Midwinter Emergence in Hibernating Timber Rattlesnakes (Crotalus horridus)

Hibernation is an important behavioral event in temperate-region reptiles for escaping periods of harsh winter temperatures. Generally considered a dormant period, observations of winter activity suggest that hibernating reptiles may be more active than initially thought. To examine winter activity in a species that commonly hibernates, Timber Rattlesnakes (Crotalus horridus), we monitored the detailed movements and body temperatures (T_bs) of free-ranging snakes over two winters. Hourly T_bs and movements of snakes throughout a five-month hibernation period were monitored for midwinter activity and potential thermoregulatory behavior. Environmental temperatures and snake operative temperatures were used to estimate time periods when snakes were at or on the surface. Visual observations of snakes basking on the surface were uncommon; however, hourly recorded snake T_bs revealed that 69% of the snakes emerged to the surface to bask two or more times for a total of 60 emergence events from 14 individuals. Snake T_bs (N = 53,041) during hibernation were 11.1 ± 3.5℃ (mean ± SD) and ranged from 1.1–33.7℃. Counter to our prediction, calculated estimates of metabolic expenditure associated with increasing T_b (via basking or surface emergence) during hibernation had little effect on the total energy budget required to survive winter. Additional metabolic expenditure attributable to multiple basking events (e.g., 10 basking events) can be offset by acquiring as little as 1.0 g of rodent during the active season.