Body temperatures and winter activity in overwintering Timber Rattlesnakes (Crotalus horridus) in Tennessee, USA

Abstract

At high latitudes and elevations, snakes spend considerable time in overwintering refugia. Although brumation is generally associated with periods of inactivity, some evidence supports the occurrence of limited above and below ground activity during winter. Observations of such events are rare due to the inaccessibility of the typical subterranean refugia of snakes. Our study examined occurrences of both surface and subterranean activity during winter in the Timber Rattlesnake, <i>Crotalus horridus</i>. We monitored hourly body temperatures (T_bs) and small-scale above and below ground movement bouts throughout the overwintering period in Tennessee, USA. High frequency monitoring of body temperatures and movement patterns allowed us to identify mid-winter activity as well as shuttling behavior during ingress and egress. We recorded environmental temperatures and snake operative temperatures to estimate periods when snakes were surface active. Snake ingress into brumation occurred on 10 October ± 12 d, and egress occurred on 7 April ± 17 d. We recorded 53,041 T_bs (mean snake T_b = 11.0 ± 3.6°C; range 1.1–33.7°C) collected over two overwintering periods (2011–2012 and 2012–2013). Snakes made on average 6.1 ± 1.2 movement bouts throughout winter, accumulating a total distance of 146.4 ± 35.5 m. All individuals made small (< 10 m) movements throughout winter. We speculate that milder winters and the increased prevalence of suitable surface temperatures will promote additional winter activity.