Naomi Butchart, age 9, of Butte, Mont., for her question:
WHY DO SOME ANIMALS HIBERNATE?
Hibernation is a sleeplike state that some animals go into during winter. Animals that hibernate do so to protect themselves against the cold and to reduce their need for food.
In cold weather, animals lose heat to their surroundings more quickly than in warm weather. If certain animals stayed active, they would need large amounts of food to keep their body temperatures up. But food is harder to find in winter than in any other season. Hibernation solves this winter problem.
True hibernation takes place only among warm blooded animals. True hibernators include redpolls and swifts among the birds; and brown bats, ground squirrels, hamsters, hedgehogs, marmots and fat tailed lemurs among the mammals.
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 and wake up 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.
Many people think that bears hibernate, but they do not hibernate in the true sense. They sleep through the winter, but their body temperature does not drop much below normal. Biologists use the term "carniborean lethargy" to describe this winter sleep of bears.
Some bats hibernate every day and become active again every night. Some hummingbirds spend their nights in hibernation. This kind of periodic hibernation is called diurnal hibernation.
Animals that hibernate generally eat large amounts of food in the fail. The food is stored as fat in their bodies and used as food during hibernation. A hibernating animal's body temperature is much lower than normal and its rate of breathing and its heartbeat are extremely slow.
Scientists are still trying to find out what makes animals hibernate. Some believe that the "trigger" that tells the animals to hibernate is in a part of the brain called the hypothalamus. Others believe the "trigger" may be in the adrenal glands.
Hibernation is common among cold blooded animals. Insects such as butterflies and moths can achieve it by changing from a caterpillar into a pupa or protective cocoon.
Many highly developed cold blooded animals such as frogs, lizards, snakes, toads and turtles simply cool down as the air around them cools down. In winter, their body processes almost cease. Unlike true hibernators, they do not become active until warm weather arrives.
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.