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.