[From the U.S. Government Printing Office, www.gpo.gov]



                                                                     FY 1992 FINAL PRODUCT Task 15
                                                                             Bird Surveys- Rr, Thrt, Endang.


                                 CEEffects of Marsh Size on Incidence Rates and
                                                Avian Community Organization within
                                                                the Lower Chesapeake Bay























                                                                                       Bryan D. Watts
                                                          Center for Conservation Biology
                                                                     College of William.& Mary

                                          This paper is funded in part by a grant from the National Oceanic and
                                          Atmospheric Administration. The views exprbssed hereimare, those of
                             i-Q180W  I   the author and do.not necessarily reflect.the views of NOAA,or any of
                               -=M'      -its sub-agencies










                                   Effects of Marsh Size on Incidence Rates and
                                                Avian Community Organization within
                                                                 the Lower Chesapeake Bay









                                                            4























            F 1*
    V@o




                                                                                       Bryan D. Watts
                                                          Center for Conservation Biology
                                                                     College of William & Mary

                                          This paper is funded in part by a grant from the National Oceanic and
                             S4           Atmospheric Administration. The views expressed herein are those of
                                          the author and do not necessarily reflect the views of NOAA or any of
                                          its sub-agencies
















                              Effects of Marsh Size on Incidence Rates and
                                 Avian Community Organization within
                                       the Lower Chesapeake Bay
                                              (Final Report)










                                             Bryan D. Watts
                                     Center for Conservation Biology
                                       College of William & Mary
                                         Williamsburg, VA 23185








                                          Project sponsored by:



                               Virginia Department of Environmental Quality
                             Virginia Coastal Resources Management Program


                             Virginia Department of Game and Inland Fisheries
                                Nongame and Endangered Species Program






                                             November 1993

















                                                  ABSTRACT


                 Bird abundance and species richness was assessed in 50 salt marshes located in the

          lower Chesapeake Bay. Ten spatial replicates of 1, 2, 3, 4, and 5 ha marshes with similar

          vegetational composition were included. Over 4,800 observations were made of 100 species.

          Marsh area was a good indicator of overall species richness and bird abundance. The slopes

          of species-area relationships were consistent with those derived in an earlier study involving

          a broader range of marsh sizes. Species loss rates were highest for those species using the

          marsh directly. Of all primary users, obligate species showed the most dramatic declines

          with decreasing marsh size. Differences between obligate and facultative species in loss rates

          resulted in a directional shift in community composition with increasing marsh size. The

          form of incidence functions varied between species and species groups. Increases in

          incidence rates ranged from 40 to 70% for obligate breeders and 20 to 40% for facultative

          breeders. Species that used marshes as primary or alternate foraging areas exhibited variable

          incidence patterns.

                 Patterns in both species-area relationships and marsh availability were used to

          formulate size-specific management recommendations. Marshes greater than 50 ha. in size

          generally support the best examples of unique marsh-bird communities. Because these

          marshes are rare, they should be the focus of acquisition and management programs.

          Marshes between 5 and 50 ha. are also relatively rare and likely support the bulk of all

          obligate marsh users. Marshes of this size should be formally recognized and given special








          attention when considering requests for marsh alteration. Marshes between 1. and 5 ha are

          relatively common and have variable value depending on actual size and particular species of

          interest. Marshes of this size should be considered on an individual basis taking into account

          specific species of concern and the local context of the marsh.












                                               INTRODUCTION


                 The widespread conversion of natural land for human use has resulted in the

          fragmentation and insularization of many formerly continuous habitats as well as the

          reduction in size of natural habitat patches. Fragmentation and its consequences has been

          studied in many habitats within North America by inspecting species-area curves (e.g.

          Forman et al. 1976, Robbins 1980, Coleman et al. 1982) or by documenting faunal

          relaxation within recently isolated patches (e.g. Whitcomb et al. 1981, Lynch and Whigham

          1984, Wilcove et al. 1986). In general, bird species richness increases with habitat size

          often due to the elevation of incidence rates for area-sensitive species. Understanding the

          extent to which size alone may limit diversity within patches or the distribution of species

          between patches is critical to designing habitat management plans or selecting conservation

          areas to protect avian communities.

                 Tidal salt marshes form an important transition zone between shallow water habitats

          and a host of upland types. Throughout most of our history, societal views of these habitats

          have led to enormous investments in their destruction. Consequently, only half of all historic

          marshes remain. Over the past thirty years, several important socioeconomic services have

          been attributed to tidal salt marshes including among others: 1) water quality protection, 2)

          flood damage protection, 3) erosion control, and 4) habitat for fish and wildlife.

          Enumeration of these benefits has, over time, led to a shift in societal perceptions resulting in

          the enactment of protective legislation. However, the ultimate success of these programs in









          preserving unique marsh communities, depends, to a great extent, on our understanding the

          species involved.

                 Relatively few studies have examined avian community dynamics within tidal salt

          marshes. In 1992, species/area relationships were investigated within salt marshes of the

          lower Chesapeake Bay (Watts 1992). This study documented that patch size was one of the

          single best indicators of species richness for a number of bird groups and that many

          individual species were area-sensitive. Results also suggested that the marsh-bird community

          observed in large marshes appeared to collapse as marsh size was reduced from 5.0 to 1.0

          ha. Because marshes within this size range are relatively common, refinement of occupancy

          patterns would allow projection of marsh values to a much larger fraction of the total

          marshes. This information need was the impetus for the current study.



                 The primary objectives of the study were:

                 1) To examine the relationship between marsh-bird communities and patch size

                 between 1 and 5 ha.


                 2) To examine patterns of community organization related to patch size.

                 3) To refine incidence functions for obligate marsh users across the range of marsh

                 sizes.


                 4) To investigate the use of selected marsh components by common marsh-bird

                 species.







                                                       2










                                                  STUDY SITE


                 This study was conducted along the western shore of the lower Chesapeake Bay

          between Grandview Beach (city of Hampton) and New Point Comfort (Mathews County),

          (see Figure 1). The broad land arc within these boundaries contains some of the most

          extensive wetlands remaining in the lower Bay including over 1300 tidal marshes with a total

          area of approximately 6,200 ha. Adjoining uplands remain rural with only scattered

          population centers.

                                                   METHODS


                 This study was conducted within 50 tidal marshes ranging in size from 0.8 to 6.1 ha.

          Marshes included 10 spatial replicates of 5 different size categories (size categories include

          1, 2, 3, 4, and 5 ha). Wetland inventory maps and summaries (Barnard 1975, Moore 1976,

          Silberhorn 1981a, 1981b) were used to screen all marshes within the study area for potential

          study sites. The list of total marshes (N > 1300) was initially reduced based on compliance

          with the general size categories outlined above. Because adequate marshes of exact sizes did

          not exist, non-overlapping ranges were established for each of the 5 size categories. Size

          ranges employed were 0.8 - 1.2 ha, 1.6 - 2.4 ha, 2.8 - 3.2 ha, 3.6 - 4.5 ha, and 4.9 - 6.1 ha

          for size classes 1, 2, 3, 4, and 5 respectively. Area means for marshes actually used were

          0.92 + 0.193 (mean + IS.E.), 1.96 + 0.350, 2.96 + 0.207, 3.94 + 0.987, and 5.42 +

          0.424 for classes 1, 2, 3, 4, and 5 respectively.

                 Because vegetation type is likely a primary factor in determining marsh use for many

          bird species, vegetational composition was controlled for in the selection process. Marshes

          were considered for use only if they were dominated (greater than 90% coverage) by and



                                                         3

























         Figure 1: Map of study area and Chesapeake Bay region. Black dots indicate the location
         of individual study marshes.




















                      I








































                                                                           LOCATION OF
                                                                       STUDY MARSHES





         Figure 1








          contained the five target plant forms including: smooth cordgrass (Spartina alterniflora),

          black needlerush (Juncus roemerianus , saltgrass (Distichlis spicata , saltmeadow hay

          (Spartina patens , and salt bush (either Iva frutescens or Baccharis hamilifolia). These plant

          forms were chosen because they were locally common and representative of marsh vegetation

          on a regional scale. All of the study marshes chosen met the following composition

          requirements: smooth cordgrass C> 30%), black needlerush (> 20%), saltgrass and

          saltmeadow hay combined (> 15%), and salt bush (> 10%). Controlling for vegetational

          composition in this way allows for the direct assessment of size effects and provides an

          opportunity to more closely examine bird/vegetation relationships. In addition to selecting

          for size and vegetational composition, an attempt was made to locate marshes on points of

          land extending out into the bay proper rather than along the headwaters of small tributaries.

          However, because of the large number of marshes needed, some marshes of each size group

          were located a considerable distance from the Bay's edge.

