Missy McAninch, 7, of Des Moines, Iowa, for her question:
DO BEARS HIBERNATE IN WINTER?
Did you know that some animals become dormant in the summer when water is scarce? Biologists call this summer period of dormancy " estivation. " Desert animals and some living in or near the water estivate each summer. Included here are various kinds of lizards, snails, frogs and snakes. You don't hear about this type of summer hibernation too often.
Hibernation is a sleep like state into which some animals enter each winter. The animals who hibernate want to protect themselves against the cold and also reduce their own need for food.
When cold weather comes, many animals lose heat to their surroundings more quickly than they do during warm weather. If they were to stay active, they would have to eat large amounts of food to keep their body temperatures up. But since food is often hard to find during the winter months, the wonders of nature have made it possible for some animals to take long naps and thereby avoid the food finding problem.
Most people believe that bears hibernate. They do not, in the true sense. Bears do indeed sleep through much of the winter, but their body temperatures do not drop much below normal, as is the case with hibernating animals. The correct way to describe the bear's winter sleep is carnivorean lethargy.
Animals that hibernate eat large amounts of food in the fall, and they store up much fat. During the winter months, then, their bodies use the stored food. A hibernating animal's body temperature drops to a rate far below normal and his breathing and heart rates become extremely slow. When the animal is in this state, he needs practically no food to stay alive.
Some scientists believe that the trigger responsible for telling the animal to start his hibernation routine is in the part of the brain called the hypothalamus. Others say it may be in the adrenal glands.
True hibernation takes place only among warm blooded animals such as the brown bats, ground squirrels, hamsters and hedgehogs. True hibernators do not have to wait until the warm weather arrives before they become active. They can arouse themselves when they want to and actually take a series of short naps all winter long rather than one long sleep.
Hibernation is common in some cold blooded animals such as frogs, snakes and turtles. Unlike true hibernators, they do not become active until warm weather arrives.
Some bats hibernate every day and become active again every night. Some types of hummingbirds spend their nights in hibernation. This type of periodic hibernation is called diurnal hibernation.
Some insects such as butterflies and moths can achieve a type of hibernation by changing from a caterpillar into a protective cocoon.