William Hampton, age 13, of Twin Falls, Idaho, for his question:
WHY DO SOME ANIMALS HIBERNATE?
Hibernation is the sleeplike state that some animals go into during the winter. These animals hibernate to protect themselves against the cold and to reduce their need for food.
Scientists aren't sure what actually makes animals hibernate. Some believe the "trigger" that tells them to hibernate is in a part of the brain called the hypothalamus. Others say the "trigger" may be in the adrenal glands.
But something wisely tells certain animals it is time for winter. Hibernation helps to solve many of their problems. By reducing their need for food, they are able to live with much lower body temperatures. The breathing rate and the heartbeat become extremely slow. Animals in such a condition use little energy and need little food to stay alive.
True hibernation takes place only among warm blooded animals. True hibernators include redpolls and swifts among the birds and brown bats, ground squirrels, hamsters, marmots, hedgehogs and fat tailed lemurs.
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 seem to be able to arouse themselves when they want to, even in the coldest weather. In fact, true hibernators spend the winter taking a series of short naps rather than one long sleep.
Some bats hibernate every day and become active again every night.
Some cold blooded animals also hibernate. Included are some insects, frogs, lizards, snakes, toads and turtles. In winter, their body processes slow down so much that they almost stop. Unlike the true hibernators, however, they do not become active until warm weather arrives.
Do bears hibernate? Lots of people believe that they do. But they do not hibernate in the true sense. They sleep through the winter, but their body temperatures do not drop much below normal. Biologists call the winter sleep of the bear carnivorean lethargy.
Some hummingbirds spend their nights in hibernation and are active during the day. This kind of periodic hibernation is called diurnal hibernation.
Some insects, such as butterflies and moths, can achieve hibernation by changing from a caterpillar into a pupa or a protective cocoon.
A few kinds of animals become dormant in the summer when water is scarce. Biologists call this summer dormancy "estivation."
Some desert animals and animals living in or near water estivate. They include various kinds of snails, frogs, snakes and lizards.
A number of adult insects, including houseflies, mosquitoes, ladybugs and some moths and butterflies, also hibernate. They spend the winter in barns, cellars, attics, caves, holes in trees, burrows in the ground or other protected places.