                 All potential study marshes were visited between early April and early May to

          determine the feasibility of accessing and surveying the marsh. Marshes that were difficult

          to survey or reach were eliminated from further consideration. After all study marshes had

          been selected, a scaled field map of each marsh was produced. Maps were generated

          electronically by digitizing the outline of marsh inventory maps into a computer graphics

          program and then annotating prominent landmarks (see Figure 2 for example). To set up

          study marshes, two census points were established within each study marsh. Two points

          were used here because it was determined in a previous study (in similar marshes) that this





                                                       5

























          Figure 2: Illustration of example marsh field map. Note the location of survey points
          within the marsh.





                                    Example Marsh Map


                                MARSH
                                  G219
                                  (5ha)




                                                                              CAUCUS BAY






                                                                             Pt 2









                                   Pt 1
                       %            Pond, --M
                                                                               dl@l













           Figure 2


                                                              6








          would be enough to saturate marshes within this size range. Census points were placed in

          prominent positions within the marsh to make coverage as even as possible.

                To survey birds within study marshes a combination of the line transect (Emlen 1971,

          1977) and point count (Blondel et al. 1981, Morrison et al. 1981) method was used. The

          observer began the survey upon entering the marsh and walked a prescribed route stopping at

          both census points to listen and watch for birds. Playbacks were used during point counts to

          increase the detection rates for Clapper and Virginia Rails. Survey tapes were produced that

          consisted of 50 sec of male advertisement calls for both species separated by 10 sec of quite.

          Each point count consisted of 4 min of the tape recorded calls (including 2 50 sec periods for

          each species) followed by a 4 min listening period. Each marsh survey lasted approximately

          40 min. This amount of time was more than adequate to provide a complete accounting of

          all birds utilizing the marsh. Throughout the study, an attempt was made to spend the same

          amount of time in each marsh. This procedure ensured that sampling effort was comparable

          between surveys regardless of marsh size.

                All 50 focal marshes were surveyed 4 times over the three month study period. To

          reduce seasonal bias, marshes were surveyed in 4 rounds where all marshes were surveyed in

          each round and the survey order was randomly determined. Because many of the birds of

          interest in this study exhibit distinctly different peaks of calling and residency, a split

          approach to surveys was used. Two survey rounds were conducted between 8 May and 31

          May. This early period is the time when rails of interest are most vocal on territories and

          when many transients utilize marshes. Because many passerines have spring migration

          periods that extend into early June, the later survey rounds were not begun until 18 June.



                                                       7









          Late surveys were delayed until this date in an attempt to minimize the number of birds

          detected that really represented transients. Two survey rounds were conducted between 18

          June and 18 July.

                 In addition to differences in the seasonal timing of breeding, rails and passerines

          differ in their daily activity patterns. During the breeding season, rails call most intensively

          from about 12:00 to 4:00 AM. However, birds also call during the early morning and late

          evening, and playback studies conducted during the early morning have had relatively good

          response rates (e.g. Glahn 1974, Repking and Ohmart 1977). Just after dawn is the optimum

          activity period for most passerines and other birds of interest. For this reason, all marsh

          surveys were conducted within the time window between dawn and 5 hrs after dawn. This

          time period was believed to be the best compromise for the various bird groups of interest.

          Data Collected


                 All birds detected during formal surveys were placed in one of three "user"

          categories. These included: category 1 - bird in direct contact with marsh (e.g. Seaside

          Sparrow perched in salt bush), Category 2 - bird not in direct contact with marsh but

          foraging on prey just over the marsh surface (e.g. Barn Swallow foraging over marsh),

          category 3 - bird flying over marsh but under 50 m in altitude (e.g. Laughing Gull milling

          around over marsh), or associated with water within 50 m of shoreline (e.g. Osprey foraging

          for fish in shallows next to marsh).

                 Before the beginning and after the completion of each survey, several environmental

          parameters were measured. These included: time of day, ambient temperature, estimated





                                                         8








          wind speed, percent cloud cover, and current tide height. A full analysis of these variables

          and their influence on survey results will not be presented here.

          Substrate Use,

                 In order to examine how species used the marsh and, in addition, how different marsh

          features contributed to overall species richness, marshes were subdivided into 15 "marsh

          components" (description and code name given in Table 1). Marsh components were then

          grouped loosely according to hydrology and topography (marsh zones and associated

          components shown in Table 1). It should be noted that these groupings were established as a

          convenience for presentation and that many marsh components may be located in various

          places within a specific marsh. A generalized marsh profile illustrating the approximate

          location of marsh zones is given in Figure 2. Figure 3 illustrates, in more detail, the various

          components included in each marsh zone. All observations of birds considered to be using

          the marsh directly were placed in 1 of the 15 marsh components.




                                                    RESULTS


                 Marsh surveys resulted in the detection of over 4,880 birds of 100 species (see

          Appendix I for a complete list of species and scientific names). Although species richness

          was high overall, relatively few species accounted for the majority of observations. For

          example, two species (Red-winged Blackbird and Laughing Gull) accounted for greater than

          25% of the total observations and 7 species represented greater than 50%.

                 The majority of species observed used the study marshes directly (i.e. were category

          1 species) as nesting and or as foraging habitat. Using a criterion of > 50% to place species



                                                         9










       Table 1: Descriptions of marsh components and sections.

       Marsh       Code/                  Component
       Section     Name                   Description


       Water Components
            OW - Open Water: Open water along margin of marsh.
            MF -  Mudflat: Exposed mud along margin of marsh.
            TG -  Tidegut: Narrow tidegut extending into marsh.
            TP -  Tidepool: Permanently or regularly filled depression
                             with no direct connection to tidegut.

       Low Marsh
            TC -  Tall Cordgrass: Tall, dense form of Spartina
                             alterniflora.
            LC -  Low Cordgrass: Low, sparse form of S. alterniflora.
            SL -  Wet Slew:  Regularly inundated low depression
                             typically surrounding a shallow tidepool or
                             terminus of a small tidegut. Depression is
                             dominated by sparse, mixed stands of S.
                             patens, Distichlis spicata, and Salicornia
                             virginica.
            BN - Black Needlerush: Dense stands of Juncus roemerianus.


       High Marsh
            SG - Saltgrass: Dense upper stands of D. spicata.
            SM - Saltmeadow Hay: Dense upper stands of S. patens.
            SB - Saltbush: Live standing plant of    "Iva frutescens or
                             Baccharis hamilifolia.
            SN - Dead Pine Snag: Dead standing pine snag.

       Marsh-upland Transition Zone
            WM - Wax Myrtle: Shrub of Myrica cerifera.
            DS - Deciduous Saplings: Hummock or clump of small
                             deciduous saplings.
            LP - Live Pine: Live pine (Pinus taeda) along marsh edge.














                                         10



























          Figure 3: Illustration of general marsh profile showing the relationship between hydrology,
          topography and marsh zones.











                                             GENERAL           MARSH PROFILE





                                                                                    HIGH MARSH ZONE            owl          qN_
             Fj                      WATER ZONE
            Spring Tide
            High Tide                                                                        @fllf
            Low Tide                                                                           MARSH-UPLAND TRANSITION

                                                              LOW MARSH ZONE
                                                                                                3H ZONE

























         Figure 4: Illustration showing the 4 marsh zones and their respective marsh components.
         Key to marsh component codes is given in Table 1.










                    ow    MF           TG      TP
                               Ml@




            WATER ZONE









                           HC   Lc    SL    BN





            LOW MARSH ZONE






                          SG   SB SM
                                         SN






            HIGH MARSH ZONE






                     wm             DS   LP







    Figure 4MARSH-UPLAND TRANSITION

                               12








          in user categories, 7 1. 0 % of the species were classified as category 1, 5. 0 % as category 2,

          and 24.0% as category 3 (Appendix H gives a complete breakdown of marsh use by species).

          For all species combined, 62.0% of the total observations were of birds directly contacting

          the marsh, 9.6% were of birds foraging over the marsh surface and 28.4% were of birds

          associated with the marsh.


                 All species observed were placed in one of four different categories based on their

          primary relationship to the marsh during the study period (category designations were based

          on 1992 habitat results and various accounts within the literature). Categories used include:

          Obligate Breeder - those species that breed exclusively or nearly so in tidal salt marshes,

          Obligate Forage - those species for which the salt marsh represents a primary foraging

          habitat but nest outside the marsh, Facultative Breeder - those species that nest within the

          salt marsh but may also be found nesting in one to several upland habitats, Facultative

          Forager - those species that breed outside the marsh and for whom the marsh represents an

          occasional or alternate foraging habitat.

                 The majority (81.0%) of species observed using marshes directly were actually

          facultative users. Observations were dominated by primarily upland species that utilize

          marshes as alternative breeding and or foraging habitat. Facultative users were mostly

          incidental foragers (59.0%) but also contained breeding species (22.0%). Although obligate

          users accounted for only 19.0% of the species observed, they accounted for over 35.'0% of

          the total individuals.









