Trade-off between Thermal Quality and Predation Risk at Timber Rattlesnake Gestation Sites

Trade-offs can cause conservation measures designed to improve habitat for one aspect of a species life history to inadvertently decrease its suitability in other ways. We explored the potential trade-off between thermal characteristics and risk of predation in important habitat for Timber Rattlesnakes (Crotalus horridus). Although typically a woodland species, pregnant C. horridus congregate in sunny, rocky clearings known as gestation sites that provide improved thermal habitat for embryonic development. Gestation sites can become overgrown with vegetation and, thus, sites may vary in canopy openness. We hypothesized that gestation sites with more canopy openness will be warmer but leave the snakes more exposed to predators. We used hemispherical photography to calculate canopy openness and operative temperature models to quantify thermal quality. Rattlesnake foam models and time-lapse cameras were deployed to quantify the relative predator richness and risk of predation. We found that more-open gestation sites were warmer than enclosed sites. We found that potential for predator encounters was similarly common regardless of gestation site canopy openness. However, we did find that predator species richness increased with canopy openness, with the most dangerous predators (raptors, mustelids, and felids) being only present at the most-open gestation sites. These results suggest that conservation actions for C. horridus that involve opening up the canopy at existing gestation sites may have unintended fitness consequences, as more dangerous predators appear to visit these more-open sites.