 centimeters (cm) (3.9 in) of the surface 
(Muth and Fisher 1992, p. 33). Mayhew (1965, p. 115) found that the 
majority of lizards hibernated within 5 cm (2 in) of the surface, with 
one as deep as 20 cm (8 in) below the surface.
    Flat-tailed horned lizards generally lie close to the ground and 
remain motionless when approached (Wone and Beauchamp 1995, p. 132); 
however, they may occasionally bury themselves in loose sand if it is 
available (Norris 1949, p. 176), and even more rarely, flee (Young and 
Young 2000, p. 12). Their propensity to remain motionless and bury in 
the sand, along with their cryptic coloration and flattened body, make 
them difficult to detect visually, which serves as a way to evade 
predators but also makes them difficult for surveyors to find in the 
field (FTHLICC 2003a, pp. 9, 65; Grant and Doherty 2007, p. 1050) (see 
also ``Population Dynamics'' section, below).
    Additional life-history information is available in the Flat-tailed 
Horned Lizard Rangewide Management Strategy (FTHLICC 2003a, pp. 6-11).

Setting and Habitat

    The flat-tailed horned lizard is endemic (restricted) to the Salton 
Trough and the region north of the Gulf of California in northwest 
Sonora, Mexico, both of which lie within the Lower Colorado Subdivision 
of the Sonoran Desert (Shreve and Wiggins 1964, p. 6). The climatic 
conditions over the range of the flat-tailed horned lizard are 
characterized by hot summer temperatures, mild winter temperatures, and 
little rainfall. Winter rainfall predominates in the western portion of 
the species' range while summer rainfall predominates in the eastern 
portion of the species' range (Shreve and Wiggins 1964, pp. 17-20, 49, 
50; Johnson and Spicer 1985, p. 14). Periods of drought are not 
uncommon (Shreve and Wiggins 1964, p. 18).
    Although the region in northwest Sonora, Mexico, represents roughly 
half of the current range of the flat-tailed horned lizard, its 
distribution within the Salton Trough has been more dynamic. As 
discussed below, the geologic and land use changes in the Salton Trough 
have substantially shaped the status of the species today.
    To better understand population trends of the flat-tailed horned 
lizard relative to the geologic setting and its current distribution 
within sandy habitat, we are providing a summary of the recent geologic 
history of the area in the following paragraphs (summarized from Parish 
1914, pp. 85-114; Sykes 1914, pp. 13-20; Durham and Alison 1960, pp. 
47-91; van de Kamp 1973, pp. 827-848; Waters 1983, pp. 373-387; Blount 
and Lancaster 1990, pp. 724-728; Blount et al. 1990, pp. 15,463-15,482; 
Stokes et al. 1997, pp. 63-75; Patten et al. 2003, pp. 1-6; Li et al. 
2008, pp. 182-197).
    The Salton Trough (Trough) is a low-elevation valley that 
represents the northwestward continuation of the Gulf of California. 
During the period starting at least several million years ago, as sea 
levels rose and fell, the Gulf of California filled the present-day 
Salton Trough, often extending the Gulf northward into the present-day 
San Gorgonio Pass, east of Cabazon, California. The Colorado River 
flowed into the Gulf at roughly the same geographical area as today, 
but with the Gulf extending to a more northerly point, the river flowed 
into the Gulf mid-way along its length.
    The Colorado River, which originates in the Rocky Mountains and 
flows through the Grand Canyon, historically transported large 
quantities of fine-grained sediment. Where the river joined the Gulf, 
sediments were deposited forming a broad delta. These sediments 
continued to increase and created a barrier that divided the Gulf into 
a land-locked northern portion (the Trough) and a marine-linked 
southern portion (the Gulf). The northern portion, which remains below 
sea level but without a direct connection with the ocean, eventually 
dried out. However, the Colorado River continued to meander across its 
delta and seasonal flooding promoted avulsion (i.e., abandonment of an 
old river channel and the creation of a new one). Thus, the river would 
sometimes flow into the Gulf and sometimes into the Trough, the lowest 
point of which--referred to as the Salton Basin--is about minus 84 
meters (m) elevation (277 feet (ft) below sea level).
    Water from the meandering Colorado River periodically filled the 
Salton Basin to varying depths (and areal extent), depositing sediments 
in the process. The lake that periodically formed, especially in its 
recent but prehistoric incarnations, is referred to by most authors as 
Lake Cahuilla. Its maximum depth depended on elevation of the delta, 
which is now about 12 m elevation (39 ft above sea level). The Lake was 
full as recently as the early 1600s, but smaller, shallower 
manifestations were present at various times since then (including the 
modern Salton Sea, discussed below). When Lake Cahuilla was full, the 
Colorado River water flowed into the Basin from the southeast, marked 
today by the Alamo River and New River channels, and exited the Basin 
farther west along a southerly route, marked today by the R[iacute]o 
Hardy channel, ultimately emptying into the Gulf of California. 
Floodwaters and sediments also periodically flowed into Laguna Salada, 
in northwestern Baja California, Mexico. Thus, even areas of the 
present-day Imperial, Mexicali, and San Luis Valleys that

[[Page 14212]]

were never or were less-frequently inundated by Lake Cahuilla, were 
regularly influenced by hydrologic forces associated with the Colorado 
River. Despite being in the middle of one of the driest deserts in 
North America, some of these areas were, at least periodically, part of 
an intricate water distribution system of channels, sloughs, and 
lagoons.
    Water also flowed into the Trough from surrounding highlands, 
bringing locally derived sediments with it. One notable inflow is 
marked by the present-day Whitewater River that flows into the Basin 
from the north. Water from the local sources would occasionally result 
in standing water in the Basin, but these sources could not compete 
with the sheer volume the Colorado River periodically provided.
    After flowing into the Trough for a period of time, the Colorado 
River would eventually meander back and once again flow into the Gulf. 
Over time, Lake Cahuilla would then become dry and the transported 
sediments would become exposed, with local sediment sources 
predominating the north end of the Trough, and Colorado River-derived 
sediments predominating the south end of the Trough. During dry 
periods, the fine-grained sediments in the Trough would be transported 
and sorted by prevailing winds. Thus, much of the Trough outside of 
those areas that were regularly influenced by the flooding and 
meandering of the Colorado River was ultimately blanketed with soft, 
friable (crumbly) or arenaceous (sandy) soils. Similarly, sediments 
deposited in the Colorado River delta and along the northeast shore of 
the Gulf of California were transported by winds where they formed 
areas of soft, friable (crumbly) or arenaceous (sandy) soils, including 
the ``sand sea'' of the Gran Desierto de Altar.
    As a result, typical flat-tailed horned lizard habitat today 
includes areas of these sandy flats as well as the associated valleys 
created by these geologic events. Turner et al. (1980, p. 14) stated 
the best habitats are generally low-relief areas with surface soils of 
packed, fine sand or low-relief areas of pavement (hardpan) overlain 
with loose, fine sand. However, the available scientific information 
indicates that flat-tailed horned lizards may occur in areas with soil 
substrates and plant associations that differ from these 
generalizations, as described below.
    Flat-tailed horned lizards are also known to occur at the edges of 
vegetated sand dunes, on barren clay soils, and within sparse Atriplex 
spp. (saltbush) plant communities. Although Turner et al. (1980, p. 15) 
suspected that these recorded occurrences were actually individuals 
that had dispersed from more suitable habitats, Wone et al. (1991, p. 
16) questioned this conclusion (see also Wone and Beauchamp 1995, p. 
132; Beauchamp et al. 1998, p. 213), suggesting instead that flat-
tailed horned lizards regularly occupy at least some of these areas.
    Within a creosote plant community in the West Mesa area, Muth and 
Fisher (1992, p. 61) found that flat-tailed horned lizards preferred 
sandy substrates with white bursage and Psorothamnus emoryi (Emory 
dalea), and avoided areas with creosote and Tiquilia plicata (fanleaf 
crinklemat). In Arizona, Rorabaugh et al. (1987, p.103) found flat-
tailed horned lizard abundance correlated with Pleuraphis rigida (big 
galleta grass) and sandy substrates, but they suggested that the 
presence of sandy substrates was more important than grass.
    Several researchers have investigated the relationship between 
density of perennial plants and flat-tailed horned lizard abundance. 
The observed relationships varied among studies. For example, Altman et 
al. (1980, p. ii) and Turner and Medica (1982, p. 815) found the 
relative abundance of flat-tailed horned lizards was significantly and 
positively correlated with perennial plant density in creosote-white 
bursage plant communities (that is, horned lizard abundance increased 
as perennial plant density increased). In contrast, Beauchamp et al. 
(1998, p. 210) found flat-tailed horned lizards to be present in higher 
densities in sparsely vegetated areas with large patches of concretions 
(i.e., a volume of sedimentary rock in which a mineral cement fills the 
spaces between the sediment grains), gravel, and silt, than in areas 
that were sandy or densely vegetated. Altman et al. (1980, p. 7) also 
reported finding flat-tailed horned lizards in desert pavement areas. 
Foley (2002, p. 54) found little correlation in substrate texture and 
distribution of flat-tailed horned lizards, when using three 
experimental treatments consisting of sandy, rocky and mixed 
substrates. However, Wright and Grant (2003, p. 3) found flat-tailed 
horned lizard abundance was positively correlated with percentage of 
sand cover. Thus, flat-tailed horned lizard habitat includes a variety 
of soils and other plant associations, but the habitat is best 
characterized as sandy flats and valleys in a creosote-white bursage 
plant association.
    Plants and harvester ants are important components to flat-tailed 
horned lizard habitat because they comprise its primary food chain. 
Seeds make up the primary food of harvester ants (Johnson 2000, p. 92). 
The ants often collect seeds from annual plants, including some 
nonnative species (Rissing 1988, p. 362), but they also gather seeds 
from perennial plants (Gordon 1980, p. 72). Thus, a simplified food 
chain for the flat-tailed horned lizard may be described as follows: 
Plants produce seeds, harvester ants eat the seeds, and flat-tailed 
horned lizards eat harvester ants.

Range and Distribution

    A species' range is the region over which it is distributed. The 
range of the flat-tailed horned lizard includes the Salton Trough and 
the region north of the Gulf of California. In general, this range 
includes portions of southeastern California (eastern San Diego County, 
central Riverside County, and southwestern Imperial County) and 
southwestern Arizona (southwestern Yuma County) in the United States, 
and northeastern Baja California and northwestern Sonora in Mexico 
(Turner and Medica 1982, p. 815) (Figure 1). Within its range, the 
flat-tailed horned lizard is limited to areas below an upper elevation. 
Although the species has been recorded as high as 520 m (1,706 ft) 
above sea level (Turner et al. 1980, p. 13), flat-tailed horned lizards 
are more commonly found below about 230 m (about 750 ft) in elevation 
(FTHLICC 2003a, p. 3).
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    Extensive manmade changes, chiefly for agriculture, have occurred 
over a large portion of the land within the Salton Trough. Below we 
present a summary of the history of agricultural development in the 
Salton Trough (summarized from Furnish and Ladman 1975, pp. 83-107; 
Woerner 1989, pp. 109-112; Imperial Irrigation District [IID] 2002, pp. 
3.1-66 to 3.1-77; Patten et al. 2003, pp. 1-6).
    Near the start of the 20th century, a canal was built to import 
water to the Salton Trough from the Colorado River. The Salton Basin is 
below sea level and much of the rest of the Salton Trough is at a lower 
elevation than where the head of the canal was located. Thus, with the 
regionally abundant sunshine and river-sediment soils, the importation 
of water by a gravity-fed system allowed agriculture to proliferate. 
For example, by 1904 approximately 60,700 ha (150,000 ac) were in 
cultivation.
    Unlike the current canal, the original canal was poorly designed 
because it had no headgate to regulate flows into the canal. Prior to 
extensive dams on the Colorado River, the river was prone to flooding. 
The high waters of one such flood during the winter of 1904-05 flowed 
into the canal. Soon, nearly the entire Colorado River flowed through 
the canal, releasing water into the Salton Basin. Part of the flow 
followed the two historical riverbeds (the Alamo River and the New 
River) that were deepened and widened by the torrent. Despite heroic 
efforts, the flow continued until 1907. The Salton Basin filled to a 
depth of about 22 m (72 ft) (at its deepest point) and covered about 
121,400 ha (300,000 ac), thus creating the modern Salton Sea.
    Although the ``creation'' of the Salton Sea is often times 
described as an accident, the inundation of the Salton Basin by water 
flowing from the Colorado River from 1905 to 1907 was merely the most 
recent of many such inundations over historical and prehistorical times 
(see ``Setting and Habitat'' section above). Even without the canal, 
the flood of 1905 may have naturally flowed into the Basin.
    Since the formation of the modern Salton Sea, agricultural 
practices in the region have maintained the water levels of the Salton 
Sea. If too much irrigation water is allowed to evaporate in the 
fields, salt levels, which are high in Colorado River water, build up 
in the soil, making it inhospitable for crops. To prevent this 
hypersalinization of the soils, a surplus of water is used for 
irrigation. The excess water drains by gravity from the fields through 
a network of ditches into the Salton Sea. Even with the high 
evaporation rates in the desert climate, inflow rates of drainage water 
have been high enough to maintain, and, for a time, even increase, the 
surface water elevation of the Salton Sea.
    Efforts to bring irrigation water to the region continued through 
the 1900s, and the system of irrigation canals was eventually improved 
and expanded. In addition to the Imperial Valley, the Coachella Canal 
was constructed to bring water to the southern Coachella Valley, 
allowing irrigated agriculture to develop north of the Salton Sea. 
Similar canal systems were built in Mexico, allowing agriculture to 
develop and expand in the Mexicali and San Luis Valleys. Because these 
systems were gravity fed, the distribution canals within the region 
were dictated by elevation, which in turn, determined where irrigated 
agricultural development occurred. Thus, the majority of agricultural 
development was confined within the outer-most (highest elevation) 
canals. Moreover, croplands (and associated urbanization and 
infrastructure) were contiguous in the Salton Trough region, with 
little to no intervening undeveloped natural areas. Additionally, 
smaller amounts of agricultural development using pumped groundwater 
have occurred on a smaller scale outside these areas.
    The geographically confined agricultural growth in the region is 
currently limited by the amount of water available from the Colorado 
River, which is dependent on annual precipitation in the Upper and 
Lower Colorado River Basins. The amount of irrigation water that can be 
delivered to the Salton Trough from the Colorado River is limited by 
interstate and international agreements (Furnish and Ladman 1975, pp. 
83-107). Water conservation and transfer agreements completed in 2003 
with the San Diego County Water Authority, Imperial Irrigation 
District, Metropolitan Water District of Southern California, and 
Coachella Valley Water District has reduced the amount of water 
available in the Imperial Valley and some fields have been fallowed, 
resulting in a decrease in the amount of irrigated agriculture in this 
region (IID 2006, p. 1).
    Aerial and satellite imagery (Carlsbad Fish and Wildlife Office 
geographic information system (GIS) files) illustrates the development 
of active cultivation and associated urbanization and infrastructure 
extending from the present-day delta of the Colorado River, with a 
longer fork extending north-northwest through the Mexicali and Imperial 
Valleys to the Coachella Valley (punctuated by the Salton Sea), and a 
smaller fork extending northeast through the eastern Mexicali Valley 
and the San Luis Valley (Lower Colorado River Valley) to Yuma. Although 
there are specimens of flat-tailed horned lizards collected 
historically from within the now-altered region (Funk 1981, p. 281.1; 
Johnson and Spicer 1985, pp. 14-24), areas of agricultural and urban 
development do not constitute habitat for the flat-tailed horned 
lizard, and this continuous swath of altered land use is no longer 
occupied by flat-tailed horned lizards.
    The current distribution of the flat-tailed horned lizard is often 
described within four, geographically descriptive ``populations.'' We 
use the term population in this document to refer to a loosely bounded, 
regionally distributed collection of individuals of the same species. 
These four populations are defined as:
    (1) The Coachella Valley Population, including those individuals 
northwest of the Salton Sea, California;
    (2) The Western Population, including those individuals in the 
areas west of the Salton Sea and the Imperial Valley, California, and 
west of the Mexicali Valley, Baja California, Mexico;
    (3) The Eastern Population, including those individuals in the 
areas east of the Salton Sea and the Imperial Valley but west of the 
Colorado River; and
    (4) The Southeastern Population, including those individuals in the 
areas east of the Colorado River, extending from Yuma south into Mexico 
and east to the Gulf of California.
    These current designations closely follow the description of 
populations discussed in our January 3, 2003, analysis (68 FR 331), 
although in that document we used the United States-Mexico border to 
further divide the populations (see Figure 1 above). Additionally, 
these populations roughly correspond to those used by Mulcahy et al. 
(2006, pp. 1807-1826) in their analysis of flat-tailed horned lizard 
genetic data (see below for details). At the end of the Background 
section, below, we summarize these four populations in greater detail. 
We also use these four population names to identify the geographical 
habitat they occupy.

Populations and Genetics

    The separation of the four populations of flat-tailed horned 
lizards described above in the ``Range and Distribution'' section is 
supported by genetic data, to varying degrees. Analyses of 
mitochondrial DNA data (Mulcahy et al. 2006, pp. 1807-1826; see also 
Mendelson et al. 2004, pp. 1-42) and nuclear microsatellite data 
(Culver and

[[Page 14215]]

Dee 2008, pp. 1-14) revealed significant differences in the prevalence 
of certain alleles in flat-tailed horned lizard populations on either 
side of the Colorado River; that is, the Southeastern Population 
differs from the other three populations. These analyses also showed 
that more gene flow has occurred near the Colorado River delta, 
suggesting the shifting course of the river over time in this area 
posed less of a barrier than the more stable portions of the river 
channel farther north (Mulcahy et al. 2006, p. 1822; Culver and Dee 
2008, p. 11). Although Culver and Dee (2008, p. 10) noted genetic 
variation in some individuals across the Southeastern Population, they 
found that flat-tailed horned lizards in Arizona are ``not genetically 
isolated from neighboring populations in Mexico.'' Thus, the flat-
tailed horned lizards east of the Colorado River (i.e., the 
Southeastern Population) may be considered one population that is 
significantly and genetically distinct from the populations west of the 
river (i.e., the Coachella Valley, Western, and Eastern Populations).
    The three populations west of the Colorado River also showed 
varying levels of genetic differentiation. Mulcahy et al. (2006, p. 
1821) noted the Eastern Population ``was significantly differentiated 
from [the Western and Coachella Valley Populations], suggesting that 
there has not been substantial gene flow across the Imperial Valley 
since the drying of Lake Cahuilla.'' However, the difference between 
the Coachella Valley and Western Populations was less pronounced. 
Although their difference was supported by the presence of haplotypes 
unique to the Coachella Valley Population (Mulcahy et al. 2006, Table 1 
on p. 1811, and p. 1817), the difference between the Western and 
Coachella Valley Populations was not statistically significant (the 
other populations had unique haplotypes, too). This lack of significant 
difference suggested to the authors that the Coachella Valley 
Population ``had more recent gene flow'' with the Western Population 
(Mulcahy et al. 2006, p. 1821). Thus, genetic data readily support 
three of the four geographic populations described above, but the 
distinction between the Western and Coachella Valley Populations is 
weak or equivocal. This suggests that the Coachella Valley Population 
was not a separate population historically, but is one now because it 
was ``created'' by an artificial barrier resulting from past 
agricultural and urban development.

Management and Populations

    Three notable management mechanisms are in place within the U.S. 
portion of the flat-tailed horned lizard range: the Interagency 
Conservation Agreement, which includes the Flat-tailed Horned Lizard 
Rangewide Management Strategy (Rangewide Management Strategy); the 
Coachella Valley Multiple Species Habitat Conservation Plan (Coachella 
Valley MSHCP); and the Lower Colorado River Multi-Species Conservation 
Plan (Lower Colorado MSCP). Implementation of the Interagency 
Conservation Agreement has recently positively affected and is 
anticipated to continue to positively affect the status of flat-tailed 
horned lizard populations in the United States and, to a lesser extent, 
in Mexico. The recently permitted Coachella Valley MSHCP is also worth 
noting because it is a regional habitat conservation plan (HCP) 
developed under section 10 of the Act that covers the flat-tailed 
horned lizard in the Coachella Valley, an area addressed at length in 
our previous withdrawals. Additionally, the Lower Colorado MSCP is also 
an HCP that addresses the flat-tailed horned lizard.
Interagency Conservation Agreement and Flat-tailed Horned Lizard 
Rangewide Management Strategy
    In June of 1997, the Service, Bureau of Land Management (BLM), 
Bureau of Reclamation (BOR), U.S. Marine Corps, U.S. Navy, Arizona Game 
and Fish Department, California Department of Fish and Game (CDFG), and 
California Department of Parks and Recreation (CDPR) entered into an 
Interagency Conservation Agreement. All signatories agreed to:
    (1) Further develop and implement the objectives, strategies, and 
tasks of the Flat-tailed Horned Lizard Rangewide Management Strategy 
[original, FTHLICC 1997, pp. 1-106; revised: FTHLICC 2003a, p. 104; see 
below];
    (2) As needed for the conservation effort, and as available, 
provide program personnel with facilities, equipment, logistical 
support, and access to lands under their control;
    (3) Participate regularly in Interagency Coordinating Committee and 
Management Oversight Group meetings to enhance communication and 
cooperation, and to help develop annual or other work plans and 
reports;
    (4) Develop and distribute public information and educational 
materials on the conservation effort;
    (5) Provide ongoing review of, and feedback on, the conservation 
effort;
    (6) Cooperate in development of major media releases and media 
projects;
    (7) Keep local governments, communities, the conservation 
community, citizens, and other interested and affected parties informed 
on the status of the conservation effort, and solicit their input on 
issues and actions of concern or interest to them;
    (8) Whenever possible, develop voluntary opportunities and 
incentives for local communities and private landowners to participate 
in the conservation effort; and
    (9) Assist in generating the funds necessary to implement the 
conservation effort.
    The purpose of the Rangewide Management Strategy is to provide a 
framework for conserving sufficient habitat to maintain several viable 
populations of the flat-tailed horned lizard throughout the range of 
the species in the United States. The Rangewide Management Strategy was 
developed by an interagency working group over a 2-year period. Despite 
being a voluntary agreement, many of the measures to conserve flat-
tailed horned lizards are formally incorporated into planning documents 
of participating agencies, such as the Bureau of Land Management's 
California Desert Conservation Area Plan.
    As part of the Interagency Conservation Agreement, agencies 
delineated specific areas under their jurisdiction as Management Areas. 
As of 2009, approximately 185,653 ha (458,759 ac) of the flat-tailed 
horned lizard habitat managed by signatories of the Interagency 
Conservation Agreement exists within five Management Areas (see Table 1 
below) (FTHLICC 2009, p. 10). These Management Areas include the 
Borrego Badlands, West Mesa, and Yuha Desert (also referred to as the 
Yuha Basin) in the Western Population, the East Mesa in the Eastern 
Population, and the Yuma Desert in the Southeastern Population (Figure 
2). Additionally, the Ocotillo Wells State Vehicular Recreation Area 
(SVRA) was designated as a research area.

[[Page 14216]]

[GRAPHIC] [TIFF OMITTED] TP15MR11.042

    The five Management Areas were designed to include large areas of 
public land in the United States where flat-tailed horned lizards have 
been found, and to include most flat-tailed horned lizard habitat 
identified by the FTHLICC (1997, p. 35) as ``key'' areas for survival 
as determined in previous studies (Turner et al. 1980, pp. 1-47; Turner 
and Medica 1982, pp. 815-823; Rorabaugh et al. 1987, pp. 103-109). 
Management Areas were proposed based on standard principles of preserve 
design, utilizing the best information available at the time (FTHLICC 
2003a, p. 47).
    The Management Areas were delineated to include areas as large as 
possible, while avoiding extensive, existing and predicted management 
conflicts (such as off-highway vehicle (OHV) open areas). The 
Management Areas are meant to be the core areas for maintaining self-
sustaining populations of flat-tailed horned lizards in the United 
States (FTHLICC 2003a, p. 24). The Management Areas constitute roughly 
42 percent of the U.S. current distribution. Although the majority of 
lands within each Management Area are State or federally owned, some 
private inholdings occur within Management Area boundaries.
    The 2003 Rangewide Management Strategy includes measures to avoid, 
minimize, and compensate impacts to the flat-tailed horned lizard and 
its habitat from construction projects and other development activities 
permitted by signatory agencies. As described in detail in the 
Rangewide Management Strategy (FTHLICC 2003a, pp. 58-60), the avoidance 
and minimization measures include (in part) avoidance of flat-tailed 
horned lizard Management Areas and the Research Area, project oversight 
and compliance measures, minimized project footprint, use of existing 
roads rather than creating new roads, use of barrier fencing, and 
project-specific habitat restoration. The Rangewide Management Strategy 
outlines avoidance, minimization, and mitigation measures intended to 
limit the impacts from permitted projects within the Management Areas 
to a maximum of 1 percent of the total area of each Management Area 
(FTHLICC 2003a, pp. 24-43). Additionally, the Rangewide Management 
Strategy (FTHLICC 2003a, pp. 60-62) describes compensation measures for 
projects within and outside the Management Areas where residual effects 
would occur after all reasonable on-site mitigation has been applied. 
The goal of compensation under the Rangewide Management Strategy is to 
``prevent the net loss of [flat-tailed horned lizard] habitat and make 
the net effect of a project neutral or positive to [flat-tailed horned 
lizards] by maintaining a habitat [baseline]'' (FTHLICC 2003a, p. 61). 
Compensation funds may be used ``to acquire, protect, or restore [flat-
tailed horned lizard] habitat both within and contiguous with 
[Management Areas]'' (FTHLICC 2003a, p. 60). Compensation ratios range 
from one-to-one to six-to-one (meaning, in latter ratio for instance, 
that six acres-worth of compensation will be required for every one 
acre of impact), depending on the location and nature of the impacts 
(FTHLICC 2003a, p. 61). Funds obtained through compensation associated 
with implementation of the Rangewide Management Strategy are being used 
to consolidate land ownership within the Management Areas or to enhance 
flat-tailed horned lizard habitat (FTHLICC 2003a, p. 25; FTHLICC 2010, 
p. 8). The original and current acreages of each Management Area are 
listed in Table 1.

[[Page 14217]]



     Table 1--Area (hectares and acres) of Flat-tailed Horned Lizard Management Areas Owned by Signatories to the Interagency Conservation Agreement
 Implementing the Flat-tailed Horned Lizard Rangewide Management Strategy and Area Owned by Non-signatories (Predominantly Private) in 1997 and Through
  2009, Plus Area and Percentage of Project-related Impacts Permitted by Signatories Within Each Management Area (Sources: FTHLICC 1997, p. 74; FTHLICC
                                                 2003a, p. 48; FTHLICC 2009, p. 10; FTHLICC 2010, p. 8)
--------------------------------------------------------------------------------------------------------------------------------------------------------
                                                                                                                                            Percent of
                                                                     Area of non-                                          Total area     total area of
                                    Area of        Area of non-     signatory lands    Total area of    Total area of    permitted for   management area
       Management area          signatory lands   signatory lands      added to       signatory lands  management area    impact as of    permitted for
                                    in 1997           in 1997       signatory lands       in 2009                             2009         impact as of
                                                                      since 1997                                                          2009 (percent)
--------------------------------------------------------------------------------------------------------------------------------------------------------
Borrego Badlands.............  14,771 ha         2,388 ha (5,900   592 ha *(1,464    15,363 ha         17,159 ha        0 ha (0 ac)....  0.0
                                (36,500 ac).      ac).              ac).              (37,964 ac).      (42,400 ac).
West Mesa....................  46,256 ha         8,822 ha (21,800  2,624 ha (6,483   48,880 ha         55,078 ha        86.77 ha         0.16
                                (114,300 ac).     ac).              ac).              (120,785 ac).     (136,100 ac).    (214.42 ac).
Yuha Desert..................  23,148 ha         1,214 ha (3,000   0 ha (0 ac).....  23,148 ha         24,362 ha        35.90 ha (88.70  0.15
                                (57,200 ac).      ac).                                (57,200 ac).      (60,200 ac).     ac).
East Mesa....................  43,868 ha         2,792 ha (6,900   1,380 ha (3,410   45,248 ha         46,660 ha        38.40 ha (94.90  0.08
                                (108,400 ac).     ac).              ac).              (111,810 ac).     (115,300 ac).    ac).
Yuma Desert..................  46,741 ha         6,273 ha (15,500  6,273 ha (15,500  53,014 ha         53,014 ha        10.50 ha (25.95  0.02
                                (115,500 ac).     ac).              ac).              (131,000 ac).     (131,000 ac).    ac).
                              --------------------------------------------------------------------------------------------------------------------------
    Total....................  174,784 ha        21,489 ha         10,869 ha         185,653 ha        196,273 ha       171.57 ha        0.09
                                (431,900 ac).     (53,100 ac).      (26,857 ac).      (458,759 ac).     (485,000 ac).    (423.97 ac).
--------------------------------------------------------------------------------------------------------------------------------------------------------
* Includes 350 ha (864 ac) owned by the Anza-Borrego Foundation.

    Representatives from the agencies participating on the Rangewide 
Management Strategy (also known as the Interagency Coordinating 
Committee) meet several times a year to coordinate and implement 
management actions (FTHLICC 2003a, pp. 1-104). The Interagency 
Coordinating Committee regularly documents progress made to conserve 
the flat-tailed horned lizard collectively or by participating agencies 
(FTHLICC 1998, pp. 1-11; FTHLICC 1999, pp. 1-13; FTHLICC 2001, pp. 1-
24; FTHLICC 2003b, pp. 1-32; FTHLICC 2004, pp. 1-33; FTHLICC 2005, pp. 
1-37; FTHLICC 2006, pp. 1-34; FTHLICC 2007, pp. 1-33; FTHLICC 2008a, 
pp. 1-35; FTHLICC 2009, pp. 1-38; FTHLICC 2010, pp. 1-33). These 
reports document and summarize the progress member agencies have made 
towards implementation of the Planning Actions identified in Rangewide 
Management Strategy (FTHLICC 2003a, pp. 25-32). The reports indicate 
that progress by signatory agencies has been made in the following 
areas: (1) Designation of the five Management Areas and the one 
Research Area; (2) requiring actions by permittees to follow the 
avoidance, minimization, and mitigation measures outlined in the 
Rangewide Management Strategy; (3) rehabilitating damaged and degraded 
habitat within the Management Areas; and (4) purchase of lands for 
flat-tailed horned lizard conservation from willing sellers. Although 
some lower priority actions (tasks), such as research on natural 
barriers, remain outstanding, the committee reports that nearly all 
tasks, many of which are ongoing or multi-year actions, are on schedule 
(FTHLICC 2010, pp. 21-25). Thus, despite being a voluntary agreement, 
the signatory agencies generally have been implementing the Interagency 
Conservation Agreement and associated Rangewide Management Strategy by 
meeting regularly, working to implement the measures of the Rangewide 
Management Strategy including providing personnel, developing and 
distributing public information, and providing ongoing review and 
feedback.
Coachella Valley Multiple Species Habitat Conservation Plan (Coachella 
Valley MSHCP)
    Our past assessments of the status of the flat-tailed horned 
lizard, particularly the 2003 withdrawal (68 FR 331), addressed the 
Coachella Valley in detail; thus, for consistency we again address the 
Coachella Valley here and elsewhere in this document. Since the 2003 
withdrawal, and even since our June 28, 2006, withdrawal (71 FR 36745), 
we have issued an incidental take permit for a large, regional HCP in 
the Coachella Valley. The Coachella Valley MSHCP is a large-scale, 
multi-jurisdictional habitat conservation plan encompassing about 
445,156 ha (1.1 million ac) in the Coachella Valley of central 
Riverside County. An additional 27,923 ha (69,000 ac) of Tribal 
reservation lands distributed within the plan area boundary are not 
included in the Coachella Valley MSHCP. The Coachella Valley MSHCP 
addresses 27 listed and unlisted ``covered species,'' including the 
flat-tailed horned lizard. On October 1, 2008, the Service issued a 
single incidental take permit (TE-104604-0) under section 10(a)(1)(B) 
of the Act to 19 permittees under the Coachella Valley MSHCP for a 
period of 75 years. Participants in the Coachella Valley MSHCP include 
eight cities (Cathedral City, Coachella, Indian Wells, Indio, La 
Quinta, Palm Desert, Palm Springs, and Rancho Mirage); the County of 
Riverside, including the Riverside County Flood Control and Water 
Conservation District, Riverside County Parks and Open Space District, 
and Riverside County Waste Management District; the Coachella Valley 
Association of Governments; Coachella Valley Water District; Imperial 
Irrigation District; California Department of Transportation; 
California State Parks; Coachella Valley Mountains Conservancy; and the 
Coachella Valley Conservation Commission (the created joint powers 
regional authority). The Coachella Valley MSHCP was designed to 
establish a multiple species habitat conservation program that 
minimizes and mitigates the expected loss of habitat and incidental 
take of covered species, including flat-tailed horned lizard (USFWS 
2008, pp. 1-207, and Appendix A, pp. 298-328). The Coachella Valley 
MSHCP is also a ``Subregional Plan'' under the State of

[[Page 14218]]

California's Natural Community Conservation Planning (NCCP) Act, as 
amended.
    The permit covers incidental take resulting from habitat loss and 
disturbance associated with urban development and other proposed 
covered activities. These activities include public and private 
development within the plan area that require discretionary and 
ministerial actions by permittees subject to consistency with the 
Coachella Valley MSHCP policies. An associated Management and 
Monitoring Program is also included in the Coachella Valley MSHCP and 
identifies specific management actions for the conservation of the 
flat-tailed horned lizard and its habitat.
    The Coachella Valley MSHCP identifies a reserve system that, upon 
full implementation, will establish 21 conservation areas that are 
either adjacent to each other or are linked by biological corridors. 
The acquisition program for the plan's reserve system is designed to 
conserve 52,484 ha (129,690 ac) during the first 30 years. This program 
is to be implemented such that acquisitions occur commensurate (in 
``rough step'') with impacts from urban development that is covered 
under the plan.
    The flat-tailed horned lizard is now known to occur only at two 
locations within the Coachella Valley MSHCP area, the Thousand Palms 
and Dos Palmas conservation areas (CVCC 2010, p. 13) (see also 
Description of Specific ``Populations'' section below). Table 2 
describes the amount of flat-tailed horned lizard habitat conserved and 
identified to be conserved through implementation of the Coachella 
Valley MSHCP. Additionally, plan implementation is expected to limit 
impacts of development and other covered activities on lands within 
conservation areas but that have not yet been acquired for conservation 
as part of the Coachella Valley MSHCP reserve system. The plan also 
designates one core habitat area (as used in that plan, this refers to 
an area that is large enough to maintain a self-sustaining 
population)--the Thousand Palms conservation area--and commits to 
establishing two more self-sustaining populations in other parts of the 
reserve system, if feasible, to benefit the flat-tailed horned lizard. 
Because of the distances separating appropriate parts of the reserve 
system, relocation of flat-tailed horned lizards will be required to 
re-establish or enhance populations in suitable habitat areas that have 
the potential to, but currently do not, support self-sustaining 
populations. Additionally, the plan calls for Management and Monitoring 
Programs that are expected to conserve this species in the plan area. 
Required management activities include limiting activities that degrade 
flat-tailed horned lizard habitat, evaluation and management of edge 
effects and other impacts through adaptive management, control of 
invasive species where necessary, and restoration and enhancement of 
degraded habitat as necessary according to monitoring results (CVAG 
2007, p. 9-123). In our evaluation of the potential impacts of the 
plan's implementation on the flat-tailed horned lizard (USFWS 2008, p. 
178), we concluded: ``After reviewing the current status of this 
species, environmental baseline for the action area, effects of the 
proposed action, and cumulative effects, it is the Service's biological 
opinion that the action, as proposed, is not likely to jeopardize the 
continued existence of the flat-tailed horned lizard. Loss of the 
Coachella Valley population would have a negligible [effect] on the 
status of the species as a whole, since it makes up approximately 1 
percent of the current range of the flat-tailed horned lizard. 
Persistence of the species in the Plan area is likely only with 
effective Plan implementation.''

      Table 2--Area of Flat-tailed Horned Lizard Habitat Conserved,
  Anticipated To Be Conserved, Impacted, and Anticipated To Be Impacted
          Through Implementation of the Coachella Valley MSHCP
------------------------------------------------------------------------
       Criterion (source)           Thousand Palms        Dos Palmas
------------------------------------------------------------------------
Flat-tailed horned lizard        1,318 ha (3,256 ac)  608 ha (1,503 ac)
 habitat area conserved at
 permit issuance in 2008 (CVAG
 2007, p. 9-115).
Additional flat-tailed horned    274 ha (678 ac)      107 ha (265 ac)
 lizard habitat area conserved
 in 2008 (CVCC 2009, p. 79).
Additional flat-tailed horned    8 ha (20 ac)         0 ha (0 ac)
 lizard habitat area conserved
 in 2009 (CVCC 2010, pp. 39 &
 51).
Total flat-tailed horned lizard  1,600 ha (3,954 ac)  715 ha (1,768 ac)
 habitat area under
 conservation through 2009
 (calculated).
Total flat-tailed horned lizard  1,707 ha (4,219 ac)  2,078 ha (5,134
 habitat area expected to be                           ac)
 conserved by MSHCP
 implementation (CVAG 2007, p.
 9-115).
Percent flat-tailed horned       94%                  34%
 lizard habitat area conserved
 through 2009 compared to
 amount required upon full
 implementation of the plan
 (calculated).
Area of flat-tailed horned       0 ha (0 ac)          0 ha (0 ac)
 lizard habitat impacted by
 permitted activities through
 2009 (CVCC 2009, p. 79; CVCC
 2010, pp. 39 & 51).
Area of flat-tailed horned       44 ha (108 ac)       163 ha (403 ac)
 lizard habitat anticipated to
 be impacted by permitted
 activities (CVAG 2007, p. 9-
 115).
Percent flat-tailed horned       2%                   7%
 lizard habitat area
 anticipated to be impacted
 compared to total area of flat-
 tailed horned lizard habitat
 in conservation area
 (calculated).
------------------------------------------------------------------------

Lower Colorado River Multi-Species Conservation Plan (Lower Colorado 
River MSCP)

    The Lower Colorado River MSCP is a joint effort by Federal and non-
Federal (State, local, and private) entities with management authority 
for storage, delivery, and diversion of water; hydropower generation, 
marketing, and delivery; and land management or Native American Trust 
responsibilities along the Lower Colorado River, to address regulatory 
requirements under sections 7, 9, and 10 of the Act for their 
activities. We issued the 50-year permit (TE-086834) on April 4, 2005. 
Most of the activities addressed by the Lower Colorado MSCP are outside 
the range of the flat-tailed horned lizard. The flat-tailed horned 
lizard habitat contained within the Lower Colorado River MSCP

[[Page 14219]]

planning area is under control of agencies, especially the Bureau of 
Reclamation, that have agreed to implement the Rangewide Management 
Strategy (USFWS 2005, p. 202).
    Implementation of the Lower Colorado River MSCP is expected to 
provide for the acquisition and long-term protection of 230 acres of 
existing flat-tailed horned lizard habitat that is currently 
unprotected. This action is compensation for anticipated impacts to 
approximately 128 acres of flat-tailed horned lizard habitat (USFWS 
2005, pp. 201-202). Purchase of protected habitat, potentially near the 
Dos Palmas reserve area, is scheduled to start in 2011 (BOR 2010, p. 
274). Additionally, activities covered under the permit will be 
designed to avoid or minimize effects to the species and its habitat in 
accordance the conservation needs identified in the Rangewide 
Management Strategy (USFWS 2005, pp. 201-202).
    We found that implementation of the Lower Colorado River MSCP was 
``Not Likely to Jeopardize the Continued Existence of the Species'' 
(USFWS 2005, p. 202), noting ``The habitat area that would be included 
[under the plan] is not a significant amount of the available habitat 
for the species. * * * Research and monitoring of the species within 
the [Lower Colorado River MSCP] area will contribute to understanding 
the species, its distribution, and habitat needs. * * * [and] There are 
not likely to be any adverse effects to the species' conservation 
elsewhere in the range from the issuance of an incidental take permit 
for the [Lower Colorado River MSCP]'' (USFWS 2005, p. 202).

