Hibernation is a biological mechanism some animals use to conserve energy, enabling them to cope during food shortages. During hibernation, the stored body fat is used up at a slow rate. Hibernation is characterized by a state of inactivity and low metabolic functioning, low body temperature, and slow breathing.
There is some discussion as to whether bear actually hibernates. While a bear is denning, its heart rate, breathing rate, and metabolic rate do slow down. In addition, a bear’s body temperature is reduced. Bears can go for more than 100 days without eating, drinking, or passing waste.
But compared with true hibernators like ground squirrels, a bear’s metabolic rate is significantly less depressed and its body temperature is reduced a little.