                                                        13









          Temporal Patterns

                 For all study marshes combined, species richness declined only modestly (10%) over

          the study period. Apparently, relatively few transient species utilized these smaller marshes

          during spring migration. In fact, only 18% of the species detected were exclusive to the

          early surveys compared to 10% for later surveys. Overall species richness was not

          significantly different (G-statistic < 2, P > 0.05, testing the null hypothesis that early

          late) between early and late surveys.

                 Like species richness, overall bird abundance was relatively stable over the study

          period. This result points again to the lack of transient user species during the early period.

          Overall abundance was not significantly different (G-statistic < 2, P > 0.05, testing the null

          hypothesis that early = late) between early and late surveys. However, the majority (61 %)

          of species exhibited a substantial (> 50% change in abundance) increase or decrease in

          abundance between the early and late periods (see Appendix III for seasonal occurrence

          patterns). In general, most of the species that were detected in greater numbers during early

          surveys were winter residents that moved out of the local area or transients that moved

          through the study marshes in relatively low numbers. Species that showed substantial

          increases throughout the season were dominated by facultative users that moved into marshes

          during early June to nest or forage.











                                                        14










          Effects of Marsh Size


          Communfty Response

                 For all bird groups combined, species richness was positively related to marsh size

          (see TOTAL BIRDS in Figure 5). Although the form of this relationship differed between

          user categories, all groups exhibited similar trends. All groups except category 2 users

          showed statistically significant increases (see Table 2, Figure 5) in average species richness

          across the range of marsh sizes. Similarly, all groups except category 2 species showed

          significant Log/Log regressions between species richness and actual marsh size (see Table 3).

          Species/area slopes were similar between bird groups (Table 3) with category one species

          showing the greatest declines with decreasing marsh size. This result is consistent with their

          direct relationship to the marsh. The nonsignificant results for category two species were

          likely due to the very small pool of species within the group (primarily 2-3 species of

          swallows). Like species richness, total bird abundance increased along with marsh size

          (Figure 6). However, patterns were significant for total abundance and category one species

          only (Table 2).

                 Dividing the bird community into functional groups, obligate users were influenced to

          a greater extent by marsh size than facultative users with regard to both species richness

          (Figure 7) and abundance (Figure 8). Both obligate breeders and foragers exhibited

          significant trends with increasing marsh size (Table 4). Neither facultative breeders or

          foragers showed significant trends at the 0.05 level (although facultative breeders did show a

          trend in this direction). The result of differences between facultative and obligate species in

          their response to marsh size was that the composition of the marsh-bird community changed



                                                        15
























         Figure 5: Average accumulated species richness for all species, broken down into species
         categories. Data points are means of ten replicate marshes + 1 S.E. unit.












                                          SPECIES RICHNESS
                                      FOR USER CATEGORIES



                       TOTAL SPECIES                                     CATEGORY ONE
              40                                                25


                                                                20

              30


          CA                                               go

                                                           C>
          LU                                               LU
          G6                                               - CL-
          go  20                                           co   10

              10                                                 5
                  0     1     2     3     4      5     6           0      1           3     4      5
                            MARSH SIZE (He)                                    MARSH  SIZE (He)




                       CATEGORY TWO                                    CATEGORY THREE
                4                                               14


                                                                12
                3
                                                                10


                2                                               8
            Ui                                              co)

            LU
            CL.                                             LU
            CA                                              C6
                                                            ca
                                                                4


                                                                2
                  0            2           4     5      6          0           2     3      4     5     6
                             MARSH   SIZE (He)                                MARSH  SIZE (He)




         Figure 5


                                                      16
















        Table 2: ANOVA results for species categories
        (testing between size categories).

        Species Group               F-value              P

        Species Richness
          Total User  Species         9.87             <0.001
          Category 1  Species         7.71             <0.001
          Category 2  Species         1.48               NS
          Category 3  Species         4.97             <0.01
        Abundance
          Total User  Individuals     8.57             <0.001
          Category 1  Individuals     12.26            <0.001
          Category 2  Individuals     1.03               NS
          Category 3  Individuals     1.67               NS































                                          17




















       Table 3: Results of Log/Log regressions for various species
       groups.

       Species                  Regression
       Group                    Equation                   R      F      P

       Total Users    LSpecies  = Log2.88 +  .35LogArea   .68    41.4  <.001
       Category 1     LSpecies  = Log2.34 +  .38LogArea   .61    28.7  <.001
       Category 2     LSpecies  = LogO.51 +  .20LogArea   .28      3.7 <.1
       Category 3     LSpecies  = Logl.80 +  .28LogArea   .46    12.8  <.01

       Obl. Users     LSpecies  = LogO.66 +  .67LogArea   .68    41.5  <.001
       Fac. Users     LSpecies  = Log2.14 +  .20LogArea   .30      4.7 <.05




























                                         18

























          Figure 6: Average bird abundance for all species, broken down into species categories.
          Data points are means of ten replicate marshes + 1 S.E. unit.











                                   BIRD ABUNDANCE
                               FOR USER CATEGORIES


                 TOTAL ABUNDANCE                             CATEGORY ONE
          180
          160                                       100

          140
                                                    80
        LU 120                                   tu
          100
                                                    60
          60

          60
          40                                        40

          20                                        20
                   1    2     3    4    5    6         0     1   2    3    4     5    6
                       MARSH  SIZE (He)                         MARSH SIZE (He)


                   CATEGORY TWO                           CATEGORY THREE
                                                    45

                                                    40
            12                                      35

        LU                                          30
        0                                        LU
        z   9                                    0  25
        c                                        z
        z                                           20
                                                 z
            6                                       15

                                                    10

            3                                        5
              0    1    2    3    4    5     6         0     1   2    3     4    5    6
                      MARSH SIZE (He)                           MARSH SIZE (He)






        Figure 6


                                             19


























         Figure 7: Average accumulated species richness for obligate and facultative marsh users.
         Data points are means of ten replicate marshes + I S.E. unit.














                                                                      OBLIGATE USERS

                                                10


                                                  8
                                        ca
                                        ca
                                        one
                                                  6


                                                  4
                                        co
                                        LU
                                        4UP
                                        LU        2
                                        CL
                                        C02
                                                  0
                                                         0              1              2            3             4             5              6
                                                                                  MARSH            SIZE (Ha)


                                                                 FACULTATIVE USERS

                                                20



                                                16

                                         CA
                                         co%
                                         Lu
                                                12


                                         co       8
                                         W
                                         C-130                                         -                           i
                                         Lu
                                         CL.
                                         co       4
                                                         0              1              2            3             4             5              6
                                                                                     MARSH SIZE                  (Ha)




               Figure 7


                                                                                     20
























          Figure 8: Average bird abundance for obligate and facultative marsh users. Data points are
          means of ten replicate marshes + 1 S.E. unit.













                           OBLIGATE USERS

                   90 -
                   80 -

                   70

                   60
              LU   .
                   50
                   40
                   30

                   20

                   10

                   0
                      0     1      2     3      4     5      6
                                 MARSH   SIZE (Ha)


                          FACULTATIVE USERS
                   80 -

                   70

                   60

             LU    50

                   40 -

                   30 -

                   20

                   10

                   0                                T
                       0           2      3     4     5      6

                                  MARSH  SIZE (Ha)
       Figure 8


                                       21
















       Table 4: ANOVA results for functional bird groups
        (testing between marsh size categories).

       Species Group                   F                 P


       Species Richness
          Obligate Users              12.34            <0.001
          Facultative Users           1.69               NS
       Abundance
          Obligate Breeders           8.05             <0.001
          Obligate Foragers           4.90             <0.01
          Facultative Breeders        2.92           0.1>P<0.05
          Facultative Foragers        0.90               NS
































                                          22








          between small and large marshes. Whereas obligate users accounted for only 14.4% of all

          birds detected within 1 ha marshes they accounted for 52.6% of birds detected within 5 ha

          marshes.


          Incidence Patterns


                 Incidence functions represent the probability that a species will occur in a patch of a

          given type or size. Incidence patterns were examined for selected species representing each

          of the four functional bird groups (Figures 9 - 12). All of the obligate breeders within the

          50-marsh system showed a significant increase in incidence across the range of marsh sizes.

          Willets, Seaside Sparrows, and Boat-tailed Grackles each showed increases in incidence of 60

          to 70% between 1 and 5 ha marshes. Marsh Wrens seemed to be the most area sensitive,

          reaching only 50% occurrence even within the largest marshes. In contrast, Clapper Rails

          were the least area sensitive occurring in 50% of the 1 ha marshes and all of the 5 ha


          marshes.


                 Incidence patterns for the three remaining bird groups were variable. Of the four

          common obligate foragers, only the Great Egret and Sharp-tailed Sparrow (actually a

          transient species) appear to be area sensitive over the size range examined. Great-blue and

          Green-backed herons both appear to occur in marshes with relatively high frequency

          regardless of size. All of the facultative breeders exhibited some level of area sensitivity,

          however none were dramatic. All of these species occurred in all size categories with

          relatively high frequency but did show an increase in incidence of between 20 and 40%.

