Hibernation
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- This article refers to the process of hibernation in biology. For other uses, see Hibernate.
Some examples of animals that hibernate include bats, ground squirrels and other rodents, mouse lemurs, the European Hedgehog and other insectivores, monotremes, and marsupials. Although Pliny the Elder thought that swallows hibernated, and even a keen observer like the Rev. Gilbert White (The Natural History of Selborne) believed that, birds typically do not hibernate, instead using torpor, but an exceptional bird known as the Poorwill does hibernate. Many experts believe that the processes of daily torpor and hibernation form a continuum.
One animal that some consider to be a hibernator is the bear. However, the degree of metabolic depression is much less than what is observed in smaller mammals and many prefer to use the term denning. The bear's body temperature remains relatively stable (depressed from 37° C to approximately 31° C) and it can be easily aroused. In contrast, hibernating ground squirrels may have core body temperatures as low as -2° C. Some reptile species are said to brumate, or undergo brumation, but the relatedeness of this phenomenon with hibernation is not clear.
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. Tracking devices installed on 20 basking sharks in 2002 dispelled this hypothesis.
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 present evidence in the 24 June 2004 edition of Nature that the Lesser 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 30 °C (86 °F), so hibernation is not exclusively an adaptation to low ambient temperatures. The hibernation of this lemur is strongly dependent on the thermal behaviour of its tree hole: if the hole is poorly insulated, the lemur's body temperature fluctuates widely, passively following the ambient temperature; if well insulated, the body temperature stays fairly constant and the animal undergoes regular spells of arousal. Dausmann found that hypometabolism in hibernating animals is not necessarily coupled to a low body temperature.
Noise and vibration from snowmobiles, all-terrain vehicles 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.
Latent hibernation
Recent research suggests that hibernation may exist as a latent ability in many mammals, possibly even humans[link]. If true, human hibernation may be used for long-haul space flight and to extend human life span in some cases (for example a patient waiting for a donor organ may survive longer in a state of hibernation, increasing the likelihood that a suitable organ can be found before the patient dies).See also
- Dormancy
- Estivation - a state of dormancy similar to hibernation, except it is used in the summer
- Torpor - regulated hypothermia for less than a day, often used by birds
- Hibernation induction trigger
External links
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