Hibernation

Hibernation is a a state of resting (torpor) or deep sleep some animals go into to conserve energy, usually during the winter. During hibernation they slow their metabolism to very low levels, with body temperature and breathing rates lowered, gradually using up body fat which was stored up during the warmer months during which the animal was active. The level of torpor varies; some hibernating animals stir as often as once a week, while others sleep through the entire time.

Both land-dwelling and aquatic mammals hibernate; polar bears are the best-known example of hibernation. Other animals that hibernate include mice, bats, terrapins, and newts. Aquatic animals can hibernate either in or out of water. Red Eared Terrapins hibernate in water, burying themselves in the mud at the bottom of a pond, whereas newts can hibernate on land or in the water.

Some species of mammals hibernate while gestating young, which are born shortly after the mother stops hibernating.

Animals that undergo a state of dormancy similar to hibernation during the summer can be said to estivate.