Hibernation; Part II

What is hibernation? Learn more about how some animals survive cold winters.

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Obligate hibernators enter hibernation based on seasonal timing cues rather than as a response to stressors from the environment. Unlike them, Facultative hibernators enter hibernation only when either cold-stressed, food-deprived, or both. Only mammals hibernate. However, a few birds, including hummingbirds, do something similar.