Bear cubs leaving the den

Black bears are most active between April and November. By late November bears ready themselves for the long winter ahead. They spend the entire winter in a small den. Most commonly, bears dig out dens under the roots of an overturned tree or in a hillside, but sometimes they may select a sheltered rock cave, a hollow tree, hollow stump or a nook in a dense thicket, brushpile or conifer stand. Near urban areas, they may make their den in road culverts or foundations of abandoned buildings. The dens are usually just big enough to accommodate the bear itself, or a sow and her cubs. Typically, the dens are only about 4 feet wide and lined with leaves, moss and bark. Sometimes, part of the bear is exposed to the outside and becomes covered with snow.

Once snug in their dens, bears fall into torpor, or a deep sleep, and live off the body fat they, hopefully, accumulated during their autumn eating binge. This deep winter sleep, is not a state of true hibernation, because their body temperature, heartbeat, respiration and metabolism do not drop to the near-death state that occurs in true hibernating mammals, such as chipmunks, ground squirrels or woodchucks. Dormant bears can be easily awakened from their winter sleep. At times, bears walk around in winter. This may be due to a warm spell, or because they are under stress because they did not have an adequate supply of fat before they entered their winter dens.

Once bears emerge from their dens in mid-March, they wander considerable distances in search of food. Boars range the farthest. They make their home in a 15 to 27-square mile area. Sows generally restrict their home boundaries to a 5-square mile radius. They may not eat much for the first few days out of the den since they are just waking up. When they first emerge, their coats look healthy and shiny, but soon they begin to shed their winter coat and then their fur looks dull, worn and patchy.

If a sow gives birth during January or early February, her cubs will crawl out of the den with her when she awakens from her long winter's nap. She communicates with her cubs by voice signals including loud "woof-woof" and whimpering sounds.

Bears mate in June and early July when the sows become reproductively responsive for a few days.

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During the 225-day (7 1/2 months) gestation period, the fertilized egg floats free in the uterus of the sow for the first 5 to 6 months. Then, in late November or early December, the egg implants itself into the uterine wall and begins to grow. This phenomenon is called delayed implantation. The eggs grow in the female until January or early February when the cubs are born. Their mother is still in her winter sleep when they are born. Sometimes the mother gives birth to a single cub or triplets, but the norm is two cubs.

At birth, cubs are tiny: only 6 to 8 inches long, weighing only 7 to 12 ounces! Their eyes are closed and their fur is sparse. They grow slowly for the first few days but then develop more rapidly. They open their eyes in about 25 to 30 days. The cubs eventually leave their den in late March with the female.