Population Dynamics

    Flat-tailed horned lizards are difficult to detect, which limits 
the effectiveness of surveys for the species (FTHLICC 2003a, pp. 9, 65; 
Grant and Doherty 2007, p. 1050). As a result, not only is presence and 
especially absence difficult to determine, but determining the size, 
trend, and demography of populations is problematic as well. The 
history of flat-tailed horned lizard monitoring and the shortcomings of 
the techniques used are described in the Rangewide Management Strategy 
(FTHLICC 2003a, p. 64) and our 2003 withdrawal document (68 FR 332-
333). Monitoring using more rigorous data collection and analytical 
methodologies has been conducted as part of the implementation of the 
Rangewide Management Strategy (FTHLICC 2003a, pp. 64-66; FTHLICC 2008b, 
pp. 1-38). The results from this monitoring effort are described below.
    As detailed in the Flat-tailed Horned Lizard Monitoring Plan 
(FTHLICC 2008b, pp. 1-38), flat-tailed horned lizard monitoring 
consists of two surveys used in tandem: (1) Occupancy estimation 
surveys and (2) demographic plot surveys. Occupancy estimation was 
designed to determine whether the distribution (but not numbers of 
individuals or densities) of flat-tailed horned lizards in the 
management and research areas is stable, increasing, or decreasing. 
This component of the monitoring was meant to detect large-scale 
changes in the status of flat-tailed horned lizard distribution in the 
Management Areas. The monitoring of demographic plots was designed to 
delineate flat-tailed horned lizard population dynamics and trends by 
estimating abundance each summer and yearly survival, recruitment, and 
population growth rate between years. This component was meant to 
gather more in-depth information on a smaller number of plots. However, 
the demographic plots were non-randomly established within areas known 
or suspected to support greater densities of flat-tailed horned 
lizards. The Management Areas overall were selected because they 
provided generally high-quality flat-tailed horned lizard habitat. 
However, the use of the two complementary survey types, one dispersed 
and coarse and the other focused and narrow, allows managers to draw, 
with caution, more detailed conclusions about an entire Management Area 
than they could have otherwise done by interpreting just one of the 
survey types alone. Below we summarize the information available from 
these monitoring efforts (source: USFWS 2010a, pp. 1-76).
    Occupancy surveys were conducted at West Mesa (2005 and 2009), East 
Mesa (2006), Yuha Desert (2008), and Ocotillo Wells State Vehicular 
Recreation Area (SVRA) (2006-2009). Separate occupancy analyses of 
these areas were conducted based on three survey methodologies: visual 
observations of flat-tailed horned lizards, lizard scat observations, 
and a combination of visual and scat observations. Multi-year analyses 
also were conducted for a subset of 53 plots in Ocotillo Wells SVRA 
that were surveyed annually from 2006 to 2009. Our analysis indicates 
the combined visual-and-scat surveys were the most likely to correctly 
yield a statistically significant result (i.e., this survey methodology 
had the greatest statistical power). Although there are no comparable 
historical data with which to provide context, our analysis suggests 
that the level of occupancy of flat-tailed horned lizards within the 
surveyed areas seemed relatively high at all sites. For example, 
visual-and-scat survey results show that flat-tailed horned lizards 
occupied at least 80 percent of the Management Areas in the years 
surveyed, except in the West Mesa Management Area in 2005, which had a 
low level of survey effort that year. Additionally, results from the 
53-plot subset with multi-year data from 2006 to 2009 suggested that 
the level of flat-tailed horned lizard occupancy stayed about the same 
or may have even increased slightly over time. Moreover, our analysis 
showed considerable support to conclude that there was no linear 
decline in the proportion of survey plots occupied by flat-tailed 
horned lizards. These results only reflect the occupancy of flat-tailed 
horned lizards within the areas surveyed and do not necessarily reflect 
the level of occupancy throughout the range of the species; 
nevertheless, we conclude from the above results that the level of 
occupancy within the survey areas is not low, and that there is no 
indication of a decline.
    Data from the demographic plots were gathered from six 9-hectare 
(22.2-acre) plots at the following flat-tailed horned lizard Management 
Areas: East Mesa (1 plot, 2007-2009), West Mesa (1 plot, 2007-2009; 1 
plot, 2008-2009), Yuha Desert (1 plot, 2007-2009), and Yuma Desert (2 
plots, 2008-2009). Hatchlings were captured at all Management Areas 
except East Mesa (which was surveyed prior to the time that flat-tailed 
horned lizards eggs would have been likely to have hatched), indicating 
that flat-tailed horned lizards were reproducing. The presence of 
hatchlings during 2008, and especially 2009, suggested that 
reproductive conditions were favorable in those years.
    Because of the complexities of analyzing a cryptic species, we used 
two methodologies to calculate flat-tailed horned lizard abundance. 
Because the surveyed plots were not closed (meaning flat-tailed horned 
lizards could move in and out of the areas being surveyed), we used two 
different methods (calculations) to estimate the ``effective survey 
area'' so that we could translate abundance (number of individuals) 
into densities (number of individuals per unit area). Using the first 
method (using a mean maximum distance moved buffer strip to estimate 
effective survey area), the density of adult flat-tailed horned lizards 
ranged from 0.3 to 3.3 individuals per ha (0.1 to 1.3 individuals per 
ac), while the second method (using a hierarchical, spatially indexed 
capture-recapture model to estimate effective survey area) yielded a 
range from 0.7 to 4.4 individuals per ha (0.3 to 1.8

[[Page 14220]]

individuals per ac). The results from the second method are likely to 
be more realistic because they incorporated additional spatial 
information.
    Other estimates of density of flat-tailed horned lizards are 
available in the scientific literature, but comparisons between and 
among the different studies (including the recent monitoring) are 
confounded by differing survey and analysis methodologies. 
Nevertheless, the above densities at the three California Management 
Areas were generally within the range of estimates reported by Grant 
(2005, pp. 39-40) during 2002-2004. Similarly, the densities of adult 
flat-tailed horned lizards at the Yuma Desert Management Area reported 
above were generally similar to the ranges of estimates presented by 
Young and Young (2000, p. 28) during 1997-1998, Young et al. (2004b, p. 
i) during 2003, and Young and Royle (2006, p. 9) in 2005. Comparisons 
to even earlier estimations of flat-tailed horned lizard densities, 
although even more tenuous because of differing methodologies, are also 
within similar ranges. Despite similar ranges in densities reported 
from the various studies through time, the increased statistical and 
methodological rigor of recent efforts has reduced the level of 
uncertainty in the results. Thus, these recent density estimates are an 
improvement over older estimates.
    The available data indicate that flat-tailed horned lizard 
abundances and densities have remained relatively stable from 2007 to 
2009; however, with only 3 years of standardized monitoring, these data 
cannot yet provide meaningful inferences about long-term trends. 
Additionally, no abundance or density information is available for the 
lower-quality habitat areas outside the demographic plots. However, the 
complementary coarse-scale occupancy survey data mentioned above 
suggests flat-tailed horned lizards are widely distributed spatially 
and, in at least at one Management Area, temporally consistent. This 
conclusion suggests that flat-tailed horned lizard population trends in 
the surveyed lower-quality habitat areas are not dissimilar to those of 
the surveyed higher-quality habitat areas. Moreover, because the recent 
(2007-2009) and older (1997-2005) density estimates are all generally 
within similar ranges, this suggests the overall density of flat-tailed 
horned lizards within the surveyed Management Areas has not markedly 
decreased over the past decade or so. Thus, with the previously 
mentioned caveats in mind, we conclude that flat-tailed horned lizard 
populations in the Management Areas are not low and have not declined 
since 2007, and probably not declined since 1997.

Description of Specific ``Populations''

    As stated earlier, we have divided the current range of the flat-
tailed horned lizard into four populations based on geographic locales. 
The 2003 Rangewide Management Strategy includes a GIS-based map 
(FTHLICC 2003a, p. 5) of the ``current distribution'' of the flat-
tailed horned lizard. Except for the Coachella Valley Population, where 
the flat-tailed horned lizard is now limited to two occurrences, we 
used the GIS data as a basis for our assessment of the distribution of 
flat-tailed horned lizard populations. A summary of these populations 
is presented below.
    Coachella Valley Population (California)--The ``current 
distribution'' within the Coachella Valley as defined by the Rangewide 
Management Strategy (FTHLICC 2003a, pp. 3-5) does not represent the 
best scientific distribution information available for this region. 
Urban and agricultural development has continued in the Coachella 
Valley, and there are many areas of unsuitable or degraded habitat. In 
addition to areas of unsuitable habitat, many of which serve as a 
barrier to flat-tailed horned lizard movement, other potential manmade 
barriers exist, including several major highways, a railway, and 
canals. The only area within the Coachella Valley proper that is now 
known to be occupied by flat-tailed horned lizards is in the Thousand 
Palms reserve (CVCC 2010, p. 13). Other areas of potentially suitable 
habitat occur in the region, including areas that were formerly known 
to be occupied (Barrows et al. 2008, p. 1891), although recent surveys 
have not detected any flat-tailed horned lizards (CVCC 2010, p. 13). 
Thus, the ``current distribution'' as defined by the Rangewide 
Management Strategy (FTHLICC 2003a, pp. 3-5) does not accurately 
reflect the area occupied by flat-tailed horned lizards in the 
Coachella Valley; as such, we do not use a GIS-based assessment for the 
Coachella Valley as we do for the other geographical ``populations.''
    The Coachella Valley MSHCP is the primary driver of monitoring and 
management activities for the Coachella Valley Population of the flat-
tailed horned lizard because the Rangewide Management Strategy does not 
include any Management Areas in this region. The Coachella Valley 
Population area is the smallest of the four geographic ``populations,'' 
and we primarily identify it as a separate population to be consistent 
with our past analyses. Flat-tailed horned lizards also occur in the 
vicinity of the Dos Palmas Preserve near the northeast shore of the 
Salton Sea (Turner and Medica 1982, p. 817; FTHLICC 2003a, pp. 2-6; 
CVCC 2010, p. 13). The Dos Palmas population is small and likely 
isolated from other populations because of the presence of the Salton 
Sea to the west; canals, roads and urban and agricultural development 
to the northwest; and canals, roads and urban and agricultural 
development to the southeast. However, not all of these barriers are 
likely to completely restrict flat-tailed horned lizard movement (see 
the Factor E discussion, below). The genetic affinities of the Dos 
Palmas population are not known. Geographically, the flat-tailed horned 
lizards at Dos Palmas Preserve could arguably be considered part of 
either the Western Population or Eastern Population (see below); 
however, because the true affinities of this population are not known, 
and because the Dos Palmas reserve area is covered under the Coachella 
Valley MSHCP and its associated monitoring and management, herein we 
consider the Dos Palmas flat-tailed horned lizards to be part of the 
Coachella Valley Population. The area of flat-tailed horned lizard 
habitat in the Coachella Valley Population is about 3,785 ha (9,353 ac) 
(see Table 2).
    Western Population (California and Baja California)--This 
population includes flat-tailed horned lizards in the areas west of the 
Salton Sea, the Imperial Valley, and the Mexicali Valley. Using a GIS-
based assessment to estimate the area of this portion of the ``current 
distribution'' as defined by the Rangewide Management Strategy (FTHLICC 
2003a, pp. 3-5), we estimated that the Western Population occupies 
341,989 ha (845,073 ac). Of this acreage, approximately 253,020 ha 
(625,226 ac) is within the United States. Within the U.S. portion of 
the Western Population, approximately 48,262 ha (119,258 ac), or about 
19 percent, is non-Federal or non-State owned, or is more likely to be 
developed. The habitat within this area is mostly intact except for a 
few developed areas, but as discussed in the ``Barriers and Small 
Populations'' section under Factor E, potential manmade barriers to 
flat-tailed horned lizard movement (in addition to areas of urban and 
agricultural development) include Interstate 8; State Routes 78, 86, 
and 98; two railways; the fence and other activities along the 
international border in the United States, and Mexico Federal Highway 2 
in Mexico. The Rangewide Management Strategy designates three 
Management Areas in this population area, including Borrego Badlands, 
West Mesa, and Yuha Desert

[[Page 14221]]

(see Table 1), and a research area at the Ocotillo Wells SVRA. Much of 
the westernmost portion of this population is within Anza-Borrego 
Desert State Park. Additionally, private lands are scattered throughout 
the U.S. portion, with large aggregations in the Borrego Springs area 
and in the vicinity of (but outside of) Ocotillo Wells SVRA. The range 
of the flat-tailed horned lizard in this population also extends 
southward into Mexico, crossing the international border at the Yuha 
Desert and continuing south along the east side of the Peninsular 
Ranges and west of Laguna Salada in Baja California (FTHLICC 2003a, pp. 
2-5). The status of the population in this portion of the range in 
Mexico is poorly known, but there have been few substantive changes to 
the landscape in this area. Additionally, flat-tailed horned lizards 
were observed recently near Cerro Prieto, Baja California, which is 
east of the Sierra de Los Cucapahs (Sierra Cucap[aacute]) and west of 
the agricultural areas of the Mexicali Valley (A. Calvo Fonseca, 
Pronatura Noroeste, in litt. 2010). This recent detection is outside of 
the current distribution as depicted in the Rangewide Management 
Strategy (FTHLICC 2003a, p. 5).
    Eastern Population (California and Baja California)--This 
population includes flat-tailed horned lizards in the areas east of the 
Salton Sea and the Imperial Valley but west of the Colorado River. 
While the isolated population at Dos Palmas Preserve could be included 
as part of either the Eastern Population or the Coachella Valley 
Population based on its geographic location, for the purposes of our 
analysis of threats to the species we consider the Dos Palmas Preserve 
population to be part of the Coachella Valley Population because of the 
similarity of potential threats when compared to the populations in the 
Coachella Valley, and its inclusion within the Coachella Valley MSHCP 
plan area. Using a GIS-based assessment to estimate the area of the 
Eastern Population portion of the ``current distribution'' (as defined 
by the Rangewide Management Strategy (FTHLICC 2003a, pp. 3-5)), we 
estimated that the Eastern Population occupies 169,617 ha (419,133 ac). 
Of this acreage, approximately 146,121 ha (361,073 ac) is within the 
United States. Within the U.S. portion of the Eastern Population, 
approximately 5,844 ha (14,441 ac), or about 4 percent, is non-Federal 
or non-State owned, or is more likely to be developed. The area 
occupied by the Eastern Population is mostly intact except for a few 
developed areas, but potential manmade barriers to flat-tailed horned 
lizard movement (in addition to areas of urban and agricultural 
development) include Interstate 8, State Routes 78 and 98, the All-
American Canal and the Coachella Canal, and the international border 
fence in the United States (see ``Barriers and Small Populations'' 
section under Factor E, below). The Rangewide Management Strategy 
designated the East Mesa Management Area within the area occupied by 
the Eastern Population (see Table 1). The geographic extent of the 
Eastern Population also includes the Algodones Dunes (also known as the 
Imperial Sand Dunes or Glamis Sand Dunes), a portion of which is 
designated Wilderness, and a narrow strip of habitat south of the 
international border at the southern edge of the Algodones Dunes 
(FTHLICC 2003a, pp. 2-5). The portion of the Eastern Population area in 
Mexico is bound by agricultural development (unsuitable habitat) on the 
west, south, and east. The status of the portion of the Eastern 
Population in Mexico is poorly known, but flat-tailed horned lizards 
were observed recently in this area (A. Calvo Fonseca, in litt. 2010).
    Southeastern Population (Arizona and Sonora)--This population 
includes flat-tailed horned lizards in the areas east of the Colorado 
River, extending from Yuma, Arizona, south and east to the Gulf of 
California in northwestern Mexico. In Arizona, the flat-tailed horned 
lizard occurs in Yuma County, ranging over the Yuma Desert south of the 
Gila River and west of the Gila and Butler Mountains (Rorabaugh et al. 
1987, p. 104; FTHLICC 2003a, pp. 2-6). The Rangewide Management 
Strategy designated the Yuma Desert Management Area within the area 
occupied by the Southeastern Population (see Table 1). In Mexico, the 
flat-tailed horned lizard ranges from the international border in the 
Yuma Desert south and east through the Pinacate Region to the sandy 
plains around Puerto Pe[ntilde]asco and Bahia de San Jorge along the 
Gulf of California (Johnson and Spicer 1985, p. 13; Gonz[aacute]les-
Romero and Alvarez-Cardenas 1989, p. 519; FTHLICC 2003a, pp. 2-5). 
About 60 percent of the flat-tailed horned lizard habitat in Sonora 
lies within two Mexican Federal natural protected areas: the Upper Gulf 
of California and Colorado Delta Biosphere Reserve, and the Pinacate 
and Gran Desierto de Altar Biosphere Reserve (CEDO 2001, p. 3).
    Using a GIS-based assessment to estimate the area of this portion 
of the ``current distribution'' as defined by the Rangewide Management 
Strategy (FTHLICC 2003a, pp. 3-5), we estimated that the area occupied 
by the Southeastern Population is 1,073,551 ha (2,652,802 ac), by far 
the largest of the four population areas. Of this acreage, 
approximately 67,922 ha (167,839 ac) is within the United States. 
Within the U.S. portion of the Southeastern Population, approximately 
5,158 ha (12,746 ac), or about 8 percent, is privately owned; an 
additional 5,832 ha (14,411 ac), or about 9 percent, is State of 
Arizona-owned lands. The habitat within the Southeastern Population 
area is mostly intact except for a few developed areas, but potential 
barriers to flat-tailed horned lizard movement (in addition to areas of 
urban and agricultural development) include Interstate 8 and the Yuma 
Areas Service Highway in the United States; the international border 
(combined with Mexico Federal Highway 2); Mexico Federal Highway 8; and 
a railway in Mexico (see ``Barriers and Small Populations'' section 
under Factor E, below).
    In summary, using a GIS-based assessment to estimate the size of 
the current distribution of the flat-tailed horned lizard as defined by 
the Rangewide Management Strategy (FTHLICC 2003a, p. 5), we estimated 
that the three population areas (excluding the Coachella Valley 
Population) comprise roughly 1,585,000 ha (3,916,600 ac), of which 
approximately 467,000 ha (1,154,000 ac) (less than 30 percent) is 
within the United States and approximately 1,100,000 ha (2,718,000 ac) 
(more than 70 percent) is within Mexico. The area of flat-tailed horned 
lizard habitat occupied or likely to be occupied that already is or is 
expected to be conserved in the Coachella Valley Population is about 
3,785 ha (9,353 ac) (see Table 2).

Previous Federal Actions

    In 1982, we first identified the flat-tailed horned lizard as a 
category 2 candidate species for listing under the Act (47 FR 58454; 
December 30, 1982). Category 2 candidate species were ``taxa for which 
information now in possession of the Service indicates that proposing 
to list the species as Endangered or Threatened is possibly 
appropriate, but for which sufficient data on are not currently 
available to biologically support a proposed rule'' (47 FR 58454). We 
again identified the flat-tailed horned lizard as a category 2 
candidate species in our 1985 notice of review (50 FR 37958; September 
18, 1985). In 1989, we elevated the species to category 1 status (54 FR 
554; January 6, 1989). Category 1 included species ``for which the 
Service currently has substantial information on hand to support the 
biological appropriateness

[[Page 14222]]

of proposing to list as endangered or threatened'' (54 FR 554). We 
maintained the category 1 status for the flat-tailed horned lizard in 
our 1991 notice of review (56 FR 58804; November 21, 1991).
    On November 29, 1993, we published in the Federal Register a 
proposed rule to list the flat-tailed horned lizard as a threatened 
species under the Act (58 FR 62624). On February 22, 1994 (59 FR 8450), 
we published a notice reopening the public comment period and 
announcing that we had scheduled a public hearing on March 22, 1994, in 
Imperial, California, in response to a request from the public. Our 
November 15, 1994, candidate notice of review stated that we had 
proposed to list the species as threatened (59 FR 58982).
    Subsequently, the passage of Public Law 104-6, 109 Stat. 73 on 
April 10, 1995, resulted in a delay in our final listing determination 
for the flat-tailed horned lizard. Although the statute's primary 
purpose was to provide additional funds for overseas military 
operations, it also included a rider that withdrew funding for listing 
determinations. Through a series of moratoria, funding restrictions, 
and continuing resolutions, this restriction in use of funds remained 
in effect until April 26, 1996, when the Omnibus Appropriations Act was 
enacted (Pub. L. 104-134, 110 Stat. 1321, (1996)), which contained a 
moratorium on certain listing activities but allowed the President to 
waive the moratorium. On April 26, 1996, President Clinton suspended 
the provision limiting implementation of Section 4 of the Act (61 FR 
24667; May 16, 1996). Earlier in 1996, our notice of review had 
indicated that we had proposed to list the species as threatened (61 FR 
7596; February 28, 1996).
    On January 21, 1997, the Bureau of Land Management (BLM) announced 
in the Federal Register that the draft Flat-tailed Horned Lizard 
Rangewide Management Strategy was available for public comment (62 FR 
3052). On May 16, 1997, in response to a lawsuit filed by the Defenders 
of Wildlife and other plaintiffs to compel us to make a final listing 
determination on the flat-tailed horned lizard, the District Court in 
Arizona ordered us to issue a final listing decision within 60 days. In 
June 1997, several State and Federal agencies, including the Service, 
signed an Interagency Conservation Agreement committing to implement 
the recently finalized Flat-tailed Horned Lizard Rangewide Management 
Strategy (FTHLICC 1997, pp. 1-106). Pursuant to the Interagency 
Conservation Agreement, cooperating parties agreed to take voluntary 
steps aimed at ``reducing threats to the species, stabilizing the 
species' populations, and maintaining its ecosystem'' (see FTHLICC 
2003a, p. 80).
    On July 15, 1997, we issued a final decision to withdraw the 
proposed rule to list the flat-tailed horned lizard as a threatened 
species (62 FR 37852). We based the withdrawal on three factors: (1) 
Population trend data did not conclusively demonstrate significant 
population declines; (2) Some of the threats to the flat-tailed horned 
lizard habitat had abated since the proposed rule was issued; and (3) 
Our conclusion that the recently approved Interagency Conservation 
Agreement would ensure further reductions in threats (62 FR 37852).
    On December 30, 1997, the Defenders of Wildlife and others filed a 
complaint in the U.S. District Court for the Southern District of 
California challenging our 1997 withdrawal of the proposed rule. On 
June 16, 1999, the District Court upheld our decision to withdraw the 
proposed listing rule. The District Court's decision was appealed and 
on July 31, 2001, the Ninth Circuit Court of Appeals vacated the 
previous ruling of the District Court. The case was remanded back to 
the Secretary because: (1) The withdrawal of the proposed rule did not 
expressly consider whether the flat-tailed horned lizard is likely to 
become an endangered species within the foreseeable future in a 
significant portion of its range; and (2) The withdrawal of the 
proposed rule did not ``address the lizard's viability in a site-
specific manner with regard to the putative benefits of the Interagency 
Conservation Agreement.'' In accordance with the Appeals Court's 
ruling, we published a document in the Federal Register on December 26, 
2001, reinstating the 1993 proposed rule and opening a 120-day public 
comment period (66 FR 66384).
    On May 30, 2002, we published a document in the Federal Register 
reopening the public comment period for an additional 60 days (67 FR 
37752) and announced that we would be holding public hearings in El 
Centro, California, on June 19, 2002. On September 24, 2002, we 
published in the Federal Register another document (67 FR 59809) 
announcing the reopening of the public comment period for an additional 
15 days to allow for peer review, additional public comment on the 
proposed rule, and submittal of information that became available since 
our 1997 withdrawal.
    On January 3, 2003, we again published in the Federal Register a 
decision to withdraw the November 29, 1993, proposed rule to list the 
flat-tailed horned lizard as a threatened species (68 FR 331). The 
Service found the lizard to be ``in danger of extirpation in the 
Coachella Valley'' (68 FR 348); however, we determined that the 
Coachella Valley is not a significant portion of the species' range. We 
concluded in the January 3, 2003, withdrawal that the flat-tailed 
horned lizard populations on either side of the Imperial Valley-Salton 
Sea and in Arizona were not likely to become endangered in the 
foreseeable future and that listing the species was not warranted.
    The Tucson Herpetological Society and others filed a complaint with 
the District Court for the District of Arizona challenging the January 
3, 2003, withdrawal of the proposed rule. In a ruling issued on August 
30, 2005, the District Court for the District of Arizona issued an 
order granting plaintiffs' motion for summary judgment, citing our 
failure to specifically evaluate the lost habitat of the flat-tailed 
horned lizard, and whether the amount of lost habitat represented a 
significant portion of the species' range. On December 7, 2005, we 
published a document in the Federal Register reinstating the 1993 
proposed rule (70 FR 72776). On March 2, 2006, we announced in the 
Federal Register that we were reopening the public comment period on 
the 1993 proposed rule for 14 days for the purpose of soliciting 
comments and information relevant to the specific issue identified in 
the District Court's November 2005 ruling (i.e., whether the flat-
tailed horned lizard's lost historical habitat rendered the species 
likely to become in danger of extinction in the foreseeable future 
throughout all or a significant portion of its range) (71 FR 10631). On 
April 21, 2006, we announced in the Federal Register an additional 
public comment period on the 1993 proposed rule from April 21, 2006, to 
May 8, 2006 (71 FR 20637).
    After re-examining the lost historical habitat of the flat-tailed 
horned lizard in relation to our January 3, 2003, withdrawal, we 
determined that the lost historical habitat is not a significant 
portion of the species' range, and its loss does not result in the 
species likely becoming endangered in the foreseeable future throughout 
all or a significant portion of its range. We published our decision in 
the Federal Register on June 28, 2006, to once again withdraw the 
November 29, 1993, proposed rule to list the flat-tailed horned lizard 
as a threatened species (71 FR 36745).
    Following a supplemental complaint from Tucson Herpetological 
Society and others challenging the 2006 withdrawal

[[Page 14223]]

of the proposed rule to list the flat-tailed horned lizard under the 
Act, the United States District Court for the District of Arizona (the 
District Court) granted summary judgment in favor of the Secretary of 
the Interior (Tuscon Herpetological Society v. Kempthorne, 04-CV-00075-
PHX-NVW); however, this ruling was appealed to the Court of Appeals for 
the Ninth Circuit. In a ruling issued on May 18, 2009, the Court of 
Appeals for the Ninth Circuit reversed the District Court's ruling when 
it determined that in the context of the analysis of whether the 
lizard's lost historical range constituted a significant portion of the 
species' range, the administrative record did not support what the 
Court of Appeals for the Ninth Circuit viewed as the Service's 
conclusion that flat-tailed horned lizard populations were stable and 
viable throughout most of its current range.
    On November 3, 2009, the District Court remanded the 2006 
withdrawal to the Service for further consideration and reinstated the 
1993 proposal to list the species. The District Court ordered the 
Service to complete this reconsideration in accordance with the 
deadlines set forth in 16 U.S.C. 1533(b). On March 2, 2010, we 
published a notice in the Federal Register announcing the reinstatement 
of the 1993 proposed rule, the reopening of the public comment period 
for 60 days, and the scheduling of public hearings (75 FR 9377). Public 
hearings were held in Palm Desert, California, on March 23, 2010, and 
Yuma, Arizona, on March 24, 2010.

Summary of Factors Affecting the Species

    Section 4 of the Act (16 U.S.C. 1531 et seq.) and the regulations 
that implement the listing provisions of the Act (50 CFR part 424) set 
forth the procedures for adding species to the Federal Lists of 
Endangered and Threatened Wildlife and Plants. A species may be 
determined to be an endangered or threatened species due to one or more 
of the five factors described in section 4(a)(1) of the Act (Factors A 
through E).
    We evaluated threats to the flat-tailed horned lizard under the 
five listing factors in the 1993 proposed rule to list the flat-tailed 
horned lizard as threatened under the Act (58 FR 62624). Subsequent 
documents in 1997 and 2003 withdrawing the proposed rule to list the 
species included additional evaluations (62 FR 37852; 68 FR 331). The 
2003 document withdrawing the proposed rule was the most comprehensive 
and the most recent five-factor analysis. The 2006 document withdrawing 
the proposed rule (71 FR 36745) did not address the five factors in 
detail because its scope was limited by a court order (see Previous 
Federal Actions section). In this document, we use the best scientific 
and commercial data available to evaluate current potential threats to 
flat-tailed horned lizard and its habitat rangewide per the five 
listing factors, and we provide brief summaries of the 1993 and 2003 
evaluations for context.

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

    For this factor, we evaluated the present (current) or threatened 
(anticipated) impacts that may be affecting the habitat or range of the 
flat-tailed horned lizard. This factor does not address historical or 
past actions that resulted in destruction, modification, or curtailment 
of the species' habitat or range. Past actions that destroyed, 
modified, or curtailed the species' habitat or range are not threats in 
and of themselves. Any persisting ramifications of such past actions 
that may be threats to the species are addressed under Factor E (other 
natural or manmade threats), below. However, for Factor A, we do look 
to past actions to inform our evaluation of potential future threats 
affecting the species' habitat or range in that the history of past 
actions allows us to predict the likelihood of such actions continuing 
into the foreseeable future.
    In the 1993 proposed rule (58 FR 62625-62626), we identified 
historical flat-tailed horned lizard habitat losses that resulted in 
the curtailment of the species' range under Factor A. We noted threats 
that were current or anticipated at that time, including agricultural 
and urban development, off-highway vehicle (OHV) use, geothermal energy 
development, sand and gravel extraction operations, military training 
activities, and construction of roads and utility corridors. We also 
mentioned that flat-tailed horned lizard habitat had been fragmented, 
causing isolation of populations (curtailment of the species' range) 
(see below for additional discussion on fragmentation). Additionally, 
the 1993 proposed rule also mentioned gold mining as a potential 
threat. There are currently no gold mines in flat-tailed horned lizard 
habitat, and we are not aware of any proposals for new gold mines; 
therefore, we do not expect gold mines to become a threat in the 
foreseeable future.
    In the 2003 withdrawal document (68 FR 341-345), we found that 
current and anticipated urban and agricultural development was limited 
to a few, small areas and did not constitute a significant threat to 
the species. However, we did state that past agricultural, urban, and 
associated infrastructural development (such as canals and roads) had 
fragmented the species' range, which we discuss below as a separate 
threat under Factor A.
Fragmentation and Past Habitat Loss
    Because of our past treatment of fragmentation in our previous 
rules, we are providing a discussion of fragmentation as a term and its 
application to the five-factor analysis for the flat-tailed horned 
lizard. This discussion should: (1) Provide a clear definition of the 
term that we use in this document, and (2) acknowledge that our lack of 
clarity for this term in past documents may have resulted in unanswered 
questions as to how the flat-tailed horned lizard may have been 
affected by historical development in the Salton Trough. Because of the 
connection between fragmentation and historical habitat loss, we also 
describe how historical habitat loss was addressed in past assessments.
    In the 2003 withdrawal document, we defined fragmentation as the 
``breaking up of a habitat or ecosystem into smaller parcels'' (68 FR 
341). This definition is similar to the more detailed version used by 
Wilcove et al. (1986, p. 237) who defined habitat fragmentation as 
occurring ``when a large expanse of habitat is transformed into a 
number of smaller patches of smaller total area, isolated from each 
other by a matrix of habitats unlike the original.'' Thus, 
fragmentation is a process, one that inextricably involves habitat loss 
(Fahrig 1999, p. 87). However, in addition to the effects associated 
with habitat loss, fragmentation also includes the effects associated 
with the fractured nature of that habitat after its transformation 
(Fahrig 2003, p. 487). The implication is that the biological 
properties of the remaining, small, isolated patches of habitat have 
changed during or as a result of the fragmentation of the habitat (van 
den Berg et al. 2001, p. 225). In other words, after some portion of 
the habitat of a species has been destroyed, that species may be 
impacted by one or more secondary effects (threats) associated with 
reduction in the size of remaining habitat patches (or the populations 
of the species therein) and the isolation of those patches (and 
populations) from each other (Andr[eacute]n 1994, p. 355). Thus, the 
effects of fragmentation include: (1) The effects associated with the 
ongoing loss of habitat; and (2) the subsequent, secondary effects that 
are the current ramifications of past habitat loss.

[[Page 14224]]

Because multiple secondary effects may be related or correlated to each 
other (Fahrig 2003, pp. 491-492), the term fragmentation, as it has 
been used in the scientific literature and by the Service in past 
assessments of this species, is ambiguous (Haila 2002, p. 321). Because 
of this ambiguity, in applying the Act's five listing factors to the 
flat-tailed horned lizard, we will address current and anticipated 
habitat loss under Factor A, and the relevant, identifiable secondary 
effects (including threats associated with fragmentation) to the 
species under Factor E.
    Our past assessments describe in detail and attempted to quantify 
the historical development in the Salton Trough (58 FR 62626; 62 FR 
37857; 68 FR 341-345; 71 FR 36751), as did the scientific literature 
(such as Johnson and Spicer 1985, p. 38, 45-48; Rorabaugh et al. 1987, 
p. 106; Hodges 1995, pp. 1-18; Hodges 1997, pp. 1-16; Piest and Knowels 
2002, pp. 1-4; FTHLICC 2003a, pp. 2-3; Piest and Knowels 2006, pp. 1-
4). These documents have, to a greater or lesser extent, estimated the 
areal extent of current and historical flat-tailed horned lizard 
habitat in all or certain portions of its range. One of the more 
detailed of such analyses was Hodges (1997, pp. 15-16), who concluded 
that 503,161 ha (1,243,341 ac) out of 979,016 ha (2,419,200 ac), or 
about 51 percent, of flat-tailed horned lizard habitat in the United 
States had been destroyed by past development.
    However, such calculations, no matter how carefully crafted, are 
necessarily based on assumptions of what areas constituted historical 
habitat for the species (such as Hodges 1997, p. 10). Because much of 
the area within the range of the flat-tailed horned lizard was 
converted to agricultural and urban development during the early half 
of the 20th century (see Background section, above) prior to any 
systematic surveys for the flat-tailed horned lizard, little reliable 
information exists on the historical distribution of the species 
(Barrows et al. 2008, p. 1886).
    We questioned the validity of such assumptions in our past 
assessments. For example, Hodges (1997, pp. 5, 7, and 16) included the 
area now inundated by Salton Sea as historical habitat, but we stated 
in our 2003 withdrawal that the Salton Sea area could arguably be 
considered ephemeral historical habitat. In our 2006 withdrawal, we 
concluded that the former lakebed of historical Lake Cahuilla 
(including and beyond the present-day Salton Sea) likely was not 
habitat important to the flat-tailed horned lizard (71 FR 36750-36751). 
The information on the genetics of flat-tailed horned lizard 
populations raises further doubts about the validity of the assumptions 
made in earlier assessments, both by us and by others, of historical 
flat-tailed horned lizard habitat.
    As discussed above (see Background section), genetic data readily 
support three of the four geographic populations as distinct, 
indicating that these populations generally had little genetic 
interchange among each other (Mulcahy et al. 2006, pp. 1807-1826; 
Culver and Dee 2008, pp. 1-14). This lack of genetic exchange suggests 
a barrier separated, and likely still separates, these populations. As 
discussed in the Background section, the areas within the present-day 
Imperial Valley, Mexicali Valley, and San Luis Valley were historically 
interlaced by a network of Colorado River-influenced water courses, 
including the Alamo River, the New River, and the R[iacute]o Hardy (or 
their precursors or equivalents). Historically, these ``rivers'' were 
dependent upon the Colorado River for water and only transported water 
periodically. Prior to the increase of agricultural development and 
prior to the digging of the irrigation canal and subsequent flood that 
created the Salton Sea early in the 20th century (see Background 
section), some areas along these river channels were characterized by 
Parish (1914, p. 88) as having ``channels, sloughs, and lagoons.'' 
These hydrologically influenced areas likely did not contain flat-
tailed horned lizard habitat, as defined in the Background section. As 
such, not all of the area between the present-day Salton Sea and the 
Gulf of California, including areas outside the lakebed of historical 
Lake Cahuilla, historically supported flat-tailed horned lizard 
habitat. This information further supports our conclusion presented in 
our 2006 withdrawal that the ``area of the historical range 
periodically inundated by Lake Cahuilla was not important to the long-
term viability of the flat-tailed horned lizard because this area was 
frequently unavailable and likely contained little quality habitat'' 
(71 FR 36750).
    Because of the extensive manmade changes to the landscape, we 
cannot precisely determine with any degree of specificity how much of 
the area was historically flat-tailed horned lizard habitat. Moreover, 
we maintain that much uncertainty exists with any attempt to precisely 
quantify the amount of flat-tailed horned lizard habitat that has been 
destroyed by historical agricultural development, as has been attempted 
in the past. We agree with the conclusions of previous assessments, 
both by us and by others, that portions of the Coachella, Imperial, 
Mexicali, Yuma, and San Luis Valleys once provided suitable areas of 
flat-tailed horned lizard habitat. We also agree that historical 
agricultural development (and, to a lesser extent, urban development) 
destroyed large areas with flat-tailed horned lizard habitat, thus 
curtailing the size of the Coachella Valley, Western, Eastern, and 
Southeastern flat-tailed horned lizard populations in both the United 
States and Mexico. However, the effects of past actions are better 
addressed under Factor E.
    In the sections below, we address the present or threatened 
destruction, modification, or curtailment of the habitat or range of 
the flat-tailed horned lizard. We evaluate the current and anticipated 
effects associated with several types of land development, the invasion 
of nonnative plants, OHV activity, and military training. We first 
describe the respective threats in general terms and then assess those 
threats to the habitat or range of the flat-tailed horned lizard, 
focusing on subareas (such as identified populations or Management 
Areas) within the species' range, where appropriate.
Development
    We define development as commercial and residential development 
(i.e., urban development), and the conversion of land for any 
agricultural purpose. Such development not only includes the obvious 
associated infrastructure (e.g., roads, pipelines, canals, and power 
lines), but also reservoirs, power generation facilities, and resource 
extraction operations such as drilling and mining.
    For the purpose of evaluating the threats to a species and its 
habitat, we focus on the developmental activities that threaten to 
convert land from a natural or undeveloped state to land no longer 
suitable as habitat for the species. We consider both the direct and, 
where appropriate (within the context of Factor A), the indirect 
effects of such developmental activities. While land development 
typically has a similar effect, that is the destruction or modification 
of habitat, differing land uses resulting from development activities 
can lead to different indirect effects. We therefore distinguish among 
the types of development when evaluating the effects of such 
development on a species or its habitat.
    For this evaluation of flat-tailed horned lizard under Factor A, we 
determine whether development is a current or anticipated threat to 
flat-

[[Page 14225]]

tailed horned lizard habitat. Below, we address agricultural and urban 
development, as well as development associated with energy generation 
projects.

Agricultural Development

    Within the dry Colorado Desert, agricultural activity is 
substantially dependent upon irrigation water imported from the 
Colorado River. As discussed in the Background section, most of the 
agricultural development within the range of the flat-tailed horned 
lizard occurred early in the 20th century. Because Colorado River water 
is a finite resource, agricultural development is no longer expanding 
into new areas and destroying flat-tailed horned lizard habitat to any 
substantial degree. Information available from the Coachella Valley 
Water District (CVWD 2002, p. 1; 2003, p. 1; 2004, p. 1; 2005, p. 25; 
2006, p. 27; 2007, p. 25; 2008, p. 25; 2009, p. 25) indicates a slight 
decline in the amount of irrigable acres and a fairly steady though 
variable amount of water delivered from 2001 to 2008, indicating that 
new agricultural development has not occurred in the Coachella Valley 
within the past decade or so. Also, fields are being fallowed in the 
Imperial Valley because less water is available for irrigation in this 
area (IID 2006, p. 1). Thus, conversion of land for agriculture is no 
longer considered a threat to flat-tailed horned lizard habitat in the 
Coachella Valley and in the Imperial Valley portions of the Western and 
Eastern Populations, and is not considered to be a threat in the 
foreseeable future.
    In contrast, recent agricultural development has destroyed flat-
tailed horned lizard habitat in other areas. Between 2002 and 2006, an 
unreported but minority fraction of 1,534 ha (3,790 ac) of flat-tailed 
horned lizard habitat was developed for agricultural use in Arizona 
(Piest and Knowles 2006, p. 1). Rodriguez (2002, p. 21) also recorded 
recent agricultural development in Mexico; however, the majority of the 
agricultural development in the Mexicali and San Luis Valleys occurred 
in the early to mid-20th century, closely following the historical 
agricultural development north of the border (Furnish and Ladman 1975, 
pp. 84-88). Additionally, about 60 percent of the flat-tailed horned 
lizard habitat in Mexico lies within two Mexican Federal natural 
protected areas, the Upper Gulf of California and Colorado Delta 
Biosphere Reserve (la Reserva de la Biosfera del Alto Golfo de 
California y Delta del R[iacute]o Colorado), and the Pinacate and Gran 
Desierto de Altar Biosphere Reserve (la Reserva de la Biosfera El 
Pinacate y Gran Desierto de Altar) (CEDO 2001, p. 3), where 
agricultural development is limited by Mexican law.
    Agricultural activities outside of the areas receiving Colorado 
River water are severely restricted by the climate of the Salton Trough 
region, including in Mexico. Thus, while recent agricultural 
development destroyed areas of flat-tailed horned lizard habitat in the 
Southeastern Population, the overall acreages were small, especially 
compared to the amount of habitat available in the Southeastern 
Population.
    Agricultural development, most of which occurred between 1945 and 
the 1980s (Mills 2009, p. 28), occurred in the Borrego Springs area of 
the habitat occupied by the Western Population. The Borrego Springs 
area uses a local aquifer for irrigation, and the area does not receive 
Colorado River water; however, the aquifer is overdrawn (County of San 
Diego 2008, p. 8; Mills 2009, p. 4). We do not anticipate substantial 
amounts of agriculture to expand into adjoining natural lands in this 
area (see Mills 2009, pp. 40-42). Moreover, the area of private lands 
in the Borrego Valley is constrained within Anza-Borrego Desert State 
Park. As a result, we believe that agricultural development no longer 
threatens flat-tailed horned lizard habitat in the Borrego Springs 
portion of the Western Population, nor will it in the foreseeable 
future.
    In conclusion, the available information indicates that the vast 
majority of the agricultural development within the range of the flat-
tailed horned lizard took place in the historical past and only a small 
amount of development has been documented in recent times. Because 
conversion of land to agriculture in the region is limited by the 
availability of irrigation water and that water is limited, we do not 
expect agriculture to expand significantly into adjoining flat-tailed 
horned lizard habitat in the future. Moreover, increased demand for 
water outside the region has resulted in a decreased amount of Colorado 
River water available for agriculture in the Imperial Valley, which has 
resulted in the fallowing of fields in this area. Therefore, we 
conclude that agricultural development is not a substantial threat to 
the flat-tailed horned lizard throughout its range, nor is it 
anticipated to be in the foreseeable future.

