Evaluation of headstarting and release techniques for population augmentation and reintroduction of the smooth green snake

Abstract

AbstractHeadstarting is a conservation technique for improving survival of species with high juvenile mortality by accelerating growth rate and increasing body size of captive‐born young. With reptiles, headstarts are often kept active year‐round to achieve body size goals and increase survival, omitting overwintering (brumation). As brumation is part of the life cycle of reptiles, there may be tradeoffs related to temperature response post‐release when reptiles are kept active. Upon release into habitats, reptiles are either soft released, where acclimation is provided with in situ enclosures, or hard released without acclimation, directly into habitat. Soft releases have resulted in greater survival and site fidelity than hard releases, but evaluations with snakes are rare. We used a comparative approach to examine effects of brumation versus year‐round activity on prerelease growth and survival of smooth green snake Opheodrys vernalis headstarts. We estimated short‐term post‐release daily survival rates of headstarts and compared movements of hard and soft released snakes. Despite decreases in body mass during brumation, prerelease body size, growth rate and survival did not differ among brumation treatments. Brumated headstarts exhibited rapid compensatory growth, attaining the size of active headstarts within 2 months of brumation. We observed qualitative evidence of reproductive potential in brumated snakes with the production of spermatozoa and unfertilized eggs, which was absent in active headstarts. The short‐term survival rate of all headstarts during post‐release tracking was 0.83 (±0.01), but we lacked power to examine differences in survival among release treatments. Daily movements did not differ among release treatments. Soft releases had slightly greater recaptures, facilitating monitoring. Although brumation comparisons produced equivalent prerelease growth and survival, as a precautionary measure for post‐release survival, we recommend incorporating brumation into headstarting efforts. While further study with other reptiles is warranted, we recommend a comparative framework in planning headstarting efforts with additional species.