Hibernation is light. The heart rate slows to as low as 8 beats per minute. Breathing slows to one breath in 45 seconds. Fertilized eggs now implant in the uterus of female bears that became pregnant in June. Last year's cubs sleep through their first birthday, cozy in the den nest with their warm mother.
Hibernation is the way bears conserve energy through the season when their food supply disappears.
They sleep for months without eating, drinking, urinating, or defecating. Hibernators with lower body temperatures, such as chipmunks, woodchucks, and ground squirrels, cannot do this. These other mammals must awaken every few days, raise their temperatures to over 94 degrees F, move around in their burrows, and urinate. Some of them must also eat and defecate. This, in turn, means that a black bear can react to danger faster than most other hibernators whose body temperatures may be less than 40 degrees.