Urban Development

    Like agricultural development, urban development largely occurred 
in the historic past. Many of the urban centers in the region that 
serve agricultural communities are contained within agricultural areas. 
While urbanization has continued as the human population within the 
region has grown (FTHLICC 2003a, p. 12; Indrelunas 2010, pp. 1-3), most 
of this urban development associated with these urban centers has come 
at the expense of former croplands. As such, this development is not 
currently destroying substantial amounts of available flat-tailed 
horned lizard habitat (FTHLICC 2003a, p. 12). However, certain areas of 
urban development not associated with active or past agriculture have 
resulted in the destruction of flat-tailed horned lizard habitat. This 
impact is most evident in the Coachella Valley where urban development 
not associated with agricultural communities continues today 
(Indrelunas 2010, pp. 1-3). This growth is corroborated by the number 
of domestic water meter services, which grew by over 25 percent from 
2001 to 2008 (CVWD 2002, p. 1; 2003, p. 1; 2004, p. 1; 2005, p. 25; 
2006, p. 27; 2007, p. 25; 2008, p. 25; 2009, p. 25). This urban growth 
is occurring in the surrounding desert areas, which likely include 
flat-tailed horned lizard habitat. Our interpretation of past and 
recent aerial imagery supports this trend.
    The flat-tailed horned lizard now appears to be restricted to two 
occurrences within the Coachella Valley MSHCP plan area, the Thousand 
Palms conservation area and the Dos Palmas conservation area (CVCC 
2010, p. 13). The Coachella Valley MSHCP includes numerous measures to 
minimize and mitigate impacts of urban development on the flat-tailed 
horned lizard (see Coachella Valley Multiple Species Habitat 
Conservation Plan (Coachella Valley MSHCP) section above for a detailed 
discussion). Approximately 94 percent of the potential habitat where 
flat-tailed horned lizards are known to occur in the Thousand Palms 
conservation area is land that is already protected (Table 2), 
including about 62 percent that is part of the Coachella Valley 
National Wildlife Refuge. Similarly, approximately 34 percent of the 
habitat at Dos Palmas is protected (Table 2). The high level of 
protection of flat-tailed horned lizard habitat at the Thousand Palms 
conservation area translates into a low magnitude of threat from urban 
development at this location. In contrast, because only about one-third 
of the flat-tailed horned lizard habitat at the Dos Palmas conservation 
area is currently in protected status, the potential magnitude of urban 
development at the latter location is

[[Page 14226]]

greater. However, because this area of habitat is farther away from 
existing urban areas, the immediacy of the threat of urban development 
is likely lower, even without the protections for flat-tailed horned 
lizard included in the Coachella Valley MSHCP plan (which requires the 
protection of the Dos Palmas conservation area). Therefore, the overall 
threat from urban development of flat-tailed horned lizard habitat in 
the Coachella Valley Population is low.
    Most of the area occupied by the U.S. portion of the Western 
Population of flat-tailed horned lizards is owned by the State of 
California (more than 27 percent) or by the Federal government (more 
than 52 percent), and the vast majority of the U.S. portion of the 
Eastern Population is federally owned (more than 95 percent). Much of 
the State of California land in the Western Population is administered 
by California State Parks, including Anza-Borrego Desert State Park and 
Ocotillo Wells State Vehicular Recreation Area. We do not expect any 
substantive urban development activities on State Park-administered 
lands. However, such development, should it occur, would likely follow 
the avoidance, minimization, and compensation measures of the Rangewide 
Management Strategy because California State Parks is a signatory 
agency to the Interagency Conservation Agreement.
    Additionally, much of the Federal land is administered by the BLM, 
which is a signatory to the Interagency Conservation Agreement. 
Moreover, the BLM has incorporated the Rangewide Management Strategy 
into the California Desert Conservation Area (CDCA) Plan under the 
Federal Land Policy and Management Act of 1976 (43 U.S.C. 1701 et seq.) 
(FLPMA). The CDCA Plan directs BLM's permitting of development projects 
on the lands the plan covers, including the U.S. portions of the 
Western and Eastern Populations. Thus, the avoidance, minimization, and 
compensation measures in the Rangewide Management Strategy are 
implemented by BLM on these lands, which reduces the impact such 
development to flat-tailed horned lizard habitat. Other federally owned 
lands in these areas are lands owned by the Navy, which is also a 
signatory to the Interagency Conservation Agreement. Not only do we 
anticipate that the Navy's participation in the Rangewide Management 
Strategy will continue, which will limit the amount of impact to flat-
tailed horned lizard habitat, but the Navy's use of these lands, 
largely as bombing ranges, will result in little urban development on 
these lands. As such, we expect the amount of impact from urban 
development on areas of flat-tailed horned lizard habitat owned by the 
State of California and the Federal government in the Western and 
Eastern Population to be small now and within the foreseeable future 
because little urban development is likely on State Park lands and most 
military lands, and what development that may occur on Federal lands 
will be minimized through implementation of the Rangewide Management 
Strategy, including through implementation of the CDCA Plan on BLM 
lands.
    Moreover, the designation of the Borrego Badlands, West Mesa, and 
Yuha Desert Management Areas offer protective mechanisms for 96,599 ha 
(238,700 ac) (Table 1) of flat-tailed horned lizard habitat within this 
population. Impacts from permittee actions are limited to 1 percent of 
the area within Management Areas (FTHLICC 2003a, p. 33). As described 
above, we expect minimal or no urban development on Federal and 
California State lands within the area occupied by the Western 
Population and Eastern Population, but urban development may occur 
within private lands. Although private inholdings are scattered 
throughout the Federal and State lands in the region, few 
concentrations of private land exist. The largest concentration of 
private inholdings within the areas occupied by the Western Population 
occurs in and around the community of Borrego Springs, California. 
Urban development in this area is limited to a finite area within the 
Borrego Springs area, which is an area of private lands completely 
surrounded by Anza-Borrego Desert State Park. Additionally, development 
in this area may be further restricted by a limitation in the amount of 
available groundwater (Mills 2009, p. 4). As we concluded in 2003 (68 
FR 342), even if urban development continues, this area is small enough 
that it is unlikely that the combined urban or agricultural development 
in or around this geographically limited area poses a significant 
threat to the flat-tailed horned lizard throughout its range. Moreover, 
limited water and isolation of the remaining private lands scattered 
within the public lands likely will prevent any large-scale urban 
development in the region, further reducing the effects that 
urbanization may have on the Western Population of the flat-tailed 
horned lizard. Because the Mexican portion of the Western Population is 
isolated from other inhabited areas by the Sierra de Los Cucapahs and 
the dry lakebed of Laguna Salada, we believe urban development in this 
area is likely similarly limited by available resources and isolation. 
Thus, we conclude that urban development is not a threat to the species 
in the Western Population, nor is it likely to become a threat in the 
foreseeable future.
    As discussed above, we expect impacts from urban development on 
Federal lands in the Eastern Population to be limited. Moreover, the 
designation of the East Mesa Management Area offers protective 
mechanisms for 45,248 ha (111,810 ac) (Table 1), or about 27 percent of 
the Eastern Population, of flat-tailed horned lizard habitat within 
this population. Impacts from permittee actions are limited to 1 
percent of the area within each Management Area (FTHLICC 2003a, p. 33). 
Additionally, 10,654 ha (26,327 ac), or about 6 percent of the Eastern 
Population, is designated as a Wilderness Area where urban development 
is prohibited. Most urban development occurs on private property, and 
less than 5 percent of the U.S. portion of the Eastern Population area 
occurs on private property. Limited water and isolation of the private 
lands likely prevent any substantive urban development in the region, 
including the small amount of habitat in Mexico. Thus, we conclude that 
urban development is not a threat to the species in the Eastern 
Population, nor is it likely to become a threat in the foreseeable 
future.
    Urban development has occurred recently in the Southeastern 
Population of flat-tailed horned lizards. Areas of recent urbanization 
include development near the communities of Yuma, Arizona (Piest and 
Knowles 2006, p. 1); San Luis R[iacute]o Colorado, Sonora, Mexico 
(Rodriguez 2002, p. 23); and Puerto Pe[ntilde]asco, Sonora, Mexico 
(Rodriguez 2002, p. 23). Most (about 84 percent) of the flat-tailed 
horned lizard habitat in Arizona is federally owned, where urban 
development is less likely, and most of the U.S. Federal land in the 
Southeastern Population is within the 53,014-ha (131,000-ac) Yuma 
Desert Management Area (Table 1), where impacts from permittee actions 
are limited to 1 percent of the area (FTHLICC 2003a, p. 26). 
Additionally, avoidance and minimization measures are in place within 
the Barry M. Goldwater Range, Arizona, to prevent or limit impact to 
the flat-tailed horned lizard and its habitat from military development 
(USFWS 1996, pp. 18 and 58). Nevertheless, development impacts may 
occur. For example, construction by Marine Corps Airs Station, Yuma, of 
a new aircraft landing field and associated infrastructure for the F-
35B

[[Page 14227]]

Joint Strike Fighter at the Barry M. Goldwater Range is expected to 
permanently remove 33.5 ha (82.7 ac) of flat-tailed horned lizard 
habitat, plus have additional long-term adverse effects on a 17.8 ha 
(44 ac) (USFWS 2010b, p. 46). Even so, this project includes 
minimization measures called for by Rangewide Management Strategy, 
thereby reducing the impact of this development to the species and its 
habitat (USFWS 2010b, pp. 10-12, 45). Thus, we conclude that urban 
development in Arizona is not a significant threat to the species, nor 
is it likely to become a threat in the foreseeable future.
    In Mexico, urban development is likely within the foreseeable 
future around San Luis R[iacute]o Colorado, Puerto Pe[ntilde]asco, and 
elsewhere along the Gulf of California coast. Despite an increase in 
accessibility to remote areas (B[uacute]rquez and Mart[iacute]nez-
Yr[iacute]zar 1997, p. 390), the vast majority of the habitat for the 
Southeastern Population in Mexico remains isolated with respect to 
urban development, because urban development requires access to other 
resources, which are not necessarily available with mere physical 
access. Moreover, compared to the 1,005,630 ha (2,484,966 ac) of flat-
tailed horned lizard habitat in the Mexican portion of the Southeastern 
Population, roughly 60 percent of which lies within two Mexican Federal 
natural protected areas where development is limited (CEDO 2001, p. 3), 
we expect the amount of urban development to be relatively small. Thus, 
we conclude that urban development is not a significant threat to the 
species in the Mexican portion of the Southeastern Population, nor is 
it likely to become a threat in the foreseeable future.
    Therefore, despite some urban development occurring in the 
Southeastern Population, we believe that this development is small 
relative to the overall amount of flat-tailed horned lizard habitat in 
the Southeastern Population and is unlikely to significantly increase 
in the foreseeable future; thus, this development does not pose a 
substantial threat to the species in the Southeastern Population, nor 
is it likely to become a threat in the foreseeable future.
    In conclusion, flat-tailed horned lizard habitat has been lost to 
urban development in the Coachella Valley, and we expect urbanization 
to continue there. The available information indicates the distribution 
of the species in the Coachella Valley is now limited to two 
occurrences that are within two Coachella Valley MSHCP conservation 
areas (CVCC 2010, p. 8); although nearly all of the flat-tailed horned 
lizard habitat in the Thousand Palms reserve is already protected, most 
of the Dos Palmas reserve is not (see Table 2). Implementation of the 
Coachella Valley MSHCP is expected to limit the impacts to the flat-
tailed horned lizard and its habitat (USFWS 2008, Appendix A, p. 317). 
Furthermore, in our evaluation of the potential impacts of the plan's 
implementation on the flat-tailed horned lizard (USFWS 2008, p. 178), 
we concluded: ``After reviewing the current status of this species, 
environmental baseline for the action area, effects of the proposed 
action, and cumulative effects, it is the Service's biological opinion 
that the action, as proposed, is not likely to jeopardize the continued 
existence of the flat-tailed horned lizard. Loss of the Coachella 
Valley population would have a negligible [effect] on the status of the 
species as a whole, since it makes up approximately 1 percent of the 
current range of the flat-tailed horned lizard. Persistence of the 
species in the Plan area is likely only with effective Plan 
implementation.'' Because of the limited amount of private land, urban 
development is also only likely to destroy relatively small amounts of 
flat-tailed horned lizard habitat in the Western, Southeastern, and 
Eastern Populations. Additionally, in areas of flat-tailed horned 
lizard habitat in the United States and Mexico where urbanization has 
the potential to occur, it is likely that the amount of urban 
development will be limited by the availability of water and the 
isolated nature of many of these areas. The implementation of the 
Rangewide Management Strategy further restricts development in the 
United States, limiting impacts inside designated flat-tailed horned 
lizard Management Areas to 1 percent of the area. In Mexico, urban 
development is likely to be limited within the Federal natural 
protected areas (Rodriguez 2002, p. 25). Therefore, we conclude that 
urban development is not a significant threat to flat-tailed horned 
lizard habitat throughout its range, nor is it anticipated to become a 
significant threat in the foreseeable future.

Energy Generation Facility Development

    The analyses in the 1993 proposed rule and 2003 withdrawal document 
both identified development of geothermal energy facilities as a 
potential threat to flat-tailed horned lizard habitat. Since then, 
increased interest in renewable forms of electrical generation has 
resulted in a greater number of proposed energy development facilities 
and their associated infrastructure. Recent proposals not only include 
geothermal facilities, but also projects harnessing solar radiation and 
wind. Examples of recent proposals that may affect flat-tailed horned 
lizard habitat include the following: geothermal projects near the 
Superstition Mountains (Navy 2008, pp. 1-40) and the Truckhaven area 
west of Salton City (BLM 2007a, pp. 1-3), solar projects near Plaster 
City (BLM and CEC 2010, p. ES-1), and a wind project west of the 
community of Ocotillo (Ocotillo Express 2009, p. 1). Because the 
development of energy generation facilities occurs within the range of 
the flat-tailed horned lizard habitat, we assess the magnitude of this 
development to the species below.
    Similar to other forms of development, energy generation projects 
may result in destruction or modification of flat-tailed horned lizard 
habitat. These projects can include buildings, roads, power lines, and 
pipelines, although they differ in the details. For example, geothermal 
plants typically include wells and pipelines (often aboveground), solar 
plants typically include solar collecting arrays (using various 
technologies to convert solar energy to electrical energy), and wind 
farms have lines or arrays of wind turbines.
    The total acreage of potential development for renewable energy 
facilities is small compared to the overall range of the species. For 
example, in California, the BLM maintains a GIS database of rights-of-
way applications for energy generation facilities. Additional permits 
are needed before the potential facilities listed in the database can 
be built, and even if they obtain all of the necessary permits, it is 
not guaranteed that all of them will be built. Moreover, some of these 
right-of-way applications have been rejected, denied, or withdrawn. 
However, assuming that the facilities in the BLM database are built, 
the total area of development on BLM land for all of the applications 
on file as of December 2010 would be about 2,585 ha (6,387 ac) in the 
Eastern Population, and 18,841 ha (46,556 ac) in the Western 
Population. The BLM data only include areas of BLM (Federal) land and 
do not include what, if any, nearby private land that may also be 
developed as part of these energy projects. We do not have data for the 
potential impacts to private lands adjacent to these areas, but we made 
a rough assessment of the adjacent private land that may potentially be 
included in these projects which may add about 260 ha (about 640 ac) to 
the impacts in the Eastern Population and about 10,600 ha (about 26,000 
ac) to the impacts in the Western Population. Using these values,

[[Page 14228]]

the energy development in the Eastern Population may impact roughly 
2,845 ha (7,030 ac) of BLM and private lands, which is about 1.7 
percent of the Eastern Population area, and the energy development in 
the Western Population may impact roughly 29,441 ha (72,750 ac) of BLM 
and private lands, which is about 8.6 percent of the Western Population 
area. Combined, these projects--assuming that they are all built, which 
is not likely--would impact a total of about 2 percent of the nearly 
1.6 million ha (3.9 million ac) of the total range of the species 
(using 2003 ``current distribution'').
    Although we expect additional energy development facilities may be 
constructed elsewhere within the range of the species, including in 
Arizona and Mexico, we are not aware of any specific proposals that are 
as large as those proposed in California. Therefore, we conclude that 
the total acreage of potential development for renewable energy 
facilities is small compared to the overall range of the species. 
Additionally, on lands managed by signatory agencies to the Interagency 
Conservation Agreement, we expect the impacts to flat-tailed horned 
lizard habitat (whether inside or outside of designated Management 
Areas) will be further reduced because of the avoidance, minimization, 
and compensation measures of the Rangewide Management Strategy.
    Moreover, because of the avoidance and minimization measures, 
including the 1-percent impact limit in flat-tailed horned lizard 
Management Areas, most of the energy generation facilities have been 
proposed outside of the Management Areas, although some impacts to 
Management Areas are anticipated resulting from related infrastructure 
development (FTHLICC/MOG 2010, p. 2). For example, the 2,454-ha (6,063-
ac) Imperial Valley Solar project site is proposed outside of the flat-
tailed horned lizard Management Areas called for by the Rangewide 
Management Strategy, but an associated transmission line is expected to 
run for about 12 kilometers (km) (7.5 miles (mi)) within the Yuha 
Desert Management Area. However, this proposed transmission line was 
routed along an existing powerline corridor to minimize effects to 
flat-tailed horned lizard habitat in the Management Area (BLM and CEC 
2010, pp. B.1-18, C.2-9, and C.2-42).
    While project sites may be proposed within flat-tailed horned 
lizard Management Areas, the Rangewide Management Strategy limits the 
total acreage of impacts for a given Management Area to no more than 1 
percent. As of 2009, signatory agencies control approximately 196,273 
ha (485,000 ac) of flat-tailed horned lizard habitat in the designated 
Management Areas and have collectively permitted activities on 171.57 
ha (423.97 ac), or 0.09 percent (Table 1). Thus far, signatory agencies 
have consistently implemented the Rangewide Management Strategy, even 
in permitting development electrical generation facilities. Moreover, 
the implementation of the Rangewide Management Strategy is not 
completely voluntary at this point; aspects of the Rangewide Management 
Strategy have been incorporated into documents that implement 
regulatory mechanisms, including the Federal Land Policy and Management 
Act (43 U.S.C.1701 et seq.) (FLPMA), which affects development on BLM 
lands (see Factor D). Many of the anticipated energy development 
facilities are on BLM lands or otherwise would require easements or 
access across BLM lands; thus, the development of these energy 
generation facilities would be subject to the provisions of the 
Rangewide Management Strategy through implementation of FLPMA.
    In sum, the overall acreage of potential impacts from development 
of energy facilities is likely to be small compared to the total range 
of the species, including private lands likely to be developed. 
Moreover, because of the prevalence of Federal and State lands in the 
U.S. portions of the range of the flat-tailed horned lizard and because 
most of this land is managed by signatories to the Interagency 
Conservation Agreement implementing the Rangewide Management Strategy, 
we expect that the vast majority of proposed energy development 
projects that are likely to affect flat-tailed horned lizard habitat in 
the United States will be subject to the avoidance, minimization, and 
compensation measures incorporated into the Rangewide Management 
Strategy, including in areas outside of designated Management Areas. 
The signatories to the Interagency Conservation Agreement have been 
actively implementing the Rangewide Management Strategy since its 
inception, and have committed to its continued implementation. 
Additionally, the Rangewide Management Strategy has been incorporated 
into the CDCA Plan, which means it will be implemented as a regulatory 
mechanism (as opposed to a voluntary agreement). Although the Rangewide 
Management Strategy is not in effect in Mexico, the amount of habitat 
that is likely to be destroyed by energy development projects in that 
country is likely to be small relative to the total amount of habitat. 
Therefore, we anticipate the development of energy generation 
facilities does not now nor in the foreseeable future pose a 
significant threat to flat-tailed horned lizard and its habitat.
Invasive, Nonnative Plants
    In our 2003 withdrawal document, we included the effects of 
invasive, nonnative plants as a potential threat to flat-tailed horned 
lizard habitat (68 FR 345). However, we concluded that nonnative plants 
did not pose a substantial threat because of the limited extent to 
which such plants had established themselves in flat-tailed horned 
lizard habitat (68 FR 345). The available literature also suggests 
invasive, nonnative plants are a potential threat to flat-tailed horned 
lizard habitat (such as Hodges 1997, pp. 4, 5, and 9; CEDO 2001, p. 2; 
FTHLICC 2003a, pp. 18-19; Hammerson et al. 2007, p. 4), but specifics 
on how nonnative species are impacting flat-tailed horned lizard 
habitat are generally lacking.
    The perennial nonnative tree, Tamarix aphylla (athel pine), has 
been planted as a windbreak in the Coachella Valley. This tree can 
reduce or prevent wind-transport of sand, thereby reducing available 
flat-tailed horned lizard habitat there (England 1983, p. 152). 
Although T. aphylla typically spreads vegetatively by adventitious 
roots or submerged stems, the species can spread sexually by seed 
following flood events (Walker et al. 2006, pp. 191-201). While perhaps 
not as invasive as other species of Tamarix (Cal-IPC 2003, p. 4), T. 
aphylla trees have been removed in some Coachella Valley MSHCP reserve 
areas in the Coachella Valley as management to improve habitat (FTHLICC 
1999, p. 4). Moreover, the population of flat-tailed horned lizards in 
the Coachella Valley proper is now found only in the Thousand Palms 
reserve area (CVCC 2010, p. 8), where the plan's habitat management is 
focused. Therefore, we do not consider T. aphylla to be an invasive, 
nonnative species that is threatening flat-tailed horned lizard 
habitat.
    Nonnative annual plants, such as Brassica tournefortii (Saharan 
mustard), Schismus barbatus (common Mediterranean grass), and Salsola 
kali (Russian thistle), can blanket certain areas of the Colorado 
Desert in years with higher amounts of rainfall (Brown and Minnich 
1986, pp. 411-422; Lovich and Bainbridge 1999, p. 318; FTHLICC 2003a, 
p. 18; Yurkowsky 2005, in litt., Anza-Borrego Desert State Park; 
Barrows

[[Page 14229]]

et al. 2009, pp. 673-686). Such nonnative plants may adversely affect 
flat-tailed horned lizard habitat throughout its range by altering fire 
regimes (Brown and Minnich 1986, pp. 418-421; Brooks and Esque 2002, 
pp. 334-336); stabilizing Aeolian soils (i.e., soil that is transported 
from one place to another by wind; Barrows et al. 2009, p. 684); 
changing plant assemblages (Barrows et al. 2009, p. 683); and changing 
the availability of seeds for harvester ants, the primary food source 
for the flat-tailed horned lizard (Gordon 1980, p. 70). Dense stands of 
plants, which are typical of invasive, nonnative plant species in years 
of higher amounts of rainfall, also may challenge the locomotor 
abilities of the wide-bodied flat-tailed horned lizard (Newbold 2005, 
p. 17).
    Plant growth will vary annually in the Colorado Desert because of 
the variable amount and timing of rainfall that the region receives. 
Moreover, annual plants die by the end of spring, and in the harsh 
desert climate the amount of standing biomass of the annual plants, 
once dead, quickly decreases (Barrows et al. 2009, p. 684). We expect 
the amount and timing of rainfall within the range of the species will 
continue to be variable into the foreseeable future, even with the 
potential effects of climate change (Field et al. 1999, pp. 8-10). As a 
result, the effects of invasive, nonnative plants are generally short-
lived in areas of flat-tailed horned lizard habitat (Barrows et al. 
2009, p. 673), and because of the likelihood of continued variability 
in precipitation, we expect the potential effects of invasive, 
nonnative plants to continue to be short-lived into the foreseeable 
future. With the potential exception of increased occurrence of 
wildland fires, we do not believe that the growth of invasive, 
nonnative plants poses a lasting, significant threat to flat-tailed 
horned lizard habitat now or in the foreseeable future. We examine the 
potential threat of wildland fire below.
    Fires typically are rare events in the western Sonoran Desert 
because of the natural ``limited biomass, wide spacing between shrubs 
and sparse ground cover'' (Brown and Minnich 1986, p. 411). However, 
the periodic increase in the amount of available fuel from nonnative, 
annual plants in years of heavy precipitation has allowed the 
frequency, size, and intensity of fires in desert plant communities to 
increase (Brown and Minnich 1986, p. 411; Brooks and Berry 2006, pp. 
117-118; Trader et al. 2006, p. 314; see also Rorabaugh 2010, p. 191). 
Moreover, many of the native perennial plants within the range of the 
flat-tailed horned lizard typically take a long time to recover after a 
fire (O'Leary and Minnich 1981, pp. 61-66; Brown and Minnich 1986, p. 
411; Brooks and Esque 2002, p. 330). Thus, fire can change the species 
composition of the perennial and annual plant communities. Moreover, 
provided enough water (rainfall) is available, annual plants, 
especially nonnative species, proliferate after a fire (Minnich 1994, 
p. 104), which may provide additional fuel and promote additional 
wildfires. Plant communities in areas with recurrent fires may convert 
from vegetation types dominated by native shrubs into types dominated 
by nonnative annual grasses and forbs (type conversion) (Brown and 
Minnich 1986, p. 411). Type conversion appears to be occurring near the 
highly urbanized areas, such as the Coachella Valley (Brown and Minnich 
1986, p. 411), where increased human activity offers higher numbers of 
ignition sources (Brooks and Esque 2002, p. 337), but not in the more 
remote areas of flat-tailed horned lizard habitat. Moreover, the amount 
of rainfall is a critical factor in how much plant growth occurs 
(Barrows et al. 2009, p. 673). The amount of rainfall is unpredictable 
within the range of the flat-tailed horned lizard, and is likely to be 
so for the foreseeable future. It is not clear how the fire regime will 
be affected long term, but in the foreseeable future, wildland fire 
does not appear to be a threat.
    Additionally, it is unclear whether this localized change in 
vegetation affects the specific habitat components upon which flat-
tailed horned lizards rely. For example, flat-tailed horned lizards 
take refuge under perennial shrubs for shade and to avoid predators 
(Muth and Fisher 1992, pp. 1-77; Sherbrooke 2002, pp. 109-120). Fire 
typically kills the existing desert shrubs, but shrubs do regrow after 
a fire, although the plant species composition is likely to have 
changed (Brown and Minnich 1986, pp. 411). Thus, during the period of 
time following fire while shrubs are regrowing, flat-tailed horned 
lizards will have fewer options for thermoregulation and predator 
avoidance. While this condition is not permanent, it remains unclear if 
the change in plant species composition will have a lasting effect on 
the flat-tailed horned lizard, especially if type conversion were to 
occur. Nonetheless, because this change in plant species composition is 
localized, we conclude any potential effects are low in magnitude at 
the species level, likely temporary, and thus not a significant threat 
to the species.
    Another potential threat to the flat-tailed horned lizard that may 
arise from a change in plant species composition after a fire is that 
harvester ants, the primary food of the flat-tailed horned lizard, 
could be affected. Fire likely kills individual harvester ants on the 
surface at the time of the fire, but evidence suggests the underground 
colonies survive (Zimmer and Parmenter 1998, p. 282; Underwood and 
Christian 2009, p. 325). As described in the Background section, 
harvester ants eat seeds of annual and perennial plant species. 
Although changes in plant composition may alter the type and quantities 
of available seeds consumed by ants, ant forage likely will not be 
eliminated, and may even increase because of the increase in annual 
plants (Zimmer and Parmenter 1998, p. 282; Underwood and Christian 
2009, p. 325). For example, several of the species found by Gordon 
(1980, p. 72) to be important to harvester ants were also species of 
plants found by Brown and Minnich (1986, p. 416) to do well after a 
fire. Therefore, wildland fire does not appear to pose a threat to 
harvester ants.
    In conclusion, the spread of invasive, nonnative plants does not 
appear to be a significant threat to flat-tailed horned lizard habitat 
throughout its range at this time, nor is it likely to become a 
significant threat in the foreseeable future.
Off-Highway Vehicles (OHVs)
    The analyses in the 1993 proposed rule and 2003 withdrawal document 
included OHV activity as a potential threat to the flat-tailed horned 
lizard. The Rangewide Management Strategy also describes off-highway 
(OHV) or off-road vehicle activity as a potential threat (FTHLICC 
2003a, pp. 12-14). We consider OHVs to be all vehicles used off-road, 
including, but not limited to, automobiles, dune buggies, motorcycles, 
all-terrain-cycles, four-wheelers, and military vehicles. OHV activity 
includes, but is not limited to, recreational, military, law-
enforcement (such as Border Patrol), and trans-border trafficking 
activities. As discussed in the Background section, flat-tailed horned 
lizard habitat typically consists of sandy flats and valleys occupied 
by plant species that are typical of the creosote-white bursage plant 
association. The presence of ants as a food source is also important.
    OHV activity may modify flat-tailed horned lizard habitat because 
of impacts to vegetation (Luckenbach 1975, p. 4; Vollmer et al. 1976, 
p. 115; Bury et al. 1977, p. 7; Lathrop 1983, p. 164; Luckenbach and 
Bury 1983, p. 280; Groom et al. 2007, p. 133), soil

[[Page 14230]]

disturbance (Luckenbach 1975, p. 4;, Bury et al. 1977, pp. 16-18;, Webb 
1983, pp. 51-79), and introduction of nonnative plants (Brooks and Lair 
2005, p. 8). Additionally, some but not all areas with high OHV 
activity have been shown to have fewer harvester ant colonies (McGrann 
et al. 2006, p. 77).
    Past studies of OHV impacts on lizards (Busack and Bury 1974, p. 
182; Bury et al. 1977, p. 10; Luckenbach and Bury 1983, p. 273; Klinger 
et al. 1990, pp. 1-17; Beauchamp et al. 1998, p. 214; Gardner 2002, p. 
14; Wright and Grant 2003, p. 30) have been largely inconclusive or 
cannot be readily applied across the range of the flat-tailed horned 
lizard (that is, they have limited ``inference space'' (Ratti and 
Garton 1994, pp. 1-23)). Luckenbach and Bury (1983, p. 278) reported 
that a pronounced reduction in flat-tailed horned lizard abundance 
around the Algodones Dunes had been anecdotally noted by scientists. 
Marked declines in herbaceous and perennial plants, arthropods, 
lizards, and mammals in OHV-used areas compared with nearby control 
areas were also reported by Luckenbach and Bury (1983, p. 265). The 
declines, however, were for the Colorado Desert fringe-toed lizard (Uma 
notata) and beetles, and did not include flat-tailed horned lizards or 
ants. Additionally, research has been conducted in creosote-dominated 
habitats in the Mojave Desert. Researchers compared reptile metrics 
(measures) between sites used differentially by OHVs and control sites 
(Bury et al. 1977, pp. 1-23). Bury et al. (1977, p. 11) found a 
significant decrease in numbers of reptiles on OHV-used areas compared 
to numbers on control sites in the Mojave Desert. However, the highest 
number of desert horned lizards on any one plot occurred on a 
moderately used OHV site (Bury et al. 1977, p. 10). In research 
conducted by both Busack and Bury (1974, p. 182) and Bury et al. (1977, 
p. 1), there appeared to be an inverse relationship between increased 
use of OHVs and the abundance of lizards; this means that, as OHV use 
increased, lizard abundance decreased. Additionally, McGrann et al. 
(2006, pp. 77-79) found that the density of flat-tailed horned lizards 
was lower in areas of high OHV activity, as was the average body mass 
of individual flat-tailed horned lizards, suggesting the habitat 
quality--including harvester ant abundance--in some high-use OHV areas 
was not as good; however, the authors also noted that small sample size 
may have allowed qualitative differences between sites sampled to 
affect their results.
    Research in the Ocotillo Wells SVRA found flat-tailed horned 
lizards at higher densities in non-sandy habitats than sandy habitats 
within the SVRA, which differed from most other research findings 
(Beauchamp et al. 1998, pp. 213-214). However, it was unclear if flat-
tailed horned lizards were found in these atypical habitat types 
because they are more variable in habitat use than previously thought, 
because these habitat types are more available in the Ocotillo Wells 
SVRA than other areas in which flat-tailed horned lizards have been 
studied, or as a response to OHV activity (Beauchamp et al. 1998, p. 
214).
    OHV activity occurs in the Western, Eastern, and Southeastern 
Populations, but the amount (intensity, frequency) of OHV activity 
varies across the landscape, with greater amounts of activity in areas 
designated for OHV use and areas near existing roads, and lesser 
amounts in areas where OHV use is not permitted or areas that are away 
from easy access. In the Coachella Valley, OHV activity is expected to 
be controlled in protected habitat areas through implementation of the 
Coachella Valley MSHCP (CVAG 2007, pp. 9-117) and OHV activity is not 
identified as a conservation issue in the annual report for 2009 (CVCC 
2010, p. 14). In our evaluation of the potential impacts of the plan's 
implementation on the flat-tailed horned lizard (USFWS 2008, p. 178), 
we concluded: ``After reviewing the current status of this species, 
environmental baseline for the action area, effects of the proposed 
action, and cumulative effects, it is the Service's biological opinion 
that the action, as proposed, is not likely to jeopardize the continued 
existence of the flat-tailed horned lizard. Loss of the Coachella 
Valley population would have a negligible [effect] on the status of the 
species as a whole, since it makes up approximately 1 percent of the 
current range of the flat-tailed horned lizard. Persistence of the 
species in the Plan area is likely only with effective Plan 
implementation.'' Additionally, approximately 94 percent of the 
potential habitat where flat-tailed horned lizards are known to occur 
in the Thousand Palms conservation area is land that is already 
protected (Table 2), including about 62 percent that is part of the 
Coachella Valley National Wildlife Refuge.
    OHV activity along the United States-Mexico international boundary 
(border) was identified as a potential threat to the flat-tailed horned 
lizard and its habitat (FTHLICC 2003a, p. 12). The amount of impact to 
flat-tailed horned lizard habitat along the border is not clear. To put 
the potential impact in context of the range of the species, we assumed 
an area of high impact from border-related OHV activity to be within a 
1-km (0.6-mi)-wide zone north of the border. We estimate that the total 
area of flat-tailed horned lizard habitat within that ``zone'' is about 
12,662 ha (31,288 ac), or about 0.8 percent of the range of the 
species, comprising 2,318 ha (5,728 ac), 5,012 ha (12,385 ac), and 
5,332 ha (13,176 ac) of the Western, Eastern, and Southeastern 
Populations, or about 0.7 percent, 3 percent, and 0.5 percent of those 
populations, respectively. This zone of assumed high activity is a 
broad-brush assessment (for example, the All-American Canal runs along 
the border in the Eastern Population, likely confining any border-
related OHV activities in certain areas to less than 1 km (0.6 mi)). 
Nevertheless, the zone is small compared to the range of the species 
and the three populations, individually. Moreover, since 2008, the U.S. 
Customs and Border Protection constructed the ``border fence,'' which 
is a vehicle and, in some areas, pedestrian barrier, plus associated 
infrastructure, in certain areas between the United States and Mexico. 
Although some areas of the border are not fenced, the areas of flat-
tailed horned lizard habitat along the border are fenced (USCBP 2008a, 
p. 1-5; USCBP 2008b, p. 2-4; Rorabaugh 2010, p. 181). Prior to 
construction of the border fence, the new fence and associated 
infrastructure was anticipated to result in reduction of the amount of 
illegal, cross-border traffic (USCBP 2008b, p. 3-18). Additionally, as 
part of the installation of the border fence, a stabilized patrol road 
on the U.S. side was constructed. The use of the road was also expected 
to result in an overall decrease in ground disturbance because Border 
Patrol agents would patrol from vehicles on the road rather than 
through OHV activity (USCBP 2008a, p. 2-7). Indeed, evidence suggests 
the border fence has reduced illegal cross-border traffic and 
associated OHV activity (Rorabaugh 2010, p. 190), thereby reducing the 
amount of potential impact to flat-tailed horned lizard habitat along 
the border from illegal trans-border OHV activity and subsequent law-
enforcement OHV activity by the Border Patrol.
    Moreover, the scientific literature is mixed and inconclusive with 
respect to the impact of OHV activity on the flat-tailed horned lizard 
and its habitat. Setser and Young (2000, p. 11) and Setser (2001, p. 
12) found flat-tailed horned lizards avoided areas disturbed by OHVs. 
However, there was no difference in flat-tailed horned lizard habitat 
use between areas within 10 m

[[Page 14231]]

(33 ft) of OHV trails and sites farther away from OHV trails (Setser 
and Young 2000, p. 11; Setser 2001, p. 12). Setser and Young (2000, p. 
11) and Setser (2001, p. 12) concluded that: (1) OHV use might render 
sites less suitable to flat-tailed horned lizard use, because of the 
impacts of OHV activity on vegetation and soil characteristics; or (2) 
OHV trails occur on sites not preferred by flat-tailed horned lizards 
(e.g., barren ground with no plants or rocks). However, Gardner (2002) 
and Setser (2004, p. 54) suggested that OHV activity did not have an 
effect on flat-tailed horned lizards at different areas in the Ocotillo 
Wells SVRA, on the basis of observations.
    In summary, while there has been some research on the adverse 
effects of OHV activity on vegetation, soils, and flat-tailed horned 
lizards, its applicability to flat-tailed horned lizard populations is 
limited and unreliable because of the lack of scientific rigor 
associated with the research designs. Additionally, the effects of OHV 
activity on flat-tailed horned lizard populations were not the primary 
research questions. Nevertheless, these studies have utility in 
generating hypotheses concerning variation in degree of OHV use and 
flat-tailed horned lizard abundance. At this time, we conclude that the 
available studies do not collectively show that OHV activity causes 
declines in flat-tailed horned lizard populations throughout the range 
of the species or that adverse OHV impacts pose a significant threat to 
flat-tailed horned lizard habitat. Management activities, including 
efforts to reduce conflicts with actions that impact flat-tailed horned 
lizard habitats, would be enhanced by focused research. Impacts of OHV 
activity on flat-tailed horned lizard populations should be studied 
using rigorous research designs to yield conclusions with high degrees 
of certainty (Ratti and Garton 1994, pp. 1-23) regarding the effects of 
OHV activity on flat-tailed horned lizard populations across the range 
of the species. In conclusion, OHV activity does not appear to be a 
significant threat to flat-tailed horned lizard habitat throughout its 
range at this time, nor is it likely to become a significant threat in 
the foreseeable future.
Military Training Activities
    The Rangewide Management Strategy (FTHLICC 2003a, p.15) summarizes 
military activity within the range of the flat-tailed horned lizard. 
The species occurs on two military installations: (1) The western Barry 
M. Goldwater Range, administered by Marine Corps Air Station (MCAS) 
Yuma, and (2) Naval Air Facility (NAF) El Centro. MCAS Yuma manages 
approximately 46,458 ha (114,800 ac) within the 53,014-ha (131,000-ac) 
Yuma Desert Management Area, while NAF El Centro manages approximately 
12,060 ha (29,800 ac) within the 55,078-ha (136,100-ac) West Mesa 
Management Area and 3,440 ha (8,500 ac) in the 46,660-ha (115,300-ac) 
East Mesa Management Area. The U.S. Marine Corps and U.S. Navy are 
signatories to the Interagency Conservation Agreement implementing the 
Rangewide Management Strategy.
    The training ranges are primarily used for aircraft-related 
training. Activities that have the potential to impact flat-tailed 
horned lizard habitat include non-exploding bombing practice, ground-
based training, target maintenance, clean up of target sites, road 
maintenance, mobile target activity, and target and run-in-line 
grading. Most military activities are confined to previously disturbed 
areas, so the amount of destruction or modification of flat-tailed 
horned lizard habitat is limited (FTHLICC 2003a, p.15). Additionally, 
the military is committed to be good stewards of lands they control, 
and the two installations have incorporated measures to benefit the 
flat-tailed horned lizard and other wildlife resources into their 
planning, training, and management activities (Navy 2001, chapter 3; 
USAF and USMC 2007, p. 1-8 and chapter 5). Therefore, we do not 
anticipate military training activities to substantially affect flat-
tailed horned lizard habitat now or in the foreseeable future.
Summary of Factor A Threats
    Flat-tailed horned lizard habitat could potentially be impacted by 
urban or agricultural development. However, due to the remote location 
and increasingly limited availability of water, urbanization and 
agricultural conversion of flat-tailed horned lizard habitat will 
likely be limited in the United States and Mexico over the foreseeable 
future. We note that development of energy facilities is increasing, 
especially in the southwestern United States; however, the overall 
acreage of impact from these projects, assuming all of the proposed 
right-of-way applications are constructed, is small compared to the 
range of the species. In the United States, we expect development 
impacts to occur outside of the existing Management Areas due to 
avoidance and minimization measures that result from implementation of 
the Rangewide Management Strategy. As of 2009, signatory agencies 
control approximately 185,653 ha (458,757 ac), or about 40 percent of 
flat-tailed horned lizard habitat in the United States, within the 
Management Areas, of which only 0.09 percent has been permitted for 
impacts. Furthermore, in the United States, most of the species' 
habitat is federally or State (such as California State Park) owned, 
where impacts to habitat from development are anticipated to be 
minimal. In Mexico, the amount of development that may occur in flat-
tailed horned lizard habitat is small relative to the large amount of 
habitat that is available, and thus the effects to the species are 
expected to be low in magnitude. Therefore, current or anticipated 
future urban, agricultural, or energy development throughout the 
species' range is not currently a substantial threat to the flat-tailed 
horned lizard, nor do we expect it to become a substantial threat in 
the foreseeable future.
    Invasive, nonnative plants could increase the potential for 
wildland fire in a desert environment where wildland fire is naturally 
infrequent. Research suggests that invasive, nonnative plant conversion 
of flat-tailed horned lizard habitat is limited to urbanized and 
adjacent areas, and is not a substantive threat to the species' habitat 
throughout its range. Also, frequent OHV activity has the potential to 
affect flat-tailed horned lizard habitat; however, the available 
studies do not collectively show that OHV activity causes declines in 
flat-tailed horned lizard populations throughout the range of the 
species or that adverse OHV impacts pose a significant threat to flat-
tailed horned lizard habitat. Lastly, military training activities have 
limited impacts on the ground and are not expected to substantially 
affect flat-tailed horned lizard habitat. We do not consider the 
potential threats analyzed above to be substantial threats to the flat-
tailed horned lizard, either individually or in combination. Therefore, 
based on our review of the best available scientific and commercial 
information, we find the flat-tailed horned lizard is not threatened by 
the present or threatened destruction, modification, or curtailment of 
its habitat or range, either now or in the foreseeable future.

