Greg Burleson, age 11, of Phoenix, Ariz., for his question:

DOES HIBERNATION DIFFER FROM ESTIVATION?

The only important difference is related to the seasons. Animals that sleep through the cold winter months are said to hibernate. Those that go into a state of retirement to escape periods of heat and drought are said to estivate. In both cases, the body processes slow down and the animal sinks into a state of dormancy, which is deeper than ordinary sleep.

Both hibernation and estivation help an animal to survive through a spell of severe weather. In our temperate zones, many warm blooded and cold blooded animals hibernate to cope with the winter. Farther south, frogs and snails, lizards and even fishes estivate to avoid hot, dry spells. Snakes may hibernate in the North and estivate in the South. In both cases, the body processes slow down and the animals sink into a state of dormancy.