Which type of hibernator hibernates only when cold-stressed, food-deprived, or both?

A facultative hibernator hibernates only when cold-stressed, food-deprived, or both.

Unlike an obligate hibernator, which enters hibernation according to seasonal timing cues, a facultative hibernator can adjust its response to immediate environmental conditions. If food is plentiful or temperatures remain suitable, it may avoid true hibernation or remain in a less extreme dormant state.

The distinction is physiological as well as ecological. Facultative hibernation helps an animal conserve energy when resources suddenly become scarce, rather than committing it to an annual winter program regardless of conditions. The response can therefore vary between individuals, years, and habitats.

Prairie dogs provide a useful comparison: the black-tailed prairie dog is facultative, whereas the closely related white-tailed prairie dog is obligate. Chipmunks are also often discussed in this context, although prolonged winter sleep in some chipmunks does not always meet the strictest definition of true hibernation because body temperature may not fall as far.