why do animal hibernate?

Hibernation is the condition in which the animals go dormant during winters by lowering their metabolic activities. This can be seen in reptiles, fish and amphibians. To combat the problem of food shortage during hibernation, these animals eat a lot of food and store in the form of excess fat. This is supplied in the form of energy while sleeping.

During hibernation, an animal's body temperature, heart rate, breathing, and other metabolic activities slow down significantly in order to conserve energy. While resources are scarce, hibernation allows animals like bears, chipmunks, and bats to use their stored energy much more slowly. Black bears, hummingbirds and squirrels hibernate in the winter because a long, chilly season of little food and warmth is no picnic for these animals. ... Hibernation is a process of lowering an animals body temperature and slowing down its heartbeat into order to conserve energy during times of scarcity and stress.