Torpor, sometimes called temporary hibernation[1] is a (usually short-term) state of decreased physiological activity in an animal, usually characterized by a reduced body temperature and rate of metabolism. Animals that go through torpor include birds (even tiny hummingbirds, notably Cypselomorphae) and some mammals such as mice and bats.[2] During the active part of their day, animals that undergo daily torpor maintain normal body temperature and activity levels, but their temperature drops during a portion of the day (usually night) to conserve energy. Torpor is often used to help animals survive during periods of colder temperatures, as it allows the organism to save the amount of energy that would normally be used to maintain a high body temperature.
Torpor may extend for a longer period of time, Lungfish switch to the torpor state if their pool dries out and tenrecs switch to the torpor state if food is scarce during the summer in Madagascar.
Some animals seasonally go into long periods of torpor-like inactivity known as hibernation or aestivation.
Bats, especially species in temperate regions suffering harsh winters, rely upon torpor to survive. Lowering the body temperature to the ambient temperature allows them to enter torpor for prolonged periods at a lower metabolic cost. Oxygen consumption, heart rate and breathing rates are all lowered significantly meaning less energy is required to survive. Torpor is important in daily cycles to conserve energy as well as prolonged torpor, or hibernation. Pre-hibernation feeding builds up layers of fat which are used as the energy source during torpor. Arousal from torpor in bats is facultative not obligate, meaning that they don't have to waken to eat, etc. but that noise or other external stimuli can wake them. Waking them increases their metabolism and therefore has a high energy cost. If disturbed, young bats or those with inadequate fat reserves may starve.
Torpor is alternatively used as a reference to any non-physiological state of inactivity. As an example, recently naturalists have learned that female crocodiles enters a deep torpor without aggression during their short egg laying period. In Buddhism torpor is one of the Five Hindrances.
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