          None of the facultative foragers showed any definite tendency toward area sensitivity. The

          Northern Flicker occurred in approximately 40% of the marshes surveyed regardless of size.



                                                       23


























          Figures 9 - 12: Incidence functions for selected obligate breeders, obligate foragers,
          facultative breeders, and facultative foragers. Data points indicate the proportion of ten
          replicate marshes in which the species was observed.





                                                     % OCCURRENCE                                                        % OCCURRENCE
                                                       r-3     .9h.  .4m      CD
                                              CD       Q       (D                                                               4@-     4m        CD
                                    oil                                                                         0       0       40      0         a      c@


                                                                                          W
                                                                                          m

                                                                                          c/)


                                                                                          m
                                      CA                                                               M
                                                                                                       ca
                                      ca  W                                               cn           co)   ca                                                                       % OCCURREN
                                      iq                                                  -0           iq                                                                                      J@-
                                      m                                                   >            m                                                     m                 0       c@      C3
                                                                                          33

                                                                                          0


                                                                                                                                                                           to

                                                                                                             cn


                                                                                                                                                                      CA
                                                     % OCCURRENCE                                                          % OCCURRENCE                               cn   w
                                                       ro       P.     cm      co      C)l                                      A.      am        co     c@           N
                                                       0        0      c@      c@      CD                               C3      40      c@                            m







                                                                                                            h3


                                                                                                                                                                           cn
                                                                                                      co)
                                        ca
                                           CAI -                                                      ca    co
                                                                                          0           iq
                                                                                                      m
                                                                                                                                                             :13
                                                                                                                                                             m
                                                                                          >                                                                  z
                                                                                          0


                                                                                          m
                                           cn                                                               cn











                             INCIDENCE FUNCTIONS
                          FOR OBLIGATE FORAGERS


           GREEN-BACKED HERON                      GREAT-BLUE HERON
      100                                   100 -

      80                                     80 -
                                           UA
   au
   zo so
   Uj                                      Ui 60

      40                                     40

      20
                                             20

        0                                     0
         1       2              4       5       1       2      3       4       5'
                   MARSH SIZE (He)                       MARSH SIZE (He)


               GREAT EGRET                      SHARP-TAILED SPARROW
      100                                   100


   LU 80                                   UA 80
   z                                       Q
   LU                                      z
   cc so                                   UA
                                             80

   Q
      40
                                             40

      20                                     20

        0        T!                           0
                 2       3      4       5       1       2      3       4       5
                   MARSH SIZE (He)                       MARSH SIZE (He)






        Figure 10


                                            25











                                  INCIDENCE FUNCTIONS
                            FOR FACULTATIVE BREEDERS


                EASTERN KINGBIRD                                YELLOWTHROAT
      100                                            100


        80                                            80
                                                   LU
     LU
        60
                                                   L, 60
     Uj                                            0
     cc                                            cc
     'c 40                                            40
     C.3
     0  20                                            20

        0
                                                        0                           4        5
           1        2        3        4        5          1       2
                       MARSH SIZE  (He)                              MARSH SIZE (He)

                 SONG SPARROW                              RED-WINGED BLACKBIRD
        100
                                                     100
        80                                         lu 80
        60                                         LU 60
                                                   Ic
     LU                                            cc
     cc 40                                         U
                                                      40
     CJ
     0  20                                            20


         0                                              0
            1       2        3        4        5          1       .2       3        4        5
                      MARSH  SIZE (He)                               MARSH SIZE (He)








         Figure 11


                                                     26











                            INCIDENCE FUNCTIONS
                        FOR FACULTATIVE FORAGERS


           NORTHERN FLICKER                          CAROLINA WREN
    100                                      100


     80                                       80
                                           LU
  LU
     60                                    Uj 60
   U


                                              40
  0  40                                    Q

  0
  an 20                                       20

       0                                      0
                                                                       4
         1      2       3      4      5          1      2                     .5
                  MARSH SIZE (Ha)                         MARSH SIZE (He)


           CHIPPING SPARROW                         COMMON GRACKLE
    100 -                                    100


     80                                      so
   LU
   0                                       lu
   LZ 60                                   Q 60
   U                                       z
                                           LU
                                           cc
     40                                    =40
                                           Q
     20                                    020


       o                                      0
         1      2       3      4      5         1       2      3      4
                    MARSH SIZE (He)                      MARSH SIZE (Ha)






       Figure 12


                                           27








         The three remaining species exhibited somewhat erratic patterns over the size range

         suggesting that some factor other than size is determining marsh use.



         Patterns of Vegetation Use

                Species richness and total bird numbers were compiled for the four marsh zones

         (Figure 13). Species richness was found to be highest in the high marsh zone followed

         closely by the marsh-upland transition. Sixty-four and 61 % of all birds detected were found

         in these two zones respectively at least once during the study. The water zone had the

         fewest number of species with the low marsh zone being intermediate. Patterns in overall

         bird abundance paralleled those of species richness closely. Over 68% of all birds detected

         were observed in either the high marsh zone or marsh-upland transition. This is compared to

         only 32% in the water and low marsh zones combined. The water components combined

         only accounted for 10% of the individuals detected.

                The majority of species detected were in the marsh-upland transition zone and were

         associated with either deciduous saplings (52%) and or live pines (50%), (Figure 13). These

         two marsh components also accounted for over 25% of the birds detected overall. Within

         the high marsh zone, many species were associated with either dead snags (42%) or salt bush

         (39%). Combined these two components accounted for 29% of all birds detected. Of all

         water and low marsh components, only black needlerush contained over 20% of the species

         detected. Likewise, black needlerush is the only component that individually accounted for

         over 5 % of the total individuals.






                                                      28

























         Figure 13: Relative species richness and abundance for individual marsh zones and marsh
         components. Relative species richness values calculated as accumulated richness/100 (total
         species detected within marsh system). Relative abundance values calculated as total
         individuals/N (total individuals observed within the entire marsh system).













                     OVERALL USE OF MARSH ZONES
               70

                      m Species Richness
               60 -
                      0 Abundance
               50

           LU
               40

           cc  30
           U-
           LU  20

           <   10

           Cr   0
                      WATER LOW -MARSHHIGH MARSHTRANSITION

                                    MARSH ZONE



                  RELATIVE USE OF MARSH COMPONENTS

               60

               50      0 Species Richness
                       0 Abundance
           0
               40


           C3  30

           U-  20

               10

           LU
           cc   0
                   OW MF TG TP TC LC SL BN SG SM SB SN WMDS LP
                                MARSH COMPONENTS
                     L



























      Figure 13


                                      29








                 Patterns of marsh use were compiled for individual species. Information for common

          obligate breeders, obligate foragers, facultative breeders, and facultative foragers is presented

          in figures 14 through 17 respectively. In general, the obligate breeders were distributed

          widely across the marsh. Seaside Sparrows and Marsh Wrens utilized black needlerush and

          salt bush extensively. Both of these species utilize dense stands of vegetation for cover and

          singing posts within breeding territories. Clapper Rails also depend on the dense vegetation

          for cover throughout the day and are seen only sporadically foraging in the low marsh during

          the light hours. Willets utilize the entire marsh, foraging widely within the low marsh and

          using the high marsh for nesting and roosting. Boat-tailed Grackles are similar, feeding

          within the low marsh and roosting within the marsh-upland transition zone where they

          typically nest.

                 Observations of the common obligate foragers were skewed to the water and low

          marsh areas. All of the heron and egret species observed utilize the marsh primarily as

          foraging habitat and are typically seen hunting in the water components or low marsh

          depending on tide level. However, these species may also be observed roosting around the

          periphery of the marsh particularly during high tide periods. The Sharp-tailed Sparrow is an

          obligate marsh user that, within the lower Chesapeake Bay, is a transient species and winter

          resident. Sharp-tails were observed within the dense vegetation but also in foraging areas

          within the low marsh. All common, facultative species were observed most frequently

          within the high marsh or marsh-upland transition zones. The vegetative structure of these

          portions of the marsh are similar to early successional upland habitats where these species

          are more commonly found during the breeding season.



                                                        30
























         Figures 14 - 17: Relative occurrence of selected species within the 15 focal marsh
         components. Selected species are presented for obligate breeders, obligate foragers,
         facultative breeders, and facultative foragers. Values indicate number of individuals
         observed within specific marsh component/total number of individuals observed directly
         using study marshes. Only relatively common category 1 species (those species with greater
         than 50% of individuals observed directly using the marsh) are presented.