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

    Within the context of this listing factor, overutilization is the 
capture or collection of individuals of a species to an extent (at a 
high enough rate) to affect the status of the species. Historically, in 
the United States, flat-tailed horned lizards may have been among the 
species of horned lizard

[[Page 14232]]

collected for the curio trade (Bolster and Nicol 1989, pp. 2 and 7). 
Flat-tailed horned lizard were identified by Stewart (1971, p. 33) as 
utilized in the pet trade. This species was also collected for 
scientific and educational purposes (Bolster and Nicol 1989, p. 9). 
However, the collection of the flat-tailed horned lizard is now 
prohibited except by permit in California (California Administrative 
Code 40.10, Title 14) and Arizona (Arizona Game and Fish Regulation, 
Title 17, R12-4-443, Commission Order 43). The flat-tailed horned 
lizard is also listed in the Official Mexican Norm NOM-059-ECOL-2001, 
Mexico's threatened species law, as a threatened species in Mexico 
(SEMARNAT 2002, p. 134), and collection is prohibited without a permit. 
Because of the difficulty in locating these cryptically colored 
lizards, we expect unauthorized recreational collection to be rare. In 
Mexico, Hammerson et al. (2007, p. 5) noted that the species may be 
utilized in the pet trade. As noted in Rodriguez (2002, p. 26), some 
people in Mexico have flat-tailed horned lizards in their yards, but it 
is unclear whether those lizards are prevented from moving out. We have 
no information on the magnitude of the pet trade, but horned lizards in 
general are known to be difficult to keep alive as captive pets 
(Stewart 1971, p. 34), including in Mexico (Rodriguez 2002, p. 26). 
This suggests that the pet trade is small. The information we have, 
although limited, does not suggest that the amount of utilization that 
has occurred recently, regardless of purpose, has significantly 
affected the status of the flat-tailed horned lizard. Therefore, based 
on our review of the best scientific and commercial information, we 
find that overutilization for any purpose is not a threat to the flat-
tailed horned lizard, now or in the foreseeable future.

C. Disease or Predation

    Disease occurs to some extent in nearly all wildlife populations, 
but it is only a threat if the disease is virulent to the extent that 
it significantly impacts the population. We are not aware of any 
reports of disease in flat-tailed horned lizards. Thus, we do not 
consider disease to be a threat to the flat-tailed horned lizard 
anywhere within its range, nor is there any evidence to suggest it is 
likely to become a threat in the foreseeable future.
    Predation occurs naturally, and nearly all populations of wildlife 
species are subject to some level of predation. Predation of flat-
tailed horned lizards is known to occur. For example, 16 of 42 radio-
tagged flat-tailed horned lizards were depredated in a 2-year study 
(Muth and Fisher 1992, p. 33), although the rate of predation they 
observed may have been affected by the presence of the radio tags 
themselves by making the otherwise cryptically colored lizard more 
apparent to predators. For predation to be a significant threat to the 
flat-tailed horned lizard, predation rates must be high enough to 
affect the status of the species such that mortality from predation 
outpaces births resulting in an overall population decline. Predation 
has been identified as a potential threat to the flat-tailed horned 
lizard (FTHLICC 2003a, pp. 16-17). A summary from multiple sources in 
the scientific literature is presented in the Rangewide Management 
Strategy (FTHLICC 2003a, p. 16), which identifies known or likely 
predators to be six species of birds, five species of reptiles, two 
species of mammals, and one arthropod. Of these, the round-tailed 
ground squirrel (Spermophilus tereticaudus) and the loggerhead shrike 
(Lanius ludovicianus) were highlighted as major predators (FTHLICC 
2003a, p. 16; see also Young and Young 2000, p. 60; Young et al. 2004a, 
p. 65). Most of these predators occur naturally (including 
historically) in areas occupied by flat-tailed horned lizards; thus, 
predation is not a threat that has emerged recently.
    However, information from the scientific literature suggests that 
the populations of some of these predators are now higher as a result 
of manmade changes to the landscape, resulting in increased predation 
of flat-tailed horned lizards in these areas (FTHLICC 2003a, pp. 16-17; 
Young and Young 2005, p. 8). For example, Barrows et al. (2006, pp. 
492-493) found evidence suggesting that loggerhead shrikes and other 
avian predators were responsible for reduced populations of flat-tailed 
horned lizards near wildland-urban interface, and Young and Young 
(2005, p. 8) suspected round-tailed ground squirrel populations are 
similarly augmented with manmade changes to landscape, resulting in 
similar declines in flat-tailed horned lizard populations in and around 
urban areas. Additionally, the cryptic coloration that allows flat-
tailed horned lizards to blend in with desert soils may be of little 
use on paved roads, allowing increased levels of predation (Young and 
Young 2000, p. 62). However, much of the range of the flat-tailed 
horned lizard is remote, away from areas of manmade change. Thus, for 
the flat-tailed horned lizard, predation does not appear to be 
excessively high throughout its range but instead localized near 
developed areas. This suggests that the observed high level of 
predation of flat-tailed horned lizards is an ``edge effect'' 
associated with the interface between natural areas and areas of urban 
and agricultural development. Because the proportion of developed areas 
within the range of the species is small in comparison to the 
undeveloped areas, we do not consider increased predation associated 
with urbanization to be a significant threat to the species. We further 
consider predation as a secondary effect of development, which is 
discussed under Factor E, below.
Summary of Factor C Threats
    Disease does not appear to be a threat at this time, nor is it 
likely to become a significant threat in the foreseeable future. 
Predation likely occurs in some human-altered areas at higher than 
typical rates; however, compared to the distribution of the species, 
relatively few flat-tailed horned lizards are likely subjected to 
increased predation. Therefore based on our review of the best 
scientific and commercial information, we find the flat-tailed horned 
lizard is not threatened by disease or predation, now or in the 
foreseeable future.

D. The Inadequacy of Existing Regulatory Mechanisms

    In the 1993 proposed rule to list the species, we identified 
several State (Arizona and California), U.S. Federal, and Mexican 
Federal laws and other existing regulatory mechanisms that could 
provide benefits to the flat-tailed horned lizard (58 FR 62627), and we 
concluded that these regulatory mechanisms were inadequate to protect 
the species or its habitat (58 FR 62628). In 1997, we also noted 
several State (Arizona and California), U.S. Federal, and Mexican 
Federal laws, but particularly noted the benefits provided to the flat-
tailed horned lizard by the Interagency Conservation Agreement 
implementing the Rangewide Management Strategy (62 FR 37858-37859). In 
2003, we again noted several State (Arizona and California), U.S. 
Federal, and Mexican Federal laws and other existing regulatory 
mechanisms that could provide benefits to the flat-tailed horned lizard 
(68 FR 346).
    Because the Interagency Conservation Agreement implementing the 
Rangewide Management Strategy is voluntarily implemented on the part of 
the signatories, we do not consider it to be a regulatory mechanism per 
se. Some entities have incorporated the Interagency Conservation 
Agreement into other regulatory mechanisms; in such cases, the 
Interagency

[[Page 14233]]

Conservation Agreement is mentioned in the context of those regulatory 
mechanisms. Additionally, two habitat conservation plans (HCPs) within 
the range of the flat-tailed horned lizard cover the species and 
provide mitigation for and conservation of habitat. While 
implementation of these HCPs will provide localized benefits to the 
flat-tailed horned lizards populations within the HCP boundaries, these 
HCPs cover a very small portion of the flat-tailed horned lizard's 
range and will not substantially influence the overall status of the 
species. The Interagency Conservation Agreement and the two HCPs are 
discussed in greater detail in the Background section above.
    In the preceding analyses of the threats to the flat-tailed horned 
lizard under Factors A, B, and C, and in our analysis of threats under 
Factor E, below, all of the threats presented are of low magnitude, are 
non-imminent, and/or cover very small portions of the species' range. 
In the sections that follow, we first discuss the existing regulatory 
mechanism(s) that would be removed as a result of the withdrawal of the 
proposed rule to list the species. Then we review the existing 
regulatory mechanisms that would remain in effect to address the 
potential threats discussed herein under the other listing factors.
U.S. Federal Laws

Section 7(a)(4) of the Act

    The Act contains provisions for Federal agencies to confer with the 
Secretary on any action that is likely to jeopardize the continued 
existence of any species proposed to be listed under the Act. Commonly 
called a ``conference,'' this requirement would no longer apply to the 
flat-tailed horned lizard once the withdrawal of the proposed listing 
rule is finalized. A conference opinion is an advisory mechanism by 
which the Service recommends measures to avoid adverse effects or 
jeopardy to the species. There are no requirements to implement 
reasonable and prudent measures and terms and conditions or for 
adoption of reasonable and prudent alternatives to avoid impacts to 
species or habitat. In this regard, the conference opinion requirement 
under the Act provides little if any additional regulatory protection 
for this species; although it may provide some benefits to the flat-
tailed horned lizard by informing Federal agencies of potential adverse 
effects to the species that may result from their activities. However, 
the survival of the flat-tailed horned lizard is not dependent on any 
protections afforded by the application of section 7(a)(4) of the Act 
because the potential threats facing the flat-tailed horned lizard are 
not substantial (see the other listing factors).

Incidental Protection Via Other Listed Species

    The withdrawal of the proposed rule to list the flat-tailed horned 
lizard will not affect the listing status of other listed species, and 
the flat-tailed horned lizard may receive some level of protection in 
the United States through implementation of the Act because of 
overlapping ranges or proximity to other federally listed species. 
These associated federally listed species include Coachella Valley 
fringe-toed lizard (Uma inornata), Astragalus lentiginosus var. 
coachellae (Coachella Valley milk-vetch), Astragalus magdalenae var. 
peirsonii (Peirson's milk-vetch), bighorn sheep in the Peninsular 
Ranges (Ovis canadensis nelsoni), and desert tortoise (Gopherus 
agassizii).
    The federally threatened Coachella Valley fringe-toed lizard is 
restricted to the Coachella Valley, but its distribution overlaps with 
the northern portion of the flat-tailed horned lizard's range in the 
Coachella Valley. However, the flat-tailed horned lizard may use 
additional habitat within the Coachella Valley in which the fringe-toed 
lizard does not occur. The Coachella Valley MSHCP addresses the 
Coachella Valley fringe-toed lizard, Coachella Valley milk-vetch, and 
the flat-tailed horned lizard. Federal actions not covered by the 
Coachella Valley MSHCP that may affect the Coachella Valley fringe-toed 
lizard, the Coachella Valley milk-vetch, or both are subject to 
consultation with the Service under section 7 of the Act. These 
consultations may include avoidance or minimization measures that 
benefit the listed species and, where they co-occur, the flat-tailed 
horned lizard. Similarly, consultations on the federally endangered 
bighorn sheep of the Peninsular Ranges may include measures that 
benefit flat-tailed horned lizards in the Western and Coachella Valley 
Populations where suitable habitat for both species is in close 
proximity at the toe of slope of the mountains; however, the amount of 
such overlap is likely to be minimal. Likewise, the flat-tailed horned 
lizard may marginally benefit from consultations addressing the 
federally threatened Astragalus magdalenae var. peirsonii and the 
federally threatened desert tortoise where they co-occur, but these 
areas of overlap are also likely minimal. When the flat-tailed horned 
lizard overlaps with other listed species, we anticipate impacts to the 
species and its habitat may be avoided or minimized.

Approved Habitat Conservation Plans--Section 10(a)(1)(B) of the Act

    Under section 10(a)(1)(B) of the Act, the Service may issue 
``incidental take'' (i.e., taking of endangered species that is 
incidental to, but not the purpose of, carrying out of an otherwise 
lawful activity, see 50 CFR 402.02) permits for listed animal species 
to non-Federal applicants, which provide exemptions to the take 
prohibitions under section 9 of the Act. To qualify for an incidental 
take permit, applicants must develop, fund, and implement a Service-
approved habitat conservation plan that, among other requirements, does 
not jeopardize the continued existence of covered species, and details 
measures to minimize and mitigate the impact of the approved incidental 
taking on covered species. As discussed in the Background section and 
under Factor A, there are two existing incidental take permits that 
include the flat-tailed horned lizard as a covered species: the 
Coachella Valley MSHCP and the Lower Colorado MSCP. Regardless of the 
withdrawal of the proposed rule to list the species, the existing HCPs, 
and the conservation they provide, would remain in effect.
Additional U.S. Federal Mechanisms

Federal Land Policy and Management Act

    The Federal Land Policy and Management Act of 1976 (43 U.S.C. 1701 
et seq.) (FLPMA), which provides overall direction to the BLM for 
conservation and management of public lands, allows the agency to 
participate in Interagency Conservation Agreements. Section 601 
required the preparation of the California Desert Conservation Area 
(CDCA) Plan. The CDCA Plan was amended to formally incorporate the 
Rangewide Management Strategy into BLM's land use planning, including 
formal adoption of the BLM-controlled Management Areas comprising the 
East Mesa Flat-tailed Horned Lizard Management Area, West Mesa Flat-
tailed Horned Lizard Management Area, and Yuha Desert Flat-tailed 
Horned Lizard Management Area (BLM 2004, p. 2). Additionally, section 
103(a) of the FLPMA defines an Area of Critical Environmental Concern 
(ACEC), which allows creation of areas ``where special management 
attention is required * * * [for] fish and wildlife resources.'' BLM 
lands comprise much of the U.S. range of the flat-tailed horned lizard, 
including the aforementioned Management Areas.

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Additionally, the BLM has designated ACECs for wildlife resources 
within the range of the flat-tailed horned lizard. The BLM's 
implementation of FLPMA, through land management plans that incorporate 
certain provisions of the Rangewide Management Strategy including the 
avoidance, minimization, mitigation (compensation), and management 
measures, helps to reduce the severity of existing potential threats to 
the flat-tailed horned lizard, especially development and OHV activity. 
We conclude FLPMA is an adequate regulatory mechanism within the 
confines of its applicability--that is, allowing BLM to better manage 
flat-tailed horned lizard habitat and implement the Rangewide 
Management Strategy on BLM lands. Because much of the U.S. portion of 
the range of the flat-tailed horned lizard is comprised of BLM land, 
FLPMA is an important regulatory mechanism that helps to reduce the 
already low-level threats to the species in these areas. Implementation 
of the CDCA Plan, as amended, and the incorporated provisions of the 
Rangewide Management Strategy will continue regardless of the 
withdrawal of the proposed listing rule for the species.

National Environmental Policy Act

    The National Environmental Policy Act (NEPA) (42 U.S.C. 4321 et 
seq.) requires all Federal agencies to formally document, consider, and 
publicly disclose the environmental impacts of major Federal actions 
and management decisions that have significant effects on the human 
environment (including natural resources), but NEPA does not require 
that mitigation alternatives be implemented. Additionally, NEPA applies 
only to actions by Federal agencies, so private landowners are not 
required to comply with NEPA unless a Federal agency is involved 
through provision of Federal funding or a Federal permit. Although NEPA 
requires disclosure of the effects of proposed Federal actions, it does 
not afford direct protection to the flat-tailed horned lizard.

Fish and Wildlife Coordination Act

    Through the Fish and Wildlife Coordination Act (16 U.S.C. 661 et 
seq.) (FWCA), we may recommend discretionary conservation measures to 
avoid, minimize, and offset impacts to fish and wildlife resources 
resulting from Federal projects and water development projects 
authorized by the U.S. Army Corps of Engineers. Therefore, FWCA may 
provide some protection for the species and its habitat through 
avoidance and minimization measures that may be incorporated into 
Federal projects. We conclude FWCA is an adequate regulatory mechanism 
within the confines of its applicability, but its applicability is 
limited. The minor benefits provided by FWCA will continue regardless 
of the withdrawal of the proposed rule to list the flat-tailed horned 
lizard.

Sikes Act

    In 1997, section 101 of the Sikes Act (16 U.S.C. 670a) was revised 
by the Sikes Act Improvement Act to authorize the Secretary of Defense 
to implement a program to provide for the conservation and 
rehabilitation of natural resources on military installations. To do 
so, the Department of Defense was required to work with Federal and 
State fish and wildlife agencies to prepare an Integrated Natural 
Resources Management Plan (INRMP) for each facility with significant 
natural resources. The INRMPs provide a planning tool for future 
improvements; provide for sustainable multipurpose use of the 
resources, including activities such as hunting, fishing, trapping, and 
non-consumptive uses; and allow some public access to military 
installations to facilitate their use. Implementation of the measures 
included in these plans is subject to funding availability. The primary 
purpose for military lands, including most areas of flat-tailed horned 
lizard habitat, is to provide for military support and training.
    Two major military installations are within the U.S. range of the 
flat-tailed horned lizard, the MCAS Yuma (within the Barry M. Goldwater 
Range) and the NAF El Centro, both are signatories to the Interagency 
Conservation Agreement and are implementing the Rangewide Management 
Strategy. Both installations have incorporated aspects of the Rangewide 
Management Strategy into their respective INRMPs, including avoidance 
and minimization measures, plus monitoring and management activities 
(Navy 2001, pp. 3-14 to 3-16; USAF and USMC 2007, pp. 6-2 and 6-8; see 
also USAF et al. 2006 entire). Additionally, areas designated as Flat-
tailed Horned Lizard Management Areas under the Rangewide Management 
Strategy include military-owned areas (FTHLICC 2003a, pp. 51-53). 
Regardless of the withdrawal of the proposed rule to list the species, 
the application of the Sikes Act would continue and the benefits to the 
flat-tailed horned lizard would continue within the confines of its 
applicability--that is, providing benefits to the flat-tailed horned 
lizard and its habitat on military facilities and implementing the 
Rangewide Management Strategy on military lands.
California State Laws

California Endangered Species Act

    The flat-tailed horned lizard is not listed under the California 
Endangered Species Act (CESA), the State's primary regulatory mechanism 
to protect species. Therefore, CESA provides no benefit to the flat-
tailed horned lizard.

California Environmental Quality Act

    The California Environmental Quality Act (CEQA) (chapter 2, section 
21050 et seq. of the California Public Resources Code) requires State 
and local government agencies to consider and disclose environmental 
impacts of projects and to avoid or mitigate them where possible. Under 
CEQA, public agencies must prepare environmental documents to disclose 
environmental impacts of a project and to identify conservation 
measures and project alternatives. Section 15380 of the CEQA Guidelines 
indicates that species designated as ``species of special concern'' 
(see below) should be included in an analysis of project impacts if 
they can be shown to meet the criteria of sensitivity outlined therein 
(Comrack et al. 2008, p. 2). However, CEQA itself does not guarantee 
that conservation measures will be implemented; the lead agency may 
either require mitigation through changes to a project, or determine 
that overriding considerations make mitigation infeasible (CEQA Sec. 
21002). In the latter case, projects may be approved that cause 
significant environmental damage, such as impacts to species or their 
habitat. Therefore, whether CEQA is an adequate regulatory mechanism 
within the confines of its applicability depends on the law's 
application and the determination of the lead agency involved. The 
minor benefits provided by CEQA will continue regardless of the 
withdrawal of the proposed rule to list the species.

Natural Community Conservation Planning Act

    The NCCP program is a cooperative effort involving the State of 
California and numerous private and public partners to protect regional 
habitats and species. The primary objective of NCCPs is to conserve 
natural communities at the ecosystem scale while accommodating 
compatible land use, including urban development (http://www.dfg.ca.gov/habcon/). Natural Community Conservation Plans help 
identify and provide for the regional or area-wide protection of 
plants, animals, and their habitats, while allowing compatible and 
appropriate economic activity. Many NCCPs are developed in

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conjunction with habitat conservation plans prepared under the Act, 
including the Coachella Valley MSHCP. Regardless of the withdrawal of 
the proposed rule to list the flat-tailed horned lizard, the existing 
NCCPs, and the protections they provide, would remain in effect.

California Administrative Code

    California Administrative Code 40.10, Title 14, prohibits the 
collection of flat-tailed horned lizards without a permit. Therefore, 
we conclude the California Administrative Code is an adequate 
regulatory mechanism within the confines of its applicability--that is, 
limiting or preventing overutilization of the flat-tailed horned lizard 
in California. The benefits provided by California Administrative Code 
40.10, Title 14, will continue regardless of the withdrawal of the 
proposed rule to list the flat-tailed horned lizard.

Species of Special Concern

    The State's Species of Special Concern (SSC) designation is an 
administrative designation that carries no formal legal status. 
According to Comrack et al. (2008, pp. 1-4), its intent is to focus 
attention on animals deemed to be at conservation risk, stimulate 
research, and achieve conservation and recovery of these animals before 
they meet California Endangered Species Act criteria for listing as a 
State endangered or threatened species. The flat-tailed horned lizard 
is on the list of reptile and amphibian species of special concern in 
California (Jennings and Hays 1994, pp. 134-141).
    As stated in Comrack et al. (2008, p. 2), sections 15063 and 15065 
of the CEQA Guidelines, which address how an impact is identified as 
significant, are particularly relevant to SSCs. Project-level impacts 
to listed (endangered, threatened, or rare species) species are 
generally considered significant, thus requiring lead agencies to 
prepare an Environmental Impact Report to fully analyze and evaluate 
the impacts. Moreover, section 15380 of the CEQA Guidelines indicates 
that SSCs should be included in an analysis of project impacts if they 
can be shown to meet the criteria of sensitivity outlined therein 
(Comrack et al. 2008, p. 2). In assigning ``impact significance'' to 
populations of non-listed species, analysts usually consider factors 
such as population-level effects, proportion of the taxon's range 
affected by a project, regional effects, and impacts to habitat 
features.
    Therefore, we conclude the State's Species of Special Concern 
designation is an adequate regulatory mechanism within the confines of 
its applicability--that is, an administrative designation that 
increases the level of awareness and analysis (such as under CEQA) for 
flat-tailed horned lizard in California. The benefits provided by the 
Species of Special Concern designation will continue regardless of the 
withdrawal of the proposed rule to list the flat-tailed horned lizard.
Arizona State Laws

Arizona Game and Fish Regulation

    Arizona Game and Fish Regulation, Title 17, R12-4-443, Commission 
Order 43 prohibits the collection of flat-tailed horned lizards without 
a permit by indicating that there is no ``open season'' to collect the 
species (AGFD 2009, p. 8). Additionally, the Arizona Game and Fish 
Department has included the flat-tailed horned lizard on the draft List 
of Wildlife of Special Concern in Arizona, which the State uses to 
prioritize species for planning and funding purposes, although State 
regulations do not exist in Arizona to protect this species' habitat at 
this time. We conclude Arizona Game and Fish Regulation is an adequate 
regulatory mechanism within the confines of its applicability--that is, 
limiting or preventing overutilization of the flat-tailed horned lizard 
in Arizona. The benefits provided by the Arizona Game and Fish 
Regulation, Title 17, R12-4-443, Commission Order 43 will continue 
regardless of the withdrawal of the proposed rule to list the flat-
tailed horned lizard.
Mexican Federal Law

Official Mexican Norm

    The Official Mexican Norm NOM-059-ECOL-2001, Mexico's threatened 
species law, lists the flat-tailed horned lizard as a threatened 
species (SEMARNAT 2002, p. 134). The Mexican law may be implemented to 
modify development projects or support creation of Natural Protected 
Areas, but successful implementation occurs by individuals or groups 
outside of the Mexican government. We conclude Official Mexican Norm 
may be an adequate regulatory mechanism within the confines of its 
applicability--that is, reducing threats to the species in Mexico. The 
benefits provided by the Official Mexican Norm NOM-059-ECOL-2001 will 
continue regardless of the withdrawal of the proposed rule to list the 
flat-tailed horned lizard in the United States.
Summary of Factor D
    With the withdrawal of the proposal to list the flat-tailed horned 
lizard, the only change in regulatory protections would be the removal 
of the conference requirement under section 7(a)(4) of the Act. Since a 
conference opinion is only advisory in nature, we do not expect this 
change to have any significant effect on the status of the species. The 
remainder of the existing regulatory mechanisms summarized above will 
remain in place and will continue to provide benefits to the species. 
The aforementioned existing regulatory mechanisms provide some level of 
protection for the species and its habitat. This includes several laws 
or mechanisms that reduce potential threats, such as State laws that 
restrict the collection of flat-tailed horned lizards, or planning 
documents developed under FLPMA or the Sikes Act that incorporate 
measures from the Rangewide Management Strategy. Therefore, we conclude 
the existing regulatory mechanisms are not inadequate and do not 
threaten the species throughout all or a significant portion of its 
range, now or in the foreseeable future.

E. Other Natural or Manmade Factors Affecting Its Continued Existence

    For Factor E, we assess the natural or manmade threats to the 
species that were not addressed under the previous four factors. In the 
1993 proposed rule to list the species as threatened and in the 2003 
withdrawal document, we considered the potential effects of pesticide 
spraying and prolonged drought under this factor. Also in these two 
Federal Register publications, we addressed the effects of OHV use on 
the species and its habitat under Factor A. Similarly, in those earlier 
assessments, we addressed the potential effects associated with 
fragmentation on the species and its habitat under Factor A. Also, in 
our 2006 withdrawal document (71 FR 36750-36751), the scope of which 
was limited by court order, we addressed historical habitat loss as a 
component of Factor A on the grounds that Factor A addresses the 
curtailment of a species' habitat or range as a threat to its continued 
existence, but this rationale was flawed because Factor A, as discussed 
here and under Factor A in the present document, is limited to current 
and anticipated losses of habitat, not past losses. Because of the 
confusion presented in previous analyses, we have emphasized in the 
current analysis the differences between present and future habitat 
loss from past habitat loss, including how ``fragmentation'' as a 
concept interacts with the topic of habitat loss.
    To address explicitly the previously identified threat of 
``fragmentation,'' we

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need to address the specific threats encompassed by that ambiguous 
term. However, these threats include ones that are best addressed under 
separate listing factors under the Act. As mentioned previously, the 
term fragmentation includes habitat loss. Factor A addresses present 
(current) or threatened (anticipated) destruction, modification, or 
curtailment of a species' habitat or range. Factor A does not address 
threats posed by past losses of habitat. How the species is affected by 
past habitat loss--or in other words, the present-day ramifications of 
those past actions of habitat destruction--is better addressed under 
Factor E. The effects of past habitat loss include in particular the 
effects of manmade barriers on populations and edge effects. Barriers 
may divide otherwise intact populations into smaller populations, and 
those smaller populations may be more susceptible to other effects (see 
below).
    Thus, below, we assess the effects of barriers and small 
populations and edge effects. We also assess the previously identified 
potential effects to the species from pesticide spraying, OHV use, and 
prolonged drought; we also address the potential effects associated 
with global climate change not previously identified.
Barriers and Small Populations
    As mentioned previously, as used herein a ``population'' refers to 
a loosely bounded, regionally distributed collection of individuals of 
the same species. Thus, individuals of a given species when considered 
together within some boundary may be considered a population. For 
example, the group of individuals bounded within the entire range of 
the species may be considered a population, sometimes referred to as 
the ``entire population'' or ``population as a whole.'' Similarly, 
groups of individuals within the entire population may be considered to 
occur separately from each other, forming multiple populations. In 
typical usage, a separation is often a literal separation--that is a 
physical division, by a barrier for instance--but it may also be a 
figurative separation; for example, an arbitrary grouping of 
individuals for the purposes of discussion. Regardless of the criteria 
used to separate and group individuals, a species may be considered to 
comprise one or more populations, depending on how the term is used. 
Moreover, because the term is loosely defined, a given population could 
be considered to consist of other smaller populations, sometimes 
hierarchically referred to as ``subpopulations.'' For the purposes of 
our discussion of barriers and small populations, below, we primarily 
refer to populations as being physically separated, or potentially so.
    Barriers prevent or severely limit contact (genetic interchange) 
between populations. Thus, an artificial barrier can split a population 
into two (or more) populations (Jackson 2000, p. 4). For animals that 
can move freely (vagile animals), like the flat-tailed horned lizard, 
barriers prevent individuals from moving from one area into another. 
Barriers not only include physical hindrances that prevent movement 
(e.g., a wall or a river), but may also include areas that a species 
may be disinclined to enter (e.g., unsuitable habitat) or areas of 
increased mortality (e.g., busy roads, or areas with an elevated number 
of predators) across which individuals would be unlikely to 
successfully traverse.
    The division of populations into other, smaller populations may or 
may not be deleterious; it largely depends on the size of the resulting 
populations, with small populations more likely to experience problems 
than large populations, as discussed below. Moreover, small populations 
may be disproportionately affected by other natural and manmade factors 
compared to large populations, such as edge effects, also discussed 
below. Thus, the creation of artificial barriers results in habitat 
loss (see Factor A) and may also affect the species through potential 
effects associated with the subsequent isolation, which largely depends 
upon the size of the resulting populations. Because the threats from 
barriers and small populations are connected, we discuss the potential 
threats faced by small populations generally and then discuss the 
potential effects of barriers and small population sizes on the flat-
tailed horned lizard.
    The decline of a population is determined by a number of forces and 
factors that are often grouped into intrinsic and extrinsic. As 
described by Soul[eacute] and Simberloff (1986, pp. 27-28), ``extrinsic 
forces include deleterious interactions with other species (increases 
in predation, competition, parasitism, disease or decreases in 
mutualistic interactions) and deleterious events or changes to habitat 
or the physical environment. Intrinsic factors include random variation 
in genetically based traits of the species and interactions of these 
traits with the environment. These include: (1) Demographic 
stochasticity, which is random variation in sex ratio [and] in birth 
and death rates, * * * (2) social dysfunction or behaviors that become 
maladaptive at small population sizes; [and] (3) genetic deterioration 
brought on by inbreeding, genetic drift and other factors.'' For a 
population to become extirpated (locally extinct), these extrinsic and 
intrinsic forces and factors must significantly affect the population. 
These forces and factors are more likely to be significant to small 
populations (Goodman 1987, pp. 11-34; Pimm et al. 1988, pp. 757-785; 
Lande 1993, pp. 911-927; Frankham 1996, pp. 1500-1508; Henle et al. 
2004, pp. 207-251).
    Our 1993 and 2003 assessments of the flat-tailed horned lizard have 
described flat-tailed horned lizard populations as ``fragmented.'' As 
discussed previously, fragmentation is an imprecise term, but one that 
clearly is associated with the breaking up of populations into smaller 
populations through the introduction of artificial barriers. As 
discussed in the Background section, historical agricultural 
development (and its associated urban development) has largely occurred 
in contiguous blocks. These large swaths of human-created non-habitat 
have, for the most part, exacerbated natural barriers separating the 
Western, Eastern, and Southeastern Populations, and severed the 
somewhat tenuous connection between the Coachella Valley Population and 
the Western Population. As a consequence of the past development, the 
geographical area occupied by these four populations became smaller. 
With the decrease in the amount of habitat area, we expect populations 
of flat-tailed horned lizards in those areas to also be smaller (a 
decrease in the abundance of individuals) (such as Hokit and Branch 
2003, p. 261).
    The point at which a population becomes a ``small population'' is 
not clear and varies by species-specific or situational-specific 
factors. There is disagreement among scientists and considerable 
uncertainty as to the population size adequate for long-term 
persistence of wildlife populations; however, there is agreement that 
population viability over the long term is more likely to be ensured if 
population sizes are in the thousands of individuals rather than 
hundreds (Traill et al., 2010, p. 32, see also Reed et al. 2003, p. 30, 
Table 3 therein). In vertebrates, a population of 5,000 is often used 
as a minimum number needed for high likelihood of viability over the 
long term (Traill et al., 2010, p. 32), while Reed et al. (2003, p. 30) 
estimated that roughly 7,000 breeding-age adults is the minimum number 
necessary for a vertebrate population to likely remain viable over the 
long term. However, as stated by Thomas (1990, p. 324), ``there is no 
`magic' population size that guarantees the persistence of animal 
populations.'' He went on to note

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that populations of some vertebrates have survived for decades with 
population sizes of hundreds or even dozens of individuals, adding 
``populations that occupy habitat fragments that are far too small to 
hold thousands of individuals may still possess great conservation 
potential'' (Thomas 1990, p. 326). Moreover, the amount of time that 
most authors consider to be ``long term'' is many decades or even 
centuries (for example, see Shaffer 1981, p. 132; Soule and Simberloff 
1986, p. 28; Traill et al. 2010, p. 31; see also Reed et al. 2003, p. 
30, Table 3 therein). Although minimum population sizes for shorter 
time periods would be correspondingly smaller (see Figure 1 in Traill 
et al. 2010, p. 31), we use the long-term population size to be 
conservative.
    As discussed in the Background section, and discussed further in 
the present section, the distribution of the flat-tailed horned lizard 
is divided into discrete populations. Thus, to assess the threat 
implied by the term ``fragmentation,'' it is more appropriate to 
consider the individual populations than to assess the population-as-a-
whole. Below we assess the four geographical Populations. We first 
examine the Western, Eastern, and Southeastern Populations, each as a 
whole. Then, looking at those three Populations further, we note that 
potential barriers within the larger Populations may divide each 
Population into smaller subpopulations. Lastly, we examine the 
Coachella Valley Population. We treat the Coachella Valley Population 
separately from the other three Populations because the current 
distribution of flat-tailed horned lizards in the Coachella Valley 
occurs in two widely isolated areas and are more like the 
subpopulations created by barriers within the Western, Eastern, and 
Southeastern Populations. Thus, we take advantage of the concepts 
developed in our discussion of barrier-created subpopulations to assess 
the Coachella Valley Population.

Western, Eastern, and Southeastern Populations

    There are no direct, reliable estimates of flat-tailed horned 
lizard population size for the four geographically separated 
populations. The size of the Western Population, Eastern Population, 
and Southeastern Population areas are 341,989 ha (845,073 ac), 169,617 
ha (419,133 ac), and 1,073,551 ha (2,652,802 ac) respectively 
(Coachella Valley Population area is discussed separately, below). Even 
at the lowest (most conservative) estimated density of adult flat-
tailed horned lizard of 0.3 individuals per ha (0.1 individuals per ac) 
(see Background section) there are likely more than 50,000 adult flat-
tailed horned lizards in the Western Population, 85,000 in the Eastern 
Population, and 322,000 in the Southeastern Population. We acknowledge 
that there are numerous assumptions in these calculations that limit 
accuracy of the extrapolated population sizes; however, even using the 
most conservative density value, these three populations are of 
sufficient size such that any threats associated with small populations 
would be unlikely. However, there are potential barriers that may 
subdivide the otherwise apparently continuous Western, Eastern, and 
Southeastern Populations. We examine subdivisions within these three 
populations, below.

