WETLANDS, Vol. 13, No. 2, Special Issue, June 1993, pp. 130-136 © 1993, The Society of Wetland Scientists

E V A L U A T I O N OF CAPTURE TECHNIQUES FOR A M P H I B I A N , R E P T I L E , A N D S M A L L M A M M A L C O M M U N I T I E S I N S A T U R A T E D F O R E S T E D W E T L A N D S

Joseph C. Mitchell Department of Biology University of Richmond

Richmond, Virginia 23173

Sandra Y. Erdle and John F. Pagels Department of Biology

Virginia Commonwealth University Richmond, Virginia 23284-2012

Abstract: We evaluate the effect of different capture techniques on estimates of species richness and diversi ty for several amphibian, reptile, and small mammal communit ies in saturated forested wetlands in 'southeastern Virginia and South Carolina. Each technique yields different and biased quantitative results because of variat ion in catchability within and among taxonomic groups. Drift fences with pitfall traps seem to be a useful technique for most taxa, but complete inventories require supplemental methods. Standardized arrays of coverboards in saturated forested wetlands may be useful only for specific taxa. Our abili ty to generalize about the structure of terrestrial vertebrate communit ies and their value in saturated forested wetlands is l imited because current data sets were obtained with different capture techniques. We recommend that standardized techniques and sampling efforts be used in future assessments of vertebrate communi t ies in saturated forested wetlands so that comparisons can be made across t ime and space.

Key Words: Amphibians, reptiles, small mammals, community ecology, species diversity.

INTRODUCTION

Compared to other wetland habitats in eastern North America, terrestrial vertebrate communities have been little studied in saturated forested wetlands. Studies by Gibbons (1970), Semlitsch and Pechmann (1985), and Pechmann et al. (1988, 1991), for example, have elu- cidated patterns of wetland use by amphibians and reptiles in southeastern pocosins. Other studies fo- cused on these animals in temporary pond wetlands (Braswell 1988, Dodd and Charest 1988). We are un- aware of published studies that have examined com- munity structure of amphibians or reptiles in saturated forested wetlands in the mid-Atlantic region. Studies of small mammal community structure in wetlands of eastern North America have been limited to compar- isons of species composition among habitat types and inventories of specific areas (Wharton et al. 1981, Clark et al. 1985). In the mid-Atlantic region, Rose and his students (e.g., Rose 1981, Breidling et al. 1983, Rose et al. 1990) have studied various aspects of small mam- mal communities in a variety of habitats in the Great Dismal Swamp. Dowler et al. (1985) compared small mammal community composition of a forested wet-

130

land with several other habitats in the Great Swamp of New Jersey.

In this paper, we evaluate the effect of different cap- ture techniques on estimates of species richness and diversity in several amphibian, reptile, and small mammal communities in saturated forested wetlands. We demonstrate that direct comparisons of commu- nity structure among sites are tenuous because each of the techniques used yields different quantitative re- suits.

MATERIALS AND METHODS

At 12 sites in forested wetland and adjacent habitats in southeastern Virginia east of the Dismal Swamp in the City of Chesapeake (Erdle and Pagels 1991), we installed drift fences with pitfalls. Each 5-m drift fence was made from plastic-coated fabric (0.3 m high) to which we attached a 30 × 45 cm flap of the same ma- terial to prevent leaves from filling the number 10 tin can (3.8-1) pitfalls. Two pitfalls were sunk flush to the ground surface on each side at the ends of the drift fence. In addition, an average of five 16-oz (0.47-1)

Mitchell et aL, CAPTURE TECHNIQUES FOR TERRESTRIAL VERTEBRATES 131

Table 1. Comparison of small mammal communities using isolated pitfall trapping and drift fences with pitfalls in a range of habitats in historical Dismal Swamp in southeastern Virginia. Sampling period: July 1990--October 1991. See Materials and Methods for descriptions of capture techniques,

Species Drift Fence with #10 Cans Isolated 16 oz. (0.47-liter) Cans Cryptotis parva (Say) Sorex longirostris Bachman Sorex hoyi Baird Blarina brevicauda (Say) Blarina earolinensis (Bachman) Reithrodontomys humuhs (Audubon & Bachman) Peromyscus leucopus (Rafinesque) Microtus pennsylvanicus (Ord) Microtus pinetorum (Le Conte) Oryzomys palustris (Harlan) Total Number of species Trap nights (TN) Captures per 100 TN H' j,

