Burrow Use and Survival of Newly Metamorphosed Gopher Frogs (Rana capito)

—The transition from aquatic to terrestrial habitat is thought to be a period of high mortality for amphibians. We used radio telemetry to estimate survival and study factors influencing survivorship of newly metamorphosed Gopher Frogs (Rana capito). Predation was very high and only 12.5% of frogs survived their first month in the terrestrial habitat. All documented predation occurred during the frogs’ initial 12 days in the uplands, and snakes (Coluber constrictor and Thamnophis sirtalis) were the major predators. Also, frogs were preyed upon by mammals and birds and killed by vehicles along dirt roads. Survival rates varied among ponds, with the survival rate at one pond being significantly lower than survival rates at three other ponds. Survival of frogs was dependent on their use of underground refuges, particularly burrows excavated by Gopher Tortoises (Gopherus polyphemus) and small mammals. Using underground refuges reduced the risk of mortality to only 4% of that faced by frogs while in the open environment; in fact, all surviving frogs located a burrow within their initial eight days in the terrestrial habitat and remained there for the duration of tracking. Our results demonstrate the dependence of Gopher Frogs on underground refuges and suggest that the availability of burrows near breeding ponds influences survival of juveniles and, thus, the recruitment of adults. Amphibian populations can be affected by mortality during the egg, larval, juvenile, and adult life stages. However, several population models indicate that amphibian populations are most sensitive to mortality during the terrestrial juvenile and adult stages (Taylor and Scott, 1997; Biek et al., 2002), particularly juveniles (Hels and Nachman, 2002; Vonesh and De la Cruz, 2002). In addition to sustaining local populations, juvenile amphibians are thought to be responsible for most interpond dispersal, thereby contributing to regional persistence and influencing metapopulation dynamics (Breden, 1987; Berven and Grudzien, 1990; Funk et al., 2005). Despite the importance of juveniles to populations, information is lacking on many basic features of life history and demography of this life stage. The transition from aquatic to terrestrial habitat is thought to be a period of high mortality for amphibians, and mortality appears to be highest immediately after metamorphosis (Trenham et al., 2000; Altwegg and Reyer, 2003; Rothermel and Semlitsch, 2006). Factors thought to directly influence postmetamorphic survival of amphibians include body size at metamorphosis (Berven, 1990; Morey and Reznick, 2001), lipid levels at metamorphosis (Scott et al., 2007), and habitat quality, which includes suitable terrestrial habitat (Rothermel and Semlitsch, 2006), as well as the availability of refuges (Loredo et al., 1996; Rothermel and Luhring, 2005). Refuges provide amphibians with protection from predation (Denton and Beebee, 1993; Spieler and Linsenmair, 1998) and minimize the effects of adverse weather conditions (Seebacher and Alford, 2002; Rothermel and Luhring, 2005). Newly metamorphosed amphibians are unfamiliar with the locations of refuges in the terrestrial habitat, which puts them at a high risk of predation and desiccation, which is exacerbated by their small body size (Thorson, 1955; Newman and Dunham, 1994). Thus, refuges are particularly important to juveniles, and locating and using suitable refuges may be an important correlate of juvenile survival. This may be true especially for species that use distinct, spatially discrete refuges, such as the Gopher Frog (Rana capito). Gopher Frogs breed in temporary or semipermanent ponds but spend the majority of their lives in the surrounding terrestrial habitat, where they seek shelter in underground refuges, such as the burrows of Gopher Tortoises (Gopherus polyphemus) and several species of small mammals, as well as stump holes (Lee, 1968; Franz, 1986; Jensen and Richter, 2005). Because of their secretive nature, Gopher Frogs (R. capito and the closely related Dusky Gopher Frog, Rana sevosa) are very difficult to locate and capture in terrestrial habitats; thus, 1 Corresponding Author. Present address: School of Marine and Tropical Biology, James Cook University, Townsville, Queensland 4811 Australia. E-mail: betsy. [email protected] Journal of Herpetology, Vol. 43, No. 3, pp. 431–437, 2009 Copyright 2009 Society for the Study of Amphibians and Reptiles