Subpopulations Within the Western, Eastern, and Southeastern 
Populations

    For the flat-tailed horned lizard, as a diminutive terrestrial 
animal, a number of manmade changes to the landscape may serve as 
barriers (see FTHLICC 2003a, p. 14). These include: (1) Railways, 
canals, and certain types of roadways that are physical hindrances to 
the movement of flat-tailed horned lizards; (2) developed areas 
(unsuitable habitat) into which flat-tailed horned lizards may be 
disinclined to enter; and (3) busy roadways, powerline corridors, and 
areas adjacent to developed areas (that have artificial perches and 
nearby artificial food sources resulting in higher densities of 
predators) that are areas of increased mortality for flat-tailed horned 
lizards (FTHLICC 2003a, p. 14; see also Boarman et al. 1997, pp. 54-58; 
Fagan et al. 1999, pp. 165-182; Jackson 2000, pp. 1-14; Germaine and 
Wakeling 2001, pp. 229-237; Young and Young 2005, pp. 1-11; Barrows et 
al. 2006, pp. 486-494; Shepard et al. 2008, pp. 288-296).
    We expect these potential barriers will be variable in how 
thoroughly they prevent movement of flat-tailed horned lizards, and 
thus variable in the extent to which they prevent contact between 
individuals and separate populations. Canals generally extend for long 
distances without overcrossings, and flat-tailed horned lizards may be 
reluctant to use (go over) what few crossings exist (bridges); as such, 
canals are likely impermeable barriers in the same way the Colorado 
River has separated populations. However, as discussed below, roadways 
and railways, and the infrastructure associated with border security 
may or may not constitute complete barriers.
    Depending on how roads are constructed, they may serve as physical 
hindrances to the movement of flat-tailed horned lizards. For example, 
raised roadbeds, steep curbs, and roadway dividers may contribute to 
making a roadway a physically impassible barrier for flat-tailed horned 
lizards. Similarly, railways may serve as physical barriers. However, 
bridges and culverts, especially those with larger-sized openings, may 
allow flat-tailed horned lizards to cross under the physical 
impediments along roads and railways (Painter and Ingraldi 2007, p. 
17). Although it is not known whether the openings under such 
structures are used regularly by the species in the wild, it is likely 
that the undercrossings with natural substrates created by larger 
culverts, and especially bridges, are used to some extent. 
Additionally, blowing sand, which is not atypical for much of the range 
of the flat-tailed horned lizard, may build up along roadways and 
railways. Thus, it is possible that accumulated sand, at least until 
the sand is cleared by maintenance crews, may provide a ``bridge'' over 
the physical structures that prevent flat-tailed horned lizard 
movement. For example, the railway through the sandy Gran Desierto de 
Altar may be less of a barrier than railways in less sandy portions of 
the species' range due to blowing and drifting sands that may provide 
passage over tracks.
    Additionally, roads that do not serve as physical hindrances may be 
barriers for other reasons. Flat-tailed horned lizards, particularly 
males (Young and Young 2000, p. 19), are often sighted on paved roads 
(Mayhew 1965, p. 104; Turner and Medica 1982, p. 822; Johnson and 
Spicer 1985, p. 40; Stebbins 2003, p. 304). This, combined with their 
propensity to not flee from oncoming traffic (Young and Young 2000, p. 
60), may make flat-tailed horned lizards particularly susceptible to 
traffic-related road mortality (Nicola and Lovich 2000, p. 211; Gardner 
et al. 2001, p. 10). The stretches of multi-lane highways (Interstate 8 
and State Route 86) that cross areas within the current range of the 
flat-tailed horned lizard have, on average, over 25,000 vehicles pass 
over them daily, while the smaller, two-lane highways of State Routes 
78 and 98 within the species' range have roughly 3,500 to 5,500 
vehicles per day, on average (Caltrans 2008, electronic data). The 
increased level of vehicle traffic on the multi-lane highways along 
with the greater number of physical hindrances that may result from 
multiple lanes is more likely to serve as a barrier than the smaller, 
two-lane

[[Page 14238]]

highways. For example, the population of flat-tailed horned lizards 
occupying the small part of the Southeastern Population north of 
Interstate 8 (1,018 ha (2,516 ac)) (see below) is small enough and 
isolated enough to exhibit some evidence of inbreeding or genetic drift 
(Culver and Dee 2008, p. 2), suggesting Interstate 8 in this area is an 
effective barrier preventing movement of flat-tailed horned lizards 
(see below). However, Interstate 8 likely poses less of a physical 
hindrance where it crosses the Eastern Population where blowing sand 
fills in gaps along the road edge, although the traffic volume remains 
high. Another way roadways may be barriers is that the cryptic 
coloration that allows flat-tailed horned lizards to blend in with 
desert soils may be of little use on paved roads, allowing increased 
levels of predation (Young and Young 2000, p. 62) (see Factor C, 
Disease and Predation). Thus, even though flat-tailed horned lizards 
may be able to physically cross two-lane roads (Barrows 2006, p. 119), 
these roads may be barriers to flat-tailed horned lizards for other 
reasons.
    However, it is not clear whether roadways or other potential 
barriers are complete barriers. They may instead be ``semipermeable'' 
barriers, reducing contact between populations, but not stopping it. 
This may be especially true for small roads, especially gravel and 
unsurfaced roads and OHV ``routes.'' Although the amount of contact 
needed to maintain population connectivity of flat-tailed horned 
lizards is not known, Mills and Allendorf (1996, p. 1517) suggested 
that if 1 to 10 individuals per generation successfully cross a 
semipermeable barrier, that level of movement is likely sufficient to 
maintain the connection between populations, provided the overall 
population is of sufficient size. Thus, a potential barrier would have 
to severely limit flat-tailed horned lizard movement throughout its 
length and at all times for it to be a complete barrier; as such, only 
a few potential barriers are likely complete barriers.
    The ``tactical infrastructure,'' including fencing, lighting, and 
access and patrol roads (collectively, the ``border fence''), along 
portions of the international border has the potential to serve as a 
barrier. The actual fencing in these areas includes vehicle and 
pedestrian fences that are constructed to allow movement of small 
animals (USCBP 2008a, pp. 1-4 to 1-6 and Appendix B; USCBP 2008b, pp. 
2-5 and 8-9). Although the shifting sand has meant some of the small 
slots that were incorporated into fine-mesh pedestrian fence to allow 
movement of flat-tailed horned lizards are no longer at ground level 
(FTHLICC 2010, p. 10), the shifting sand has also resulted in gaps 
under the fence that flat-tailed horned lizards may use to cross under 
the fence (Rorabaugh 2010, p. 190). Thus, we do not anticipate the 
fence proper to be a complete physical hindrance to flat-tailed horned 
lizard movement. The additional infrastructure and activity may deter 
flat-tailed horned lizard movement or allow for increased mortality. 
However, in total, we do not believe the level of activity to be high 
enough to be a complete barrier to flat-tailed horned lizard movement 
(see also Rorabaugh 2010, p. 190). For example, genetic data from both 
sides of the border in the Southeastern Population suggests that 
populations of flat-tailed horned lizards in Arizona are not 
genetically isolated from neighboring populations in Mexico (Culver and 
Dee 2008, p. 10). As such, the border fence is likely a semipermeable 
barrier, not a complete barrier, for the species.
    To assess the threat of barriers to the flat-tailed horned lizard, 
we examined maps of the region, including GIS data and aerial and 
satellite imagery. The areas in which flat-tailed horned lizards are 
currently distributed contain numerous potential manmade barriers. As 
mentioned above, the Coachella Valley Population area has numerous 
barriers, and the flat-tailed horned lizard is only known from two 
relatively small areas. Thus, as summarized below, we focused our 
attention on the three relatively contiguous Western, Eastern, and 
Southeastern Populations.
    For this analysis, we used GIS data of the species' ``current 
distribution'' as delineated by the 2003 Rangewide Management Strategy 
to examine the size of the areas between those features we considered 
likely barriers. Barriers divide the areas of habitat into subareas--
termed herein as ``parts.'' Similarly, barriers divide populations of 
flat-tailed horned lizards into smaller populations, or subpopulations. 
Features we considered potential likely barriers included: (1) The All-
American Canal and the Coachella Canal, which are likely to be complete 
barriers throughout their lengths; and (2) Interstate 8; State Routes 
78, 86, and 98; Mexico Federal Highways 2 and 8; the (old) coastal 
highway (which is being upgraded to a multi-lane highway, but we do not 
have GIS data for the new route); the international border; and several 
railways, which are likely to be semipermeable barriers to varying 
degrees along their lengths.
    For the purposes of dividing the areas into ``parts,'' we assumed 
all potential barriers were complete barriers; however, in the analysis 
that follows we discuss the situations in which such barriers may be 
semipermeable. Additionally, for the purposes of the analysis, where 
two or more potential barriers are adjacent to each other (e.g., 
portions of Interstate 8 and the All-American Canal), we mapped them as 
a single barrier. All of the area values (hectares and acres) are 
approximate and are not as precise as the values given; however, we 
believe they are sufficiently accurate for this coarse-scale analysis 
(especially because we used conservative estimates of flat-tailed 
horned lizard densities).
    We used the conservative estimated density of 0.3 adult flat-tailed 
horned lizards per ha (0.1 per ac) to determine whether potentially 
isolated parts between barriers were likely to contain more than 7,000 
adults, in other words, to be large enough to avoid threats that may be 
associated with small population size (see above). Where populations 
were ``small,'' we also present other potential population sizes using 
higher densities, including the still-conservative, but perhaps more 
realistic (for certain ``parts''), value of 0.7 individuals per ha (0.3 
per ac) (see Population Dynamics section, above).
    As described in the Population Dynamics section in the Background, 
these density estimates were derived from data that were collected at 
sites in the northern portion of the species' range. As a result, we 
are confident that the density estimates used are conservative. We do 
not have density estimates for the southern portion of the species' 
range; thus, we do not know if 0.3 or 0.7 individuals per ha (0.1 or 
0.3 per ac) are as conservative. Nevertheless, because these values are 
at the low end of a fairly wide range (0.3 to 4.4 adults per ha (0.1 to 
1.8 per acre)), we believe them to be within the density range even in 
the southern areas of the species' distribution.
    Additionally, as discussed near the beginning of the ``Barriers and 
Small Populations'' section, above, the point at which a population 
becomes ``small'' varies from species to species and from situation to 
situation. Stated another way, the forces and factors that are more 
likely to be significant threats to a ``small'' population of a given 
species are not guaranteed to be significant threats to a given 
population of a given size. We have limited information on the effects 
such forces and factors may have on the flat-tailed horned lizard. For 
example, even though information in the scientific literature suggests 
the previously mentioned population north Interstate 8 is exhibiting 
some evidence of inbreeding or genetic drift (Culver

[[Page 14239]]

and Dee 2008, p. 2), we do not have specific information as to whether 
or to what degree that population's status is being affected; the 
information in the scientific literature (as discussed above) suggests 
that this population is likely facing a greater risk from threats 
associated with genetic deterioration, but we have no data (one way or 
the other) to assess that particular population's status. Thus, for the 
purposes of evaluating the potential threats associated with the 
implied meaning of ``fragmentation'' to the flat-tailed horned lizard, 
we have assumed that the populations of flat-tailed horned lizards in 
areas that we identified as small, isolated parts are likely to 
experience adverse effects associated with small population size.
Western Population
    The potential barriers listed above split the Western Population 
area into 12 parts (Table 3, Figures 3 and 4), four of which are likely 
to support populations greater than 7,000 individuals, even with the 
most conservative of the estimated densities. These include: (1) The 
area north of State Route 78 (77,566 ha (191,670 ac)) (Part W-1; Table 
3), which includes the Borrego Badlands Management Area and Ocotillo 
Wells SVRA; (2) the area immediately south of State Route 78 (89,105 ha 
(220,183 ac)) (Part W-3; Table 3), which includes the West Mesa 
Management Area; (3) the area in the vicinity of the southeastern 
corner of Anza-Borrego Desert State Park (42,443 ha (104,879 ac)) (Part 
W-5; Table 3); and (4) the long, narrow area south of Mexico Federal 
Highway 2 in Baja California (74,254 ha (183,486 ac)) (Part W-12; Table 
3). Although the long, narrow nature of the area in Baja California may 
make threats more pronounced (Faaborg et al. 1995, p. 366), it remains 
a large habitat area. Thus, it is likely flat-tailed horned lizards in 
these four areas are not ``small populations.''

 Table 3--The Size (Area) of the ``Parts'' Created by Barriers (See Text) Within the Western Population and Our
    Determination as to Whether the Specified Part is Unlikely To Be at Risk of Deleterious Effects of Small
         Populations at the Conservative Densities of 0.3 or 0.7 Individuals Per ha (0.1 or 0.3 per ac)
----------------------------------------------------------------------------------------------------------------
                                                                  Is this part large enough to avoid deleterious
                                                                  effects associated with small populations when
                                                                           the density is assumed to be:
     Part identifier (country)             Area of part \1\      -----------------------------------------------
                                                                  0.3 individuals per ha  0.7 individuals per ha
                                                                       (0.1 per ac)            (0.3 per ac)
----------------------------------------------------------------------------------------------------------------
W-1 (U.S.).........................  77,566 ha (191,670 ac).....  yes...................  yes.
W-2 (U.S.).........................  8,777 ha (21,688 ac).......  no....................  no.
W-3 (U.S.).........................  89,105 ha (220,183 ac).....  yes...................  yes.
W-4 (U.S.).........................  539 ha (1,331 ac)..........  no....................  no.
W-5 (U.S.).........................  42,443 ha (104,879 ac).....  yes...................  yes.
W-6 (U.S.).........................  4,081 ha (10,083 ac).......  no....................  no.
W-7 (U.S.).........................  19,527 ha (48,252 ac)......  no....................  yes.
W-8 (U.S.).........................  110 ha (272 ac)............  no....................  no.
W-9 (U.S.).........................  10,873 ha (26,867 ac)......  no....................  yes.
W-10 (Mex.)........................  294 ha (726 ac)............  no....................  no.
W-11 (Mex.)........................  14,420 ha (35,632 ac)......  no....................  yes.
W-12 (Mex.)........................  74,254 ha (183,486 ac).....  yes...................  yes
----------------------------------------------------------------------------------------------------------------
\1\ Area values are estimated through a GIS-based assessment. Despite the level of precision presented, area
  values are approximate; however, we believe they are accurate enough to draw the conclusions presented.

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[[Page 14241]]


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BILLING CODE 4310-55-C
    Of the remaining eight populations, three (Parts W-4, W-8, and W-
10; Table 3) were remnants of a few hundred hectares each, totaling 
less than 1,000 ha (2,500 ac). If the flat-tailed horned lizards in 
these areas are isolated from other flat-tailed horned lizard 
populations, we expect they will be ``small populations'' and that 
they, therefore, are more likely to be negatively impacted by the 
deleterious effects associated with small populations sizes. Although 
the populations in these parts may have some connection to their 
respective adjacent parts, Parts W-4, W-8, and W-10 are very small and 
on the periphery, and any such connection would likely be tenuous at 
best.
    Of the five remaining parts, three (located between Interstate 8 on 
the north and Mexico Federal Highway 2 to south) (Parts W-7, W-9, and 
W-11; Table 3) were large enough to likely support more than 7,000 
flat-tailed horned lizards if the density of flat-tailed horned lizards 
was 0.7 individuals per ha (0.3 per ac). Given that the two U.S. areas 
contain the Yuha Desert Management Area, an area that was selected to 
be a Management Area because it is likely to support higher densities 
of flat-tailed horned lizards and where one of the demographic plots 
from which the data for density estimates were gathered (see Population 
Dynamics section, above), and the one in Mexico is immediately adjacent 
to the Yuha Desert Management Area, we believe it is reasonable to 
conclude that the density of 0.7 individuals per ha (0.3 per ac) is a 
realistic but still conservative density estimate to use. Moreover, as 
mentioned above, the border fence is likely a semipermeable barrier, 
allowing some connectivity between the Yuha Desert Management Area and 
the areas of habitat south of the international border. Thus, it is 
likely flat-tailed horned lizards in these areas are not ``small 
populations.''
    One of the last two remaining parts is the area between Interstate 
8 and the railway to the north (Part W-6; Table 3); it is over 4,000 ha 
(9,900 ac). This part should have some connectivity with the areas to 
the north because it is unlikely the railway is a complete barrier, and 
it may even have limited connection to the south across Interstate 8 
because of culverts and bridges, especially the large bridge that 
allows Interstate 8 to span the typically dry South Fork Coyote Wash at 
the far west end of Part W-6 (BLM and CEC 2010, p. C.2-22; USFWS 2010c, 
p. 57). A 2,630-ha (6,500-ac) solar generation facility has been 
proposed in this area, which is likely to transform much of it into 
unsuitable habitat. However, requirements for the construction and 
operation of the solar generation facility include avoidance of impacts 
to the major washes that cross the site, which would allow the 
possibility of connectivity (USFWS 2010c, p. 57).
    The last area, between State Route 86 and the Salton Sea, is over 
8,000 ha (19,800 ac) (Part W-2; Table 3, Figure 3). The multi-lane 
State Route 86 is likely a substantial barrier, but our interpretation 
of aerial imagery suggests there are several bridges that may allow 
some connection. That connection, combined with the size of the area, 
may reduce the risk this population will suffer from threats associated 
with ``small populations.''
    In sum, for the Western Population, assuming the identified 
potential barriers are complete barriers (which is not likely, as 
explained above, although we do not know how permeable they may be), 
and assuming the most conservative density of 0.3 flat-tailed

[[Page 14242]]

horned lizards per ha (0.1 per ac), we calculate that nearly 83 percent 
of the area is in parts of sufficient size such that the populations of 
flat-tailed horned lizards therein are not likely to be substantially 
affected by the factors associated with small population size. If we 
assume a slightly less conservative density (though still at the low 
end of the reported range) of 0.7 individuals per ha (0.3 per ac), we 
calculate about 96 percent of the area within the Western Population is 
in large enough blocks to not be substantially affected by small 
population size. Thus, the Western Population is not substantially 
composed of ``small populations.'' Therefore, we conclude the flat-
tailed horned lizards in the Western Population are not substantially 
threatened by effects associated with barriers that subdivide 
populations or the deleterious effects that may follow, nor do we 
expect barriers to be a threat in the foreseeable future.
Eastern Population
    The potential barriers listed above split the Eastern Population 
area into nine parts within three subareas (Table 4). Two major canals, 
which we expect are complete barriers, divide the overall area. The 
east-to-west-flowing All-American Canal isolates the southern roughly 
20 percent (southern subarea) from the northern 80 percent, which in 
turn is divided by the southeast-to-northwest-flowing Coachella Canal, 
essentially splitting the northern area in half (East Mesa subarea on 
the west and the Algodones Dunes subarea to the east). We discuss parts 
within these three subareas separately below.

 Table 4--The Size (Area) of the ``Parts'' Created by Barriers (See Text) Within the Eastern Population and Our
     Determination as Whether the Specified Part Is Unlikely To Be at Risk From Deleterious Effects of Small
         Populations at the Conservative Densities of 0.3 or 0.7 Individuals per ha (0.1 or 0.3 per ac)
----------------------------------------------------------------------------------------------------------------
                                                                  Is this part large enough to avoid deleterious
                                                                  effects associated with small populations when
                                                                           the density is assumed to be:
     Part identifier (country)             Area of part \1\      -----------------------------------------------
                                                                  0.3 individuals per ha  0.7 individuals per ha
                                                                       (0.1 per ac)            (0.3 per ac)
----------------------------------------------------------------------------------------------------------------
E-1 (U.S.).........................  16,863 ha (41,669 ac)......  no....................  yes.
E-2 (U.S.).........................  156 ha (385 ac)............  no....................  no.
E-3 (U.S.).........................  12,135 ha (29,986 ac)......  no....................  yes.
E-4 (U.S.).........................  50,270 ha (124,220 ac).....  yes...................  yes.
E-5 (U.S.).........................  50,721 ha (125,334 ac).....  yes...................  yes.
E-6 (U.S.).........................  8,968 ha (22,160 ac).......  no....................  no.
E-7 (U.S.).........................  2,867 ha (7,085 ac)........  no....................  no.
E-8 (U.S.).........................  4,140 ha (10,230 ac).......  no....................  no.
E-9 (Mex.).........................  23,496 ha (58,060 ac)......  yes...................  yes.
----------------------------------------------------------------------------------------------------------------
\1\ Area values are estimated through a GIS-based assessment. Despite the level of precision presented, area
  values are approximate; however, we believe they are accurate enough to draw the conclusions presented.


[[Page 14243]]

[GRAPHIC] [TIFF OMITTED] TP15MR11.045

    The southern subarea of the Eastern Population--that is, south of 
the All-American Canal--is divided by the international border, with 
the part between the canal and border totaling 8,968 ha (22,160 ac) 
(Part E-6; Table 4), and the part on the Mexico side of the 
international border totaling 23,496 ha (58,060 ac) (Part E-9; Table 
4). However, as mentioned previously, the border fence is probably a 
semipermeable barrier. As such, we expect the area of flat-tailed 
horned lizard habitat to the south of the All-American Canal (Parts E-6 
and E-9 combined) could be considered together. However, we estimate 
that roughly 6,400 ha (15,800 ac) in the easternmost portions of these 
two parts contain areas of deep, actively shifting sands of the 
Algodones Dunes that are likely rarely used by flat-tailed horned 
lizards. Despite this, the area is large enough so as to likely not be 
affected by the deleterious effects associated with ``small 
populations.''
    The East Mesa subarea (the western half of the northern 80 percent) 
is divided into four parts. The smallest part (Part E-2; Table 4) is a 
very small, isolated remnant of potential habitat (156 ha (385 ac)) at 
the far northern end of the Eastern Population area; it is a small 
population and may be at greater risk from the deleterious effects 
associated with small populations. The next smallest part is a triangle 
of flat-tailed horned lizard habitat between Interstate 8 and the All-
American Canal (Part E-8; Table 4). It is 4,140 ha (10,230 ac), likely 
too small of an area to support a ``large population,'' and the busy, 
multi-lane Interstate 8 probably has low ``permeability'' for flat-
tailed horned lizard movement. The third part in the East Mesa subarea 
(Part E-5; Table 4), the area north of Interstate 8, south of State 
Route 78 and west of the Coachella Canal, is 50,721 ha (125,334 ac) and 
includes the East Mesa Management Area, which is considered to be 
higher-quality flat-tailed horned lizard habitat. This part is large 
enough to support a large population; moreover, it is likely that the 
density in this area is at the higher end of the range of density 
estimates--thus, the population is likely much larger and not at risk 
of deleterious effects associated with small populations. The fourth 
part in the East Mesa subarea (Part E-3; Table 4), the area to the 
north of State Route 78 and west of the Coachella Canal, is 12,135 ha 
(29,986 ac) and unlikely to support a ``large population'' of flat-
tailed horned lizards at the most conservative density. However, 
because of this area's proximity to the East Mesa Management Area, it 
likely supports higher densities of flat-tailed horned lizards such 
that at 0.7 flat-tailed horned lizards per ha (0.3 per ac), this part 
would support a population that would not be at risk from threats 
associated with small population size. Moreover, State Route 78 in this 
area, because blowing sand has filled in any gaps along the road's edge 
such that it is not a physical hindrance and it has a lower traffic 
volume (Caltrans 2008, electronic data), is likely a semipermeable 
barrier, allowing contact of flat-tailed horned lizards between the two 
areas (north and south of the highway). As such, we expect the area of 
flat-tailed horned lizard habitat north of Interstate 8 and west of the 
Coachella Canal (Parts E-3 and E-5 combined) is large enough so as to 
not be affected now or in the foreseeable future by the deleterious 
effects associated with small populations.
    The Algodones Dunes subarea (the eastern half of the northern 80 
percent) is divided into three parts. The part north of Interstate 8, 
south of State Route 78 and east of the Coachella

[[Page 14244]]

Canal, is 50,270 ha (124,220 ac) (Part E-4; Table 4), large enough to 
support a large population at the most conservative density estimate. 
However, this area is mainly composed of the Algodones Dunes, which is 
an area of deep, actively shifting sand that is likely rarely used by 
flat-tailed horned lizards (Turner et al. 1980, p. 14). Flat-tailed 
horned lizards in this area are likely (naturally) restricted to the 
peripheral portions of the dunes. Moreover, large portions of this 
region include areas of intense recreational OHV activity, including 
portions of the peripheral areas of the dunes, which may reduce the 
habitat quality in those areas (see Factor A). The third part of this 
subarea (Part E-1; Table 4), the area north of State Route 78, is 
16,863 ha (41,669 ac), at the most conservative density estimates 
supporting a population that may be at risk from the deleterious 
effects of small population size. This part is also mainly composed of 
the deep, actively shifting sands of the Algodones Dunes, suggesting 
that higher densities of flat-tailed horned lizards are unlikely. 
However, unlike the areas to the south of State Route 78, most of the 
area is designated as Wilderness and, as such, OHV activity is 
prohibited. Moreover, as in the East Mesa subarea, State Route 78 is 
likely a semipermeable barrier, allowing contact of flat-tailed horned 
lizards between the two areas (north and south of the highway). Thus, 
the areas on the periphery of the Algodones Dunes are likely used by 
flat-tailed horned lizards within parts E-1 and E-4, but the majority 
of these two parts, the areas of deep, shifting sands of the Algodones 
Dunes, likely contributes little to the Eastern Population, and likely 
contributed little even before the manmade barriers and OHV activity. 
The smallest part (Part E-7; Table 4), between the All-American Canal 
and Interstate 8, in the southeast corner of the Eastern Population 
area, is about 2,867 ha (7,085 ac). Using the conservative density 
estimate, the population of flat-tailed horned lizards in this part may 
be at risk of deleterious effects associated with small populations. 
This part, though sandy, is not dominated by the deep, actively 
shifting sands of the main dunes.
    In sum, for the Eastern Population, assuming the identified 
potential barriers are complete barriers (which is not likely, see 
above, although we do not know how permeable they may be), and assuming 
the most conservative density of 0.3 adult flat-tailed horned lizards 
per ha (0.1 per ac) for all the parts, we calculate that about 73 
percent of the area is in large enough blocks that the populations of 
flat-tailed horned lizards therein are not likely to be affected by 
threats associated with small populations. However, the Eastern 
Population is divided by the All-American Canal and the Coachella 
Canal, which we expect are complete barriers to flat-tailed horned 
lizards. As such, the Eastern Population area is divided into three 
subareas. The size of the population in the portion east of the 
Coachella Canal, the Algodones Dunes subarea, is not clear because much 
of the area includes the deep-sand areas of the Algodones Dunes, which 
is likely low-quality habitat for the flat-tailed horned lizard. As 
such, even using our conservative density estimate, this area likely 
supports--naturally, even prior to any manmade effects--fewer flat-
tailed horned lizards compared to the other subareas in the Eastern 
Population than would be expected from its size. For the subarea south 
of the All-American Canal, the border fence between part E-6 and E-9 is 
likely permeable to some extent, but roughly 6,400 ha (15,800 ac) in 
the easternmost portions of these two parts contain areas of deep, 
actively shifting sands of the Algodones Dunes that are likely rarely 
used by flat-tailed horned lizards. Thus we expect the populations of 
flat-tailed horned lizards in parts E-6 and E-9 are connected, and even 
subtracting the area of deep sand in the east of these two parts, the 
subarea south of the All-American Canal is large enough to likely 
support a population of flat-tailed horned lizards that is unlikely to 
be substantially affected by the threats associated with small 
population size. For the subarea west of the Coachella Canal and north 
of the All-American Canal, the populations of flat-tailed horned 
lizards in parts E-3 and E-5 are likely connected because State Route 
78 likely is a semipermeable barrier. Moreover, Part E-5 contains the 
East Mesa Management Area where the density of flat-tailed horned 
lizards is likely greater than the most conservative 0.3 adults per ha 
(0.1 per ac) density estimate. Similarly, Part E-3 likely supports a 
population of flat-tailed horned lizards at a density greater than the 
most conservative 0.3 adults per ha (0.1 per ac). Thus, if we (1) 
exclude parts E-1, E-4, and the deep-sand areas at the east end of 
parts E-6 and E-9 because these areas are naturally poor-quality 
habitat and are likely rarely used by flat-tailed horned lizards; and 
(2) consider part E-3, E-5, and the non-deep-sand portions of E-6 and 
E-9 (combined; see above) as likely supporting large populations of 
flat-tailed horned lizards, then about 93 percent of the Eastern 
Population area likely supports populations of flat-tailed horned 
lizards that are large enough to be unlikely affected by threats 
associated with small populations. Therefore, we conclude that, 
overall, the flat-tailed horned lizards in the Eastern Population are 
not substantially threatened now or in the foreseeable future by 
effects associated with barriers that subdivide populations or the 
deleterious effects that may follow.
Southeastern Population
    Identified potential barriers divide the Southeastern Population 
area into 13 parts (Table 5). By far, the largest single part (Part SE-
5; Table 5, Figures 6 and 7) is in Mexico between the international 
border and the Mexicali to Puerto Pe[ntilde]asco railway, northwest of 
Mexico Federal Highway 8. It is over 720,000 ha (1,779,000 ac) and 
includes the bulk of the Gran Desierto de Altar where the species 
occurs in the sandy flats and low, more-stabilized dunes within this 
region (Rorabaugh 2008, p. 39; Rorabaugh and Young 2009, p. 183), but 
the deep, actively shifting sands of much of this area are likely 
rarely used by flat-tailed horned lizards (Rodriguez 2002, p. 18; 
Rorabaugh and Young 2009, p. 182). Nevertheless, the sheer size and 
limited manmade alterations to the area suggests that this area likely 
supports a population large enough to avoid the deleterious effects 
associated with small populations, even if they are limited to the 
peripheral portions of the ``sand sea.'' This large part touches nearly 
all of the other parts in the Southeastern Population, and in our 
discussion of the other parts, we refer to this large, central part as 
the Gran Desierto part.

[[Page 14245]]



 Table 5--The Size (Area) of the ``Parts'' Created by Barriers (See Text) Within the Southeastern Population and
    our Determination as Whether the Specified Part Is Unlikely To Be at Risk of Deleterious Effects of Small
         Populations at the Conservative Densities of 0.3 or 0.7 Individuals per ha (0.1 or 0.3 per ac)
----------------------------------------------------------------------------------------------------------------
                                                                  Is this part large enough to avoid deleterious
                                                                  effects associated with small populations when
                                                                           the density is assumed to be:
     Part identifier (country)             Area of part \1\      -----------------------------------------------
                                                                  0.3 Individuals per ha  0.7 Individuals per ha
                                                                        (0.1 per ac)            (0.3 per ac)
----------------------------------------------------------------------------------------------------------------
SE-1 (U.S.)........................  56,736 ha (140,198 ac).....  yes...................  yes.
SE-2 (U.S.)........................  1,018 ha (2,516 ac)........  no....................  no.
SE-3 (U.S.)........................  8,804 ha (21,755 ac).......  no....................  no.
SE-4 (U.S.)........................  1,364 ha (3,371 ac)........  no....................  no.
SE-5 (Mex.)........................  720,168 ha (1,779,573 ac)..  yes...................  yes.
SE-6 (Mex.)........................  8,354 ha (20,643 ac).......  no....................  no.
SE-7 (Mex.)........................  496 ha (1,226 ac)..........  no....................  no.
SE-8 (Mex.)........................  110,242 ha (272,414 ac)....  yes...................  yes.
SE-9 (Mex.)........................  110,857 ha (273,934 ac)....  yes...................  yes.
SE-10 (Mex.).......................  5,175 ha (12,788 ac).......  no....................  no.
SE-11 (Mex.).......................  10,585 ha (26,156 ac)......  no....................  yes.
SE-12 (Mex.).......................  833 ha (2,058 ac)..........  no....................  no.
SE-13 (Mex.).......................  38,919 ha (96,171 ac)......  yes...................  yes.
----------------------------------------------------------------------------------------------------------------
\1\ Area values are estimated through a GIS-based assessment. Despite the level of precision presented, area
  values are approximate; however, we believe they are accurate enough to draw the conclusions presented.

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    The railway that runs from Mexicali to Puerto Pe[ntilde]asco and 
south, along with the `old' coastal highway (see above), create four 
parts, three small and one large, along the coast of the Gulf of 
California northwest of Puerto Pe[ntilde]asco. The three small parts 
along the coast are 8,354 ha (20,643 ac) (Part SE-6; Table 5), 496 ha 
(1,226 ac) (Part SE-7; Table 5), and 5,175 ha (12,788 ac) (Part SE-10; 
Table 5). These parts may be at risk from the deleterious effects 
associated with small populations; however, the road and railroad 
separating them from the Gran Desierto part are likely not complete 
barriers. We expect that blowing sand periodically covers the railway 
line and any gaps along the sides of the road, allowing some level of 
connectivity between flat-tailed horned lizard populations on the coast 
with those in the Gran Desierto part. Similarly, the one large coastal 
part northwest of Puerto Pe[ntilde]asco (110,242 ha (272,414 ac)) (Part 
SE-8; Table 5) is also likely connected with the Gran Desierto part; 
however, Part SE-8 is likely large enough by itself to support a 
population large enough that it would not be at risk from deleterious 
effects of small populations. Because we do not believe these four 
parts are completely isolated, the population of flat-tailed horned 
lizards along the coast of the Gulf of California northwest of Puerto 
Pe[ntilde]asco is likely not at risk from the deleterious effects 
associated with small populations.
    Mexico Federal Highway 8, the northeast to southwest-running 
highway from Sonoita (on the international border, outside of the range 
of the flat-tailed horned lizard) to Puerto Pe[ntilde]asco, separates 
the Gran Desierto part from the southeastern-most portion of the 
Southeastern Population. The southward continuation of the railway and 
the parallel-running coastal highway further divides this portion into 
a total of four parts. One of these parts is very small (833 ha (2,058 
ac)) (Part SE-12; Table 5) and confined to a narrow strip along the 
coast. It may be at greater risk of deleterious effects associated with 
small populations. Another narrow coastal part is larger (10,585 ha 
(26,156 ac)) (Part SE-11; Table 5) and could support enough flat-tailed 
horned lizards to avoid deleterious effects of small populations if the 
densities were 0.7 individuals per ha (0.3 per ac). However, this area 
includes a portion of the urban development of Puerto Pe[ntilde]asco, 
and densities may be lower. The southernmost (coastal) part (Part SE-
13; Table 5) is also separated by the railway-highway combination, but 
it is large (38,919 ha (96,171 ac)) and is likely to support a 
population large enough to avoid deleterious effects from small 
populations size even at the most conservative density. These three 
coastal parts are separated from the large interior part (Part SE-9; 
Table 5), which is 110,857 ha (273,934 ac) and large enough to support 
considerably more than 7,000 flat-tailed horned lizards. Additionally, 
if the railway-highway combination separating the three coastal parts 
(Parts SE-11, SE-12, and SE-13) from the larger interior part is not a 
complete barrier, which is possible because of blowing sand, then the 
two larger coastal parts could receive dispersing flat-tailed horned 
lizards from the large interior part, which may help further reduce the 
likelihood of deleterious effects associated with ``small 
populations.'' Moreover, Mexico Federal Highway 8 may also be 
permeable, suggesting that the southernmost portion of the Southeastern 
Population (Parts SE-9, SE-11, SE-12, and SE-13 combined)

[[Page 14247]]

may also be connected with the extremely large Gran Desierto part (Part 
SE-5).
    Lastly, the portion of the Southeastern Population in the United 
States is divided into four parts, including one large part (see below) 
and three smaller parts, the latter including one north of Interstate 8 
and two west of the new Yuma Area Service Highway. The part north of 
Interstate 8 is 1,018 ha (2,516 ac) (Part SE-2; Table 5) and may be at 
risk of deleterious effects associated with small populations. We 
expect the multi-lane Interstate 8 to be nearly a complete barrier 
along this stretch of the road and, as mentioned above, the evidence 
suggests that the population there may be exhibiting inbreeding or 
genetic drift (Culver and Dee 2008, p. 2). The two small parts west of 
the Yuma Area Service Highway are 8,804 ha (21,755 ac) (Part SE-3; 
Table 5) and 1,364 ha (3,371 ac) (Part SE-4; Table 5); both may have 
small populations that could be at risk from the deleterious effects of 
small population size. The large part in Arizona (56,736 ha (140,198 
ac)) (Part SE-1; Table 5) is mostly composed of the Yuma Desert 
Management Area and is large enough to avoid deleterious effects from 
small population size. Culver and Dee (2008, pp. 1-14) also sampled the 
Yuma Desert Management Area and did not report any evidence of 
inbreeding or genetic drift in flat-tailed horned lizards from this 
large part, in contrast to the small, isolated part (Part SE-2) north 
of Interstate 8.
    In sum, for the Southeastern Population, assuming the identified 
potential barriers are complete barriers (which is not likely, see 
above, although we do not know how permeable they may be), and assuming 
the most conservative density of 0.3 flat-tailed horned lizards per ha 
(0.1 per ac), we calculate that about 97 percent of the area is in 
large enough blocks that the populations of flat-tailed horned lizards 
therein are not likely to be affected by threats associated with small 
populations. However, much of the dune areas of the Gran Desierto de 
Altar are likely to have few, if any, flat-tailed horned lizards. 
Nevertheless, given the limited amount of manmade development within 
large areas of the Southeastern Population and the fact that about 97 
percent of the area contains large blocks of flat-tailed horned lizard 
habitat, the Southeastern Population is not substantially composed of 
``small populations.'' Therefore, we conclude the flat-tailed horned 
lizards in the Southeastern Population are not substantially threatened 
now or in the foreseeable future by effects associated with barriers 
that subdivide populations or the deleterious effects that may follow.
    For the Western, Eastern, and Southeastern Population areas 
combined, about 91 percent of the 1,585,157 ha (3,917,008.25 ac) area 
is in large enough blocks that the populations of flat-tailed horned 
lizards therein are not likely to be affected by threats associated 
with small populations. As mentioned above, the part that is primarily 
composed of the Gran Desierto de Altar is very large; it makes up about 
45 percent of the total area of the three populations combined and is 
larger than the Western and Eastern Population areas combined. Without 
the Gran Desierto part, about 84 percent of the total area is in parts 
that are likely to contain populations large enough to avoid 
deleterious effects associated with small populations. Thus, despite 
not having complete population data for the species throughout its 
range, through this analysis of size of the habitat areas, and 
application of conservative estimates (the smallest density value 
within the estimated range, and the largest population size value below 
which we are considering (for our analysis of this species) a ``small 
population''), we conclude that the flat-tailed horned lizard 
populations are not small and the species is not habitat-limited in the 
United States or Mexico.
    In conclusion, this evaluation suggests that despite the presence 
of multiple barriers that potentially divide the Western, Eastern, and 
Southeastern Population areas into smaller parts, most of the areas 
within the current distribution outside of the greater Coachella Valley 
are in parts large enough to support populations of flat-tailed horned 
lizards that are large enough to avoid deleterious effects associated 
with small populations. Therefore, the implied meaning of fragmentation 
is not a significant threat to the flat-tailed horned lizard throughout 
its range or within the Western, Eastern, and Southeastern Population 
areas.

Coachella Valley Population

    The Coachella Valley Population differs from the other three in 
that it has been highly affected by past agricultural development and 
recent (and continuing) urban development (see Factor A). As mentioned 
previously, the only areas with recent detections of flat-tailed horned 
lizards are within the Thousand Palms and the Dos Palmas reserves. The 
precise amount of habitat that is occupied is not known, but based on 
an analysis of habitats within the Coachella Valley MSHCP plan, the 
Thousand Palms and Dos Palmas reserves are anticipated to be 1,707 ha 
(4,219 ac) and 2,078 ha (5,134 ac), respectively (Table 2). Of these, 
94 percent of the Thousand Palms reserve is already in protected 
status, while 34 percent of the Dos Palmas reserve is protected (Table 
2). Using the conservative estimated density of 0.3 adult flat-tailed 
horned lizards per ha (0.1 per ac), neither of these reserves--
presently or even at their anticipated size--is large enough to support 
a ``large population.'' Thus, these two small, fully isolated 
occurrences may be more likely to experience deleterious effects 
associated with small population sizes. In our evaluation of the 
monitoring and management of flat-tailed horned lizard populations and 
habitat expected under the Coachella Valley MSCHP (USFWS 2008, Appendix 
A, p. 322), we stated: ``The proposed Plan provides reasonably 
competent direction for monitoring and adaptive management, but not all 
details can be anticipated beforehand and much would depend on how the 
monitoring and adaptive management is implemented. We assume the 
implementation of the monitoring and adaptive management plan would 
strictly adhere to the guidance in the Plan. The extra pressures of 
edge effects and invasive species may be buffered by management to 
prevent pressures that would push a naturally low population to 
extinction. Populations are expected to increase in numbers again if 
anthropogenic factors are effectively managed.'' Additionally, as noted 
above, even small populations in small habitat areas may be viable in 
the long term; however, for the purposes of this analysis (to be 
conservative) we are assuming they are not. Therefore, we conclude the 
continued existence of the Coachella Valley Population is likely to 
face significant threats within the foreseeable future.

