Brad Embry, age 9, of Casper, Wyo., for his question:
WHICH ANIMALS HIBERNATE?
Hibernation is a sleeplike state that some animals go into during the winter. The animals hibernate to protect themselves against the cold and to reduce their need for food.
True hibernation takes place only among warm blooded animals. True hibernators include swifts and redpolls among the birds and brown bats, ground squirrels, hamsters, hedgehogs, marmots and fat tailed lemars 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 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.
Hibernation is also 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.
Do bears hibernate? Lots of people think so, but actually they do not hibernate in the true sense. Bears sleep through the winter, but their body temperature does not drop much below normal.
Biologists call the winter sleep of bears "carnivorean lethargy."
Some bats hibernate every day and become active again every night. And some hummingbirds spend their nights in hibernation. Periodic hibernation of this type is called diurnal hibernation.
Some types of snails, frogs, snakes and lizards become dormant in summer when water is scarce.
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 heartbeat are extremely slow. Animals in such a condition use little energy and need little food to stay alive.
Scientists aren't sure 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 hypothalamous. Others believe that the "trigger" may be in the adrenal glands.
Biologists call the summer dormancy "estivation."
Some desert animals and animals living in or near water estivate.
They include lots of the animals that cannot stand the long, hot summer months on a desert.