How Do Black Bears Hibernate?

When and Why Black Bears Hibernate

Black bears hibernate during winter months when food sources are low. Seventy-five percent of their diet consists of vegetation that becomes sparse in cold winter months.

Black bears don't actually go into a true hibernation. What they go into is called a torpor. The difference is that an animal in a torpor will wake up if in danger, whereas an animal in hibernation will not. Since black bears do wake up when in danger, it is not a good idea to bother a black bear in torpor.

Black bears do not always go into torpor. Black bears only go into torpor when they live in areas where the weather gets cold and food sources become low. A black bear can go into torpor for as long as 6 months at a time.

Preparation for Torpor

In preparation for going into torpor, a black bear will eat large amounts of food to gain body fat. A black bear can gain 30 pounds a week eating mass amounts of food.

Torpor

When the weather starts to get cold and food supplies begin to dwindle, the black bear goes into its den to go into torpor. The black bear does not eat or drink for up to 6 months during torpor. The black bear is able to survive due to several factors. The black bear's body uses its stored fat as a food source. Its heart rate and metabolism drops to use less energy. The black bear rarely urinates or defecates when in torpor. It recycles its waste products to maximize nutrition and hydration. Muscle tone is kept due to the bear exercising in its sleep by shivering several times a day, which contracts all the muscles of the body. The black bear is able to keep warm during torpor by sleeping curled up in a small den and relying on warmth from a thick fur coat and a lot of body fat.

Awakening from Torpor

Male black bears and female black bears without cubs often wake up several times during winter months to go out and briefly hunt or forage for food before returning to their den to torpor again. Female black bears wake up briefly from torpor to give birth to their cubs. While in torpor, the mother bear produces breast milk to nourish the baby cub. The baby cub nurses and puts on weight and keeps warm by cuddling with its mother while its mother sleeps.

When winter is over, the black bears leave their dens to again eat and gain body fat in preparation for the next winter.

Resources

• American Bear
• Bear Aware