12 5 21 14

1 0 13 5 37 21 12 0 14 0 5 0 2 0 1 0

118 45 10 4

12,299 11,233 0.97 0.40 1.918 1.207 O.833 0.871

aluminum can pitfalls were installed nearby; none were associated with drift fences. We sampled small mam- mals, amphibians, and reptiles at the sites from July 1990 to October 1991. Our comparison of small mam- mal communities was between the drift fence with its larger pitfalls and the isolated 16-oz cans. We selected two of the 12 sites for comparison of amphibian and reptile communities sampled by our techniques with two sampled by a larger drift fence method (see below). All of these sites were in similar, seasonally-flooded microhabitats. In this comparison, combined samples from our study (3.8-1 and 0.47-1 pitfalls) were used because capture technique records were not main- tained for amphibians and reptiles; the focus at the time was on small mammals.

We compared our data from two forested wetland sites to those from two nearby forested wetland sites in southeastern Virginia (Fentress and Oceana Naval Bases, City of Virginia Beach) provided by K. A. Buhl- mann and C. A. Pague (in litt.). Their larger drift fence technique consisted of three pieces of aluminum flash- ing 7.5 x 0.5 m installed in a Y configuration with each of the arms set 7.5 m away from the open center. A 5-gallon (l 9-1) plastic bucket sunk flush to ground level at each end of each arm served as a pitfall trap. In all drift fence/pitfall arrays, 10% formalin was used to facilitate drowning and preservation of specimens for other studies (e.g., reproduction and diet, Call 1986). Sampling dates were l l May 1989-21 May 1990 for Fentress and 14 April 1989-6 March 1990 for Oceana.

Coverboards made of sheets of plywood chipboard and galvanized roofing tin (each 0.66 m x 1.33 m)

were installed in a saturated forested wetland adjacent an upper Coastal Plain stream at the Savannah River Site, Aiken County, South Carolina. Coverboards, which like rocks and logs are utilized by many am- phibians and reptiles for shelter, were laid fiat on the ground and arranged in sets of four-- two plywood and two tin per set. The plywood at this site quickly dis- integrated due to flooding, thus, the results pertain only to the amphibian and reptile specimens recorded from beneath the 60 tin coverboards. A similar arrangement of 96 coverboards (48 plywood, 48 tin) was installed in a pine plantation near a Carolina bay (Grant et al. 1992), and a 440 m drift fence made of aluminum flashing with 88 5-gallon (19-1) pitfalls spaced at 10-m intervals was installed around Rainbow Bay (Pech- mann et al. 1991). Data from the May-August 1990 sampling period were used here for all comparisons among sites and techiques. The wetland site was checked 26 times, the pine plantation site 36 times, and the drift fence daily during this period.

We calculated species diversity using the Shannon index, H' = Z p, In Pl, and evenness as J' = H' / Hmax' (Brower et al. 1990). Comparisons between H' values were made with a t-test following Zar (1984).

RESULTS AND DISCUSSION

Small Mammals

Samples of small mammal communities from south- eastern Virginia collected by drift fences and isolated can techniques differed in several ways (Table 1). Num-

132 WETLANDS, Volume 13, No. 2, Special Issue, 1993

Table 2. Small mammal community structure in a range of habitats in and near Dismal Swamp in southeastern Virginia. Five techniques are compared: drift fence with #10 tin cans, isolated 16-oz. (0.47-liter) cans, Fitch live traps, #10 fin cans in 5 x 5 m arrays, and nest boxes. The latter three are based on Rose et at. (1990). See Materials and Methods for descriptions of capture techniques.

Drift Fence Isolated Parameter # 10 Cans 16-oz. Cans Live Traps # 10 Can Array Nest Boxes

Total captures 118 45 148 153 45 No. species 10 4 10 9 2 % Insectivores 70.0 100.0 9.5 51.0 0 % Rodents 30.0 0 90.5 49.0 100.0 No. per 100 TN 0.97 0.40 1.20 0.35 0.56 H' 1.918 1.207 1.706 1.699 0.500 J' 0.833 0.871 0.741 0.773 0.722

bers o f species (x 2 = 2.57, P < 0.01) and individuals (x 2 = 32.69, P < 0.001) in the samples were signifi- cantly greater for the drift fence technique than the isolated can technique. The number o f individuals cap- tured per 100 trap nights in the drift fence technique was more than twice that for the isolated pitfall tech- nique. Diversi ty (H') was significantly higher for the drift fence sample than the isolated pitfall sample ( l l4 7 = 2.57, P < 0.02), but evenness between samples (J') was similar (Table 1).

