Temporal and thermal aspects of hibernation of black rat snakes (Elaphe obsoleta) in Ontario

Emergence in mid-April appears not to be triggered by marked reversal of thermal gradients in the hibernaculum or by changes in day length. Endogenous rhythms seem most likely to be responsible. Entry in early October may be triggered in part by outside temperatures. Considerable individual variation in emergence and entry patterns was observed. Through the winter the snakes steadily got colder, reaching their coldest point just before emergence. Given the period of inactivity immediately before and following hibernation, the active period is <4 months, which perhaps explains why the population in this study is the northernmost in the species' distribution. -from Author