                       RELATIVE FREQUENCY   (%)                RELATIVE FREQUENCY (%j,
                                   W -9@ C"   02                  r " C4 4@ cn
                       c@          C> C=P c@  I=                     C@ C). 4= CD c@






                                                 cn
                                                 m
                                                 :r.-
                                                 C/3

                  CA C)                                  CA
                     C,*                                    ca
                  C., r-                                 n                                          RELATIVE FREOU
                                                                                                       cs      ca
                                                                                                           c@ C2
                  M ca                                                                 m
                     G),                                    co
                     CO                                     GM)                                  C)
                  m                                      m  C,
                  2c ic                          :13
                    4co
                  (a ca                          C)      ce ca                                   -n
                     cn                                     w                                    --I
                                                            co                                   G')
                                                            m


                     co                                     Cl
                                                            CO



                        RELATIVE FREQUENCY                    RELATIVE FREQUENCY              "0 M
                                   CO   D. c"   0:1                   "  ca  P@   cn  cm         C,
                                                              c:l     C3 CD  C@   =0  c@         GI
                                                                                                 C03
                     Co                                                                       ca COD
                     *E                                                                          cma
                                                                                                 cn

                     GM)                                    m
                                                                                                 ic

                                                                                                 CIO
                                                            Cl

                  ca
                  =  CIO                                                                C/3
                  cl@ r-
                  a


                                                            cn
                  2C G)                                     G-)
                  M  CD                                  m co
                                                  :30                                   m
                  ca Ca                                  ca w
                     Go                                     cm
                     CA                                     CA




                     co








                                                  USE OF MARSH COMPONENTS
                                                         BY OBLIGATE FORAGERS


                                 GREEN-BACKED HERON                                                              GREAT-BLUE HERON
                  -60                                                                          -60
                     50                                                                        >.    50

                  z                                                                            z
                  ul 40                                                                        LU    40
                  0
                  LU 30                                                                        LU    30
                  w                                                                            cc
                  U.                                                                           U.
                  W  20                                                                        Lu    20
                  ?:
                  4(j 10                                                                             10
                  i-u                                                                          Uj
                  Ic                                                                           w
                       0                                                                             0
                            OW MF TO TP TC LC SL ON SO SM SO SN WM DS LP                                 OW MF TO TP TC LC SL ON SO SM SO SN WM DS LP

                                             MARSH COMPONENTS                                                              MARSH COMPONENTS



                                         GREAT EGRET                                                         SHARP-TAILED SPARROW
                  -60                                                                          F60

                     50                                                                        >- 50
                                                                                               z
                  z
                  W  40                                                                        Lu 40
                  Lu 30                                                                        'u 30
                  U.                                                                           LL
                  Lu 20                                                                              20

                     10                                                                              10
                  iU                                                                           LU
                                                                                               cc
                  cc   0                                                                             0
                            OW MF TO TP TC LC SL BN SO SM SO SN WMDS LP                                 OW MF TO TP TC LC SL ON SO SM SO SN @M D'S LP
                                            MARSH COMPONENTS                                                              MARSH COMPONENTS









             Figure 15
                          t                                                                              jai

                                                                                    32










                                          USE OF MARSH COMPONENTS
                                             BY FACULTATIVE BREE-DERS


                               EASTERN KINGBIRD                                              YELLOWTHROAT
                -60                                                          -60
                >_ 50                                                        >_ 50

                z                                                            z
                Lu 40                                                          40

                UA 30                                                        1-130
                                                                             U.
                w20                                                          w 20

                   10                                                          10
                _j                                                           j
                w                                                            lu
                cc 0   1            T- _mF                                   W 0
                       OW MF TG TP TC LC SL BN SIG SM SB SN WM DS LP               OW MF TG TP TIC LC SL BN SIG SM SB SN WM DS L@
                                    MARSH COMPONENTS                                            MARSH COMPONENTS


                               SONG SPARROW                                          RED-WINGED BLACKBIRD
                   60                                                        60

                   50                                                      >-50

                                                                           z
                z                                                          uJ40
                w 40
                LU 30                                                      w30    -
                                                                           ILL    -
                U.
                Lu 20  -                                                   Lu 20  -
                >                                                          2:
                   10 -                                                      10   -
                                                                             j

                   0
                       OWMF TG TP TC LC SL BN SG SM SB SNWMDS LP                  OWMF TG TP TC LC SL BN SIG SM SB SNWMDS LP
                                   MARSH COMPONENTS                                            MARSH COMPONENTS






           Figure 16
                                                                                                                            h



                                                                   33









                                               USE OF MARSH COMPONENTS
                                                 BY FACULTATIVE FORAGERS



                                    NORTHERN FLICKER                                                        CAROLINA WREN
                  F60                                                                     -.60
                  > 50                                                                        0
                  0                                                                       >5
                  z                                                                       0
                  lu 40                                                                   z
                                                                                          HJ40
                  NJ 30
                   c                                                                      LuB
                  Lu. 20                                                                  LU20
                  >
                       10                                                                     10
                                                                                          j
                       0                   1   1  1      t                                cc 0
                           OW MF TO TP TC LC SL BN SO SM SB SN WM DS LP                           OW MF TO TP TC LC SL BN SO SM SB SN WM DS LP
                                           MARSH COMPONENTS                                                       MARSH COMPONENTS


                                    CHIPPING SPARROW                                                        COMMON GRACKLE
                       60                                                                     60
                  aR                                                                      F
                  >.   50                                                                 >   50

                  z                                                                       z
                  au   40                                                                 W   40

                  W    30                                                                 uj  30
                  cc                                                                      w
                  U.                                                                      U.
                  Lu   20                                                                     20

                       lo                                                                     10
                  .j
                  Uj                                                                      LU
                                                                                          c       -.                                 I
                       o     . . .                                                            0
                           OW MF TO TP TC LC SL BN SO SM SB SN WM DS LP                            OW MF TO TP TC LC SL BN SO SM SB SN WM DS LP
                                          MARSH COMPONENTS                                                        MARSH COMPONENTS








              Figure 17


                                                                                34










                                                DISCUSSION


                Patch area/community breadth relationships have been documented in prairie marshes

         (Brown and Dinsmore 1986) and various upland habitats (e.g. Forman et al. 1976, Lynch

         and Whigham 1984). In 1992, Watts documented a strong relationship between overall

         species richness and patch area for tidal salt marshes of the lower Chesapeake Bay. The

         same study documented that the marsh bird community observed in large marshes appeared

         to collapse as marsh size was reduced from 5 to 1 ha. Results from the current study
         confirm this critical size range and @rther refine the patterns for various species and species

         groups.

                Across the range of sizes included, marsh area appears to be a good indicator of

         species richness and abundance for all birds as well as for particular species groups. Species

         that actually used the marshes directly showed the most rapid decline with marsh size

         followed by all species combined. Results were similar to those observed in the 1992 study

         with slopes of 0.38 and 0.35 for category one species and total species respectively compared

         to 0.46 and 0.42 for the same species groups in 1992 (over a much larger range in marsh

         sizes). Also consistent with the 1992 study, category two and three species exhibited

         comparatively weaker responses to marsh size.

                Subdividing category one species according to their functional relationship to the

         marsh, obligate users exhibited the strongest response to marsh size. Species within this

         group showed the most rapid decline (slope = 0.67) with decreasing marsh size and likely

         were the underlying reason for the relationship for all category one species. In contrast,

         facultative users showed only a weak (slope = 0.20) response to decreasing marsh size. The



                                                      35








          differences between facultative and obligate species in their response to marsh, size, resulted

          in a shift in community composition with increasing marsh size.

          Whereas obligate species accounted for only 14% of birds observed within 1 ha marshes they

          accounted for over 50% of birds within 5 ha marshes. In 1992, obligate users accounted for

          over 90 % of birds observed within the largest ( > 65 ha) marshes. This general pattern

          suggests that the marsh-bird community becomes increasingly pure (dominated by species

          unique to the habitat) as patch size increases.

                 Incidence patterns for individual species generally reflected patterns observed for

          functional bird groups. All of the obligate breeding species showed considerable increases in

          the probability of occurrence with increasing marsh size. For obligate foragers, only Great

          Egrets and Sharp-tailed Sparrows appeared to be area sensitive over the range of marsh sizes

          examined. Great-blue and Green-backed herons appeared to be area-insensitive within the

          study marshes. All of the facultative breeders were area sensitive but patterns were not as

          profound as for obligate breeders. None of the facultative foragers exhibited tendencies

          toward area sensitivity.

                 Across all levels of organization, the same general pattern was observed. Species and

          species groups that were most closely tied to the marsh were most influenced by patch size.

          Those species that are unique to and characteristic of the salt marsh ecosystem are rapidly

          lost as marsh size is reduced from 5 to I ha. This pattern is consistent with results from the

          1992 study and suggest that the marsh-bird community loses its integrity as marsh size is

          reduced below 3 to 4 ha. Clapper Rails are the only species that could be expected with any

          reliability within 1 to 2 ha marshes.



