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Squirrels, bats, marmots, wild mice, hamsters and hedgehogs are some of the animals that hibernate. They do this to save energy during the winter, as food is scarce in that season. The phenomenon only happens with warm-blooded animals (who have a constant body temperature) and who live in temperate and arctic regions, where the cold is very rigorous. “When hibernating, the animal appears to be dead, but what actually happens is a sudden reduction in its organism’s activities”, says biologist Cecília Pessutti, from the Sorocaba Zoo, SP. The body temperature drops, breathing almost ceases and the heartbeat becomes so slow that it becomes practically imperceptible. “The state of inactivity is so deep that the animal doesn’t wake up even if it is shaken”, says Cecília.
Hibernation can last for weeks and also functions as a regime that would envy any human being on a diet: the animal consumes the fat accumulated in its body or wakes up from time to time to eat food stored in the nest. Some species even lose half their weight during hibernation! The animal only abandons this interminable nap when the ambient temperature starts to rise. Contrary to popular belief, bears do not hibernate, although they spend most of the winter sleeping. The body temperature of the dreaded brown bear, for example, only drops from 38ºC to 34ºC, so technically it is not in hibernation. His metabolism is a little slower, but at any sign of danger, he wakes up on time. The same goes for beavers. Although few people know it, many animals that live in deserted, hot and dry regions also go into a deep sleep to defend themselves against the aggressions of nature.
This is the case of snails and some types of frogs and fish, such as the pirambóia, which even bury themselves in the mud when the rivers in which they live begin to dry up. In these cases, however, the phenomenon receives another name: aestivation.
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batdiet
Caves and mines are the preferred hibernation shelter for Myotis sodaliss, a species of bat that inhabits high latitudes. With just a few grams of stored fat, they lose between 25% and 50% of their weight during this period of inactivity, which lasts five to six months.
endless siesta
Marmots (Marmota caligata) burrow in hollow trees, where they can sleep for nine months non-stop, feeding on the fat stored in their bodies. During this period, the pet’s heart beats only three or four times a minute, against the normal 90 to 130 beats.
freezing inertia
Arctic squirrels (Spermophilus undulatus) spend nearly half their lives in hibernation, although during these periods they wake up every three weeks to eat and defecate. The drop in temperature is radical: the squirrel’s body can reach minus 2°C.