We can identify three types of arousal during the hibernation period, on temporal rather than physiological grounds. The first is alarm arousal, in response to a major exogenous stimulus such as a sudden large drop in environmental temperature. The second is a periodic arousal when, in the absence of external cues, the animal spontaneously begins to re-warm. The third is the final arousal in the spring when the animal does not re-enter hibernation but emerges to a sustained euthermia. Physiologically, all three are similar.