                                                        36








                 Overall, components within the high marsh and marsh-upland transition zones

          supported the greatest number of species and individuals. However, obligate species tended

          to utilize water and low marsh areas or the entire marsh surface. This result is in agreement

          with patterns observed during 1992. Facultative species used the high marsh and transition

          zones almost exclusively. This result is consistent with the similarity of the high marsh zone

          to early successional upland habitats (the more traditional breeding habitats for these species).

          The most striking contrast between these results and the 1992 study was the relatively low

          use of tidepools and other water/low marsh habitats. This difference is likely due to the lack

          of significant tidepools within the 50 study marshes. Greater than 95 % of the transient

          shorebirds as well as many of the obligate foragers observed in large marshes (> 10 ha)

          during 1992 were associated with tidepools. Several of the most abundant species that

          appeared to be obligate tidepool users in 1992 (e.g. Snowy Egrets, Semipalmated Sandpipers)

          were not prominent members of the community within the system of smaller marshes. It

          appears that significant tidepools are less common as marsh size declines such that the suite

          of species that depends on them is not present.




                                                    SUAEWARY


                 1. Patch size is a good indicator of species richness and abundance for salt marshes

          within the lower Chesapeake Bay.

                 2. Species and species groups that were obligate marsh users showed the strongest

          response to marsh size and the highest loss rates.





                                                         37








                 3. The form of the incidence function for area sensitive species is variable and

          species specific. In general, obligate breeders showed the greatest decline in occupancy rates

          with decreasing marsh size.

                 4. Due to differences in the species/area slopes between facultative and obligate

          users, community composition shifted toward obligate species as marsh size increased.

                 5. Marsh components within the high marsh and marsh-upland transition zones

          supported the greatest number of both species and individuals. However, many of the

          obligate users were associated with components of the water and low marsh zones.




                                       MANAGEMENT IMPLICATIONS




                 Results presented here and for the 1992 study indicate that many marsh-bird species

          are area sensitive and that overall species richness declines as marsh area is decreased.

          Although overall species richness is a legitimate management consideration, it should not

          always receive the highest priority in structuring criteria for habitat protection.

          Consideration should be given to species that are unique to or characteristic of the habitat.

          Both studies suggest that obligate species were by far the most area-sensitive. The

          composition of bird communities within study marshes changed from being dominated by

          facultative species to obligate species as patch size approached 4 or 5 ha. The pattern

          continues as patch size is increased beyond 5 ha finally reaching a near pure community as

          marsh size reaches 50 - 60 ha. This suggests that only marshes of a certain size support

          intact examples of marsh-bird communities. Because of this, area-specific recommendations



                                                         38









         should be constructed and considered when making decisions concerning proposals for marsh

         alteration.


                In order to structure area-specific recommendations, it is first necessary to place the

         bird/area relationships in context with the availability of different sized marshes. Figure 18

         illustrates the frequency of specific marsh size categories derived from over 1300 marshes

         within the study area. Clearly, marshes within the lower Chesapeake Bay are skewed to

         small sizes and large marshes are extremely rare. Combining the marsh-bird results with

         patterns in marsh availability, it is now possible to formulate area-specific recommendations.

                                  MANAGEMENT RECOMMENDATIONS


                Lame Marshes - Marshes that exceed 50 - 60 ha in area are extremely rare and

         appear to be required by particular species (e.g. Sedge Wren, Northern Harrier) that are

         highly area-sensitive. This result suggests that relatively few locations may support the bulk

         of the population for these species. All marshes within this size category should be identified

         and surveyed for sensitive species. Because these marshes have regional significance they

         should be targeted for acquisition and easement programs. Marsh management practices

         should be examined relative to their impact on sensitive populations and management

         strategies should be drafted for individual marshes.

                5 - 10 ha Marshes - Marshes that are between 5 and 65 ha are also relatively rare.

         These marshes support the bulk of the individuals for those species that are unique to and

         most identified with the salt marsh ecosystem. Marshes within this size range should be

         identified and given special attention when considering requests and proposals for marsh





                                                      39































  4







         Figure 18: Relative abundance of marsh sizes (within particular categories) located with the
         study area (N > 1300). Size distribution data was compiled from tidal marsh inventories
         covering the area (Barnard 1975, Moore 1976, Silberhorn 1981a, 1981b).


















                          MARSH ABUNDANCE
                                 (By Size)
                   80-
               I-R
                        62% 23% 7%        4%    <1%
                bl,
                   60-



                   40-



                   20-
                             INS%%

                      0     1     5    10    65
                              Marsh Size (Ha)









     Figure 18


                                 40









         alteration. The location of these marshes relative to other large marshes should also be taken


         into consideration.


                 1 - 5 ha Marshes - Marshes that are between 1 and 5 ha represent a substantial

         portion of the total marshes found within the lower Bay. The value of these marshes to the

         overall obligate bird community is variable and increases with size. The relationship

         between marsh size and value is also species-specific. In general, however, 4 - 5 ha marshes

         have a high probability of supporting obligate marsh users compared to 1 - 2 ha marshes and

         should be given greater consideration when making management decisions. When the goal is

         to manage individual species, the form of appropriate incidence functions should be

         examined.




































                                                      41










                                        ACKNOWLEDGEMENTS


                Funding for this study was provided through a grant from NOAA's Office of Coastal

         Resource Management and administered by the Virginia Department of Environmental

         Quality's Coastal Resource Management Program. Logistical and administrative support was

         provided by the Virginia Department of Game and Inland Fisheries' Nongame and

         Endangered Species Program. All field work was conducted by Daryl Thomas. This project

         would not have been possible without his dedication and self sufficiency. We thank the

         many landowners who permitted free access to their tidal marshes. Marian Watts provided

         original artwork and illustrations. This document if publication number 4 of the Virginia

         Center for Conservation Biology.





























                                                    42












                                            LITERATURE CITED


          Barnard, T. A. Jr. 1975. City of Hampton Tidal Marsh Inventory. Spec. Rep. No. 60. in

                 Applied Marine Science and Ocean Engineering. Virginia Institute of Marine

                 Science, Gloucester Point, VA.

          Blondel, J., C. Ferry, and B. Frochot. 1981. Point count with unlimited distance. Pp 414-

                 420 in Estimating Numbers of Terrestrial Birds. (C. J. Ralph and J. L. Scott eds).

                 Cooper Ornithological Society.

          Brown, M., and J. J. Dinsmore. 1986. Implications of marsh size and isolation for marsh

                 bird management. J. Wildl. Manage. 50:392-397.

          Coleman, B. D., M. A. Mares, M. R. Willig, and Y. Hseih. 1982. Randomness, area, and

                 species richness. Ecology, 63:1121-1133.

          Emlen, J. T. 1971. Population densities of birds derived from transect counts. Auk 88:323-

                 342.


                    1977. Estimating breeding season bird densities from transect counts. Auk 94:455-

                 468.


          For-man, R. T. T., A. E. Galli, and C. F. Leck. 1976. Forest size and avian diversity in

                 New Jersey woodlots with some land use implications. Oecologia 26:1-8.

          Glahn, J. F. 1974. Study of breeding rails with recorded calls in North-central Colorado.

                 Wilson Bull. 86:206-214.


          Lynch, J. F. and D. F. Whigham. 1984. Effects of forest fragmentation on breeding bird

                 communities in Maryland, USA. Biol. Conserv. 28:287-324.



                                                       43








         Moore, K. A. 1976. Gloucester County Tidal Marsh Inventory. Spec. Rep. No. 64 in

                Applied Marine Science and Ocean Engineering, Virginia Institute of Marine Science.

                Gloucester Point, VA.

         Morrison, M. L., R. W. Mannan, and G. L. Dorsey. 1981. Effects of number of circular

                plots on estimates of avian density and species richness. Pp. 405-408 in Estimating

                Numbers of Terrestrial Birds. (C. J. Ralph and J. M. Scott, eds). Cooper

                Ornithological Society.

         Repking, C. F., and R. D. Ohmart. 1977. Distribution and density of Black Rail

                populations along the lower Colorado River. Condor, 79:486-489.

         Robbins, C. S. 1980. Effect of forest fragmentation on breeding bird populations in the

                piedmont of the Mid-Atlantic region. Ad. Nat. 33:31-36.

         Silberhom, G. M. 1981a. Mathews County Tidal Marsh Inventory. Spec. Rep. No. 47, in

                Applied Science and Ocean Engineering, Virginia Institute of Marine Science.

                Gloucester Point, VA.

                   1981b. York County Tidal Marsh Inventory. Spec. Rep. No. 53, in Applied

                Science and Ocean Engineering, Virginia Institute of Marine Science. Gloucester

                Point, VA.


         Watts, B. D. 1992. The influence of marsh size on marsh value for bird communities of the

                lower Chesapeake Bay. Final Report to Environmental Protection Agency, 115 pp.

