AUTHORS: Benjamin C. Jellen, University of Health Sciences & Pharmacy in St. Louis; Brittany I. Neier, Federal Reserve
ABSTRACT: Though reptiles are largely eurythermic, those residing in temperate latitudes face large daily, and even greater seasonal, temperature fluctuations complicating thermoregulatory efforts. They must therefore employ strategies to avoid reaching critical thermal minimums and maximums for large portions of the calendar year. Such tactics include shuttling between microhabitats, exposure to the elements, and utilizing the various physical qualities of retreats and refuges with many species becoming fossorial during the overwintering period. Though data exists regarding the thermal ecology of temperate zone snakes during the activity period, far less is known concerning their operative body temperature (OBT) during the overwintering period and factors influencing ingress, emergence, and egress. We implanted free-ranging A. contortrix with temperature-sensitive radio transmitters and re-located individuals daily throughout the activity period (April - October) and three times weekly during the overwintering period (November - March) from 2018 - 2023. We recorded the shaded air (SAT) and surface substrate temperatures for each encounter as well as acquired data from a nearby weather station for the substrate temperature at depths of 0.1, 0.5, and 1.0 m. Though A. contortrix maintained a mean OBT of 10.6°C during the overwintering period, they experienced their lowest mean OBT in February (8.6°C). The peak emergence from overwintering coincided with the first week in April with a mean SAT of 19.4°C. However, this week was also the only week in which the mean substrate temperatures at depths of 0.1, 0.5, and 1.0 m varied by only 0.5°C (9.9 - 10.4°C) presenting an almost uniform subterranean thermal gradient for these depths and a potential cue for emergence. Though snakes made large daily linear ingress movements (x > 100m) on the day immediately following a considerable SAT drop (typically ~ 10°C), no such cues were detected during the egress period.
