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.
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Animals that hibernate include bats, some species of ground squirrels and other rodents, mouse lemurs, the European Hedgehog and other insectivores, monotremes and marsupials. Even some rattlesnakes, such as the Western Diamondback, are known to hibernate in caves every winter. Historically, Pliny the Elder believed swallows hibernated, and ornithologist Gilbert White pointed to anecdotal evidence in The Natural History of Selborne that indicated as much. Birds typically do not hibernate, instead utilizing torpor. However the Common Poorwill does hibernate. Many experts believe that the processes of daily torpor and hibernation form a continuum. Some reptile species are said to brumate, or undergo brumation, but the connection to this phenomenon with hibernation is not clear. Hibernating animals get their energy by a process known as gluconeogenesis.
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, the bear's body temperature remains relatively stable (depressed from
Hibernating ground squirrels may have abdominal temperatures as low as 0 °C, maintaining sub-zero abdominal temperatures for more than three weeks at a time, although the temperatures at the head and neck remain at 0 C or above. Before entering hibernation most species eat a large amount of food and store energy in fat deposits in order to survive the winter. Some species of mammals hibernate while gestating young, which are born shortly after the mother stops hibernating.
For a couple of generations during the 20th century it was thought that basking sharks settled to the floor of the North Sea and hibernated; however, research by Dr David Sims in 2003 dispelled this hypothesis, showing that the sharks actively traveled huge distances throughout the seasons, tracking the areas with the highest quantity of plankton. The epaulette sharks have been documented to be able to survive for long periods of time without oxygen, even being left high and dry, and at temperatures of up to
Until recently no primate, and no tropical mammal, was known to hibernate. However, animal physiologist Kathrin Dausmann of Philipps University of Marburg, Germany, and coworkers presented evidence in the 24 June 2004 edition of Nature that the Fat-tailed Dwarf Lemur of Madagascar hibernates in tree holes for seven months of the year. This is interesting because Malagasy winter temperatures sometimes rise to over
Noise and vibration from snowmobiles, all-terrain vehicles (ATV) and the like is said to sometimes awaken hibernating animals, who may suffer severely or die as a result of premature awakening in times of food shortage. However, many hibernators can return to hibernation after awakening, and deep hibernators in fact awaken many times throughout the hibernation season in what are called interbout arousals.
There are many research projects currently investigating how to achieve "induced hibernation" in humans. The ability for humans to hibernate would be useful for a number of reasons, such as saving the lives of seriously ill or injured people by temporarily putting them in a state of hibernation until treatment can be given (compare induced coma). NASA is also interested in possibly putting astronauts in hibernation for very long space journeys.
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Hibernation is a time of inactivity. Some animals hibernate, usually during the winter, when food is short. They fall into a sleep-like state. They can regulate their metabolism to consume less energy. They lower their body temperature, slow their breathing, and slow other vital functions. During hibernation, the body uses fat for energy, which the animal has typically gathered in summer and autumn.