         Whitcomb, R. F., C. S. Robbins, J. F. Lynch, B. L. Whitcomb, M. K. Klimkiewicz, and

                D. Bystrak. 1981. Effects of forest fragmentation on avifauna of the eastern





                                                    44








                deciduous forest. Pp. 125-206 in Forest island dynamics in man-dominated

                landscapes. (R. L. Burgess and D. M. Sharpe, eds). Springer-Verlag, New York.

         Wilcove, D. S., C. H. McLellan, and A. P. Dobson. 1986. Habitat fragmentation in the

                temperate zone. Pp. 237-256 in Conservation biology: the science of scarcity and

                diversity. (M. E. Soule and B. A. Wilcox eds). Sinauer Associates, Sunderland,

                Massachusetts, USA.








































                                                    45









       Appendix I: List of scientific names for species detected.

       Common Name                         Scientific Name


       Common Loon                         Gavia immer
       Double-crested Cormorant            Phalacrocorax auritus
       Mute Swan                           Cygnus olor
       Canada Goose                        Branta canadensis
       Mallard                             Anas Platyrhynchos
       Black Duck                          Anas rubrives
       Clapper Rail                        Rallus longirostris
       Virginia Rail                       Rallus limicola
       American Oystercatcher              Haematopus valliatus
       Piping Plover                       Charadrius melodus
       Killdeer                            Charadrius vociferus
       Willet                              Catoptrophorus semipalmatus
       Greater Yellowlegs                  Tringa melanoleuca
       Lesser Yellowlegs                   Tringa flavipes
       Spotted Sandpiper                   Actitis macularia
       Semipalmated Sandpiper              Calidris pusilla
       Laughing Gull                       Larus atricilla
       Ring-billed Gull                    Larus delawarensis
       Herring Gull                        Larus argentatus
       Common Tern                         Sterna hirundo
       Forster's Tern                      Sterna forsteri
       Little Tern                         Sterna albifrons
       Royal Tern                          Sterna Maxima
       Black Skimmer                       Rynchops niger
       Bald Eagle                          Haliaeetus leucocephalus
       Turkey Vulture                      Cathartes aura
       Northern Harrier                    Circus cyaneus
       Red-tailed Hawk                     Buteo lamaicensis
       Osprey                              Pandion haliaetus
       Northern Bobwhite                   Colinus virginianus
       Least Bittern                       Ixobrychus exilis
       Yellow-crowned Night-heron          Nyctanassa violacea
       Green-backed Heron                  Butorides striatus
       Snowy Egret                         Egretta thula
       Great Egret                         Casmerodius albus
       Great Blue Heron                    Ardea herodias
       Glossy This                         Plegadis falcinellus
       Rock Dove                           Columba livia
       Mourning Dove                       Zenaida macroura
       Yellow-billed Cuckoo                Coccyzus americanus
       Chimney Swift                       Chaetura velagica
       Ruby-throated Hummingbird           Archilochus colubris
       Belted Kingfisher                   Megaceryle alcyon
       Red-headed Woodpecker               Melanerpes Erythrocephalus
       Red-bellied Woodpecker              Melanerves carolinus
       Common Flicker                      Colaptes auratus




                                       46









       Appendix 1:   --- continued---

       Pileated Woodpecker                   Dryocopus pileatus
       Downy Woodpecker                      Picoides pubescens
       Eastern Kingbird                      Tyrannus tyrannus
       Great-crested Flycatcher              Mviarchus crinitus
       Eastern Pewee                         Contopus virens
       Tree Swallow                          Iridoprocne bicolor
       Purple Martin                         Progne subis
       Rough-winged Swallow                  Stelgidoptervx ruficollis
       Barn Swallow                          Hirundo rustica
       American Crow                         Corvus brachvrhvnchos
       Fish Crow                             Corvus ossifragus
       Tufted Titmouse                       Parua bicolor
       Carolina Chickadee                    Parus carolinensis
       White-breasted Nuthatch               Sitta carolinensis
       House Wren                            Troglodytes aedon
       Carolina Wren                         Thryothorus ludovicianus
       Marsh Wren                            Cistothorus valustris
       Sedge Wren                            Cistothorus platensis
       Blue-gray Gnatcather                  Polioptila caerulea
       Eastern Bluebird                      Sialia sialis
       Gray Catbird                          Dumetella carolinensis
       Mockingbird                           Mimus Polyglottos
       Brown Thrasher                        Toxostoma rufum
       American Robin                        Turdus migratorius
       European Starling                     Sturnus vulgaris
       Cedar Waxwing                         Bombvcilla cedrorum
       White-eyed Vireo                      Vireo griseus
       Red-eyed Vireo                        Vireo olivaceus
       Yellow-rumped Warbler                 Dendroica coronata
       Blackpoll Warbler                     Dendroica striata
       Prairie Warbler                       Dendroica discolor
       Pine Warbler                          Dendroica pinus
       Louisianna Waterthrush                Seiurus motacilla
       Common Yellowthroat                   Geothly-pis trichas
       Yellow-breasted Chat                  Icteria virens
       Summer Tanager                        Piranga rubra
       Northern Cardinal                     Cardinalis cardinalis
       Blue Grosbeak                         Guiraca caerulea
       Indigo Bunting                        Passerina cyanea
       House Finch                           Carpodacus mexicanus
       American Goldfinch                    Carduelis tristis
       Rufous-sided Towhee                   Pipilo erythrophthalmus
       Sharp-tailed Sparrow                  Ammospiza caudacuta
       Seaside Sparrow                       Ammospiza maritima
       Song Sparrow                          Melospiza melodia
       Chipping Sparrow                      Spizella passerina
       Field Sparrow                         Spizella pusilla
       Swamp Sparrow                         Melospiza georgiana



                                         47









       Appendix 1:   --- continued---

       Eastern Meadowlark                  Sturnella magna
       Red-winged Blackbird                Agelaius Phoenicius
       Brown-headed Cowbird                Molothrus ater
       Common Grackle                      Ouiscalus auiscula
       Boat-tailed Grackle                 Quiscalus malor
       Orchard Oriole                      Icterusspurius



















































                                       48









       Appendix II: Breakdown of marsh use categories by species.
       Categories include: one - bird in direct contact with marsh, two
       - bird not in direct contact with marsh but foraging on prey just
       over or on marsh surface, three - bird flying over marsh but
       under So m in altitude and or associated with water within 50 m
       of shoreline.


                                                         User Category
       Species                            N         one      Two        Three

       Common Loon                        2       -----     -----       100.0
       Double-crested Cormorant          10       -----     -----       100.0
       Mute Swan                          4       100.0     -----       -----
       Canada Goose                       5         40.0    -----        60.0
       Mallard                           88         34.1    -----        6S.9
       Black Duck                         8         87.S    -----        12.S
       Clapper Rail                    20S          99.5    -----          0.5
       Virginia Rail                      6       100.0     -----       -----
       American Oystercatcher             2       -----     -----       100.0
       Piping Plover                      2       100.0     -----       -----
       Killdeer                          21         66.7    -----        33.3
       Willet                          245          71.4       2.0       26.5
       Greater Yellowlegs                 7       100.0     -----       -----
       Lesser Yellowlegs                  1       100.0     -----       -----
       Spotted Sandpiper                 28         75.0    -----        25.0
       Semipalmated Sandpiper             3       100.0     -----       -----
       Laughing Gull                   394            6.6       2.3      91.1
       Ring-billed Gull                   1       -----     -----       100.0
       Herring Gull                       2       -----     -----       100.0
       Common Tern                       12         41.7    -----        58.3
       Forster's Tern                    55       -----     -----       100.0
       Least Tern                        11           9.0   -----        91.0
       Royal Tern                         2       -----     -----       100.0
       Black Skimmer                      5       -----      60.0        40.0
       Bald Eagle                         3         66.7    ----- -      33.3
       Turkey Vulture                     2       -----     -----       100.0
       Northern Harrier                   9         22.2     22.2        55.6
       Red-tailed Hawk                    9         44.4     11.2        44.4
       Osprey                          103          28.2        1.0      70.8
       Northern Bobwhite                 12       -----     -----       100.0
       Least Bittern                      1       100.0     -----       -----
       Yellow-crowned Night-heron        34       100.0     -----       -----
       Green Heron                     108          82.4    -----        17.6
       Snowy Egret                        9         66.7    -----        33.3
       Great Egret                       59         49.2    -----        50.8
       Great Blue Heron                174          50.0    -----        50.0
       Glossy This                        1       -----     -----       100.0
       Rock Dove                          2         50.0    -----        50.0
       Mourning Dove                     50         58.0    -----        42.0
       Yellow-billed Cuckoo               6         66.7    -----        33.3




