Ecology of the Southeastern Crowned Snake, Tantilla Coronata
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Copeia 2008, No. 2, 388–394 Ecology of the Southeastern Crowned Snake, Tantilla coronata Brian D. Todd1, John D. Willson1, Christopher T. Winne1, Raymond D. Semlitsch2, and J. Whitfield Gibbons1 There are very few comprehensive studies of the ecology of small-bodied snakes. Here, we describe the ecology and demography of the Southeastern Crowned Snake (Tantilla coronata) based on 1,640 captures on the Savannah River Site in the Upper Coastal Plain of South Carolina, USA from 1951–2007. Female T. coronata were significantly longer, heavier, and heavier-bodied than males but had relatively shorter tails. Clutch size based on oviductal eggs was positively correlated to maternal body mass and length. Snakes exhibited a unimodal seasonal activity pattern that peaked in summer. Pitfall captures were significantly male-biased from July– October, corresponding to the suggested mating period for this species in this part of its range. We identified three classes of animals in the population: neonates, second year animals, and older animals that included both non-reproductive subadults and reproductive adults. Longevity was at least five years for two recaptured males originally captured as mature adults. Centipede species were the exclusive prey identified from T. coronata collected on the Savannah River Site. Our study demonstrates that research on underrepresented species is possible and can contribute to understanding of snake ecology. TUDIES of snakes and their interactions with their understanding of snake ecology is likely influenced by environments and larger biological communities are easier-to-study large-bodied species, despite great abundanc- S poorly represented in broader ecological literature es of small snakes. (Gibbons, 1988; Bonnet et al., 2002). Nevertheless, herpe- The Southeastern Crowned Snake, Tantilla coronata,isa tologists have amassed considerable research illuminating member of the geographically widespread genus Tantilla,a the life history, biology, and ecology of many snake species. genus that includes approximately 63 species that occur Despite an increased understanding of many snakes, throughout North and Central America. Tantilla are diminutive species, such as the many ‘‘leaf-litter’’ or semi- generally small-bodied with dark colored heads and are fossorial snakes, are still seldom studied in any detail. In primarily semi-fossorial, nocturnal, and feed on inverte- most cases, previous studies offer small glimpses into the brates, although many species are newly described and ecology or biology of small-bodied snakes by reporting most remain unstudied (Canseco-Marquez et al., 2002; specific analyses of reproductive biology (Stewart and Sawaya and Sazima, 2003; Stafford, 2004). Tantilla coronata Brasch, 2003), seasonal activity and habitat use (Willson occurs in the southeastern United States east of the and Dorcas, 2004), or feeding ecology (Cobb, 2004). Mississippi River, and despite its inconspicuousness, can Importantly, there are very few comprehensive analyses of be locally abundant in the Sandhills and Coastal Plain the life history, demography, or ecology of small-bodied physiographic provinces. snake populations, despite increasing awareness of the Unlike most other small-bodied snakes, T. coronata have importance of such natural history studies (Greene, 2005). received some attention in previous studies and natural Although small-bodied snakes receive less attention than history reports. Observations of T. coronata have ranged their larger counterparts, they are often among the most from descriptions of habitat (Minton, 1949; Hardy, 1952; abundant snakes occupying many habitats. For example, Telford, 1966) and activity (Wright and Wright, 1957), to densities of Ringneck Snakes (Diadophis punctatus) in Kansas examinations of clutch size (Neill, 1951) and body size were estimated at 1,000 per ha (Fitch, 1975), and Godley variation (Telford, 1966). More recent studies have investi- (1980) calculated average densities of 1,200 Striped Crayfish gated patterns of seasonal activity and reproductive biology Snakes (Regina alleni) and Black Swamp Snakes (Seminatrix to a greater extent (Semlitsch et al., 1981; Aldridge, 1992; pygaea) per ha in aquatic habitats in Florida. Similarly, Aldridge and Semlitsch, 1992a, 1992b). Older accounts of Werler and Dixon (2000) report that the Rough Earth Snake the natural history of T. coronata have been hindered by (Virginia striatula) is the most abundant snake species in small sample sizes, and even among recent studies, infor- many parts of Texas. Often, comprehensive ecological mation about smaller (younger) individuals is typically studies of snakes are hampered by their secretive natures, scarce. The purpose of this manuscript is to present a their frequently cryptic behaviors and colorations, and, in much-needed comprehensive analysis of the ecology of one temperate snakes, their regular periods of inactivity. These small-bodied species of snake. We resolve previous uncer- factors may be amplified for small-bodied snakes, most of tainties about the demography of a population of T. coronata which live semi-fossorial or litter-dwelling lives and remain and present analyses of their activity, size and growth unobservable for much of the year. Consequently, our patterns, reproduction, and feeding ecology based on 1,640 1 University of Georgia, Savannah River Ecology Laboratory, Drawer E, Aiken, South Carolina 29802; E-mail: (BDT) [email protected]. Send reprint requests to BDT. 2 University of Missouri, Division of Biological Sciences, 105 Tucker Hall, Columbia, Missouri 65211-7400. Submitted: 26 December 2006. Accepted: 25 September 2007. Associate Editor: J. D. Litzgus. F 2008 by the American Society of Ichthyologists and Herpetologists DOI: 10.1643/CE-06-289 Todd et al.