Summary for Barriers and Small Populations

    Past assessments identified ``fragmentation'' as a threat to the 
flat-tailed horned lizard. Fragmentation, as a term used in 
conservation biology, is ambiguous. To address the implied meaning of 
the term, we assessed potential barriers and the resulting flat-tailed 
horned lizard population sizes throughout the species' range.
    Barriers prevent movement of individuals and, thus, restrict or 
prevent gene flow. As such, barriers subdivide larger populations into 
smaller ones. For vertebrate species, populations of more than about 
7,000 individuals are not likely to be affected by deleterious 
intrinsic and extrinsic forces and factors

[[Page 14248]]

over the long term. Not all potential barriers are complete barriers 
and some potential barriers may be ``semipermeable.'' Movement of 1 to 
10 individuals per generation across a semipermeable barrier is likely 
enough to maintain connectivity between populations.
    The populations of flat-tailed horned lizards in the Western, 
Eastern, and Southeastern Population areas are potentially divided by 
artificial manmade barriers. Flat-tailed horned lizards are difficult 
to detect, and population estimates are limited to a few, well-surveyed 
areas. Density estimates of adult flat-tailed horned lizards range from 
as low as 0.3 individuals per ha (0.1 per ac) to as much as 4.4 
individuals per ha (1.8 per ac), depending on the analysis used (see 
Background section). Our evaluation of the range of the species 
suggests that the Western, Eastern, and Southeastern Population areas 
were divided by manmade barriers into 12, 9, and 13 ``parts,'' 
respectively. Using the lowest (most conservative) estimates of 0.3 
adult flat-tailed horned lizards per ha (0.1 per ac), we calculated 
that the Western, Eastern, and Southeastern Population areas had about 
83 percent, 73 percent, and 97 percent of the areas (respectively) in 
parts likely to support populations that are large enough to avoid 
deleterious effects associated with small populations. For those 
values, we assumed all identified potential barriers were complete 
barriers; however, the circumstance for each individual part varies, 
and some of the potential barriers we identified are likely to not be 
complete barriers. As such, some of the parts we identified as separate 
may contain populations of flat-tailed horned lizards that are actually 
connected with neighboring populations. Thus, we believe these 
percentages are conservative because we used the conservative density 
estimates and the parts, as analyzed, may not actually contain separate 
populations of flat-tailed horned lizards.
    Additionally, the Coachella Valley Population area has numerous 
barriers and the remaining flat-tailed horned lizards are restricted to 
two small areas. The populations of flat-tailed horned lizards in these 
areas are likely to be affected by threats associated with small 
population size.
    We again note that we have very little specific data regarding 
whether or to what degree populations of flat-tailed horned lizards are 
actually being affected by threats associated with small population 
size. Even for the flat-tailed horned lizard population in Part SE-2, 
which may be exhibiting genetic deterioration because of isolation and 
small population size, we do not have direct information on the status 
of that population. Thus, based on information from the scientific 
literature on the potential effects of small population size, for the 
purposes of this threats assessment, we have assumed these ``small'' 
populations of flat-tailed horned lizards are being substantially 
affected by threats associated with small population size or are likely 
to be substantially affected by threats associated with small 
population size in the foreseeable future.
    Even so, our evaluation suggests that despite the presence of 
multiple barriers that potentially divide the Western, Eastern, and 
Southeastern Population areas into smaller parts, most of the area 
within the current distribution outside of the greater Coachella Valley 
are in parts large enough to support populations of flat-tailed horned 
lizards larger than 7,000 individuals, meaning they are not habitat-
limited and are not likely to suffer from threats associated with small 
populations now or in the foreseeable future. As such, the implied 
meaning of term ``fragmentation'' is not a threat to the flat-tailed 
horned lizard throughout its range.
Edge Effects
    Another effect associated with fragmentation and barriers is that 
there are more habitat edges. When two ecosystems are separated by an 
abrupt transition (an ``edge''), there may be an interaction between 
two adjacent ecosystems, known as an edge effect (Murcia 1995, p. 58). 
As noted previously, predation of flat-tailed horned lizards may be 
greater adjacent to urban and agricultural areas (Barrows et al. 2006, 
p. 486), and may extend several hundred meters (yards) from the 
neighboring developed area (Young and Young 2005, p. 7). Additionally, 
invasive, nonnative plants may also occur at higher densities along 
road edges (Gelbard and Belnap 2003, p. 420); however, native plant 
growth may also increase along roads (Lightfoot and Whitford 1991, p. 
310). Increased plant growth may lead to increased seeds, which may 
benefit harvester ants, the primary food of the flat-tailed horned 
lizard.
    Additionally, the invasive, nonnative Argentine ant (Linepithema 
humile) has been found to be a problem for coastal horned lizards 
(Phrynosoma coronatum) in habitat edges (Suarez et al. 1998, p. 2041; 
Suarez and Case 2002, p. 291). However, Argentine ants do not tolerate 
hot, arid conditions (Holway et al. 2002, p. 1610) and are not known to 
be a problem away from habitat edges in flat-tailed horned lizard 
habitat (Barrows et al. 2006, p. 492); thus, we expect the effect of 
Argentine ants to be limited to areas adjacent to edges that have water 
sources.
    Although edge effects may result in increased mortality of flat-
tailed horned lizards, primarily resulting from increased levels of 
predation, the area affected is within several hundred meters (yards) 
of the edge. As discussed in the ``Barriers and Small Populations'' 
section, much of the area occupied by the flat-tailed horned lizard is 
in large areas (or ``parts''). In such areas or parts, the ratio of 
linear edge compared to the areal size of the part is small, meaning 
large parts have larger ``interior'' areas that are not affected by 
edge effects. As such, the populations of flat-tailed horned lizards in 
large areas or parts are less likely to be substantially affected by 
edge effects. Conversely, smaller parts have a smaller percentage of 
their area that is likely to be affected by edge effects. As such, 
flat-tailed horned lizard populations in the small parts are more 
likely to be substantially affected by edge effects.
    Because ``parts'' are created by infrastructural elements 
associated with urban and agricultural development, the small ``parts'' 
are more likely near urban and agricultural areas. Moreover, because 
edge effects are most pronounced near urban and agricultural 
development, the flat-tailed horned lizards in small parts are the most 
likely to be substantially affected by edge effects. Thus, edge effects 
are an added threat faced by flat-tailed horned lizard populations in 
the small parts. As such, edge effects are not additional threats to 
the flat-tailed horned lizard, but instead are part of the threats 
faced by flat-tailed horned lizard populations in small parts. 
Therefore, like small population size, we do not believe edge effects 
are a significant threat to the flat-tailed horned lizard now or in the 
foreseeable future.
Pesticide Spraying
    Past assessments identified the spraying of pesticides as part of 
the California Department of Food and Agriculture's Curly Top Virus 
Control Program as a threat to the flat-tailed horned lizard, mainly in 
the East Mesa, West Mesa, and Yuha Desert (58 FR 62627; FTHLICC 2007, 
p. 20). As described in the program's environmental assessment (BLM 
2007b, p. 8), beet curly top virus is a disease of commercially 
important crops, and also backyard vegetable and flower gardens. The 
only known vector of beet curly top virus is an insect known as the 
sugar beet leafhopper (Circulifer

[[Page 14249]]

tenellus). The Curly Top Virus Control Program includes aerial and 
ground-based spraying of malathion, which is the only product 
registered in California for the control of sugar beet leafhopper on 
rangeland (BLM 2007b, p. 15). The areas to be sprayed (treated) are 
prioritized; treatment priorities are given to areas subject to 
perennial virus infection, areas sustaining significant infection from 
the previous year, and areas with the highest current sugar beet 
leafhopper populations (BLM 2007b, p. 8).
    Available information in the scientific literature regarding the 
effects of malathion, a broad-spectrum insecticide, on lizard species 
are equivocal, with some suggesting that malathion has substantial 
deleterious effects on lizards (such as [Ouml]zelmas and Akay 1995, pp. 
730-737; Khan 2003, pp. 821-825; Khan 2005, pp. 77-81), and others 
suggesting the effects are less pronounced (such as Holem et al. 2006, 
pp. 111-116; Holem et al. 2008, pp. 92-98). We are not aware of any 
studies examining the effects of malathion on horned lizard species.
    Flat-tailed horned lizards are insectivorous, primarily feeding on 
harvester ants. If the food source for the flat-tailed horned lizard is 
substantially affected by the spraying of malathion, the flat-tailed 
horned lizard could be affected. To address this concern, 
implementation of the Curly Top Virus Control Program in the Imperial 
Valley in 1991 included monitoring of harvester ant colonies. Results 
showed malathion killed worker ants on the surface at the time of the 
spraying, negatively affecting ant colonies temporarily; however, it 
also showed that the colonies, with the queen and other workers below 
ground, rapidly recovered (Peterson in litt. 1991, p. 10; see also BLM 
2007b, p. 75). Although that monitoring was cursory, the information 
suggests that spraying is not likely to substantially affect the 
primary food source of the flat-tailed horned lizard now or in the 
foreseeable future.
    Even if flat-tailed horned lizards or harvester ants are affected 
by malathion, the Curly Top Virus Control Program includes measures to 
limit its impact. The threat from pesticide spraying has been reduced 
by avoidance and minimization measures incorporated in the program 
since the publication of the 1993 proposed rule to list the flat-tailed 
horned lizard, including the following (BLM 2007b, p. 33):
    (1) No malathion treatments shall occur in designated flat-tailed 
horned lizard Management Areas as set forth in the Flat-tailed Horned 
Lizard Range-wide Management Strategy.
    (2) Application of malathion within the geographic range of the 
[flat-tailed horned lizard] will consist of no more than a single 
treatment per given area per year.
    (3) All application [within flat-tailed horned lizard habitat] will 
be aerial. No spraying from off-road vehicles or use of off-road 
vehicles on other than designated roads will be used within [flat-
tailed horned lizard] habitat.
    Beyond the avoidance and minimization measures incorporated into 
the Curly Top Virus Control Program, aerial spraying is conducted 
infrequently in the Imperial Valley--aerial treatments have been 
necessary only twice in the 9 years prior to the 2007 environmental 
assessment (BLM 2007b, p. 9). Additionally, the State's program 
administrator for the Curly Top Virus Control Program indicated that 
although the program will continue in the region, the frequency of 
aerial treatments in the foreseeable future is anticipated to decrease; 
instead, treatments are more likely to be implemented via ground-based 
spraying in areas near agriculture outside of flat-tailed horned lizard 
habitat (R. Clark, California Department of Food and Agriculture, pers. 
comm., 2010).
    Because of the avoidance and minimization measures incorporated 
into the Curly Top Virus Control Program, and because of the likely 
limited effects to the flat-tailed horned lizard and its food source at 
the levels that the program is expected to be implemented, we conclude 
that implementation of the Curly Top Virus Control Program is not a 
threat to the flat-tailed horned lizard.
Vehicle Activity
    Flat-tailed horned lizards may be directly affected by vehicle 
activity. The assessments in the 1993 and 2003 documents (58 FR 62624 
and 68 FR 331, respectively) identified impacts from vehicles as a 
threat to the species, especially OHV activity. Impacts of vehicle 
activity on flat-tailed horned lizard habitat are addressed in Factor 
A, above. Additionally, individual flat-tailed horned lizards may be 
killed--crushed--by vehicle activity. As discussed above, because flat-
tailed horned lizards are unlikely to flee from oncoming traffic, when 
flat-tailed horned lizards are on paved roadways they are likely to be 
killed by any vehicle activity. Additionally, flat-tailed horned 
lizards may be killed by vehicles operating off paved roads, including 
vehicle activity on established dirt or gravel roads and trails, or 
vehicle activity off established roads and trails (OHV activity as 
defined in Factor A) (Muth and Fisher 1992, p. 33). Vehicle drivers may 
not see or recognize flat-tailed horned lizards because their cryptic 
coloration makes them difficult to spot or they may be interpreted as 
rocks. Moreover, the species' propensity to freeze rather than flee 
makes them particularly susceptible. Impacts from vehicles are more 
likely when the lizards are on or near the surface; hibernating flat-
tailed horned lizards are generally buried deep enough that they are 
not crushed by vehicles driving over them (Grant and Doherty 2009, p. 
511). Additionally, most of the OHV activity in the region occurs 
during the cooler times of the year (Wone 1992, pp. 4-5), suggesting 
that fewer flat-tailed horned lizards would be on the surface during 
peak times of OHV activity.
    Moreover, the density of flat-tailed horned lizards is apparently 
naturally low. Even at the highest estimated density of 4.4 adult flat-
tailed horned lizards per hectare (1.8 per acre) (see Background), 
which is equivalent to 0.00044 individuals per square meter (0.00004 
per square foot), the chances of a flat-tailed horned lizard being run 
over by a vehicle is low, even in areas of high OHV activity (for 
example, see Nicola and Lovich 2000, pp. 208-212). Nevertheless, 
mortality of flat-tailed horned lizards resulting from OHV activity has 
been documented, even in areas of low OHV use. For example, in an area 
closed to OHV traffic, 2 of the 42 radio-tagged flat-tailed horned 
lizards were killed by illegal OHV activity, and 1 was killed by a 
vehicle on a paved road (Muth and Fisher 1992, pp. 18 and 33). However, 
in comparison, in that same study, 16 of the 42 radio-tagged flat-
tailed horned lizards were depredated over the same period (Muth and 
Fisher 1992, p. 33).
    In the past, OHV activity along the United States-Mexico boundary 
(border) from Border Patrol activity and other border-related OHV 
traffic has been specifically identified as a threat. Border-related 
OHV activity is part of our definition of OHV activity and is covered 
above. Moreover, since 2008, the U.S. Customs and Border Protection 
constructed the ``border fence,'' which is a vehicle and, in some 
areas, pedestrian barrier, plus associated infrastructure, in certain 
areas between the United States and Mexico. Although some areas of the 
border are not fenced, the areas of flat-tailed horned lizard habitat 
along the border are fenced (USCBP 2008a, p. 1-5; USCBP 2008b, p. 2-4; 
Rorabaugh 2010, p. 181). Evidence suggests the border fence has reduced 
illegal cross-border traffic and associated OHV activity (Rorabaugh 
2010, p. 190), thereby reducing the amount of

[[Page 14250]]

potential impacts to flat-tailed horned lizards along the border from 
illegal trans-border OHV activity and subsequent law-enforcement OHV 
activity by the Border Patrol.
    Because the flat-tailed horned lizard occurs naturally in low 
densities, roads are generally widely separated, and OHV activity is 
only intense in a few areas, the chances that a flat-tailed horned 
lizard being crushed by vehicle activity is low over the majority of 
the species' range; therefore, we conclude that vehicle activity is not 
a substantial threat to the species throughout its range, nor do we 
expect it to become a significant threat in the foreseeable future.
Drought and Climate Change
    The assessments in the 1993 and 2003 documents (58 FR 62624 and 68 
FR 331, respectively) included drought as a potential threat to the 
flat-tailed horned lizard. Additionally, changes in weather patterns 
associated with global climate change, particularly the timing and 
amount of rainfall in this arid region, are a potential threat to the 
species. We examine both below.
    Prolonged periods of atypically low rainfall (drought) may 
potentially affect flat-tailed horned lizard by affecting its food 
chain (see Background section). Plants produce fewer seeds during 
periods of low rain, leading to a reduction in the number of foraging 
ants (Tevis 1958, p. 698), which reduces the amount of food available 
for flat-tailed horned lizards. However, harvester ant colonies do 
appear to survive prolonged periods of drought (Tevis 1958, p. 701; 
Whitford et al. 1999, p. 165), indicating that flat-tailed horned 
lizards will have some food available. Depressed flat-tailed horned 
lizard populations associated with reduced abundance of ants are known 
to have rebounded after ant populations returned, even in small 
populations of flat-tailed horned lizards (Barrows and Allen 2009, p. 
314). Thus, we do not expect droughts to permanently affect large 
populations of flat-tailed horned lizards, although droughts may 
contribute to the extirpation of small populations. Because about 91 
percent of the area occupied by flat-tailed horned lizards are in areas 
large enough to support large populations (see ``Barriers and Small 
Populations'' section above), and because evidence shows that even 
small populations of flat-tailed horned lizards have survived periods 
of drought (see above), this suggests that it is not likely that all of 
the 9 percent of the ``small population'' area would be affected by 
drought. Therefore, we do not anticipate drought to be a significant 
threat to the species throughout its range.
    Current climate change predictions for terrestrial areas in the 
Northern Hemisphere indicate warmer air temperatures, more intense 
precipitation events, and increased summer continental drying (Field et 
al. 1999, pp. 1-63; Cayan et al. 2006, pp. 1-47; Meehl et al. 2007, pp. 
747-843). Assessments for the Sonoran Desert are few, but the region is 
expected to warm (IPCC 2007, p. 887). Indeed, since about the 1970s, 
the region appears to have experienced ``widespread warming trends in 
winter and spring, decreased frequency of freezing temperatures, 
lengthening of the freeze-free season, and increased minimum 
temperatures per winter year'' (Weiss and Overpeck 2005, p. 2065). 
Further, if summertime temperatures increase in the already typically 
hot Sonoran Desert, temperatures may exceed the ability for many 
animals, including the flat-tailed horned lizard, to survive. For 
example, Sinervo et al. (2010, p. 895) suggest that Phrynosomatid 
lizards (the family to which flat-tailed horned lizards belong) are 
susceptible to increased risk of extinction because of their 
intolerance to an increase in environmental temperatures. Increased 
temperatures would result in longer periods of time when the flat-
tailed horned lizard would be forced to seek cooler microclimates 
(shade, burrows), leaving less time available in the day for feeding or 
other necessary activities (see also Huey et al. 2010, pp. 832-833). 
However, we are not aware of any information indicating that the flat-
tailed horned lizard is being substantially affected by a reduced 
frequency of cold temperatures or increased frequency of high 
temperatures, or that it will be substantially affected in the 
foreseeable future.
    Additionally, precipitation may become more variable (Weiss and 
Overpeck 2005, p. 2065). Increased severity, frequency, or duration of 
droughts may exceed the resiliency of the flat-tailed horned lizard, or 
the species in the food chain upon which it depends. In contrast, 
models suggest that the frequency and intensity of El Ni[ntilde]o-
Southern Oscillation events may increase as a result of global climate 
change (Field et al. 1999, p. 10), which may lead to increased rainfall 
in some portions of the species' range. Although typically considered a 
benefit, increased rainfall may negatively affect harvester ant 
abundance and thus negatively affect flat-tailed horned lizards, at 
least in some areas (Barrows and Allen 2009, p. 312). Also, increased 
rainfall may disproportionately promote growth of nonnative, invasive 
plant species, which can increase the prevalence of wildland fire and 
be a physical hindrance to flat-tailed horned lizard locomotion (see 
``Invasive, Nonnative Plants'' section in the Factor A discussion, 
above).
    Thus, the effects associated with global climate change may affect 
the flat-tailed horned lizard, but at this time, the level of 
uncertainty in climate predictions is high. Moreover, we do not know 
whether such a change would substantially affect the flat-tailed horned 
lizard. While we recognize that climate change is an important issue 
with potential effects on species and their habitats, we lack adequate 
information to make accurate predictions regarding its effects to the 
flat-tailed horned lizard. We do not have any evidence to suggest that 
the flat-tailed horned lizard is being substantially affected by 
climate change at this time, or will be within the foreseeable future. 
Therefore, the effects of climate change are not a significant threat 
at this time.
Summary of Factor E Threats
    For Factor E, we assess the natural and manmade threats that affect 
the status of the species. Small populations may be disproportionately 
affected by extrinsic and intrinsic factors that reduce population 
size. Given that historical agricultural and urban development 
destroyed large swaths of potential flat-tailed horned lizard habitat, 
we assessed whether the remaining populations are large enough to 
likely avoid the deleterious effects associated with small populations. 
Within the Coachella Valley Population area, where habitat destruction 
has continued (see Factor A), flat-tailed horned lizards are now found 
only in two small locations and may be more likely to be affected by 
the deleterious effects associated with small populations. Using 
conservative estimates of flat-tailed horned lizard density in 
combination with the size of the Western, Eastern, and Southeastern 
Populations areas (as a whole), we conclude that each is large enough 
to support populations that are not likely to be affected by the 
deleterious effects associated with small populations.
    However, the Western, Eastern, and Southeastern Populations areas 
have within them potential manmade barriers (canals, roads, railways) 
that may further act as complete barriers or semipermeable barriers 
that subdivide the populations into smaller subpopulations. Thus, we 
assessed whether the areas created by these potential barriers were 
large enough to

[[Page 14251]]

likely support populations (subpopulations) that were likely greater 
than 7,000 adult individuals. Using the most conservative flat-tailed 
horned lizard density estimate of 0.3 individual adults per hectare 
(0.1 per acre), which is the lowest value in the range of estimates 
that extends to 4.4 individuals per hectare (1.8 per ac), and assuming 
(1) all potential barriers are complete barriers, which is unlikely 
because some barriers likely allow some movement of individuals (see 
above) and only 1 to 10 individuals per generation are needed to 
maintain population connectivity; and (2) 7,000 adults is the threshold 
above which a population is large enough to likely avoid the 
deleterious effects associated with small populations, which is at the 
high end of the range of estimated population thresholds, we concluded 
that about 83 percent, 73 percent, and 97 percent of the Western, 
Eastern, and Southeastern Population areas (respectively), and about 91 
percent of the area overall, are in large enough blocks that the 
populations of flat-tailed horned lizards within them are not likely to 
be affected by threats associated with small populations. Thus, the 
vast majority of the current distribution of the flat-tailed horned 
lizard occurs in blocks of habitat large enough to support populations 
greater than 7,000 adults; therefore, small population size is not a 
threat to the flat-tailed horned lizard and the species is not habitat-
limited.
    Pesticide spraying associated with the Curly Top Virus Control 
Program is not a threat to the flat-tailed horned lizard because of the 
small area within the range of the species over which it is likely to 
occur, the avoidance and minimization measures built into the program, 
and the likely limited effects of spraying on the flat-tailed horned 
lizard and its harvester ant food source. Additionally, vehicle 
activity--on paved roads, non-paved roads, and off-road--is not a 
substantial threat to the species because the chances of a flat-tailed 
horned lizard being crushed by vehicle activity are low over the 
majority of the species' range. Drought is also not likely to be a 
substantial threat to the species throughout its range. Climate change 
could potentially affect flat-tailed horned lizards, but the future 
effects of climate change are uncertain. Moreover, no substantial 
effects of climate change to the flat-tailed horned lizard are known at 
this time. Therefore, the effects of climate change are not a 
significant threat at this time.
    We do not consider the potential threats analyzed above to be 
substantial threats to the flat-tailed horned lizard, either 
individually or in combination. Therefore, based on our review of the 
best available scientific and commercial information we find the flat-
tailed horned lizard is not threatened by natural or manmade factors 
affecting its continued existence, either now or in the foreseeable 
future.

Conservation Efforts

    Before we may determine whether a species should be listed as 
endangered or threatened, section 4(b)(1)(A) of the Act requires that 
we take into account those efforts, if any, being made by any State or 
foreign nation, or any political subdivision of a State or foreign 
nation, to protect the flat-tailed horned lizard. Of particular note is 
the Interagency Conservation Agreement between and among participating 
State and Federal agencies implementing the Rangewide Management 
Strategy, which is discussed in detail in the Background section. Other 
conservation efforts include regulatory mechanisms, which are discussed 
under Factor D in the Summary of Factors Affecting the Species section.
    On April 3, 2008, the Secretary of the U.S. Department of Homeland 
Security (DHS), pursuant to his authority under section 102(c) of the 
Illegal Immigration Reform and Immigrant Responsibility Act (8 U.S.C. 
1103 note) (IIRIRA), exercised his authority to waive certain 
environmental and other laws in order to ensure the expeditious 
construction of tactical infrastructure along the United States-Mexico 
Border (i.e., the ``border fence'') (73 FR 18293). As such, activities 
associated with construction and operation of the border fence are 
exempt from regulatory mechanisms described in Factor D. These 
activities also do not need to comply with the avoidance, minimization, 
or mitigation measures described in the Rangewide Management Strategy. 
However, the Secretary committed DHS to continue to protect valuable 
natural and cultural resources (USCBP 2008a, p. ES-1). As a result, the 
U.S. Customs and Border Protection prepared Environmental Stewardship 
Plans for the portions of the United States-Mexico border that fall 
within the current distribution of the flat-tailed horned lizard (USCBP 
2008a, 2008b, entire documents). United States Customs and Border 
Protection has expressed an intent to work in a collaborative manner 
with local government, State and Federal land managers, and the 
interested public to identify environmentally sensitive resources and 
develop appropriate best management practices to avoid or minimize 
adverse impacts resulting from the installation of tactical 
infrastructure (USCBP 2008b, p. ES-1), including certain conservation 
measures from the Rangewide Management Strategy that will be 
implemented to the fullest extent applicable and practicable. Thus, 
implementation of the Environmental Stewardship Plans is best 
considered a conservation effort for the species.

Finding

    The flat-tailed horned lizard monitoring data on which we relied in 
this document are more robust than the data we relied on in our 1993 
proposed rule (58 FR 62624) and our earlier withdrawal documents (62 FR 
37852, 68 FR 331, and 71 FR 36745), thus enabling us to conclude with 
increased confidence that flat-tailed horned lizard populations in the 
Management Areas are not low in abundance or declining. Although no 
comparable historical abundance data exist, our analysis suggests that 
occupancy of flat-tailed horned lizards within survey areas is 
relatively high. Density estimates obtained through the new survey 
methodology are roughly in the same range provided by previous 
estimates, suggesting no marked declines in density since the late 
1990s. Although additional surveys are needed before the recently 
collected data can provide long-term trend information, the short-term 
data do not currently indicate declines. Because of data limitations, 
we cannot extrapolate the data rangewide; however, for the Management 
Areas surveyed (see Population Dynamics under the Background section), 
the best available scientific information suggests that population 
levels are not low and not declining. In other words, recognizing that 
the areas surveyed compose only a fraction of the overall range of the 
flat-tailed horned lizard, it is our interpretation that the available 
population data (alone and without considering potential threats) do 
not support a conclusion that the species is in danger of extinction. 
Additionally, despite the lack of long-term trend data, the general 
agreement of the recent data with the older data from the available 
scientific literature lead to our interpretation that the available 
population data (alone and without considering potential threats) do 
not support a conclusion that the species is likely to become 
endangered within the foreseeable future.
    Although our past assessments suggest that historical loss of 
habitat resulted in artificial barriers, except for the Coachella 
Valley Population, the information currently available indicate 
otherwise. We conclude that the manmade barriers resulting from

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historical agricultural and urban development merely expanded pre-
existing natural barriers. This conclusion is based on genetic data 
that show separation of the Western, Eastern, and Southeastern 
Populations occurred prior to the development of the region more than a 
century ago. Genetic data also suggest that flat-tailed horned lizards 
in the Coachella Valley had limited connection with the Western 
Population; thus, the historical agricultural development northwest of 
the Salton Sea, along with the continued development in that region, 
has created an artificial barrier at this location. As such, the 
treatment of flat-tailed horned lizards in the Coachella Valley as a 
separate population is more an artifact of manmade activities than of 
natural divisions within the flat-tailed horned lizard population as a 
whole.
    Moreover, we determined herein that the Western, Eastern, and 
Southeastern Population areas (each as a whole) are not threatened by 
the factors associated with small population size and are not habitat-
limited. Thus, ramifications of historical habitat loss are not likely 
to constitute a significant threat to the species within the 
foreseeable future in these populations. Additionally, because the 
majority of the Western, Eastern, and Southeastern Population areas are 
not subdivided by other barriers (such as canals, roads, railways, or 
border infrastructure), it is unlikely these areas would be 
substantially affected by the intrinsic and extrinsic factors, 
including edge effects, that may negatively affect small populations.
    In the Coachella Valley, the precise amount of habitat that is 
occupied is not known, but based on an analysis of habitats within the 
Coachella Valley MSHCP plan, the Thousand Palms and Dos Palmas reserves 
are anticipated to be 1,707 ha (4,219 ac) and 2,078 ha (5,134 ac), 
respectively (see Table 2). Of these, 94 percent of the Thousand Palms 
reserve is already in protected status, while 34 percent of the Dos 
Palmas reserve is protected (Table 2). These two small areas are 
unlikely to support flat-tailed horned lizard populations large enough 
to escape from being substantially affected by the intrinsic and 
extrinsic factors, including edge effects, that may negatively affect 
small populations. However, even if the Coachella Valley Population may 
be threatened by the effects of barriers and the intrinsic and 
extrinsic factors that may negatively affect small populations, the 
3,785-ha (9,353-ac) Coachella Valley Population area makes up only 
about 0.2 percent of the roughly 1,585,000 ha (3,916,600 ac) of the 
rest of the species' range and about 0.8 percent compared to the 
467,000 ha (1,154,000 ac) of the U.S. portion of that range, and the 
threats to the Coachella Valley population do not substantially 
threaten the species as a whole.
    Therefore, the effects to the species associated with the implied 
meaning of fragmentation--that is, the division of the species' 
populations into smaller populations by the introduction of manmade 
barriers and the subsequent deleterious effects that may be associated 
with small population size--are not likely to constitute a substantial 
threat to the species now or within the foreseeable future.
    Within the United States, most of the area occupied by the species 
is under Federal or State control and overseen by agencies that are 
signatories to the Interagency Conservation Agreement and associated 
Rangewide Management Strategy. Although the Interagency Conservation 
Agreement is voluntary, several signatories--including the BLM, which 
is a major landowner within the U.S. portion of the range of the flat-
tailed horned lizard--have incorporated aspects of the Rangewide 
Management Strategy into their planning documents, thus making them 
less voluntary because those plans implement existing regulatory 
mechanisms. Implementation of this strategy resulted in creation of 
five Management Areas that, as of 2009, total 185,653 ha (458,759 ac) 
of higher quality flat-tailed horned lizard habitat (Table 1). 
Management objectives also provide avoidance and minimization measures 
to reduce impacts from permitted projects and limit the development 
area within each Management Area to 1 percent. Additionally, 
implementation of the Rangewide Management Strategy calls for 
monitoring, management, land acquisition, and research; further, it 
promotes coordination with governmental and non-governmental groups in 
Mexico to provide conservation benefit for the species in that country. 
The tasks identified by the Rangewide Management Strategy have been 
consistently implemented by signatory agencies per the Rangewide 
Management Strategy's schedule. Thus, we conclude the conservation 
efforts implemented by signatories of the Interagency Conservation 
Agreement and associated Rangewide Management Strategy reduce the 
impact of existing threats in the United States and promote actions 
that benefit the flat-tailed horned lizard throughout its range, 
including Mexico.
    Threats to flat-tailed horned lizards associated with development 
activities are reduced or limited by the Interagency Conservation 
Agreement on signatory lands, particularly within Management Areas. 
Additionally, threats to the species and its habitat in areas outside 
of the Management Areas are likely restricted by the limited amount of 
water available in this arid region and remoteness of much of the 
habitat, especially in Mexico. Less remote areas, such as the Coachella 
Valley, Borrego Springs, Yuma, San Luis de Colorado, and Puerto 
Pe[ntilde]asco areas, are more likely to have urban or agricultural 
development; however, impacts in these areas are anticipated to be 
small relative to the amount of available habitat throughout the 
species' current distribution.
    Development associated with new energy facilities is likely to be 
reduced or limited by continued implementation of the Rangewide 
Management Strategy. Although few energy development projects have been 
fully permitted to date, we anticipate more will be proposed in the 
foreseeable future. Within the range of the flat-tailed horned lizard, 
we expect development within the Western Population between Interstate 
8 and the existing railway (Part W-5) to reduce the already limited 
connectivity across Interstate 8, although South Fork Coyote Wash is 
expected to continue to be a potential corridor for flat-tailed horned 
lizard movement. We conclude the remaining habitat in the Western 
Population area (i.e., north of the railway and south of Interstate 8, 
including areas designated as Management Areas) is large enough to 
support flat-tailed horned lizard populations. Also, we expect the 
total acreage of potential development for renewable energy facilities 
to be small compared to the overall range of the species, including on 
private land. Additionally, on lands managed by signatory agencies to 
the Interagency Conservation Agreement, we expect the impacts to flat-
tailed horned lizard habitat (whether inside or outside of designated 
Management Areas) will be further reduced because of the avoidance, 
minimization, and compensation measures of the Rangewide Management 
Strategy.
    Additionally, invasive, nonnative plants; vehicle activity, 
including OHV use near the United States-Mexico border and elsewhere; 
and pesticide spraying are not likely substantial threats to the 
species throughout its range. Predation is not likely a substantial 
threat in and of itself, but because several species that prey upon 
flat-tailed horned lizards likely occur in higher numbers near manmade 
areas, predation may contribute to the deleterious effects (as an 
``edge effect'') associated with urban and agricultural

[[Page 14253]]

development and increase the level of impermeability of some 
semipermeable barriers. However, we do not expect increased levels of 
predation to substantially affect the species where it occurs in large 
``parts,'' which is a majority of its range overall and within the 
Western, Eastern, and Southeastern Populations. Drought and climate 
change have the potential to affect flat-tailed horned lizards, but the 
magnitude of this threat, although unclear because of the high level of 
uncertainty associated with climate predictions, do not appear to be 
significant now or within the foreseeable future.
    Finally, we acknowledge we lack complete population data for the 
species throughout its range. However, through our analysis of size of 
the habitat areas, and application of conservative estimates (smallest 
density value within the estimated range, and largest population size 
value below which a population may be considered ``small''), we 
conclude that the flat-tailed horned lizard populations are not small 
and the species is not habitat-limited in the United States or Mexico 
at this time, nor do we expect the species to suffer from the 
deleterious effects of small population size in the foreseeable future.
    As required by the Act, we considered the species' status relative 
to one or more of the five factors described in section 4(a)(1) of the 
Act, and the standards for listing as endangered or threatened 
throughout all of its range, and we considered the conservation efforts 
being made by any State or foreign nation. We have carefully assessed 
the best scientific and commercial data available regarding the past, 
present, and reasonably anticipated future threats faced by this 
species. Our analysis of the information pertaining to the five threat 
factors did not identify threats of imminence, intensity, or magnitude, 
either individually or in combination, to the extent that the species 
requires the protection of the Act throughout its range. Further, there 
is no information to suggest that the flat-tailed horned lizard 
population is declining or is in danger of becoming an endangered 
species in the foreseeable future. Therefore, we conclude that the 
species is not in danger of extinction or likely to become so within 
the foreseeable future and is not in need of the protections afforded 
by the Act at this time.

Distinct Population Segment

    Under section 3(16) of the Act, a ``species'' is defined as 
including not only the full, taxonomically defined species (i.e., the 
species as a whole, including any and all taxonomically defined 
subspecies) but also any (individual) subspecies and any distinct 
population segment (DPS) of a vertebrate species (16 U.S.C. 1532). On 
February 7, 1996, we, along with the National Marine Fisheries Service 
(National Oceanic and Atmospheric Administration--Fisheries), finalized 
a joint policy that addresses the recognition of DPSs of vertebrate 
species for potential listing actions (DPS policy) (61 FR 4722). The 
policy was developed (1) to implement the measures prescribed by the 
Act and Congressional guidance, (2) to allow for a more refined 
application of the Act to better reflect the biological needs of the 
taxon being considered, and (3) to avoid the inclusion of entities that 
do not require protective measures of the Act. As noted in the policy 
(61 FR 4725), Congressional guidance indicates that the authority to 
list DPSs is to be used ``sparingly.''
    As mentioned previously, we proposed to list the flat-tailed horned 
lizard--the entire species throughout its range--as a threatened 
species under the Act in 1993 (58 FR 62624). Since then, we conducted 
several additional analyses on the status of the species. From the 1993 
proposed rule through the 2006 withdrawal document (71 FR 36745), we 
noted the disjunct distribution of the species. Our 2003 withdrawal 
document in particular explicitly addressed threats over four disjunct 
populations of the flat-tailed horned lizard that we identified in the 
United States, including: (1) The Coachella Valley in California, (2) 
the area west of the Salton Sea and Imperial Valley in California, (3) 
the area east of the Salton Sea and Imperial Valley in California, and 
(4) the Yuma Desert area in Arizona (68 FR 331). Additionally, we 
addressed separately the populations in Mexico.
    Also in our 2003 withdrawal document, we conducted a brief 
evaluation of a potential DPS for the Coachella Valley population (and 
only that population) in a response to a public comment (68 FR 336). We 
alluded to the population possibly being discrete (because it was 
disjunct), but we concluded that it was not significant within the 
meaning of the DPS policy because: (1) It was not ``genetically, 
behaviorally, or ecologically unique''; (2) it was not a ``large 
population'' (not necessarily as defined in the present document); and 
(3) it did not contribute ``individuals to other geographic areas 
through emigration.'' Our response concluded, ``If additional 
information becomes available that indicates the Coachella Valley 
population is biologically or ecologically significant pursuant to the 
[DPS policy], we may reconsider the status of the Coachella Valley 
population for the purpose of listing under the Act'' (68 FR 336).
    Since then, additional information has become available on the 
genetic structure of flat-tailed horned lizard populations. Genetic 
data could, as indicated by the DPS policy (61 FR 4725), inform our 
analysis of discreteness or significance. Therefore, in light of this 
new information and our past DPS analysis, we believe it is appropriate 
to evaluate potential DPSs of the flat-tailed horned lizard.
    The 1996 DPS policy specifies that we should address two elements 
prior to determining a population segment's conservation status in 
relation to the Act's standard for listing (61 FR 4725). These include: 
(1) The population segment's discreteness from the remainder of the 
species to which it belongs, and (2) the population segment's 
significance to the species to which it belongs. If we determine that a 
population segment meets the discreteness and significance standards, 
then we evaluate the level of threat to that population segment based 
on the five listing factors established by section 4(a) of the Act to 
determine whether listing the DPS as either endangered or threatened is 
warranted.
    As described in Description of Specific ``Populations'' in the 
Background section above, the distribution of the flat-tailed horned 
lizard may be divided into four, physically (geographically) separated 
populations. Below, we evaluate these populations as potential distinct 
vertebrate population segments under our DPS policy.

Discreteness

    Our DPS policy states that a vertebrate population segment may be 
considered discrete if it satisfies either of the following two 
conditions (61 FR 4725):
    (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 may provide evidence of this separation; or
    (2) It is delimited by international governmental boundaries within 
which 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.

[[Page 14254]]

First Condition for Discreteness
    As noted at various points in the Background section, each of the 
four described populations--the Coachella Valley, Western, Eastern, and 
Southeastern Populations--are geographically separated from each other 
by natural barriers, manmade barriers, or both. The four populations of 
flat-tailed horned lizards are markedly separated from each other as a 
consequence of physical factors and each may be readily circumscribed 
and distinguished from the others. Therefore, the four populations of 
flat-tailed horned lizards meet the first condition for discreteness 
under our DPS policy.
    Additionally, the Coachella Valley Population, although more 
extensive in the recent past, now consists of two isolated occurrences, 
the Thousand Palms and Dos Palmas subareas. In the Summary of Factors 
Affecting the Species section, we considered the Thousand Palms and Dos 
Palmas subareas together as the Coachella Valley Population because 
both had the potential to share similar threats due to proximity, and 
both were covered by the Coachella Valley MSHCP. However, as noted, the 
genetic affinities of the Dos Palmas subareas are not known. Thus, 
combining the Thousand Palms and Dos Palmas subareas into the Coachella 
Valley Population was a grouping of convenience, adequate for 
evaluating threats, but not necessarily for assessing the population 
segments as potential DPSs. Thus, we consider the Thousand Palms and 
Dos Palmas subareas separately in our assessment of significance for 
the Coachella Valley Population. These two occurrences are markedly 
separated from each other and from the other populations of flat-tailed 
horned lizards as a consequence of physical factors (geographical 
separation); therefore, each meets the first condition for discreteness 
under our DPS policy.
Second Condition for Discreteness
    The Western, Eastern, and Southeastern Populations extend across 
the international border with Mexico; as a result, each of these three 
populations could potentially be further divided into separate 
population segments under the policy's second condition for 
discreteness.
    Application of the second condition for discreteness (61 FR 4725) 
with respect to the flat-tailed horned lizard tests for significant 
differences in: (1) The control of exploitation, (2) the management of 
habitat, (3) the conservation status, or (4) the regulatory mechanisms 
between the United States and Mexico. Below, we present a brief 
synopsis of these four categories, combining the last two. Please refer 
to the Summary of Factors Affecting the Species and Findings sections 
of this document for additional details.
     Control of exploitation: We have no information suggesting 
that the flat-tailed horned lizard is significantly exploited on either 
side of the border (see the discussion under Factor B).
     Management of habitat: Management of flat-tailed horned 
lizard habitat is essentially the same in the United States and in 
Mexico, although the underlying mechanisms differ. For example, in the 
United States large areas are protected as Management Areas through 
implementation of the Rangewide Management Strategy, and in Mexico 
large areas are protected as National Parks and Biosphere Reserves (see 
the discussion under Factor A).
     Conservation status and regulatory mechanisms: In terms of 
actual designations of listing under the two countries' respective 
species-protection laws, the conservation status differs between the 
United States and Mexico. In the United States, as a result of this 
withdrawal, the species is not listed; in Mexico, it is listed as a 
threatened species under the Official Mexican Norm NOM-059-ECOL-2001 
(SEMARNAT 2002, p. 134). However, in the United States, existing 
conservation efforts and regulatory mechanisms reduce the magnitude of 
potential threats to the species to a point where protections afforded 
by the Act are not necessary (see the discussion under Factor D and the 
Findings and Conservation Efforts sections).
    We conclude the second condition is not satisfied because no 
significant differences exist with respect to the flat-tailed horned 
lizard across the international boundary between the United States and 
Mexico. As such, the Western, Eastern, and Southeastern Populations 
described above are discrete in themselves and not with respect to the 
international boundary between the United States and Mexico.
Conclusion for Discreteness per 1996 DPS Policy
    We conclude that each of the four population segments analyzed 
(Western, Eastern, Southeastern, and Coachella Valley) meets the 
discreteness element of the 1996 DPS policy because each can be 
considered markedly separated from the other flat-tailed horned lizard 
populations as a consequence of physical factors (first condition for 
discreteness). Within the Coachella Valley Population, flat-tailed 
horned lizards in the Thousand Palms and Dos Palmas subareas also meet 
the discreteness element of the 1996 DPS policy under the first 
condition for discreteness. None of the population segments that cross 
the United States-Mexico boundary meet the second condition for 
discreteness.