These results may be compared to samples obtained by three other techniques used by Rose et al. (1990) in the Great Dismal Swamp (Table 2). Samples of small m a m ma l s caught with Fitch live traps, a 5 x 5 m grid o f numbe r 10 cans used as pitfalls, and nest boxes made f rom num be r 10 cans differed in number o f species recorded, number o f individuals caught per 100 trap nights, and diversity indices. Evenness values were similar across all capture techniques. Pitfall traps with and wi thout drift fences were more effective for cap-

luring insectivores (specifically shrews) than rodents, and live traps and nest boxes captured more rodents than insectivores. The no. 10 can pitfall array was the only one that captured members o f both orders of small mammals in similar numbers (Table 2).

Such differences in sampling results and H' values are not l imited to southeastern Virginia. Dowler et al. (1985) summarized the composi t ion o f small m a m m a l communi t ies in five habitats in Great Swamp, New Jersey using six trap types. Data provided by R.C. Dowler (personal communica t ion) allowed us to com- pare samples taken in a forested wetland habitat. At this site a 30.5-m drift fence of a luminum flashing was erected and ten 5-gallon (19-1) pitfalls installed on one side and ten 2.6-liter plastic containers installed on the other. Ten isolated 19-1 pitfalls and ten 2.6-1 pitfalls were posit ioned nearby. Ten Sherman live traps o f two sizes (22.9 x 7.6 x 8.9 cm and 15.9 × 5.7 x 6.4 cm) were placed in a line in the same area. All trap lines were about 30.5-m apart. Each o f the six techniques yielded

Table 3. Effect of trapping techniques on assessment of small mammal communities in a saturated forested wetland in Great Swamp, New Jersey. Data were derived from Dowler et al. (1985). Trap type 1 = ten isolated 5-gallon (19-liter) pitfalls, 2 = aluminum flashing drift fence with ten 5-gallon pitfalls, 3 = aluminum flashing drift fence with ten 2.6-liter plastic pitfalls, 4 = ten isolated 2.6-liter plastic pitfalls, 5 = ten 15.9-cm Sherman live traps, and 6 = ten 22.9-cm Sherman live traps. Total trap nights for each is 1,750.

Trapping Technique

Species 1 2 3 4 5 6

Sorex cinereus Kerr 19 30 17 I 0 10 3 Blarina brevicauda (Say) 3 1 1 0 3 0 Peromyscus leucopus (Rafinesque) 9 4 0 0 55 84 Microtus pennsylvanicus (Ord) 4 2 0 0 0 0 Zapus hudsonius (Zimmermann) 7 0 0 0 0 0 Total 42 37 18 10 68 87 Number of species 5 4 2 1 3 2 Captures per 100 TN 2.4 2.1 1.0 0.6 3.9 5.0 H' !.400 0.666 0.215 0 0.591 0.150

Mitchell et al., CAPTURE TECHNIQUES FOR TERRESTRIAL VERTEBRATES 133

Table 4. Herpetofaunal communities in saturated forested wetlands in southeastern Virginia. Two techniques are compared: aluminum flashing drift fences with 5-gallon (19-liter) pitfalls (from K. A. Buhlmann and C. A. Pague, in litt.) and the combined samples from plastic drift fences with # 10 tin can pitfalls and isolated 16-oz. (0.47-liter) can pitfalls (this study). See Materials and Methods for descriptions of sites and capture techniques.

Drift Fence and Cans Drift Fence and Buckets Species Site t Site 2 Fentress Oceana

Anurans Bufo terrestris (Bonnaterre) 0 5 124 192 Rana catesbeiana Shaw 1 0 3 42 Rana clamitans Latreille in

Sonnini & LatreiUe 3 1 53 263 Rana sphenocephala Cope 0 4 121 82 Gastrophryne carolinensis

(Holbrook) 0 2 1 70 Hyla femoralis Bose in Daudin 0 0 0 1 Hyla squirella Bose in Daudin 0 0 0 2 Pseudacris brimleyi

