What Hibernation Means for Black Bears
Most animals have a tough time surviving the winter. In the Interior of Alaska, food is limited, arctic winds howl, snow falls, and severely cold temperatures persist. Some animals have adapted to hibernation as a means of survival throughout the winter. Black bears have the highest survival rate of any hibernating animal during a typical winter. To save energy and slow their metabolism, black bears enter a state known as hibernation. People used to believe that bears spent the winter in their dens and then emerged refreshed in the spring.Contrary to popular belief, hibernation is not characterized by one extended stretch of sleep but rather by shorter stretches of sleep interspersed with more active intervals. Winter is the period of the year when people sleep the longest, as opposed to the beginning or conclusion of the season. Black bears, in preparation for the long winter, gorge themselves from the middle of summer until the end of fall, consuming as much as 20,000 calories in a single day. Blueberries, which are abundant here in the Interior and are rich in carbohydrates, account for a sizable amount of this calorie intake. As omnivores, bears will also consume flesh such as ground squirrels, carrion, and whatever else they may find. A black bear’s pelt’s insulating properties are increased by more than twice as much at the end of the fall as they were at the beginning.
The bear’s metabolic rate, including its heart rate, breathing rate, and core body temperature, drops when it enters hibernation. Contrary to popular belief, bears do not maintain abnormally low body temperatures. They enter hibernation at a temperature of 88 degrees and emerge at 100 degrees Fahrenheit. Black bears maintain a body temperature that permits them to become completely attentive whenever aroused, maybe so that they can protect themselves from predators and other hazards without using too much energy. It is estimated that black bears burn off over 4,000 calories per day when hibernating, leading to a weight drop of around 20% by spring.