Northern Pacific Rattlesnakes (<i>Crotalus oreganus</i>) use thermal and structural cues to choose overwintering hibernacula

Abstract

Hibernacula play an important role in the ecology of high-latitude snakes, and communally denning species may occupy their hibernacula for half the year or more. Because of the long duration spent at hibernacula, such sites can provide multiple benefits to snakes including shelter from lethal overwinter conditions, social opportunities, and basking sites important in thermoregulation. Adequate hibernacula seem to be limited on the landscape and individuals travel several kilometres to use and reuse specific sites. We investigate orientation, physical structure, and thermal properties of sites used as hibernacula by Northern Pacific Rattlesnakes ( Crotalus oreganus Holbrook, 1840), and compare them with random sites that appear to be similar but were not used for hibernation. Hibernacula occurred primarily on south-facing talus slopes, were oriented on less-steep slopes, and were composed of rocks that were intermediate in size to randomly occurring sites. Our results suggest that the orientation and physical composition of hibernacula allow them to be stable over time, allowing snakes to repeatedly locate the sites, as well as providing predictable overwinter refuge. Hibernacula were also warmer on the surface than north-facing random sites and provided increased basking opportunities for snakes thermoregulating in early spring after emergence from hibernation.