Patterns of Survival of a Communally Overwintering Rattlesnake Using an Artificial Hibernaculum

Avoiding thermal stress by using hibernacula is fundamental to survival of snakes in temperate environments. Snakes may overwinter alone or aggregate in communal hibernacula to avoid temperature extremes. Limited information is available regarding the overwintering ecology of rattlesnakes, and basic demographic information is necessary for understanding population dynamics, habitat requirements, and management of rattlesnakes. Even less is known about the demographics of species and populations utilizing artificial hibernacula, which may become increasingly important as habitat is lost and/or becomes more fragmented. We used seven years of mark–recapture data of the Western Rattlesnake (Crotalus viridis) at an artificial hibernaculum to estimate annual apparent survival, encounter rates, and transition rates between life stages (mature vs. immature) to investigate how these rates vary over time and in response to drought conditions. Further, we described trends in body condition and age structure, as well as trends in the proportion of reproductive females. Apparent survival rates were consistent and high across the study period for all snakes (including immature and mature females and all males; 0.66). The probability of an immature female surviving and transitioning to a mature adult was high and consistent across the study period (0.73). The stable survival and transition rates observed in this study may indicate other demographic rates, such as reproductive output, may be important drivers of population dynamics. This study contributes basic knowledge about population dynamics of communally overwintering rattlesnakes and suggests survival rates were relatively stable for snakes regularly utilizing this artificial hibernaculum.