A long winter sleep of animals is called

Some animals hibernate for part or all of the winter. The animal's body temperature drops, while its heartbeat and breathing slow down using very little energy.

In the autumn season, these animals eat extra food and store it as body fat. This fat is later used for energy while hibernating. Some also store food like nuts or acorns to eat later in the winter. 

Bears, skunks, chipmunks, and some bats hibernate.