Significance

    If a population segment is considered discrete under one or more of 
the conditions described in our 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. Because 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 
does provide four possible reasons why a discrete population may be 
significant. 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 four conditions (61 FR 4725):
    (1) Persistence of the discrete population segment in an ecological 
setting unusual or unique for the taxon,
    (2) Evidence that loss of the discrete population segment would 
result in a significant gap in the range of the 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 criteria to 
be considered significant. Furthermore, the list of criteria is not 
exhaustive; other criteria may be used as appropriate. Below, we assess 
whether the four discrete populations defined above are significant per 
our DPS policy.
    First Condition--Persistence of the discrete population segment in 
an ecological setting unusual or unique for the taxon.
    None of the four primary populations of flat-tailed horned lizard 
occurs in an ecological setting unusual or unique for the species. 
Although the ecological

[[Page 14255]]

setting varies across and within the range of the four populations, 
important ecological characteristics are similar among the four 
populations (see Background section). Climatic conditions across the 
range of the four populations are characterized by hot summer 
temperatures, mild winter temperatures, and little rainfall. Across the 
four populations, flat-tailed horned lizards are associated with 
creosote-white bursage plant associations in areas characterized as 
sandy flats or valleys (see Setting and Habitat in the Background 
section).
    The ecological setting for the Coachella Valley Population as a 
whole, or the Thousand Palms and Dos Palmas subareas separately, are 
not markedly unusual or unique. The arenaceous (sandy) soils that 
support flat-tailed horned lizards in the Coachella Valley are derived 
from the surrounding areas and are compositionally different from those 
deposited by the Colorado River (van de Kamp 1973, p. 827), which is 
the source for much of the sand over a large portion of the range of 
the species (see Setting and Habitat in the Background section). 
However, the range of the flat-tailed horned lizard includes other 
areas where soils are derived from sedimentation from the surrounding 
areas, particularly the western edge of the Western Population where it 
meets lower extremities of the Peninsular Range (see Setting and 
Habitat in the Background section). Thus, evidence indicates this 
difference in substrate does not translate into an ecological setting 
unusual or unique for the flat-tailed horned lizard. We conclude that 
none of the four population segments meets the first significance 
condition.
    Second Condition--Evidence that loss of the discrete population 
segment would result in a significant gap in the range of a taxon.
    Loss of the Western, Eastern, or Southeastern population segment 
would result in a significant gap in the range of the species because 
each of these population segments represents a relatively large portion 
of the total range of the species (Table 6). In contrast, the range of 
the Coachella Valley Population as a whole, or the separate Thousand 
Palms or Dos Palmas subareas, is very small relative to the total range 
of the species. The range of the Coachella Valley Population represents 
only 0.24 percent of the total range of the species (0.80 percent of 
the U.S. portion of the range) (Table 6). The range of the Thousand 
Palms population represents only 0.11 percent of the total range of the 
species, and the range of the Dos Palmas population represents only 
0.13 percent of the species' total range (Table 6). Loss of the 
Coachella Valley population segment would not result in a significant 
gap in the range of the species. We conclude that the Western, Eastern, 
and Southeastern population segments meet the second significance 
condition, but the Coachella Valley population segment does not.

   Table 6--Size (Area) of the Populations Under Consideration To Be Potential Distinct Vertebrate Population
    Segments Under the Act. The Thousand Palms and Dos Palmas Occurrences Are Subsets of the Coachella Valley
         Population (See Description of Specific ``Populations'' in the Background Section for Details).
----------------------------------------------------------------------------------------------------------------
                                           Total range of species                U.S. portion of range only
                                  ------------------------------------------------------------------------------
            Population                                         Percent of                             Percent of
                                        Size (area) \1\          total          Size (area) \1\         total
----------------------------------------------------------------------------------------------------------------
Western..........................  341,989 ha (845,073 ac)..        21.52  253,020 ha (625,226 ac).        53.74
Eastern..........................  169,617 ha (419,133 ac)..        10.67  146,121 ha (361,073 ac).        31.03
Southeastern.....................  1,073,551 ha (2,652,802          67.56  67,922 ha (167,839 ac)..        14.43
                                    ac).
Coachella Valley.................  3,785 ha (9,353 ac)......         0.24  3,785 ha (9,353 ac).....         0.80
 (Thousand Palms subarea)........  1,707 ha (4,219 ac)......         0.11  1,707 ha (4,218 ac).....         0.36
 (Dos Palmas subarea)............  2,078 ha (5,134 ac)......         0.13  2,078 ha (5,135 ac).....         0.44
                                  ------------------------------------------------------------------------------
    Total........................  1,588,942 ha (3,926,361         100.00  470,848 ha (1,163,491          100.00
                                    ac).                                    ac).
----------------------------------------------------------------------------------------------------------------
\1\ Area values are estimated through a GIS-based assessment. Despite the level of precision presented, area
  values are approximate; however, we believe they are accurate enough to draw the conclusions presented.

    Third Condition--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.
    Populations of the flat-tailed horned lizard have not been 
introduced outside the species' historic range, so none of the four 
population segments meets the third significance condition.
    Fourth Condition--Evidence that the discrete population segment 
differs markedly from other populations of the species in its genetic 
characteristics.
    As described in Populations and Genetics in the Background section, 
the Western, Eastern, and Southeastern Populations are genetically 
cohesive populations within themselves but are significantly 
genetically differentiated from each other (Mulcahy et al. 2006, pp. 
1807-1826; Culver and Dee 2008, pp. 1-14). Thus, the evidence indicates 
that the Western, Eastern, and Southeastern Populations of flat-tailed 
horned lizards differ markedly from each other in their genetic 
characteristics.
    However, evidence shows that the Thousand Palms subarea 
(occurrence) within the Coachella Valley Population is not markedly 
different from the Western Population in its genetic characteristics, 
although the Thousand Palms occurrence within the Coachella Valley 
Population, like the Western Population, is genetically significantly 
different from the Eastern and Southeastern Populations. Although 
haplotypes unique to flat-tailed horned lizards from the Thousand Palms 
occurrence within the Coachella Valley Population have been found, 
genetic differences between these lizards and Western Population 
lizards were not statistically significant (Mulcahy et al. 2006, p. 
1811 and p. 1817). Although Coachella Valley flat-tailed horned lizards 
are currently markedly separated geographically from other flat-tailed 
horned lizard populations as a result of isolation due to past 
agricultural and urban development, genetics information suggests that 
the flat-tailed horned lizards in the Thousand Palms occurrence were 
historically not separated from Western Population flat-tailed horned 
lizards (Mulcahy et al. 2006, p. 1821). Thus, the evidence

[[Page 14256]]

indicates that the population of flat-tailed horned lizards in the 
Thousand Palm occurrence within the Coachella Valley Population does 
not differ markedly from the Western Population in its genetic 
characteristics.
    We are not aware of any genetic information on the Dos Palmas 
subarea (occurrence). [We believe the map shown by Culver and Dee 
(2008, Figure 1, p. 14) to be in error because they used the same 
samples for the Coachella Valley Population that Mulcahy et al. (2006) 
used (Culver and Dee 2008, p. 4), which indicated that genetic samples 
of flat-tailed horned lizards were collected from the Thousand Palms 
subarea (Mulcahy et al. 2006, p. 1826 and Figure 3, p. 1809) (see also 
Mendelson et al. 2004, p. 5)]. Although the genetic affinities of the 
Dos Palmas occurrence are unknown, it is likely this occurrence was 
historically connected with the Western Population through a connection 
to the north or west (when the Salton Basin was dry) or possibly the 
Eastern Population through a connection to the south along the eastern 
side of the Salton Trough when Lake Cahuilla was not full. Thus, the 
evidence suggests that the population of flat-tailed horned lizards in 
the Dos Palmas occurrence within the Coachella Valley Population is 
unlikely to differ markedly from the Western Population or Eastern 
Population in its genetic characteristics. Therefore, we conclude the 
Coachella Valley Population does not differ markedly from other 
populations of the species in its genetic characteristics.
    We believe the best scientific and commercial information available 
indicates that the Western, Eastern, and Southeastern Populations meet 
the fourth condition for significance, but that the best scientific and 
commercial information available do not support a determination that 
the Coachella Valley Population (and the Thousand Palms and Dos Palmas 
subareas, individually) meet the fourth condition for significance. We 
did not identify additional criteria for determining significance 
beyond the four identified in the 1996 DPS policy.
Conclusion for Significance Element of 1996 DPS Policy
    We conclude that the Western, Eastern, and Southeastern Populations 
of flat-tailed horned lizards meet the significance element of the 1996 
DPS policy, but that the Coachella Valley Population does not. Loss of 
the Western, Eastern, or Southeastern Population would result in a 
significant gap in the range of the species (second significance 
condition), and information indicates that each of these three 
population segments differs markedly in genetic characteristics from 
the other populations of flat-tailed horned lizards (fourth 
significance condition). In considering the importance of the Coachella 
Valley Population (the Thousand Palms and the Dos Palmas occurrences 
together) or the Thousand Palms and the Dos Palmas occurrences 
separately to the species as a whole, we determined that neither the 
Coachella Valley Population, the Thousand Palms occurrence, nor the Dos 
Palmas occurrence met any of the four significance conditions 
identified in the 1996 DPS policy, and we did not identify other 
considerations that would lead us to conclude that the respective 
population segments met the significance element of the policy, 
especially given Congressional guidance that the authority to list DPSs 
be used ``sparingly'' while encouraging the conservation of genetic 
diversity.

Conservation Status of DPSs

    As stated by our DPS policy (61 FR 4725), if a population segment 
is discrete and significant (i.e., it is a distinct population 
segment), its evaluation for endangered or threatened status will be 
based on the Act's definitions of those terms and a review of the 
factors enumerated in section 4(a). It may be appropriate to assign 
different classifications to different DPSs of the same vertebrate 
taxon.
    Above, we determined the Western, Eastern, and Southeastern 
Populations are discrete and significant, and thus, each is a distinct 
vertebrate population segment. We thus evaluate the conservation status 
of each of these three distinct population segments. We do not further 
separately evaluate the conservation status of the Coachella Valley 
Population or the two occurrences of flat-tailed horned lizards because 
we determined that these population segments do not meet the 
significance element of the 1996 DPS policy, and thus none are 
considered a distinct population segment under the Act and our DPS 
policy. For the remainder of the DPS analysis, we consider the 
Coachella Valley Population, which includes the Thousand Palms 
occurrence and the Dos Palmas occurrence, to be part of the Western 
DPS. Although it is possible that the Dos Palmas occurrence may more 
properly be placed in the Eastern DPS, for the purposes of our 
evaluation for endangered or threatened status, we are considering it 
to be within the Western DPS.
    In our analysis of section 4(a) threats, we evaluated whether 
potential threats were significant at the scale of flat-tailed horned 
lizard across its entire range, as well as whether any of the threats 
were significant at the scale of the four major populations (see 
Summary of Factors Affecting the Species section).
    For Factor A, we identified and evaluated habitat threats from 
agricultural development, urban development, energy development, 
invasive and nonnative plants, OHVs, and military training activities. 
This analysis led us to conclude that none of these potential habitat 
threats, either individually or cumulatively, is significant enough to 
cause the flat-tailed horned lizard to be in danger of extinction now 
or likely to become so within the foreseeable future throughout all of 
its range. We also conclude based on the results of this same analysis 
presented in Summary of Factors Affecting the Species that none of 
these potential habitat threats is significant enough to cause the 
Eastern, Western, or Southeastern distinct population segments of flat-
tailed horned lizard to be in danger of extinction now or likely to 
become so within the foreseeable future throughout all of their 
respective ranges.
    For Factor B, we concluded that potential threats associated with 
overutilization due to collection for the pet trade and scientific and 
educational purposes are not significant threats to flat-tailed horned 
lizards now or within the foreseeable future across its range. We also 
conclude, based on this same analysis presented in Summary of Factors 
Affecting the Species, that potential overutilization threats are not 
significant enough to cause the Eastern, Western, or Southeastern 
distinct population segments of flat-tailed horned lizard to be in 
danger of extinction now or likely to become so within the foreseeable 
future throughout all of their respective ranges.
    For Factor C, we concluded that potential threats associated with 
disease or predation were not significant threats to flat-tailed horned 
lizards now or within the foreseeable future across its range. We also 
conclude based on this same analysis presented in Summary of Factors 
Affecting the Species that potential disease or predation threats are 
not significant enough to cause the Eastern, Western, or Southeastern 
distinct population segments of flat-tailed horned lizard to be in 
danger of extinction now or likely to become so within the foreseeable 
future throughout all of their respective ranges.
    For Factor D, we concluded that existing regulatory mechanisms are 
not inadequate and do not threaten the flat-tailed horned lizard 
throughout all or a

[[Page 14257]]

significant portion of its range either now or within the foreseeable 
future. We also conclude based on this same analysis of the best 
available information presented in Summary of Factors Affecting the 
Species that any potential threats associated with inadequate existing 
regulatory mechanisms are not significant enough to cause the Eastern, 
Western, or Southeastern distinct population segments of flat-tailed 
horned lizard to be in danger of extinction now or likely to become so 
within the foreseeable future throughout all or a significant portion 
of their respective ranges.
    For Factor E, we identified and evaluated threats from other 
natural or manmade factors including barriers and small populations, 
edge effects, pesticide spraying, vehicle activity, drought, and 
climate change. This analysis led us to conclude that none of these 
potential threats, either individually or cumulatively, is significant 
enough to cause the flat-tailed horned lizard to be in danger of 
extinction now or likely to become so within the foreseeable future 
throughout all of its range. We also conclude, based on this same 
analysis of the best available information presented in Summary of 
Factors Affecting the Species, that none of these potential threats is 
significant enough to cause the Eastern, Western, or Southeastern 
distinct population segments of flat-tailed horned lizard to be in 
danger of extinction now or likely to become so within the foreseeable 
future throughout all of their respective ranges.
Conclusion for Conservation Status Element of 1996 DPS Policy
    In our analysis of the species as a whole as detailed in Summary of 
Factors Affecting the Species section, we noted potential threats from 
development, invasive species, military training, vehicle (including 
OHV) activity, barriers and small populations, edge effects, pesticide 
spraying, and climate change. Additionally, we identified regulatory 
mechanisms and conservation efforts that reduced certain threats in 
certain areas. We determined that none of the potential threats, either 
individually or cumulatively, significantly affected the species 
throughout its range. In that analysis, we also addressed (where 
appropriate) separate flat-tailed horned lizard populations, including 
the Western, Eastern, and Southeastern Populations that we have 
determined, per the analyses in this section, are DPSs. Although all of 
the identified potential threats occur to a greater or lesser degree in 
each of the three DPSs, and although the regulatory mechanisms and 
conservation efforts differ within and among DPSs, we found no one 
threat to be unique to any one DPS, nor did we find a threat that 
occurred with markedly greater magnitude in any one DPS. We therefore 
conclude that the Western, Eastern, and Southeastern distinct 
population segments of flat-tailed horned lizard also are not likely to 
be in danger of extinction now or likely to become so within the 
foreseeable future throughout all of their respective ranges.

Significant Portion of the Range

    Having determined that neither the flat-tailed horned lizard nor 
the identified distinct population segments of flat-tailed horned 
lizard meet the definition of an endangered or threatened species, we 
must next consider whether there are any significant portions of the 
range where the flat-tailed horned lizard is in danger of extinction or 
is likely to become endangered in the foreseeable future. We considered 
whether any portion of the flat-tailed horned lizard's range warrants 
further consideration. Our consideration of areas that may constitute 
significant portions of the species' range focuses on areas where the 
geographic concentration of threats may be greater relative to the 
entire range. We consider whether there are any significant portions of 
the range of the flat-tailed horned lizard (the species as a whole) or 
of the identified DPSs that are in danger of extinction or are likely 
to become endangered in the foreseeable future.
    Decisions by Ninth Circuit Court of Appeals in Defenders of 
Wildlife v. Norton, 258 F.3d 1136 (2001) and Tucson Herpetological 
Society v. Salazar, 566 F.3d 870 (2009) found that the Act requires the 
Service, in determining whether a species is endangered or threatened 
throughout a significant portion of its range, to consider whether lost 
historical range of a species (as opposed to its current range) 
constitutes a significant portion of the range of that species. While 
this is not our interpretation of the statute, we first address the 
lost historical range before addressing the current range.

Lost Historical Range

    As shown in Figure 1, the current range of the flat-tailed horned 
lizard consists of three, large, separate population areas (the 
Western, Eastern, and Southeastern Populations), plus two, small, 
isolated occurrences that, together, compose the Coachella Valley 
Population (see the Description of Specific ``Populations'' section, 
above). In our past assessments of the species, following the lead of 
the information then available to us, we concluded or implied that the 
historical range of the flat-tailed horned lizard was mostly without 
substantial discontinuities and that modern discontinuities in the 
species' range were the result of manmade changes, primarily habitat 
loss through agricultural development and the creation of the Salton 
Sea (for example, see the Factor A analyses at 58 FR 62625-62626, 62 FR 
37857, and 68 FR 341; also Rado 1981, pp. 1-21; Hodges 1997, pp. 1-23). 
This characterization of the range of the species suggested to the 
reader that the conversion from habitat to non-habitat of the large 
swath of land between the Coachella Valley, Western, Eastern, and 
Southeastern Populations is what created those now-separate populations 
and that prior to the manmade changes all of the now-lost interstitial 
areas used to be occupied flat-tailed horned lizard habitat. However, 
the best currently available information indicates that such a 
conclusion is incorrect.
    In our 2006 analyses (71 FR 36750-36751), we determined that the 
area of the historical lakebed of the former Lake Cahuilla (see 
Background section), which occupied most of the areas now under 
agriculture in the southern half, or so, of the Coachella Valley and 
most of the area now under agriculture in the Imperial Valley (for 
example, see Patten et al. 2003, p. 3), was frequently unavailable 
(through historical and pre-historical time) and likely contained 
little quality habitat for the flat-tailed horned lizard. The 2006 
analysis then addressed the now-developed areas outside of the 
historical lakebed, including remaining portions of the Coachella 
Valley and Mexicali Valley, and the San Luis Valley. However, as 
detailed in the Background and further discussed in the ``Barriers and 
Small Populations'' section of Factor E, above, the available 
information now leads us to conclude that the Western, Eastern, and 
Southeastern Populations have long been separated from each other by 
natural barriers south of the Lake Cahuilla lakebed that pre-date any 
manmade changes. Specimen data show that large amounts of this now-lost 
area was formerly occupied by the species (see, for example, Funk 1981, 
p. 281.1), but as described in the Setting and Habitat section, above, 
the evidence also shows that, in addition to the historical lakebed of 
the former Lake Cahuilla, some unknown amount of the area in the 
Mexicali Valley and the San Luis Valley, was also frequently affected 
by the deltaic meandering and avulsive

[[Page 14258]]

flooding of the Colorado River. These hydrologically active areas 
likely contained little quality habitat for the flat-tailed horned 
lizard and formed natural barriers to movement of flat-tailed horned 
lizards thereby allowing genetic differentiation among the Western, 
Eastern, and Southeastern Populations (see the Populations and Genetics 
section, above). Thus, as we found for the Lake Cahuilla lakebed in our 
2006 analyses (71 FR 36750-36751), we have also determined that these 
additional areas should not be considered part of the species' 
historical habitat.
    Therefore, we consider the flat-tailed horned lizard's historical 
habitat to be (1) habitat outside the area of the former Lake Cahuilla 
and (2) the habitat outside the areas historically subject to periodic 
flooding by the Colorado River. Because we do not know the real extent 
of the non-habitat areas that created the natural barriers separating 
the populations, we cannot reasonably estimate (quantify) the size of 
the areas that do constitute the lost historical habitat for each of 
the separate populations. As a result, the remainder of this analysis 
qualitatively considers the species' lost historical habitat.
    Because the habitat needs of the flat-tailed horned lizard are met 
within the home range of each flat-tailed horned lizard individual, the 
areas of former habitat within the lost historical range did not 
provide any special or unique features or meet any life-history needs 
that present-day flat-tailed horned lizards need to survive. In other 
words, there is no evidence in the available information to indicate 
that the habitat within the lost historical range provided special 
features for the flat-tailed horned lizard such as key breeding 
grounds, lek sites, or migratory pathways, which are examples of 
special habitat features other species need to survive. Had the habitat 
within the lost historical range provided any special or unique 
features or met any particular life-history needs of the flat-tailed 
horned lizard--in other words, had the habitat in the lost historical 
range been significant to the species--the loss of these habitat areas 
would have been detectable in further contraction in the range of the 
species or each DPS over the past 100 or so years (more than 25 flat-
tailed horned lizard generations, as described in our 2006 analysis (71 
FR 36751)), the time since most of the historical habitat was lost. 
Since the areas of historical habitat were converted to agriculture 
early in the 20th century, the distribution of the flat-tailed horned 
lizard has remained about the same, except in areas of continuing urban 
expansion where such reductions in range are attributable to continued 
habitat loss (see Factor A). (Although adequate sample sizes to 
determine population trends have been difficult to obtain in the flat-
tailed horned lizard, the distribution of the species, and thus its 
range, is based on where the species was and is detected--presence-
absence data--which is much more easily obtained.) Moreover, the 
agricultural and urban development of the now-lost historical range did 
not create any new barriers that separated the Western, Eastern, and 
Southeastern Populations (DPSs) but merely expanded upon pre-existing, 
natural barriers (see Background section). Therefore, the historical 
loss of habitat has not resulted in substantial present-day 
ramifications to the species; in other words, the lost historical range 
is not biologically significant to the flat-tailed horned lizard and 
does not contribute meaningfully to the viability of the species 
overall or to the viability of each DPS.
    Moreover, as described under Factor A, we do not expect additional 
significant conversion of flat-tailed horned lizard habitat to 
agriculture in the future in the Imperial Valley and elsewhere along 
the Colorado River given: (1) The existing limitations on the 
availability of water for irrigation, and (2) the water transfer 
agreement with San Diego that requires some fields to remain fallow 
(unirrigated); therefore, agricultural use has even decreased in this 
area (IID 2006).
    The past agricultural and urban development that created the swath 
of now-lost historical habitat in the United States and Mexico removed 
the biological features that provided habitat for the flat-tailed 
horned lizard in these areas. Much of this habitat has been permanently 
lost due to urbanization, flooding of the Salton Sea, or both. Although 
habitat lost due to agricultural uses could potentially be restored in 
certain cases in the future, most agricultural fields are isolated from 
existing flat-tailed horned lizard populations by major irrigation 
canals, such as the Coachella Canal, Highline Canal, and All-American 
Canal, as well as, depending on the site's location, one or more 
smaller canals and drains. Therefore, we do not anticipate any 
significant amount of previously lost habitat will likely become 
suitable as habitat for the flat-tailed horned lizard in the 
foreseeable future.
    In sum, we believe the lost historical habitat does not represent a 
significant portion of the range of the flat-tailed horned lizard 
because the habitat was lost decades ago and the species has not 
experienced a continuing range contraction due to the loss of this 
habitat. Most of the lost habitat was lost early in the 20th century 
and that lost habitat was not significant enough to lead to substantial 
extirpation of the species within intact habitat (which would be 
detectable through a reduction of the species' distribution). The 
historically lost habitat did not provide any special or unique 
features or meet any life-history needs of the flat-tailed horned 
lizard that made those areas any more significant than any other 
habitat. The habitat within the lost historical range was not 
continuous and contained natural barriers that separated the Western, 
Eastern, and Southeastern Populations, which means the historical loss 
of habitat did not create any new barriers within the lost historical 
range. We do not expect the agricultural development that created the 
large ``swath'' of lost habitat to continue to expand substantially, 
nor do we expect significant amounts of land that are currently under 
agriculture to become flat-tailed horned lizard habitat within the 
foreseeable future. Therefore, the lost historical range is not a 
significant portion of the range for the flat-tailed horned lizard.

Current Range

    We use the concepts of resiliency, redundancy, and representation 
(see below) as the basic tenets for determining whether a portion of a 
species' range is significant to that species. A portion of a taxonomic 
species' or DPS's range is significant if it is part of the current 
range of the species or DPS and it contributes substantially to the 
representation, resiliency, or redundancy of the species or DPS. The 
contribution must be at a level such that its loss would result in a 
significant decrease in the viability of the species or DPS.
    We chose to identify any portions of the range of the species that 
warrant further consideration as the first step in determining whether 
a taxonomic species or DPS is endangered or threatened in a significant 
portion of its range. The range of a species or DPS can theoretically 
be divided into portions in an infinite number of ways. However, there 
is no purpose to analyzing portions of the range that are not 
reasonably likely to be significant and endangered or threatened. To 
identify only those portions that warrant further consideration, we 
should, under the framework we chose for this evaluation, determine 
whether there is substantial information indicating that (i) the 
portions may be significant and (ii) the species or DPS may be in 
danger of extinction there or likely to become so

[[Page 14259]]

within the foreseeable future. In practice, we believe a key part of 
this analysis is whether the threats are geographically concentrated in 
some way. If the threats to the species are essentially uniform 
throughout its range, no portion is likely to warrant further 
consideration. Moreover, if any concentration of threats applies only 
to portions of the range that are not significant to the viability of 
the species, such portions will not warrant further consideration.
    Under this framework, if we identify any portions that warrant 
further consideration, we then determine whether in fact the species or 
DPS is endangered or threatened in any significant portion of its 
range. Depending on the biology of the species, the range of the 
species or DPS, and the threats the species or DPS faces, it may be 
more efficient for us to address the significance question first, or 
the status question first. Thus, if we determine that a portion of the 
range is not significant, we need not determine whether the species is 
endangered or threatened there; if we determine that the species or DPS 
is not endangered or threatened in a portion of its range, we need not 
determine if that portion is significant.
    The terms resiliency, redundancy, and representation are intended 
to be indicators of the conservation value of portions of the range. 
Resiliency of a species allows the species to recover from periodic or 
occasional disturbance. A species or its members within a DPS will 
likely be more resilient if large populations exist in high-quality 
habitat that is distributed throughout the range of the species or DPS 
in such a way as to capture the environmental variability found within 
the range of the species or DPS. It is likely that the larger the size 
of a population, the more it will contribute to the viability of the 
species overall. Thus, a portion of the range of a species may make a 
meaningful contribution to the resiliency of the species or DPS if the 
area is relatively large and contains particularly high-quality habitat 
or if its location or characteristics make it less susceptible to 
certain threats than other portions of the range. When evaluating 
whether or how a portion of the range contributes to resiliency of the 
species, it may help to evaluate the historical value of the portion 
and how frequently the portion is used by the species or DPS. In 
addition, the portion may contribute to resiliency for other reasons--
for instance, it may contain an important concentration of certain 
types of habitat that are necessary for members of a species or DPS to 
carry out their life-history functions, such as breeding, feeding, 
migration, dispersal, or wintering.
    Redundancy of populations may be needed to provide a margin of 
safety for the species or DPS to withstand catastrophic events. This 
does not mean that any portion that provides redundancy is a 
significant portion of the range of a species. The idea is to conserve 
enough areas of the range such that random perturbations in the system 
act on only a few populations. Therefore, each area must be examined 
based on whether that area provides an increment of redundancy that is 
important to the viability of the species.
    Adequate representation insures that the species' adaptive 
capabilities are conserved. Specifically, the portion should be 
evaluated to see how it contributes to the genetic diversity of the 
species or DPS. The loss of genetically based diversity may 
substantially reduce the ability of the species or DPS to respond and 
adapt to future environmental changes. A peripheral population may 
contribute meaningfully to representation if there is evidence that it 
provides genetic diversity due to its location on the margin of the 
species' habitat requirements.
    Applying the process described above for determining whether the 
flat-tailed horned lizard or any of the identified DPSs are likely to 
become endangered throughout a significant portion of their respective 
ranges, under this framework we next address whether any portions of 
the range of the flat-tailed horned lizard or the identified DPSs 
warrant further consideration. Based on past approaches and other 
treatments in the literature, the flat-tailed horned lizard may be 
divided into four ``populations.'' As detailed above, we conducted our 
analysis of threats to the species based, in part, upon those 
populations. Moreover, we determined that the Western Population 
(including the Coachella Valley Population), the Eastern Population, 
and the Southeastern Population were DPSs under the Act per our DPS 
policy. We found that the species as a whole is not in danger of 
extinction or likely to become endangered within the foreseeable future 
throughout all of its range. We also found that the three DPSs are not 
in danger of extinction or likely to become endangered within the 
foreseeable future throughout all of their respective ranges. Because 
we determined that the DPSs (each as a whole) are not endangered or 
threatened within those portions of the species' range, we need not 
determine if the Western, Eastern, or Southeastern DPSs (each as a 
whole) are ``significant.''
    We found that the Coachella Valley Population was faced with 
substantial threats. Also, we noted certain barrier-created ``parts'' 
within the ranges of the Western, Eastern, and Southeastern Populations 
were small enough that the flat-tailed horned lizards therein were more 
likely to suffer from threats associated with small populations (see 
``Barriers and Small Populations'' under Factor E) or were facing or 
likely to face other threats.
    An important consideration in determining what portions of the 
species' or distinct population segments' ranges may be appropriate to 
consider for this analysis is the fact that there are no specific life-
history traits of the flat-tailed horned lizard that make any one 
portion of its range significantly more important to the survival of 
the species than any other. The flat-tailed horned lizard is a small 
animal with limited abilities to move long distances, and the habitat 
features necessary for activities like breeding, feeding, and 
sheltering, may be found within or very close to the home range of each 
individual flat-tailed horned lizard. Moreover, a flat-tailed horned 
lizard's home range size (perhaps as much as 10 ha (25 ac)), although 
large compared to other horned lizard species, is very small compared 
to the overall range of the species (1.6 million ha (3.9 million ac)). 
In other words, this species does not need any particular portion of 
its range outside the general home-range area of each individual to 
meet any life history needs, such as particular breeding grounds, lek 
sites, or migratory pathways. As such, the ``parts'' identified in 
Factor E are appropriate subjects to address as potential significant 
portions of the species' range.
    Thus, because the portions of the species' range that compose the 
Coachella Valley Population and the portions of the species' range that 
are formed by the small ``parts'' of the other three populations may 
face substantial threats, we next determine whether these portions of 
the species' range are ``significant.'' As described above, we need not 
assess whether the portions of the species' range that are not facing 
substantial threats are ``significant.''
Coachella Valley Population Area
    As discussed previously, the Coachella Valley Population, which is 
peripheral to the population-as-a-whole of the species, now consists of 
two small occurrences, Thousand Palms and Dos Palmas. These two 
occurrences are small in area and, thus, likely have

[[Page 14260]]

small populations of flat-tailed horned lizards (see ``Barriers and 
Small Populations''). As such, the populations of flat-tailed horned 
lizards that comprise these occurrences may not be large enough to 
avoid deleterious effects associated with small population size (see 
``Barriers and Small Populations''). This suggests that the respective 
portions of the flat-tailed horned lizard's range in these two 
occurrences may face substantive threats and have the potential to be 
endangered or threatened; thus, we should evaluate whether the portions 
of the species' range are significant portions of the species' range. 
To do so, we assess (1) Whether the population of flat-tailed horned 
lizards in each occurrence contributes meaningfully to the resiliency, 
redundancy, and representation of the entire species; (2) whether the 
Thousand Palms occurrence contributes meaningfully to the resiliency, 
redundancy, and representation of the Western DPS; and (3) whether the 
Dos Palmas occurrence contributes meaningfully to the resiliency, 
redundancy, and representation of the Western DPS or Eastern DPS.
    Resiliency--Resiliency of a species, as described in greater detail 
above, allows the species to recover from periodic or occasional 
disturbance. The size of the flat-tailed horned lizard population at 
the Thousand Palms and Dos Palmas occurrences (each separately or the 
two combined) is likely small because the amount of available habitat 
within each of these occurrence areas are small. Small populations are 
less resilient than large populations. Additionally, neither occurrence 
nor the two combined contains an important concentration of certain 
types of habitat that are necessary for flat-tailed horned lizards to 
carry out their life-history functions because each flat-tailed horned 
lizard has the habitat types it needs within its home range. Although 
the sands in the Coachella Valley are largely derived from local 
sediments (as opposed to being derived from the Colorado River, as are 
much of the sands within the range of the species), flat-tailed horned 
lizards occur in a number of areas with locally derived sediment (see 
Background).
    Additionally, there is nothing in the available information to 
indicate that the location or characteristics of these occurrences 
(separately or combined) makes them significantly less susceptible to 
certain threats than other portions of the species' range. Moreover, 
there is no indication that these occurrences have provided value to 
the species historically. The ebbing and flowing of Lake Cahuilla 
through historical time has meant these two occurrences have likely 
been periodically disconnected from each other and from the Western DPS 
(or, for Dos Palmas, possibly the Eastern DPS). Even prior to any 
natural or manmade reductions in the geographical or numerical extent 
of these populations, they were outposts of the main population and did 
not contribute meaningfully to the viability of the larger Western 
Population (or, potentially for the Dos Palmas occurrence, the Eastern 
Population). Thus, the flat-tailed horned lizard populations in the 
Thousand Palms and Dos Palmas occurrences (each separately or the two 
combined) do not contribute meaningfully to the resiliency of the 
entire species, the Western DPS, or the Eastern DPS.
    Redundancy--Redundancy, as described in greater detail above, 
provides a margin of safety for the species or DPS to withstand 
catastrophic events. As discussed in the ``Barriers and Small 
Populations'' section under Factor E, the respective populations of 
flat-tailed horned lizards in the Thousand Palms and Dos Palmas 
occurrences, or the two combined, is more likely to be significantly 
affected by deleterious effects associated with small population size, 
including catastrophic events, than areas with larger populations (see 
the ``Other Small `Parts' of the Three DPSs'' section, below). As such, 
the Coachella Valley occurrences do not provide a significant margin of 
safety for the species. Additionally, as discussed under Resiliency, 
above, the population of flat-tailed horned lizards in each of these 
occurrences is likely small because the amount of available habitat 
within each part is small. Similarly, the entire population of the 
flat-tailed horned lizard rangewide and the respective populations of 
flat-tailed horned lizards within each DPS are each relatively large 
compared to the respective populations of flat-tailed horned lizards in 
the Thousand Palms or Dos Palmas occurrences, or the two combined, 
because the amount of available habitat throughout the species' range 
and within each DPS is relatively large compared to the Coachella 
Valley occurrences. As such, the Coachella Valley occurrences, or the 
two combined, provide an unsubstantial increment of redundancy. Thus, 
the Thousand Palms and Dos Palmas occurrences separately, or the two 
combined, do not contribute meaningfully to the redundancy of the 
entire species, the Western DPS, or the Eastern DPS.
    Representation--Representation, as described in greater detail 
above, ensures that the species' adaptive capabilities are maintained. 
The genetic differences between the Thousand Palms occurrence and the 
Western Population are not statistically significant, despite having 
some unique haplotypes (see Populations and Genetics in the Background 
section). Thus, the Thousand Palms occurrence does not contribute 
meaningfully to the maintenance of the adaptive capabilities of the 
flat-tailed horned lizard rangewide or the Western DPS. Although the 
genetic affinities of the Dos Palmas occurrence are unknown, it is 
likely this occurrence was historically connected with the Western 
Population through a connection to the north or west (when the Salton 
Basin was dry) or possibly the Eastern Population through a connection 
to the south along the eastern side of the Salton Trough when Lake 
Cahuilla was not full. Thus, the Dos Palmas occurrence likely does not 
contribute meaningfully to the maintenance of the adaptive capabilities 
of the flat-tailed horned lizard. Therefore, neither the Thousand Palms 
occurrence, the Dos Palmas occurrence, nor the two occurrences combined 
(that is, the Coachella Valley Population) contributes meaningfully to 
the representation of the entire species, the Western DPS, or the 
Eastern DPS.
    Therefore, in sum, we do not expect the Coachella Valley Population 
as a whole, or the Thousand Palms and Dos Palmas occurrences 
separately, to contribute substantially to the resiliency, redundancy, 
or representation of the species, the Western DPS, or the Eastern DPS. 
As a result of this information, we believe neither the Coachella 
Valley Population (the Thousand Palms and Dos Palmas occurrences 
combined), nor the Thousand Palms and Dos Palmas occurrences 
separately, constitute a significant portion of the range of the entire 
species, the Western DPS, or the Eastern DPS.
Other Small ``Parts'' of the Three DPSs
    In our analysis in the ``Barriers and Small Populations'' section, 
we identified certain portions, or ``parts,'' of the Western, Eastern, 
and Southeastern Population areas. In the Distinct Population Segment 
section, we determined these three Populations to be DPSs. We now 
evaluate whether any of these parts constitute a significant portion of 
the range of the flat-tailed horned lizard (the species as a whole) or 
the three DPSs. However, there is no

[[Page 14261]]

purpose to analyzing portions of a species' range that are not 
reasonably likely to be both significant portions of that species' 
range and endangered or threatened. We have chosen in this section to 
first assess whether the flat-tailed horned lizard is reasonably likely 
to be endangered or threatened within each part.
    For the reasons discussed in the Summary of Factors Affecting the 
Species section (note that the discussions go beyond the simple yes-no 
results presented in Tables 3 through 5), we believe the populations of 
flat-tailed horned lizard in the respective following parts (portions 
of the species' range) do not face significant threats: W-1, W-3, W-5, 
W-7, W-9, W-11, W-12, E-3, E-5, E-9, SE-1, SE-5, SE-8, SE-9, and SE-13 
(Figures 3 through 7). Although the specifics vary to some extent from 
part to part, none of these parts faces or is likely to face in the 
foreseeable future significant threats associated with:
    (1) Small population size, because the parts are large in size 
(area) or, for parts W-7, W-9, and W-11, likely have higher densities 
of flat-tailed horned lizards than the most conservative estimate (see 
the Barriers and Small Populations section) and, therefore, likely 
support large populations of flat-tailed horned lizards;
    (2) Significant loss of habitat from development, because what 
impacts may occur are expected to be small relative to the size of the 
parts because they are (i) remote; (ii) are receiving and are expected 
to continue receiving avoidance, minimization, and mitigation measures 
associated with the Rangewide Management Strategy (including those 
aspects that have been incorporated into agency plans that implement 
regulatory mechanisms) in the United States, or in Mexico, protections 
from biosphere reserves and listing under the Official Mexican Norm; or 
(iii) some combination thereof; and
    (3) Climate change; nonnative, invasive species; or other range-
wide threats identified in the five-factor analysis, because none of 
these potential threats are significantly concentrated in any one part.
    As a result, the flat-tailed horned lizard is not reasonably likely 
to be endangered or threatened within the parts listed above. Thus, 
these parts do not warrant further consideration in this section.
    The remaining parts, W-2, W-4, W-6, W-8, W-10, E-1, E-2, E-4, E-6, 
E-7, E-8, SE-2, SE-3, SE-4, SE-6, SE-7, SE-10, SE-11, and SE-12 
(Figures 3 through 7), are either small in area and, thus, likely have 
small populations of flat-tailed horned lizards or, in the case of 
parts E-1 and E-4, which are larger in area, likely have small 
populations of flat-tailed horned lizards because they primarily 
contain areas of deep, actively shifting sands of the Algodones Dunes 
that are likely rarely used by flat-tailed horned lizards (see 
``Barriers and Small Populations''). As such, the populations of flat-
tailed horned lizards in these parts may not be large enough to avoid 
deleterious effects associated with small population size (see 
``Barriers and Small Populations''). This suggests that the respective 
portions of the flat-tailed horned lizard's range in the latter group 
of parts may face substantive threats and have the potential to be 
endangered or threatened; thus, we should evaluate whether the portions 
of the species' range are significant portions of the species' range. 
To do so, we assess whether the population of flat-tailed horned 
lizards in each part contributes meaningfully to the resiliency, 
redundancy, and representation of the species as a whole or to each 
DPS.
    Resiliency--Resiliency of a species, as described in greater detail 
above, allows the species to recover from periodic or occasional 
disturbance. The respective populations of flat-tailed horned lizards 
in parts W-2, W-4, W-6, W-8, W-10, E-1, E-2, E-4, E-6, E-7, E-8, SE-2, 
SE-3, SE-4, SE-6, SE-7, SE-10, SE-11, and SE-12 are likely small 
because the amount of available habitat within each part is small, 
including the relatively large (in area) parts E-1 and E-4 that 
primarily consist of the deep, actively shifting sands of the Algodones 
Dunes that are likely rarely used by flat-tailed horned lizards (see 
discussions in the ``Barriers and Small Populations'' section under 
Factor E). Small populations are less resilient than large populations. 
Additionally, no one part contains an important concentration of 
certain types of habitat that are necessary for flat-tailed horned 
lizards to carry out their life-history functions because each flat-
tailed horned lizard has the habitat types it needs within its home 
range. Moreover, there is nothing in the available information to 
indicate that the location or characteristics of part W-2, W-4, W-6, W-
8, W-10, E-1, E-2, E-4, E-6, E-7, E-8, SE-2, SE-3, SE-4, SE-6, SE-7, 
SE-10, SE-11, or SE-12 makes it significantly less susceptible to 
certain threats than other portions of the species' range. Thus, none 
of the flat-tailed horned lizard populations in the remaining parts 
contribute meaningfully to the resiliency of the species as a whole or 
to each DPS.
    Redundancy--Redundancy, as described in greater detail above, 
provides a margin of safety for the species or DPS to withstand 
catastrophic events. As discussed in the ``Barriers and Small 
Populations'' section under Factor E, the respective populations of 
flat-tailed horned lizards in parts W-2, W-4, W-6, W-8, W-10, E-1, E-2, 
E-4, E-6, E-7, E-8, SE-2, SE-3, SE-4, SE-6, SE-7, SE-10, SE-11, and SE-
12 are more likely to be significantly affected by deleterious effects 
associated with small population size, including catastrophic events, 
than the respective populations of flat-tailed horned lizards in parts 
W-1, W-3, W-5, W-7, W-9, W-11, W-12, E-3, E-5, E-9, SE-1, SE-5, SE-8, 
SE-9, and SE-13. As such, the former group of parts do not provide a 
significant margin of safety for the species. Additionally, as 
discussed under Resiliency, above, the population of flat-tailed horned 
lizards in each of these respective parts is likely small because the 
amount of available habitat within each part is small, including the 
relatively large (in area) parts E-1 and E-4 that primarily consist of 
the deep, actively shifting sands of the Algodones Dunes that are 
likely rarely used by flat-tailed horned lizards (see discussions in 
the ``Barriers and Small Populations'' section under Factor E). 
Similarly, the entire population of flat-tailed horned lizards and the 
population within each DPS are each likely relatively large compared to 
the respective populations of flat-tailed horned lizards in parts W-2, 
W-4, W-6, W-8, W-10, E-1, E-2, E-4, E-6, E-7, E-8, SE-2, SE-3, SE-4, 
SE-6, SE-7, SE-10, SE-11, and SE-12 because the amount of available 
habitat throughout the species' range and within each DPS is relatively 
large compared to the parts under consideration here (see Tables 3 
through 5). As such, parts W-2, W-4, W-6, W-8, W-10, E-1, E-2, E-4, E-
6, E-7, E-8, SE-2, SE-3, SE-4, SE-6, SE-7, SE-10, SE-11, and SE-12 
provide an unsubstantial increment of redundancy. Thus, none of the 
flat-tailed horned lizard populations in the remaining parts provide a 
significant level of redundancy for the species as a whole or to each 
DPS.
    Representation--Representation, as described in greater detail 
above, ensures that the species' adaptive capabilities are maintained. 
The scientific information on the genetics of flat-tailed horned lizard 
populations indicates that the Western, Eastern, and Southeastern 
Populations (DPSs) are significantly different from each other (see 
Populations and Genetics); thus, the representation of the species is 
provided by the three Populations. Although we do not have genetic data

[[Page 14262]]

from every ``part,'' the available information suggests the genetic 
diversity is fairly uniform and does not differ significantly within 
each of the three DPSs. As such, no one part within the respective DPSs 
contributes meaningfully to the representation of the species as a 
whole or to each DPS. Moreover, as discussed in the Populations and 
Genetics section, one part, Part SE-2, shows evidence suggesting the 
genetic variability of the flat-tailed horned lizard population in that 
part has declined as a consequence of being small and isolated by a 
manmade barrier. This suggests that the species' adaptive capabilities 
in this part have declined. That is, the ability of the flat-tailed 
horned lizard population to provide adequate representation has been 
reduced in Part SE-2. It is possible the representation of the other 
parts with small populations and with complete barriers has been or may 
become similarly reduced. Therefore, it is unlikely that parts W-2, W-
4, W-6, W-8, W-10, E-1, E-2, E-4, E-6, E-7, E-8, SE-2, SE-3, SE-4, SE-
6, SE-7, SE-10, SE-11, and SE-12 contribute significantly to the 
species' adaptive capabilities, and thus, the respective parts do not 
contribute meaningfully to the representation of the species as a whole 
or to each DPS.
    In sum, we found that none of the ``parts'' identified in the 
``Barriers and Small Populations'' section constituted significant 
portions of the range of the flat-tailed horned lizard. For the reasons 
discussed in the Summary of Factors Affecting the Species section (note 
that the discussions go beyond the simple yes-no results presented in 
Tables 3 through 5), we determined that the portions of range of the 
flat-tailed horned lizard in parts W-1, W-3, W-5, W-7, W-9, W-11, W-12, 
E-3, E-5, E-9, SE-1, SE-5, SE-8, SE-9, and SE-13 are not reasonably 
likely to be endangered or threatened; thus, we did not need to 
determine whether the portions of the range that these parts 
represented are significant portions. We determined that the flat-
tailed horned lizards in the remaining parts, parts W-2, W-4, W-6, W-8, 
W-10, E-1, E-2, E-4, E-6, E-7, E-8, SE-2, SE-3, SE-4, SE-6, SE-7, SE-
10, SE-11, and SE-12, may face substantive threats and have the 
potential to be endangered or threatened. As such, we assessed whether 
any of the portions of the species' range within the parts in this 
latter group is a significant portion of the species' range overall or 
of the ranges of each DPS. We found that the portions of the species' 
range within the respective parts in this latter group likely contained 
small populations of flat-tailed horned lizards that did not contribute 
meaningfully to the species' resiliency, redundancy, or representation 
of the species as a whole or of each DPS. We determined, therefore, the 
portions of the flat-tailed horned lizard's range in parts W-2, W-4, W-
6, W-8, W-10, E-1, E-2, E-4, E-6, E-7, E-8, SE-2, SE-3, SE-4, SE-6, SE-
7, SE-10, SE-11, and SE-12 are not significant portions of the range of 
the species as a whole or of each DPS.