                                           49









       Appendix II:     --- continued---


       Chimney Swift                    29                   96.6        3.4
       Ruby-throated Hummingbird        10         30.0      10.0       60.0
       Belted Kingfisher                 9         33.3      11.1       55.6
       Red-headed Woodpecker            10         70.0     -----       30.0
       Red-bellied Woodpecker            3        100.0     -----      -----
       Common Flicker                   59         83.1                 16.9
       Pileated Woodpecker               1        -----     -----      100.0
       Downy Woodpecker                  9         88.9     -----       11.1
       Eastern Kingbird                 59         86.4        6.8       6.8
       Great-crested Flycatcher         14        100.0     -----      -----
       Eastern Pewee                     7         85.7     -----       14.3
       Tree Swallow                     26           3.8     96.2      -----
       Purple Martin                    78        -----      66.7       33.3
       Rough-winged Swallow              1        100.0     -----      -----
       Barn Swallow                     339          3.8     94.7        1.5
       American Crow                    103        71.8     -----       28.2
       Fish Crow                        25         64.0     -----       36.0
       Tufted Titmouse                  14        100.0     -----      -----
       Carolina Chickadee               22         95.5     -----        4.5
       White-breasted Nuthatch           1        100.0     -----      -----
       House Wren                       17        100.0     -----      -----
       Carolina Wren                    52        100.0     -----      -----
       Marsh Wren                       16        100.0     -----      -----
       Sedge Wren                        1        100.0     -----      -----
       Blue-gray Gnatcatcher             4        100.0     -----      -----
       Eastern Bluebird                 25         92.0     -----        8.0
       Gray Catbird                     10         90.0     -----       10.0
       Mockingbird                      39         82.1     -----       17.9
       Brown Thrasher                    7        100.0     -----      -----
       American Robin                   47         59.6     -----       40.4
       European Starling                83         80.7     -----       19.3
       Cedar Waxwing                     1        100.0     ----- -    -----
       White-eyed Vireo                  7        100.0     -----      -----
       Red-eyed Vireo                    3        100.0     -----      -----
       Yellow-rumped Warbler             4        100.0     -----      -----
       Blackpoll Warbler                 1        100.0     -----      -----
       Prairie Warbler                   8        100.0     -----      -----
       Pine Warbler                      9         88.9     -----       11.1
       Louisianna Waterthrush            1        100.0     -----      -----
       Common Yellowthroat              155       100.0     -----      -----
       Yellow-breasted Chat             16         93.8     -----        6.2
       Summer Tanager                   10         90.0     -----       10.0
       Northern Cardinal                50         88.0     -----       12.0
       Blue Grosbeak                     3        100.0     -----      -----
       Indigo Bunting                    8        100.0     -----      -----
       House Finch                      25         44.0     -----       56.0
       American Goldfinch               20         75.0     -----       25.0




                                          50









       Appendix 11:     --- continued---

       Rufous-sided Towhee              47         95.7     -----         4.3
       Sharp-tailed Sparrow             36         97.2     -----         2.8
       Seaside Sparrow                 328         87.2     -----       12.8
       Song Sparrow                     85        100.0     -----      -----
       Chipping Sparrow                 55         78.2     -----       21.8
       Field Sparrow                      9       100.0     -----      -----
       Swamp Sparrow                      2       100.0     -----      -----
       Eastern Meadowlark               12        100.0     -----      -----
       Red-winged Blackbird            671         87.6     -----       12.4
       Brown-headed Cowbird             15         86.7     -----       13.3
       Common Grackle                  294         38.8     -----       61.2
       Boat-tailed Grackle             120         69.2     -----       30.8
       Orchard oriole                   10        100.0     -----      -----
















































                                          51










       Appendix III : Total frequency of birds observed during each
       survey period for all marshes combined (list of scientific names
       given in appendix I).

                                              Census Number
       Species                           one   two three four       Total

       Common Loon                        2      0     0     0        2
       Double-crested Cormorant           2      7     0     1       10
       Mute Swan                          0      0     4     0        4
       Canada Goose                       3      2     0     0        5
       Mallard                           23    20     22    23       88
       Black Duck                         0      0     1     7        8
       Clapper Rail                      66    53     51    35      205
       Virginia Rail                      6      0     0     0        6
       American Oystercatcher             2      0     0     0        2
       Piping Plover                      2      0     0     0        2
       Killdeer                           2      3     5    11       21
       Willet                            82    71     67    25      245
       Greater Yellowlegs                 5      0     0     2        7
       Lesser Yellowlegs                  1      0     0     0        1
       Spotted Sandpiper                 13    14      0     1       28
       Semi-palmated Sandpiper            0      3     0     0        3
       Laughing Gull                     124   87     71    112     394
       Ring-billed Gull                   0      1     0     0        1
       Herring Gull                       0      1     1     0        2
       Common Tern                        4      S     2     1       12
       Forster's Tern                    12      0    11    32       55
       Least Tern                         7      2     1     1       11
       Royal Tern                         2      0     0     0        2
       Black Skimmer                      0      0     0     5        5
       Bald Eagle                         0      0     1     2        3
       Turkey Vulture                     0      1     1     0        2
       Northern Harrier                   2      1     4     2-       9
       Red-tailed Hawk                    0      3     3     3        9
       Osprey                            28    17     35    23      103
       Northern Bobwhite                  2      3     6     1       12
       Least Bittern                      0      1     0     0        1
       Yellow-crowned Night-heron        12    10      6     6       34
       Green Heron                       12    17     35    44      108
       Snowy Egret                        4      3     0     2        9
       Great Egret                       10    11     15    23       88
       Great Blue Heron                  39    43     46    46      174
       Glossy This                        0      0     0     1        1
       Rock Dove                          0      1     0     1        2
       Mourning Dove                      7      7    14    22       so
       Yellow-billed Cuckoo               1      0     4     1        6
       Chimney Swift                     13      2    14     0       29
       Ruby-throated Hummingbird          2      0     2     6       10



                                       52









       Appendix III:   --- continued---

       Belted Kingfisher                  1     2     5      1         9
       Red-headed Woodpecker              8    .0     1      1       10
       Red-bellied Woodpecker             1     1     0      1         3
       Northern Flicker                  15    19    10    15        59
       Pileated Woodpecker                0     0     1      0         1
       Downy Woodpecker                   0     2     3      4         9
       Eastern Kingbird                  15    19    18      7       59
       Great-crested Flycatcher           5     1     6      2       14
       Eastern Wood Pewee                 2     1     0      4         7
       Tree Swallow                      15     5     3      3       26
       Purple Martin                      1     1     8    68        78
       Rough-winged Swallow               0     0     1      0         1
       Barn Swallow                      83    57    113   86       339
       American Crow                     11    47    10    35       103
       Fish Crow                          8     4    10      3       25
       Tufted Titmouse                    1     1     7      5       14
       Carolina Chickadee                 8     7     6      1       22
       White-breasted Nuthatch            0     0     0      1         1
       House Wren                         1     4     7      5       17
       Carolina Wren                      8     6    23    15        52
       Marsh Wren                         5     4     4      3       16
       Sedge Wren                         1     0     0      0         1
       Blue-gray Gnatcatcher              3     1     0      0         4
       Eastern Bluebird                   7     5    10      3       25
       Gray Catbird                       6     2     2      0       10
       Mockingbird                        6     9     8    16        39
       Brown Thrasher                     1     1     3      2         7
       American Robin                     7     7     8    25        47
       European Starling                 11    27    17    28        83
       Cedar Waxwing                      1     0     0      0         1
       White-eyed Vireo                   1     2     1      3         7
       Red-eyed Vireo                     0     2     0      1         3
       Yellow-rumped Warbler              4     0     0      0-        4
       Blackpoll Warbler                  0     1     0      0         1
       Prairie Warbler                    6     1     1      0         8
       Pine Warbler                       3     2     4      0         9
       Louiaianna Wdterthrush             0     0     0      1         1
       Common Yellowthroat               42    22    41    50       155
       Yellow-breasted Chat               6     5     3      2       16
       Summer Tanager                     3     3     2      2       10
       Northern Cardinal                 12     6    19    13        50
       Blue Grosbeak                      3     0     0      0         3
       Indigo Bunting                     0     0     4      4         8
       House Finch                        5    10     8      2       25
       American Goldfinch                13     4     3      0       20
       Rufous-sided Towhee               10     7    10    20        47
       Sharp-tailed Sparrow              22    14     0      0       36
       Seaside Sparrow                   114   62    81    71       328



                                       53









       Appendix III:   ---continued---

       Song Sparrow                      30    23    17     15      85
       Chipping Sparrow                  21    10    16     8       55
       Field Sparrow                      0     2     2     5         9
       Swamp Sparrow                      2     0     0     0         2
       Eastern Meadowlark                 4     5     3     0       12
       Red-winged Blackbird              184   171   176   140      671
       Brown-headed Cowbird              10     2     2     1       15
       Common Grackle                    45    69    88     92      294
       Boat-tailed Grackle               36    45    17     22      120
       orchard oriole                     2     0     4     4       10

















































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