|Hibernation is a state of regulated hypothermia, lasting
several days or weeks that allows animals to conserve energy during the
winter. During hibernation animals slow their metabolism to very low levels,
with body temperature and breathing rates lowered, gradually using the body
fat reserves that were stored during the active warmer months. Some hibernating
animals stir as often as once a week; Other animals sleep through the entire
Both land-dwelling and aquatic mammals hibernate. Animals that hibernate include mice, bats, ground squirrels, terrapins, snakes, frogs, and newts. Though Pliny thought that swallows hibernated, and even a keen observer like the Rev.Gilbert White (The Natural History of Selborne ) agreed, birds typically do not hibernate, instead using torpor, but a rare bird known as the Poorwill does hibernate. Aquatic animals can hibernate either in or out of water. Red-eared Terrapins hibernate in water, burying themselves in the mud at the bottom of a pond. Newts are capable of hibernation on land or in the water.
One animal that some consider to be a hibernator but is not a true hibernator is the bear. The reason for that is because while its heart rates are slow, the bear's body temperature remains relatively stable and they can be easily aroused. Other non hibernators that are thought to be a hibernator are: badgers, raccoons, and opposums.
Before entering hibernation most species eat prodigious amounts of food and store energy in large 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 Phillips University, Germany and coworkers present evidence in the 24 June 2004 edition of Nature that the Madagascan fat-tailed dwarf lemur hibernates for seven months of the year in tree holes. This is interesting because Madagascan winter temperatures sometimes rise to over 30C; 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, 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.