Why do animals sleep for the winter?

They have to sleep(hibernate) in order to survive the winter. Why? well, the food that these animals need to survive will scarce on winter; basically the food is either not enough or just gone with the cold temperatures. These animals Hibernate , some all winter and other part of the winter. Hibernate is a very deep sleep. The animal's body temperatures drops,and their heartbeat and breathing slow down. The body uses very little energy. These animals prepare themselves in the Fall to be ready for hibernation on Winter. They eat extra food and stores it as body fat to use this fat for energy while hibernating. Examples: Bears, skunks, chipmunks and some bats...