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Behavior and Psychology
the sleeplike state that some animals go into during the winter
Animals that hibernate protect themselves against the cold and reduce their need for food. In cold weather, animals lose heat to their surroundings more quickly than in warm weather. If they stayed active, they would need large quantities of food to keep their body temperature up, but food is harder to find in winter. Hibernation solves this problem.
Animals that hibernate generally eat large amounts of food in the fall. The food is stored as fat in their bodies, and that fat is what sustains them during hibernation. A hibernating animal's body temperature also drops far lower than normal, and its rate of breathing and its heart beat are extremely slow. Animals in such a condition need much less energy and, therefore, far less food to stay alive.
The exact mechanism that triggers hibernation is unknown. Some scientists believe the trigger lies in a region of the brain called the hypothalamus, which also controls heartbeat, respiration, and other involuntary nervous and muscular systems. Other scientists believe the trigger is in the adrenal glands, which control the production of hormones that regulate salt and sugar balances in the body.
True Hibernation takes place only among warm-blooded animals. In true hibernation, the animal's body temperature falls close to the temperature of the surrounding air. True hibernators do not have to wait until the weather gets warm to become active, they can wake themselves up when they want to, even in the coldest weather. In fact, most true hibernators spend the winter taking a series of short naps rather than one long sleep, taking advantage of food stores in between naps. When asleep, however, a true hibernator cannot be awakened, no matter how much it is handled. If their stored food or supply of body fat is exhausted before winter is over, they simply emerge from hibernation and become active again. True hibernators include brown bats, ground squirrels, hamsters, hedgehogs, marmots, and fat-tailed lemurs among the mammals; redpolls and swifts among the birds.
left: dormice (hedgehogs) hibernating
Hibernation is also common among cold-blooded animals, especially reptiles. Many frogs, lizards, snakes, toads, and turtles simply cool down as the air around them cools down. In winter, their body processes almost cease. They take no food of any kind while hibernating, they use first the sugar and then the fat reserves in their bodies to supply the small amount of energy needed to maintain life. Many snakes come together in huge masses for hibernation, especially in regions where winter temperatures drop so low that they could be fatal; the combined body heat of all the individuals in the mass keeps the air temperature inside the den just high enough to keep the snakes alive. Unlike true hibernators, they do not become active again until warm weather arrives.
right: garter snakes hibernating
Many people believe that bears hibernate, but they do not hibernate in the true sense. Although they do sleep through the winter, their body temperature does not drop much below normal. Scientists use the term carnivorean lethargy to describe this type of winter sleep. Some bats hibernate every day and become active again every night, and some hummingbirds are active during the day and hibernate at night. This kind of periodic hibernation is called diurnal hibernation. A few kinds of animals, including several varieties of snails, frogs, snakes, and lizards, become dormant in the summer when water is scarce. Biologists call this summer dormancy estivation.
left: mother black bear 'hibernating' while her cub feeds
This page was last updated on 01/20/2017.