—Ecology of Tantilla coronata 389 captures from 1951–2007 on the Savannah River Site in died in pitfall traps, and we report masses and lengths of Aiken and Barnwell counties, South Carolina, USA. late-stage eggs from these females. To examine seasonal activity patterns, we used data MATERIALS AND METHODS collected during recent, intensive pitfall trapping studies (2004–2006; see Todd and Rothermel, 2006 for trapping design) so that we could adjust monthly captures for Study site.—The 803 km2 Savannah River Site (SRS) was trapping effort and eliminate effort-related sampling biases. established in 1951 in Aiken, Barnwell, and Allendale Specifically, we divided the number of captures in each counties in the Upper Coastal Plain of South Carolina, month by the number of total trap nights in each month. USA. The site consists predominantly of planted pine forests We used chi-square analyses to determine whether monthly and second-growth hardwood habitats but historically pitfall captures of T. coronata were sex-biased. We examined supported extensive agricultural areas prior to site establish- all data prior to analyses to ensure that statistical assump- ment (Gibbons et al., 2006). Reptiles and amphibians have tions were met (Zar, 1998). been a primary focus of extensive and intensive research on To determine feeding patterns and prey types, we the SRS since 1951 (Gibbons et al., 1997). dissected preserved animals (n 5 222) collected from 1979 to 1983 that were part of the Savannah River Ecology Data collection and analysis.—Tantilla coronata were initially Laboratory collection. We identified all prey items to the thought to be uncommon on the SRS (Freeman, 1955) but greatest taxonomic resolution possible. We also scored the have since been found to be more widely distributed gut contents of dissected animals, including both the (Gibbons et al., 1997) and have subsequently been captured stomach and intestines, as either empty, trace quantities, in large numbers during the course of herpetological half-full, or full. We used a contingency table analysis to research on the SRS. The development of effective collecting determine whether males and females differed in the techniques such as using coverboards (Grant et al., 1992) proportion grouped into each category. We used a contin- and drift fences (Gibbons and Semlitsch, 1982), as well as gency table to test whether males and females differed serendipitous captures, has led to 1,640 captures of South- significantly in the proportion that had no gut contents eastern Crowned Snakes since 1951. In general, field- versus those that had some gut contents. Only a few gravid captured animals were returned to the laboratory to record females that had been captured in this period were preserved mass to the nearest mg, snout–vent length (SVL) and tail (n 5 10), and they were excluded from gut content analyses length to the nearest mm, capture location, and capture due to their low sample size. method. Sex was determined by manual eversion of the hemipenes, cloacal probing, or dissection in the case of RESULTS animals sacrificed for use in other studies (Semlitsch et al., 1981; Aldridge and Semlitsch, 1992a, 1992b). Additionally, We recorded 1,640 captures of T. coronata from 1951–2007 we marked .600 T. coronata in the past 35 years by clipping on the SRS. Morphological data from older captures (1950s– ventral scales or by heat branding ventral and lateral scales 1970s) were not always recorded and in some cases, sex, (Winne et al., 2006), and we report information on reproductive condition, or the completeness of the tails recaptures from these efforts. were not noted and these animals were subsequently We compared SVL and mass of males and females using excluded from analyses. Males were significantly shorter analysis of variance (ANOVA). We compared relative tail than females (ANOVA: F1,467 5 81.3, P , 0.001; Table 1) but lengths of males and females using analyses of covariance had relatively longer tails (ANCOVA: F1,255 5 41.4, P , (ANCOVA) with SVL as a covariate. We compared relative 0.001; Table 1). Additionally, females were both absolutely masses of males and non-gravid females using ANCOVA heavier than males (ANOVA: F1,260 5 5.8, P 5 0.02; Table 1) with SVL as a covariate. We transformed all masses and and relatively heavier for their size (ANCOVA: F1,259 5 3.9; P lengths prior to analysis by computing natural logarithms 5 0.05).