SURVIVAL OF RADIO-IMPLANTED DRYMARCHON COUPERI (EASTERN INDIGO SNAKE) IN RELATION TO BODY SIZE AND SEX NATALIE L. HYSLOP 1,4,5 , J. MICHAEL MEYERS 2 ,ROBERT J. COOPER 1 , AND TERRY M. NORTON 3 1 Warnell School of Forestry and Natural Resources, The University of Georgia, Athens, GA 30602-2152, USA 2 USGS Patuxent Wildlife Research Center, Warnell School of Forestry and Natural Resources, The University of Georgia, Athens, GA 30602-2152, USA 3 St. Catherines Island Foundation, 182 Camellia Road, Midway, GA 31320, USA ABSTRACT: Drymarchon couperi (eastern indigo snake) has experienced population declines across its range primarily as a result of extensive habitat loss, fragmentation, and degradation. Conservation efforts for D. couperi have been hindered, in part, because of informational gaps regarding the species, including a lack of data on population ecology and estimates of demographic parameters such as survival. We conducted a 2- year radiotelemetry study of D. couperi on Fort Stewart Military Reservation and adjacent private lands located in southeastern Georgia to assess individual characteristics associated with probability of survival. We used known-fate modeling to estimate survival, and an information-theoretic approach, based on a priori hypotheses, to examine intraspecific differences in survival probabilities relative to individual covariates (sex, size, size standardized by sex, and overwintering location). Annual survival in 2003 and 2004 was 0.89 (95% CI 5 0.73–0.97, n 5 25) and 0.72 (95% CI 5 0.52–0.86; n 5 27), respectively. Results indicated that body size, standardized by sex, was the most important covariate determining survival of adult D. couperi, suggesting lower survival for larger individuals within each sex. We are uncertain of the mechanisms underlying this result, but possibilities may include greater resource needs for larger individuals within each sex, necessitating larger or more frequent movements, or a population with older individuals. Our results may also have been influenced by analysis limitations because of sample size, other sources of individual variation, or environmental conditions. Key words: Drymarchon couperi; Eastern Indigo Snake; Georgia; Mortality; Radio-implanted; Radiotelemetry; Sex; Size; Survival ESTIMATES of survival for wildlife popula- tions are essential to our understanding of population dynamics and for conservation efforts drawing from the results of population modeling (Williams et al., 2002). For some species, factors that influence survival are not well understood, thus limiting application of these estimates to conservation efforts (Mar- tin, 1995). These deficiencies in our under- standing of survival are particularly evident for many snake species (Parker and Plummer, 1987), for which the ability to locate and recapture individuals for survival analysis is often hindered by the cryptic nature and long periods of inactivity characteristic of many species. In addition, many snake species occur at naturally or artificially low densities, which can further inhibit the ability to estimate demographic parameters accurately (Parker and Plummer, 1987). Drymarchon couperi (eastern indigo snake), a federally threatened species of the south- eastern coastal plain of the United States (United States Fish and Wildlife Service, 1978), is illustrative of a species that is difficult to survey (Hyslop et al., 2009; Stevenson et al., 2003) and largely lacks data related to population ecology, including estimates of demographic parameters such as survival. Population declines at the time of federal listing were caused primarily by commercial collection coupled with extensive habitat loss (USFWS, 1978). Federal protection largely curtailed commercial take, presumably reduc- ing its impact on natural populations (Lawler, 1977). However, habitat loss, fragmentation, and degradation remain primary threats to D. couperi populations (USFWS, 1978, 1999), with additional sources of mortality including highway fatalities, wanton killings, pesticide and other chemical exposure, and illegal take (Lawler, 1977; USFWS, 1978). Upland habitats in the southeastern coastal plain were primarily dominated by longleaf pine (Pinus palustris) and wiregrass (Aristida 4 PRESENT ADDRESS: 7001 SW 111 th Pl., Miami, FL 33173. 5 CORRESPONDENCE: e-mail, hyslopn@warnell.uga.edu Herpetologica, 65(2), 2009, 199–206 E 2009 by The Herpetologists’ League, Inc. 199