Food is scarce, icy winds howl, snow falls, and bitter cold temperatures presist, at least here in the Interior. For some mammals the strategy evolved for coping with this harsh season is hibernation. Hibernation is the mechanism that black bears use to conserve energy and reduce their internal fires of metabolism. It was once believed that bears slept through the winter in cozy dens and emerged in the spring fully charged. However, far from being a long, uninterrupted sleep, hibernation consists of periods of sleep punctuated by periods of arousal.
Sleep time is long during the dead of winter but is shorter at the beginning and end of the season.
To prepare for this long season black bears feed ravenously from midsummer through the end of autumn, taking in up to 20,000 calories in a day. Here in the Interior, carbohydrate-laden blueberries contribute a large portion to this caloric intake. Bears are omnivores and will eat meat too, including ground squirrels and carrion. By the end of autumn, a black bear will have added about 4 or 5 inches of body fat and more than doubled the insulation provided by its pelt. Over the course of a hibernating season it is thought that black bears use approximately 4,000 calories a day, which results in a weight loss of about 20 percent of it body weight by spring.