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

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 impor- tant 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 hiberna- cula 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. Resume : Les hibernaculums jouent un role important dans l'ecologie des serpents des hautes latitudes et les especes qui occupent des tanieres communautaires peuvent passer la moitie de l'annee ou plus dans leurs hibernaculums. A cause de la longue periode passee dans les hibernaculums, ces sites peuvent fournir de multiples benefices aux serpents et, en particu- lier, un gite qui les protege des conditions letales pendant l'hiver, des occasions sociales et des sites pour lezarder, ce qui est important pour la thermoregulation. Les hibenaculums adequats semblent etre restreints dans le paysage et les individus se deplacent de plusieurs kilometres pour utiliser et reutiliser des sites specifiques. Nous examinons l'orientation, la structure physique et les proprietes thermiques des sites utilises comme hibernaculums par les crotales de l'Ouest (Crotalus oreganus Holbrook, 1840) et les comparons a des sites choisis au hasard qui paraissent etre semblables, mais qui ne servent pas a l'hibernation. Les hibernaculums se retrouvent principalement sur les talus d'eboulis orientes vers le sud, ils sont disposes sur des pentes moins abruptes et ils se composent de pierres de taille intermediaire par comparaison aux sites repartis au ha- sard. Nos observations indiquent que l'orientation et la composition physique des hibernaculums leur donnent de la stabilite dans le temps, ce qui permet aux serpents de les retrouver a chaque fois, tout en fournissant un refuge previsible pendant l'hiver. Les hibernaculums sont aussi plus chauds en surface que les sites aleatoires a orientation nord et ils procurent aux serpents plus d'occasions de lezarder au soleil pour leur thermoregulation apres leur emergence de l'hibernation. (Traduit par la Redaction)