- Date: circa 1802
Hibernation is a state of inactivity and metabolic depression in animals, characterized by lower body temperature, slower breathing, and lower metabolic rate. Hibernating animals conserve food, especially during winter when food is short, tapping energy reserves, body fat, at a slow rate. It is the animal's slowed metabolic rate which leads to a reduction in body temperature and not the other way around.
Hibernation may last several days or weeks depending on species, ambient temperature, and time of year, and fur on the animal's body. The typical winter season for a hibernator is characterized by periods of hibernation interrupted by sporadic euthermic arousals wherein body temperature is restored to typical levels. There is a hypothesis that hibernators build a need for sleep during hibernation more slowly than normally, and must occasionally warm up in order to eat. This has been supported by some evidence in the arctic ground squirrel.
One animal that some famously consider a hibernator is the bear, although bears do not go into "true hibernation". During a bear's winter sleep state, the degree of metabolic depression is much less than that observed in smaller mammals. Many prefer to use the term "denning". The bear's body temperature remains relatively stable (depressed from 37 °C (99 °F) to approximately 31 °C (88 °F)) and it can be easily aroused. Some reptile species are said to brumate, or undergo brumation, but the connection to this phenomenon with hibernation is not clear.