How do hibernating mammals survive for months with little food?

Hibernation is a survival strategy used by some mammals during cold or food-poor seasons. During this state, body temperature can drop dramatically, and the heart rate and breathing slow down. The animal’s metabolism also falls, reducing the need for calories. Fat reserves provide the energy needed through the winter or drought period. Species such as ground squirrels and bears show different versions of this strategy, with bears entering a lighter form of dormancy than true hibernators.