Jason Ferguson, age 10, of Kalispell, Mont., for his question:
WHY DO BEARS HIBERNATE?
Hibernation is the sleeplike state that some animals go into during the winter. They hibernate to protect themselves against the cold and also to reduce their need for food. Many people believe that bears hibernate, but they do not hibernate in the true sense.
Bears sleep through the winter, but their body temperature does not drop much below normal. Biologists use the term "carnivorean lethargy" to describe this winter sleep of bears.
Some bats hibernate every day and become active again every night. hibernation. Some hummingbirds spend their nights in hibernation. These kinds of periodic hibernation are called, respectively, nocturnal (night) or diurnal (daytime) hibernation.
True hibernation takes place only among warm blooded animals. True hibernators include redpoils 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 fails 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 or wake themselves 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.
A type of hibernation is common among cold blooded animals. Insects such as moths and butterflies 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.
Animals that hibernate do so to protect themselves and also reduce their own need for food. In cold weather, animals lose heat to their surrounds more quickly than in warm weather. If they stayed active, they would need large amounts of food to keep their body temperature up. But food is harder to find in winter than in any other season. Hibernation solves this winter problem.
Animals that hibernate generally eat large amounts of food in the fall. 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 heart beat are extremely slow. Animals in such a condition use little energy and need little food to stay alive.
Scientists are trying to find out what makes some 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.