Torpor

Torpor is a state of regulated hypothermia in an endotherm lasting just a few hours. Animals that go through torpor include small birds like hummingbirds and some small mammals such as bats. During the active part of their day these animals maintain normal body temperature and activity levels, but their body temperature drops during a portion of the day (usually night) to conserve energy. Torpor is often used to help animals survive in a cold climate, since it allows the organism to save the amount of energy that would normally be used to maintain a high body temperature.