Quantifying costs and benefits of alternative overwintering strategies in a southeastern population of Timber Rattlesnakes (Crotalus horridus)
Powers, John
Stubbs, Amber
Bartlett, Danielle
DeSantis, Dominic L.
Department of Biological and Environmental Sciences
Georgia College and State University
Milledgeville, Georgia USA
Temperate reptile populations are under strong selective pressure to minimize the costs of extreme winter temperatures. For high latitude and high elevation snake populations, this has often favored communal overwintering behavior, wherein large numbers of conspecifics aggregate at optimal sites given the limited availability of such features in the environment. Timber Rattlesnakes (Crotalus horridus) are distributed across a wide latitudinal gradient in North America, and therefore represent ideal models for exploring how variable winter selective regimes might favor different strategies. Northern C. horridus populations typically exhibit communal denning and long-distance migrations, while southern populations generally overwinter solitarily. Here, we leverage a unique intermediate population of C. horridus from central Georgia, USA that exhibits both communal and solitary overwintering. By combining remote videography, radiotelemetry, and accelerometry from 2022 to present, we quantified relative costs and benefits of communal and solitary overwintering behaviors. Migration distance (mean ± S.E.) for communal rattlesnakes (649.96±110.73) was significantly greater than that of solitary individuals (332.10±66.59) (t41.5=2.95, p=0.005). Binomial logit models revealed a positive effect of daily maximum temperature on basking frequency across all rattlesnakes (ES=0.87±0.15, p<0.001), but accounting for site type (communal vs. solitary) indicated that communal snakes basked more often than solitary snakes (ES=-2.01±0.95, p=0.03). Additionally, there was an interaction between daily maximum temperature and site type, as communal snake basking frequency displayed a positive relationship with daily maximum temperature while solitary snakes displayed a negative relationship (ES=-0.44±0.22, p=0.05). Despite higher travel costs incurred by communal snakes, individuals might trade-off these costs for increased winter basking opportunities. However, we also documented individual plasticity in this system, with several individuals shifting between communal and solitary sites across years. We have incorporated temperature data-logging at overwintering sites and physiological monitoring of snakes to better understand the proximate and ultimate drivers of these alternative overwintering strategies.