Quantifying costs and benefits of alternative overwintering strategies in a southeastern population of timber rattlesnakes (<i>Crotalus horridus</i>)

Abstract Temperate nonavian reptiles are under selective pressure to minimize the costs of low winter temperatures. For high-latitude or high-elevation snake populations, this has often favored communal overwintering behavior, whereas lower latitude populations typically overwinter solitarily. Timber rattlesnakes (Crotalus horridus) are distributed across a wide latitudinal gradient in North America and represent ideal models for exploring how variable winter selective regimes might favor different overwintering strategies. We studied a unique population of C. horridus from central Georgia, United States of America, that maintains both communal and solitary overwintering behavior. Through time-lapse videography, temperature datalogging, radio telemetry, and accelerometry, we quantified the potential costs and benefits of communal and solitary overwintering while assessing variation in individual plasticity in strategy. Migration distance (mean ± standard error [SE]) among communal rattlesnakes (561.41 ± 86.74 m) was significantly greater than solitary rattlesnakes (334.71 ± 50.48 m). Communal individuals might trade-off this cost for increased winter basking opportunities, as they exhibited greater activity levels and a reduced dependency on ambient temperature for activity relative to solitary snakes. However, there were no differences in basking frequency, body temperatures, and environmental temperatures between communal and solitary sites. We documented individual plasticity in overwintering strategy, with several males and females shifting between communal and solitary sites across years. Our results only partially explain the simultaneous maintenance of both overwintering strategies in this population. We suspect that multiple lurking variables related to individual condition are at play, such as disease (Ophidiomycosis) status and inclusive fitness benefits to communal snakes.