Summary of Significant Portion of the Range

    In summary, we examined whether the lost historical range of the 
species, the current range of the species in the Coachella Valley 
Population, or the current range of the species in the other respective 
``parts'' of the Western, Eastern, and Southeastern DPSs constituted 
significant portions of the species' or distinct population segments' 
respective ranges under the Act. We determined the lost historical 
habitat does not represent a significant portion of the range of the 
flat-tailed horned lizard because the habitat was lost decades ago and, 
despite the amount of time that has since transpired, the species has 
not experienced a continuing range contraction due to the past loss of 
habitat. Additionally, the historically lost habitat did not provide 
any special or unique features or meet any life-history needs of the 
flat-tailed horned lizards that made those areas any more significant 
than any other habitat. Moreover, the lost historical range was not 
continuous and contained natural barriers that separated the Western, 
Eastern, and Southeastern Populations.
    We also determined that neither the Coachella Valley Population as 
a whole nor the Thousand Palms and Dos Palmas occurrences separately 
contribute substantially to the resiliency, redundancy, or 
representation of the entire species, the Western DPS, or the Eastern 
DPS. Therefore, we conclude that neither the Coachella Valley 
Population as a whole nor the Thousand Palms and Dos Palmas occurrences 
separately constitute a significant portion of the range of the entire 
species, the Western DPS, or the Eastern DPS.
    Lastly, we determined that none of the ``parts'' identified in the 
``Barriers and Small Populations'' section represented a significant 
portion of the range of the flat-tailed horned lizard. We found that 
the flat-tailed horned lizards in Parts W-1, W-3, W-5, W-7, W-9, W-11, 
W-12, E-3, E-5, E-9, SE-1, SE-5, SE-8, SE-9, and SE-13 were not 
reasonably likely to be endangered or threatened; thus, we did not need 
to determine whether the portions of the range that these parts 
represented are significant portions. We determined that the flat-
tailed horned lizards in parts W-2, W-4, W-6, W-8, W-10, E-1, E-2, E-4, 
E-6, E-7, E-8, SE-2, SE-3, SE-4, SE-6, SE-7, SE-10, SE-11, and SE-12 
may face substantive threats and have the potential to be endangered or 
threatened, meaning that we needed, under our framework, to assess 
whether the flat-tailed horned lizards in these parts constituted 
significant portions of the species' range. We found that the portions 
of the species' range within the respective parts in this latter group 
likely contained small populations of flat-tailed horned lizards that 
did not contribute meaningfully to the resiliency, redundancy, or 
representation of the species as a whole or of each DPS. Thus, we 
determined the portions of the range of this latter group of parts are 
not significant portions of the range of the species as a whole or of 
each DPS. Therefore, no portion of the range of the flat-tailed horned 
lizard is a ``significant portion of [the species'] range'' under the 
Act.

Conclusion

    Threats to the flat-tailed horned lizard rangewide or within the 
three identified DPSs have been reduced, managed, or eliminated, or 
found to be less substantial than originally thought. Additionally, 
implementation of the Interagency Conservation Agreement and associated 
Rangewide Management Strategy, including those aspects of it that have 
been incorporated into documents that implement existing regulatory 
mechanisms, is an important conservation effort that reduces threats in 
the United States and benefits the species throughout its range and 
within the identified DPSs. Therefore, we conclude that none of the 
existing or potential threats are likely to cause the flat-tailed 
horned lizard as an entire species or as any one of the Western, 
Eastern, or Southeastern DPSs to be in danger of extinction or likely 
to become so within the foreseeable future throughout all or a 
significant portion of its range.

Withdrawal of Proposal To List Flat-Tailed Horned Lizard

    Based on the information discussed above, we withdraw our November 
29, 1993 (58 FR 62624), proposal to list the flat-tailed horned lizard 
(Phrynosoma mcallii) as a threatened species under the Act.

[[Page 14263]]

Peer Review

    As described in our 2003 withdrawal (68 FR 340) and in accordance 
with our July 1, 1994, Interagency Cooperative Policy for Peer Review 
in Endangered Species Act Activities (59 FR 34270), we solicited six 
individuals with scientific expertise on flat-tailed horned lizard, its 
habitat, and the geographic region in which the species occurs to 
provide their expert opinion and to review and interpret available 
information on the species' status and threats. Peer reviewer comments 
and our responses to those comments were included in our 2003 
withdrawal (68 FR 340) and are hereby included in this document by 
reference.

Summary of Comments and Recommendations

Public Comments

    All public and peer review comments we received during public 
comment periods and public hearings prior to our March 2, 2010, Federal 
Register announcement on the reinstatement of the 1993 proposed rule 
and notice of public hearings are included in this document by 
reference (see Previous Federal Action section for dates, times, and 
locations of prior comment periods and hearings).
    Since the proposed rule was reinstated on March 2, 2010 (75 FR 
9377), there has been one public comment period and four public 
hearings. During the 60-day comment period from March 2 to May 3, 2010, 
for the reinstated proposed rule, we received a total of 24 comment 
letters in response to our request for new information: 2 from Federal 
agencies (duplicate letter from 2 submitters), 4 from State or local 
agencies and governments, and 18 from organizations or individuals. 
During the public hearings on March 23, 2010, in Palm Desert, 
California, and March 24, 2010, in Yuma, Arizona, we received a total 
of 4 comments: 1 written comment and 3 oral comments. Two of these 
comments were from local government representatives and the remaining 
two from organizations or individuals. All comments received were 
reviewed for substantive issues and new information regarding the 1993 
proposed rule to list the flat-tailed horned lizard as a threatened 
species, and we address those comments below.
Comments From Federal Agencies
    Comment 1: The U.S. Navy does not support the listing of flat-
tailed horned lizard as a threatened species because: (1) Listing or 
designation of critical habitat would encroach on the ability to 
perform military readiness activities at NAF El Centro; (2) the species 
is not threatened throughout a significant portion of its range; (3) 
conservation should be implemented through the existing Interagency 
Conservation Agreement, the Rangewide Management Strategy, and the 
updated NAF El Centro INRMP; and (4) conservation should be implemented 
through a continued working partnership with other State and Federal 
agencies, including the U.S. Navy.
    Our Response: Based on the rationales provided in this document, we 
agree with the U.S. Navy that the species does not warrant listing 
under the Act. Additionally, we agree that the Interagency Conservation 
Agreement and associated Rangewide Management Strategy make important 
contributions to reducing threats to the flat-tailed horned lizard and 
its habitat through efforts contributed by the Service, BLM, BOR, U.S. 
Marine Corps, U.S. Navy, Arizona Game and Fish Department, CDFG, and 
CDPR. Although many of these efforts are voluntary, conservation 
actions are formally incorporated into planning documents of 
participating agencies (such as the NAF El Centro INRMP and BLM's 
California Desert Conservation Area Plan). We appreciate the U.S. 
Navy's support of this long-term partnership and commitment to 
conservation of sensitive species, including the flat-tailed horned 
lizard, and their habitats through its participation in the Interagency 
Conservation Agreement and implementation of the NAF El Centro INRMP. 
For additional information on the Interagency Conservation Agreement 
and the associated Rangewide Management Strategy and the U.S. Navy's 
conservation actions, please see Management and Populations under the 
Background section and Sikes Act under Factor D.
Comments From State Agencies
    Comment 2: The Arizona Department of Transportation believes the 
flat-tailed horned lizard Interagency Conservation Agreement is an 
adequate regulatory mechanism that provides strong protection for the 
species on signatory lands. Much of the remaining habitat in 
southwestern Arizona is managed by agencies that are signatories to the 
Interagency Conservation Agreement. For example, project proponents for 
the construction of Arizona State Route 195 (Yuma Area Service Highway) 
used the Rangewide Management Strategy to avoid and mitigate impacts to 
the flat-tailed horned lizard and its habitat. Additionally, the 
Arizona Department of Transportation believes the flat-tailed horned 
lizard Interagency Conservation Agreement is a viable mechanism for the 
long-term conservation of the species in the absence of listing under 
the Act.
    Our Response: We agree the Interagency Conservation Agreement and 
associated Rangewide Management Strategy is a viable conservation 
effort to promote the long-term conservation of flat-tailed horned 
lizard. The avoidance, minimization, and mitigation measures 
incorporated into the Yuma Area Service Highway project reduced impacts 
to the flat-tailed horned lizard and is an example of how the Rangewide 
Management Strategy can reduce impacts to the species associated with 
development (see Factor A).
    Comment 3: The CDPR expressed a concern that listing flat-tailed 
horned lizard as a threatened species would restrict CDPR's ability to 
manage recreational activities and park operations at Ocotillo Wells 
State Vehicular Recreation Area (SVRA), and that listing the species 
under the Act may cause OHV use to move to off-site areas with little 
or no management control. The CDPR also stated that listing the species 
may potentially reduce the number of visitors, resulting in a negative 
economic impact on the region. Further, they believe that recreational 
OHV use does not conclusively show adverse effects to the species.
    Our Response: Although OHV activity has the potential to crush 
flat-tailed horned lizards (see Factor E) and impact the species' 
habitat (Factor A), we determined it is not currently a substantial 
threat to the species throughout its range. We agree that OHV activity 
in designated and managed open or limited-use areas is preferable to 
unmanaged OHV activity elsewhere. We acknowledge CDPR's contributions 
to the Rangewide Management Strategy through monitoring and management 
at Ocotillo Wells SVRA, and we encourage CDPR's continued participation 
in the Interagency Conservation Agreement.
    Comment 4: The CDPR states that long-term studies of flat-tailed 
horned lizard are needed because annual climatic conditions can result 
in variability in population sizes. They believe that long-term studies 
and an adaptive monitoring program are warranted prior to listing the 
species under the Act.
    Our Response: We agree that more information on the effects of 
weather and climate on the flat-tailed horned lizard and its habitat 
would be helpful; however, we are required to make a determination 
based on the best available scientific and commercial

[[Page 14264]]

information. We determined the flat-tailed horned lizard does not 
require protection under the Act. CDPR's contributions to the Rangewide 
Management Strategy have included funding studies to increase the 
knowledge of the species, and we encourage CDPR's continued 
participation, including contributing to developing and implementing 
long-term studies and adaptive management programs.
Comments Related to Biology, Ecology, or Climate Change
    Comment 5: One commenter believes flat-tailed horned lizard 
populations will take longer to ``* * * rebound to stable wild 
populations than other classes of animals.'' The commenter believes 
listing flat-tailed horned lizard as a threatened species under the Act 
is warranted because of low clutch survival rates from breeding to 
maturity due to impacts from predators and human activities.
    Our Response: The commenter did not provide any information 
regarding the class of animals to which he or she was referring in 
comparison to the flat-tailed horned lizard, or any information to 
substantiate the claim that wild populations of flat-tailed horned 
lizards are not stable. With regards to the commenter's concerns about 
``low clutch survival rates from breeding to maturity due to impacts 
from predators and human activities,'' flat-tailed horned lizards are 
known to produce relatively small clutches of eggs (N = 31; mean clutch 
size = 4.7; range = 3 to 7) (Howard 1974, p. 111) compared to most 
other horned lizards (Sherbrook 2003, p. 139), and predation has been 
identified as a potential threat to the flat-tailed horned lizard 
(FTHLICC 2003a, pp. 16-17). However, available information indicates 
predation does not appear to be excessively high throughout its range, 
although it is likely higher than natural levels near developed areas. 
Such results suggest that higher levels of predation of flat-tailed 
horned lizards observed in some areas is an ``edge effect,'' but much 
of the species' distribution is away from habitat edges (see Factor C, 
Disease or Predation section).
    Comment 6: One commenter states that climate change will become 
more of an issue as ant population numbers decline because flat-tailed 
horned lizard populations will subsequently decline.
    Our Response: Flat-tailed horned lizards do feed primarily on 
harvester ants; however, what effects climate change may have on 
harvester ant populations is unclear. Although populations of harvester 
ants decline during periods of both drought and increased rain, they 
rebound as do populations of flat-tailed horned lizards (Tevis 1958, p. 
701; Barrows and Allen 2009, p. 311). Harvester ants are also capable 
of surviving extremes in temperature (Tevis 1958, p. 704). The effects 
that global climate change may have on localized climate in areas 
inhabited by flat-tailed horned lizards and harvester ants is unclear, 
and we are not aware of any evidence indicating that harvester ant 
populations will decline in the foreseeable future.
    Comment 7: One commenter stated a belief that the Service's final 
determinations in the past have been correct and the flat-tailed horned 
lizard should not be listed as threatened under the Act. The commenter 
further stated that there are more flat-tailed horned lizards known 
today compared to 20 years ago, and (with respect to climate change) 
there has been adequate rainfall to produce forage in the desert for 
this species to flourish.
    Our Response: As discussed in the Background section, the number of 
flat-tailed horned lizards is difficult to estimate. We do not have 
acceptably accurate data to show any trend, either increasing or 
decreasing, in flat-tailed horned lizard populations. Rainfall varies 
from year to year in the Colorado Desert (Shreve and Wiggins 1964, pp. 
18-20). We determine if a species needs protection under the Act based 
on analysis of the species' status relative to one or more of the five 
factors described in section 4(a)(1) of the Act, and the standards for 
listing as endangered or threatened (see Summary of Factors Affecting 
the Species section). We determined the species is not in need of the 
protections afforded by the Act at this time.
    Comment 8: One commenter provided information resulting from 
research they conducted on flat-tailed horned lizard habitat loss in 
the Coachella Valley. The commenter believes that the reasons that the 
flat-tailed horned lizard was not listed in the past are because there 
was not enough known about this species' biology and distribution, and 
the largest share of the species' distribution was on Federal (BLM, 
DOD) lands such that the species could be managed without listing. The 
commenter's opinion is that neither of the above reasons is applicable 
today. The commenter also believes the Coachella Valley has been 
underrepresented in past assessments and that construction of the 
border fence, OHV activity, and development of energy facilities pose 
threats to the species.
    Our Response: Our determination of whether to list a species is 
based on our assessment of the five listing factors described in the 
Act and the standards for listing as endangered or threatened. A 
determination is made using the best scientific and commercial 
information available. In the Summary of Factors Affecting the Species 
section, we address the potential threats that may be affecting the 
species, including those identified by the commenter. Additionally, we 
have also addressed the Coachella Valley Population in detail.
    Comment 9: One commenter opposed to the listing of the flat-tailed 
horned lizard believes that before this species should be considered 
for listing, researchers should conduct monitoring of the full desert 
ecosystem, as declines for this species may be a result of natural 
processes.
    Our Response: Our determination of whether to list a species as 
endangered or threatened is based on our assessment of the five listing 
factors described in the Act using the best available scientific and 
commercial information. These include potential threats from natural 
and manmade sources. Although anecdotal evidence suggests that flat-
tailed horned lizard populations are smaller now than compared to the 
past (for example, Luckenbach and Bury 1983, p. 278), we do not have 
data to suggest a positive or negative trend (see Population Dynamics 
in the Background section).
Comments Related to Threats
    Comment 10: Four commenters support listing the flat-tailed horned 
lizard as a threatened species, and one commenter supports listing as 
an endangered species with designated critical habitat. These 
commenters believe listing is warranted due to a number of threats, 
including: Recreation; OHV use (such as in the Yuha Desert, Coachella 
Valley, West and East Mesas, near Algodones Dunes, and near Yuma, 
Arizona); construction of the border fence and border patrol traffic; 
development (including renewable energy projects such as SES Solar Two 
Project or Ocotillo Express Wind Project); power lines (Sunrise 
Powerlink); road/highway development (Yuma Area Service Highway, El 
Golfo to Rocky Point Highway); other miscellaneous development (such as 
Travertine Point, Drop 2 Reservoir, All American Canal, Coyote Wells 
Specific Plan Project, Reynolds Atlas RV Storage Facility); nonnative 
plant invasions; predation; and climate change. In general, the 
commenters believe these threats will continue, resulting in more 
habitat lost than gained. Further, the commenter that asserts the 
species

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should be listed as endangered states that Federal protection is 
necessary to ensure the survival of the species and eventual recovery, 
and ultimately reduce the costs of recovery.
    Our Response: Although we acknowledge losses of habitat can and do 
occur through natural and manmade processes, the determination to list 
a species is made by looking at the five factors described in section 
4(a)(1) of the Act and the status of the species relative to the 
standards for listing as endangered or threatened. This determination 
is made solely on the basis of the best scientific and commercial 
information available, and takes into account regulatory mechanisms 
that many benefit the species and those efforts, if any, being made by 
any State or foreign nation, or any political subdivision of a State or 
foreign nation, to protect the species through habitat protection or 
other conservation practices. As described in the Summary of Factors 
Affecting the Species section, we assessed the potential threats to the 
species using the five factors. We also assessed the existing efforts 
and measures that benefit the species or its habitat that may 
potentially reduce threats. We determined that threats to the flat-
tailed horned lizard throughout its range, including recreational OHV 
activity; various types of development; invasive, nonnative plants; 
predation; and climate change, are not of a magnitude that it is likely 
to become endangered in the foreseeable future. Specifically, the 
identified development projects are not a significant threat to the 
species throughout its range or the respective DPSs identified in the 
Distinct Population Segment section, above, because the projects (1) 
are subject to the avoidance, minimization, and compensation measures 
of the Rangewide Management Strategy (in the United States only); (2) 
are relatively small compared to the range of the species or DPSs; (3) 
do not result in complete barriers to flat-tailed horned lizard 
movement; (4) do not result in the elimination of large ``parts'' where 
the deleterious effects associated with small population size are 
likely to substantially affect the population; (4) or a combination of 
these, as detailed in the Summary of Factors Affecting the Species 
section.
    Comment 11: One commenter believes that urban development is 
conflicting with flat-tailed horned lizard survival.
    Our Response: As described in the Urban Development section under 
Factor A, urban development within the range of the flat-tailed horned 
lizard is largely occurring within areas that were previously developed 
for agriculture and is not resulting in additional habitat loss because 
the prior agricultural conversion had already made the land unavailable 
for the species. Urban development in flat-tailed horned lizard habitat 
is occurring, but in a limited area compared to the large area occupied 
by the species. Additionally, large areas of the species' range are 
under some level of protection where urban development is prevented or 
restricted, including Management Areas created through implementation 
of the Rangewide Management Strategy, CDPR lands, BLM wilderness, 
Coachella Valley MSHCP reserves, and portions of two biosphere reserves 
in Mexico. Moreover, where urban development may occur, its impact is 
further reduced (through avoidance, minimization, and mitigation) by 
the measures that benefit the flat-tailed horned lizard (such as the 
Rangewide Management Strategy, Coachella Valley MSHCP, and Mexican 
Federal listing). Thus, we concluded that urban development is not a 
substantial threat to the species.
Comments Related to the Rangewide Management Strategy
    Comment 12: Four commenters state that the Rangewide Management 
Strategy currently in place is working to the benefit of the species, 
and there is no need to list the flat-tailed horned lizard as a 
federally threatened species. Two of these commenters further agree 
with the 2008 Annual Progress Report which states that the Interagency 
Conservation Agreement and Rangewide Management Strategy continue to 
provide an effective management focus to conserve flat-tailed horned 
lizard habitat throughout its range. Two commenters also expressed 
concern that listing the species could undermine the Interagency 
Conservation Agreement and questioned the efficacy of listing the flat-
tailed horned lizard prior to completion of the surveys called for by 
the Rangewide Management Strategy.
    Our Response: We agree with the commenters that the Rangewide 
Management Strategy is providing important conservation benefits to the 
flat-tailed horned lizard and its habitat in the United States. 
Although many of these efforts are voluntary, conservation actions are 
formally incorporated into planning documents of participating agencies 
(such as BLM's California Desert Conservation Area Plan). Moreover, 
most of the measures outlined in the Rangewide Management Strategy are 
being successfully implemented (FTHLICC 1998, pp. 1-11; FTHLICC 1999, 
pp. 1-13; FTHLICC 2001, pp. 1-24; FTHLICC 2003b, pp. 1-32; FTHLICC 
2004, pp. 1-33; FTHLICC 2005, pp. 1-37; FTHLICC 2006, pp. 1-34; FTHLICC 
2007, pp. 1-33; FTHLICC 2008a, pp. 1-35; FTHLICC 2009, pp. 1-38; 
FTHLICC 2010, pp. 1-33). Most of the benefits to the species occur 
within the United States. Although implementation of the Rangewide 
Management Strategy is also contributing to the conservation of the 
species in Mexico by promoting partnerships with local organizations in 
that country that are implementing programs that benefit the species, 
the benefits associated with the avoidance, minimization, and 
mitigation measures called for by the Rangewide Management Strategy are 
not in effect in Mexico. As such, the benefits afforded the species 
through implementation of the Rangewide Management Strategy, important 
though they may be, are limited. We appreciate the commenters' support 
of the Interagency Conservation Agreement that is benefitting the flat-
tailed horned lizard and its habitat. Please see our response to 
Comment 1 and Management and Populations under the Background section 
for more information regarding the Rangewide Management Strategy.
    Regarding the commenters' concern over the possibility that we may 
make a determination to list the species without complete flat-tailed 
horned lizard survey information, we note that we are required to make 
a final listing determination. Our determination of whether to list a 
species as endangered or threatened is based on our assessment of the 
five listing factors described in the Act using the best scientific and 
commercial information available. Although we agree population trend 
data would help us better understand the current status of the species, 
we must meet our obligations under the Act by examining the threats to 
the species. This analysis is presented in the Summary of Factors 
Affecting the Species section. We conclude that the species is not in 
need of the protections afforded by the Act at this time. Additionally, 
because we are not listing the species, the question of the potential 
effects of listing on the implementation of the Interagency 
Conservation Agreement is moot.
    Comment 13: Three commenters asserted that implementation of the 
Rangewide Management Strategy, including the designation of Management 
Areas, is not working to recover the species. The commenters stated 
that mitigation lands are insufficient to make up for losses of 
habitat, especially from threats such as OHV use and large-scale 
renewable

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energy projects. Two of the commenters stated the strategy is 
inadequate and not rangewide. A fourth commenter stated that the 
Service has relied heavily on the Rangewide Management Strategy to 
prevent the flat-tailed horned lizard's listing in the past.
    Our Response: With regard to the commenters' concerns that 
mitigation lands may be insufficient to recover the species, we 
concluded that none of the existing or potential threats are likely to 
cause the flat-tailed horned lizard as an entire species or as any one 
of the Western, Eastern, or Southeastern DPSs to be in danger of 
extinction or likely to become so within the foreseeable future 
throughout all or a significant portion of its range; thus, the species 
does not need to be ``recovered.'' Implementation of the Rangewide 
Management Strategy, including the mitigation (compensation) by the 
signatory agencies is providing for the consolidation of the existing 
Management Areas by purchasing private inholdings within the Management 
Areas. Moreover, implementation of the avoidance and minimization 
measures included in the Rangewide Management Strategy is reducing 
certain potential future threats, including development of energy 
generation facilities and associated infrastructure on signatory lands.
    With regard to the commenters' concerns that the Rangewide 
Management Strategy is not rangewide, the purpose of this strategy is 
to provide a framework for conserving sufficient habitat to maintain 
several viable populations of the flat-tailed horned lizard throughout 
the range of the species in the United States. Five Management Areas 
were designed to identify large areas of public land in the United 
States where flat-tailed horned lizards have been found, and to include 
most flat-tailed horned lizard habitat identified as key areas in 
previous studies (Turner et al. 1980, pp. 1-47; Turner and Medica 1982, 
pp. 815-823; Rorabaugh et al. 1987, pp. 103-109; FTHLICC 1997, p. 35). 
Furthermore, the Management Areas were delineated to include areas as 
large as possible, while avoiding extensive, existing and predicted 
management conflicts (such as OHV open areas). The Management Areas are 
meant to be the core areas for maintaining self-sustaining populations 
of flat-tailed horned lizards in the United States (FTHLICC 2003a, p. 
47). Although this strategy does not include Mexico, implementation of 
the Rangewide Management Strategy includes coordination with partners 
in Mexico to promote efforts to benefit the species in that country 
(FTHLICC 2009, p. 14). Additionally, approximately 60 percent of the 
habitat in Sonora (Mexico) lies within two Mexican Federal natural 
protected areas where impacts from development and other activities is 
limited (see Management and Populations in the Background section for 
further discussion).
    Regarding the use of the Rangewide Management Strategy in our past 
listing determinations (withdrawals), we did not rely solely on the 
Rangewide Management Strategy in our decisions, nor do we do so in this 
determination. As we state in our response to Comment 12, the evidence 
indicates that implementation of the Rangewide Management Strategy is 
providing important conservation benefits to the flat-tailed horned 
lizard and its habitat; however, that is but one aspect we consider. 
Our determination to list a species is made by looking at the five 
factors described in section 4(a)(1) of the Act and the status of the 
species relative the standards for listing as endangered or threatened. 
This determination is made solely on the basis of the best scientific 
and commercial information available, and takes into account those 
efforts, if any, being made by any State or foreign nation, or any 
political subdivision of a State or foreign nation, to protect the 
species through habitat protection or other conservation practices. Our 
assessment of the effects of the five listing factors on the flat-
tailed horned lizard is presented in the Summary of Factors Affecting 
the Species section. Our assessment of those efforts being made to 
protect the species through habitat protection or other conservation 
practices is presented in the Conservation Efforts section (see also 
Management and Populations under the Background section)--which, in 
this case, included the Rangewide Management Strategy. Thus, we have 
considered but have not relied solely upon the Rangewide Management 
Strategy in our determination.
    Comment 14: One commenter states that the Rangewide Management 
Strategy does not discuss impacts of the border fence (which they 
believe isolates populations) and proposed solar energy projects. 
Specifically, this commenter and a second commenter believe that the 
border fence in the Yuha Management Area and the proposed Tessera Solar 
North America Project (also known as the Imperial Valley Solar Project) 
will result in isolated populations of the species and fragmented 
habitat. Further, the second commenter believes this project will 
result in impacts to the flat-tailed horned lizard and its habitat from 
construction and maintenance, vibrations from vehicle traffic, changes 
in topography, destruction of vegetation that is a food source for 
harvester ants, and increased dust deposition on vegetation. 
Additionally, the first commenter believes the Service should analyze 
the impacts of the border fence and proposed solar projects on the 
viability of flat-tailed horned lizard populations and cumulative 
impacts of habitat loss.
    Our Response: As discussed in our Factor A and E analyses (Summary 
of Factors Affecting the Species section), we acknowledge that the 
border fence and solar (energy generation) projects may result in the 
loss or degradation of flat-tailed horned lizard habitat and 
potentially serve as barriers, isolating populations of flat-tailed 
horned lizards. Although not extensively discussed by the Rangewide 
Management Strategy, private development of solar and other energy 
generation facilities on lands controlled by signatory agencies is 
still subject to the avoidance, minimization, and mitigation measures 
called for by the Rangewide Management Strategy. For example, the 
project proponent for the Imperial Valley Solar Project designed the 
project to avoid and minimize impacts to flat-tailed horned lizard 
Management Areas and is providing funds to acquire off-site habitat 
areas as compensation for unavoidable impacts, all per the 
specifications of the Rangewide Management Strategy (BLM 2009, pp. 4-7 
to 4-10). Because of the prevalence of Federal and State lands in the 
U.S. portion of the range of the flat-tailed horned lizard and because 
most of this land is managed by signatories to the Interagency 
Conservation Agreement implementing the Rangewide Management Strategy, 
we expect that the vast majority of proposed energy development 
projects that are likely to affect flat-tailed horned lizard habitat 
will be subject to the avoidance, minimization, and compensation 
measures incorporated into the Rangewide Management Strategy (see 
Energy Generation and Facility Development section).
    Such projects may also serve as barriers to flat-tailed horned 
lizard movement. Many of the proposed and anticipated projects are 
likely to occur in the Western Population area. As described in the 
``Barriers and Small Populations'' section under Factor E, the parts of 
the Western Population north and south are large enough to likely not 
be substantially affected by the threats associated with small 
population size. Moreover, Interstate 8, which runs along the southern 
edge of the Imperial Valley Solar Project and many of the other 
proposed or anticipated energy

[[Page 14267]]

generating projects in the area, is already likely to be a substantial 
barrier to flat-tailed horned lizards within the area of the Imperial 
Valley Solar project.
    Development of renewable energy is not without impacts, but 
implementation of the Rangewide Management Strategy, either under the 
voluntary Interagency Conservation Agreement or as it is incorporated 
into existing regulatory mechanisms, is anticipated to reduce the 
direct and indirect effects, including habitat loss and isolation of 
populations. We do not believe vibrations of vehicle traffic, changes 
in topography, destruction of vegetation that is a food source for 
harvester ants, and dust on vegetation will be any more substantial 
than the actual loss or degradation of flat-tailed horned lizard 
habitat, the effects of which we anticipate to be reduced by avoidance, 
minimization, and mitigation measures of the Rangewide Management 
Strategy. Moreover, the cumulative effects of habitat loss are reduced 
through implementation of the Rangewide Management Strategy by the 
creation and maintenance of large blocks of flat-tailed horned lizard 
habitat, including the establishment of Management Areas, the 1 percent 
cap on impacts, the avoidance and minimization measures directed by the 
Rangewide Management Strategy, and the consolidation of the respective 
Management Area through the purchase of private inholdings with monies 
acquired from compensation for unavoidable impacts from development 
activities.
    Regarding the concerns raised by the commenter about the border 
fence, we also acknowledge in our Factor E analysis that tactical 
infrastructure (such as fencing, lighting, and access and patrol roads) 
along portions of the border fence area has the potential to serve as a 
barrier for flat-tailed horned lizard movement. However, installed 
fencing has been constructed to allow movement of small animals (USCBP 
2008a, pp. 1-4 to 1-6 and Appendix B; USCBP 2008b, pp. 2-5 and 8-9); 
thus, we do not anticipate the fence itself to completely hinder flat-
tailed horned lizard movement (see ``Barriers and Small Populations'' 
under Factor E). Additionally, with respect to the Yuha Desert 
Management Area, this area was selected for management protections of 
flat-tailed horned lizards because it is likely to support high 
densities of lizards (i.e., 0.7 individuals per ha (0.3 per ac), which 
is a conservative estimate). Moreover, as mentioned above, the border 
fence is likely a semipermeable barrier for small species such as flat-
tailed horned lizard, allowing some connectivity between the Yuha 
Desert Management Area and the areas of habitat in Mexico.
    Comment 15: One commenter believes the Rangewide Management 
Strategy does not provide enough protection because the document 
acknowledges that it is unknown whether the lands set aside are 
sufficient, and that the Ocotillo Wells State Vehicular Recreation Area 
is not being managed adequately. A second commenter stated that they 
believe BLM is understaffed and underfunded, which has led to its 
inability to reduce impacts on flat-tailed horned lizard Management 
Areas.
    Our Response: As described in the ``Barriers and Small 
Populations'' section under Factor E, we evaluated the size of the 
parts formed as a result of potential barriers. We calculated the 
Western, Eastern, and Southeastern Population areas, as defined herein 
and based upon the current distribution map presented in the revised 
Rangewide Management Strategy (FTHLICC 2003a, p. 5), are 341,989 ha 
(845,073 ac), 169,617 ha (419,133 ac), and 1,073,551 ha (2,652,802 ac), 
respectively. Within those three Population areas combined, we found 
about 91 percent of the area, despite containing potential barriers, is 
in large enough blocks that the populations of flat-tailed horned 
lizards are not likely to be affected by threats associated with small 
populations. Although the Rangewide Management Strategy is an important 
conservation effort that provides substantial benefit to the flat-
tailed horned lizard and its habitat, especially within the United 
States, the status of the species does not depend solely upon the lands 
set aside through implementation of the Rangewide Management Strategy. 
Similarly, the status of the flat-tailed horned lizard does not depend 
solely on management that may or may not be adequate on Ocotillo Wells 
SVRA; however, management activities that reduce threats to the species 
make important contributions to the status of the species at a local or 
regional level. Moreover, for implementation of the Interagency 
Conservation Agreement to be successful, each signatory agency should 
implement its share of the Rangewide Management Strategy (see also the 
Management and Populations in the Background section, and the 
Description of Specific Populations section for further discussion).
    Comment 16: One commenter stated that flat-tailed horned lizards 
should not be listed as a threatened species because there has been 
sufficient management in place over the past 10 years. The commenter 
believes management efforts should be implemented to eradicate 
Argentine ants (Linepithema humile), which displace the main food 
source (harvester ants) for flat-tailed horned lizards.
    Our Response: We agree with the commenter that there is sufficient 
management and conservation occurring for flat-tailed horned lizards 
(see the Finding section and Management and Populations under the 
Background section of this document for discussion of the long-term 
management of this species). We will continue to work with our partners 
to implement management actions to benefit this species.
    With regard to the commenter's concern about Argentine ants, the 
evidence indicates that Argentine ants are not a threat to flat-tailed 
horned lizards. Argentine ants do not tolerate hot, dry conditions 
(Holway et al. 2002, p. 1610). The range of the flat-tailed horned 
lizard is hot and dry (see Background section), suggesting that 
Argentine ants do not invade flat-tailed horned lizard habitat to any 
substantial degree (Barrows et al. 2006, p. 492); thus, they do not 
substantially affect the primary food of the species throughout most of 
the species' range. Therefore, we do not believe eradication of 
Argentine ants in flat-tailed horned lizard habitat is a warranted 
management action to benefit the species.
    Comment 17: One commenter states that the management strategy is 
sufficient for flat-tailed horned lizard and therefore listing this 
species is not warranted. Specifically, the commenter described the 
following management actions that are benefiting the species: (1) Since 
1997, the Imperial Irrigation District has paid $10,000 to offset 
potential project impacts to habitat; (2) although border patrol and 
unpermitted OHV use continue to impact the species, there are no 
significant trends in lizard encounter rates in Yuha Desert, East Mesa, 
or West Mesa from 1979 to 2001; (3) agricultural land development is no 
longer occurring; (4) urbanization is not occurring in Yuha Desert, 
East Mesa, or West Mesa; and (5) the Mexican Government is providing 
protections to flat-tailed horned lizards.
    Our Response: As described in our analysis above, we agree with the 
commenter's statements in general. The mitigation (compensation or off-
setting) measures associated with the Rangewide Management Strategy are 
important to consolidating the Management Areas under the control of 
signatory agencies. We agree monitoring data indicate that flat-tailed 
horned lizard populations in the surveyed Management Areas are not low 
and are not declining. We also agree that

[[Page 14268]]

agricultural and urban development are not significant threats to the 
species, as discussed under Factor A, and that the protections afforded 
to the species by Mexican laws are not inadequate.

References Cited

    A complete list of all references cited in this document is 
available on the Internet at http://www.regulations.gov. Additionally, 
a complete list of all references cited, as well as others, is 
available upon request from the Carlsbad Fish and Wildlife Office (see 
ADDRESSES).

Author

    The primary authors of this document are staff members at the 
Carlsbad Fish and Wildlife Office (see ADDRESSES above).

    Authority: The authority for this action is section 
4(b)(6)(B)(ii) of the Endangered Species Act of 1973, as amended (16 
U.S.C. 1531 et seq.).

    Dated: February 25, 2011.
Daniel M. Ashe,
Acting Director, Fish and Wildlife Service.
[FR Doc. 2011-5411 Filed 3-14-11; 8:45 am]
BILLING CODE 4310-55-P