Why do bears hibernate during winter period?

During the winter period, the food sources for the wild animals becomes very scarce. Bears bypass the winter in hibernation when their food supplies are very limited.

Bears however, are not true hibernators. Bears do what scientists call "winter lethargy," where they slowly lie dormant for a few months waking only a few times to eat. They do not defecate or urinate and their body temperature drops only about 10 degrees farenheit. The body temperature of bears stays normal. They burn an estimated 4,000 food calories a day. Their heart rate slows and their breathing is slowed as well. They do give birth during this period though and their bodies produce milk for the cub or cubs to drink. It is not technically hibernation but they do hibernate, kind-of. Yet they can exist for three months or more without food or water.

Compared with winter hibernation of animals such as woodchucks, squirrels, snakes, frogs, and so forth, the winter sleep of many bears is only a series of naps. This is because the slumber of bears in the winter may be disturbed, as their body temperature stays high and their breathing remains at the normal rate. Some will even awake on their own accord in the winter and prowl around for a few hours or days at a time.