Brant & Walker 0 0 3 1 Pseudacris crucifer

(Wied-Neuwied) 0 0 6 5 Salamanders

Ambystoma opacum (Gravenhorst) 0 1 0 0 Plethodon chlorobryonis

Mittleman 0 1 15 45 Plethodon cinereus (Green) 0 0 127 61

Snakes Carphophis amoenus (Say) 0 0 0 1 Virginia valeriae

Baird & Girard 0 0 0 1 Storeria occipitomaculata

(Storer) 1 2 0 0 Tharnnophis sirtalis (Linnaeus) 0 0 1 0

Lizards Scincella lateralis (Say) 1 2 0 1 Eumecesfasciatus (Lirmeaus) 0 0 0 1

Turtles Terrapene carolina (Linnaeus) 0 0 0 2 Kinosternon subrubrum (Bonnatere) 1 0 0 0

Totals 7 18 462 774 Number of species 5 8 10 16 Trap nights (TN0 1,318 1,318 1,584 1,782 No. amphibians/100 TN 0.30 1.06 29.10 42.99 No. reptiles/100 TN 0.22 0.30 0.06 0.45 H' 1.475 1,904 1.636 1.827 J' 0.917 0.916 0.682 0.659

different species compositions, numbers of captures per 100 trap nights, and estimates o f species diversity (Table 3).

Mammalogists have historically used a wide array o f techniques to capture small mammals . These fall into four categories: live traps (e.g., Fitch and Sherman traps), snap traps, pitfalls o f various sizes arranged in grid patterns or associated with a drift fence, and nest boxes (Davis 1982, Call 1986). Each technique samples

the small m a m m a l communi ty differently because of variation in catchability among species groups (Rose et al. 1990, Pagels et al. 1992). Catchability of insec- tivores in live traps is very low compared to pitfalls. Conversely, catchability o f rodents is higher in live traps than in most pitfall techniques. The difference between groups holds for small m a m m a l communit ies in saturated forested wetlands (reviewed here), as well as in other types o f habitats (Williams and Braun 1983,

134 WETLANDS, Volume 13, No. 2, Special Issue, 1993

Table 5. Sampling for amphibians and reptiles with cov- erboards in saturated forested wetlands. Data for the cov- erboard and drift fence studies at the Rainbow Bay site (Grant et al. 1992) are compared to data for the saturated forested wetland site (see text for site descriptions). H' values are based on numbers of individuals for each species. All data are from the Savannah River Ecology Site, Aiken County, South Carolina, May-August 1990.

Parameter

SFW Rainbow Bay, SC (SRS) Cover- Cover- boards boards Drift Fence

Anurans 5 7 2,449 Salamanders 6 242 3,390 Turtles 0 0 208 Lizards 4 48 2,166 Snakes 8 15 1,626 Total 23 312 9,839 No. of species 10 11 27 Coverbd encounters 1,560 3,456 Trap nights (TN) 10,648 No./100 encounters or TN 1.47 9.03 92.40 H' 2.07 0.97 2.58 J' 0.88 0.39 0.78

Kirkland and Sheppard, in press). Complete invento- ries of small mammal communities require the si- multaneous use of several capture techniques--pitfalls with live traps (Szaro et al. 1988) or pitfalls with snap traps (Kirkland and Sheppard, in press). Either of these combinations should adequately assess terrestrial small mammal communities in saturated forested wetlands of the mid-Atantic region.

Amphibians and Reptiles

The larger aluminum flashing drift fences with 5-gallon (19-0 buckets captured many more amphib- ians and yielded significantly larger numbers of cap- tures per 100 trap nights (×2 = 23.96-46.25, P < 0.001, all comparisons) than the plastic-coated fabric drift fences with number l0 cans (our data) (Table 4). De- spite the fact that all species recorded are found throughout southeastern Virginia (Tobey 1985), the arrays with the small pitfalls, even with the additional isolated pitfalls, captured half the number of species recorded by the arrays with the large (19-1) pitfalls. Species composition of the samples also differed be- tween sites within techniques and between capture techniques (Table 4). This holds true for amphibians and reptiles separately as weIl as when these groups are combined. The differential capture effectiveness between techniques yielded different H' and J' values.

The primary technique used for inventorying ter-

restrial amphibian and reptile communities has been direct collecting by hand or observation (Jones 1988), but indirect methods, particularly funnel traps and drift fences with pitfalls (Campbell and Christman 1982, Gibbons and Semlitsch 1982), have been used in a number of studies. Funnel traps are effective for cap- turing some snakes, lizards, and frogs but are ineffec- tive in capturing salamanders and arboreal snakes and lizards. Funnel traps captured few forest vertebrates in northwestern conifer forests (Bury and Corn 1987). Drift fences with pitfall traps have proven to be effec- tive in capturing most small-to-medium-sized terres- trial vertebrates. This technique has its limitations, however. Dodd (1991) experimentally showed that several species of frogs climbed or hopped over drift fences and that newts passed under fences in tunnels made by other animals.

