Joe Massey, age 12, of Hattesburg, Miss., for his question:
WHAT HAPPENS DURING AN ANIMAL'S HIBERNATION?
Hibernation is a word that comes from the Latin word meaning "to pass the winter." Hibernation is a state of very deep sleep into which some animals fall as a way of getting through the cold months.
Various animals go through different degrees of hiberation. The very deepest form is almost like death. While an animal is in this state, its bodily functions almost stop. The heartbeat slows a great deal and the temperature of the body drops until it is just barely above that of the surrounding air.
With the lowering of body temperature there is also a drop in the rate of breathing. The animal needs less oxygen because the fuel stored as fat in the body is burned more slowly.
Often an animal will lose 40 percent of its body weight during a long period of hibernation.
The European hedgehog, the dormouse and the woodchuck burrow beneath the frost line and go into very deep states of hibernation.
Many insects spend the winter sleeping under pieces of bark. Snakes crawl into holes or cracks in rocks and stay dormant throughout the winter, often curling together in groups to share body heat. Frogs and turtles bury themselves in pond mud.
Some insects secrete a chemical called glycerol that acts much the way an antifreeze acts: It allows the insects to tolerate cold temperatures.
Some bears and rodents enter deep sleep that somewhat decreases the body's metabolic rate, but these are not true hibernators. They may awaken on warmer days of the winter and feed. Bears also sometimes give birth during their winter slow down.
Other animals, including some birds, go into daily periods of reduced metabolism. Birds cannot enter into a state of prolonged hibernation since these animals do not have enough insulation to survive long winters.
Certain chemical changes within the bodies of some animals seem to play an important part in determining their schedules of hibernation. The ground squirrel, for example, will go underground at a certain time, reduce its body temperature drastically within a few hours and then become dormant, even though the temperature outside may still be well above the freezing mark.
The ground squirrel then will very suddenly burst out of hibernation at winter's end.
The squirrel during hibernation has a metabolic rate that is about 10 percent below normal. Its heart will beat between 10 and 20 times per minute instead of the normal 200 to 300. And the squirrel during hibernation will breathe only four times per minute instead of the usual 100 to 200.
Some animals that live in regions with extreme summer heat may enter into a state that is similar to the winter sleep of hibernation. The summer sleep is called estivation.