The coverboard technique used in the saturated for- ested wetland site in South Carolina yielded fewer in- dividuals but a similar number of species compared to results derived from the pine plantation site (Table 5). However, number of captures per 100 coverboards in the pine site was six times greater than in the wetland site. The high number of salamanders captured in the pine site substantially influenced the comparatively low H' and J' values. Numbers of individuals obtained by the drift fence technique were several orders of mag- nitude higher than those obtained by the coverboards in the two sites where this method was used (Table 5). Species richness sampled with coverboards was 37- 40% of that recorded by the drift fence technique.

Assessment of herpetofaunal diversity with stan- dardized arrays of coverboards has only recently been undertaken. Grant et al. (1992) compared herpeto- faunas at several sites using the coverboard technique and at a site using a drift fence with pitfall technique. Our comparison of the results between the saturated forested wetland site and an upland site suggests that coverboards are less effective in the wetland habitat. This may be due to the fact that coverboards may stand for periods of time under water. Nevertheless, this technique may be valuable in assessing populations of selected species, such as ground skinks and pletho- dontid salamanders (Grant et al. 1992).

General Remarks

Because of the wide range of body sizes, behaviors, and habitat selection of amphibians, reptiles, and small mammals utilizing saturated forested wetlands, com- plete inventories are difficult to obtain. If the primary objective of a study is to obtain a complete inventory of the terrestrial vertebrate fauna, then multiple sam- piing techniques should be employed.

Assessments of community structure for terrestrial

Mitchell et aL, CAPTURE TECHNIQUES FOR TERRESTRIAL VERTEBRATES 135

vertebrates in saturated forested wetlands have lagged behind such assessments in other habitats (e.g., Jones 1988, Olson and Knopf 1988). The data available for saturated forested wetlands in the mid-Atlantic states provide valuable information for a few specific sites, but because different techniques have been used in each study, comparisons of diversity indices and evenness among sites should not be viewed as accurate indica- tors. Important assumptions for the Shannon diversity index are that all species in the community are rep- resented in the sample and that the number captured for each species is a random sample of the true pop- ulation (Poole 1974). Samples lacking rare species have little effect on H' but a serious effect on Hmax' and J' (Brower et al. 1990). Because evenness estimates are not independent of the number of species, their values are usually overestimates of true evenness and can be reasonably compared only when the number of species is similar (Brower et al. 1990). Unfortunately, each capture technique used in prior studies of terrestrial vertebrates in saturated forested wetlands provides a biased sample of the numbers of individuals and spe- cies.

We recommend that future studies involving inven- tories of these communities in saturated forested wet- lands use standardized sampling efforts so that com- parisons can be made across t ime and space. Standardized techniques for small mammals have been recommended by Kirkland and Sheppard (in press) and Handley and Varn (in press), and for amphibians by Heyer et al. (in press). Combinations of the large drift fence and large pitfalls with supplemental capture techniques for vertebrates not well sampled by pitfalls may yield comparative data sets, as long as sampling efforts (e.g., time and number of traps) are the same. I f specific taxonomic groups (e.g., mice or shrews) are the targets of study, then more specific capture tech- niques could be employed. The important point is, however, that different researchers should use the same technique and sampling effort for the same taxa. Oth- erwise, comparisons of sampling results will continue to be problematic.

ACKNOWLEDGMENTS

We thank Robert C. Dowler, Harvey M. Katz, and Anne H. Katz for providing original capture data from their Great Swamp study. Christopher A. Pague and Kurt A. Buhlmann of the Division of Natural Heritage, Virginia Department of Conservation and Recreation, kindly allowed us to use their data for the Fentress and Oceana sites. The coverboard data for the forested wetland site on the Savannah River Site, Aiken Coun- ty, South Carolina were kindly provided by J. Whitfield Gibbons and Bruce W. Grant. Kristen L. Uthus cal-

culated Shannon diversity indices and evenness values for the samples compared in this paper. Gordon L. Kirkland, Jr. thoroughly reviewed the manuscript.

Some of the data presented in this paper were de- rived from field research supported by the Department oi'Defense and U.S. Fish and Wildlife Service through The Nature Conservancy and the Division of Natural Heritage, Virginia Department of Conservation and Recreation.

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Manuscript received 2 March 1992; revisions received 21 July 1992 and 29 September 1992; accepted 6 October 1992.