Sunday, November 29, 2009

A Year in the Life of a Black Bear

JANUARY: Birth of cubs begin in dens. Mothers lick the blind and nearly hairless cubs clean, and keeps them warm. After giving birth, the mother resumes her deep sleep, waking now and then to tend to the cubs' needs. She eats their feces and moves into position so cubs can easily nurse. Cubs do not hibernate. They snuggle under their mother, who makes a special cove for them under her chest by folding her front paws and drawing her hind legs alongside her body. The cubs aren't strong enough to wander away. They just want to stay with their warm mother.

FEBRUARY: Hibernation, birth and care of cubs continues. A hibernating bear sleeps in a curled-up position so that its crown is against the den floor and its nose is near its tail. This position minimizes a bear's surface area and reduces heat loss from the areas with thinnest fur (muzzle, legs, and underside).

MARCH: Hibernation and care of cubs continues. In adult males, levels of the hormone testosterone begin to rise.

APRIL: Most bears come out of their dens. Adult males are first to emerge from hibernation. Mothers with cubs come last. Food is very scarce. Adult males begin to roam. Most other bears remain lethargic and slow-moving, eating mainly aspen catkins and willow catkins. All but baby bears have been losing weight.

MAY: The forest habitat begins to green up. Lethargy ends. Bears eat sprouting grass, emerging herbs and young tree leaves. Cubs taste what their mother eats, but swallow little except milk. Lactating (nursing) mothers are losing weight. Other bears are slowly gaining weight.

JUNE: Green plants become mature and bears don't prefer them as much, but ant pupae become abundant. Bears switch to a favorite diet of ant pupae. Bears now begin to fatten up for winter as carbohydrate-rich berries get ripe. Mating season begins. Males roam widely to find females without cubs. Cubs begin eating solid food. Lactating mothers stop losing weight, and others are gaining weight slowly.

JULY: Cherries, blueberries, serviceberries, wild sarsaparilla berries and raspberries begin ripening and become the major bear foods. All bears gain weight rapidly if their natural foods are in good supply. Mating season ends towards the end of the month.

AUGUST: Viburnum berries, dogwood berries, wild plums, hawthorn berries, mountain-ash berries, and hazelnuts ripen. Bears switch to hazelnuts if the nuts are abundant, otherwise continue feeding on berries. They continue to gain weight.

SEPTEMBER: Acorns ripen. Berries and hazelnuts become scarce. Bears who are eating acorns continue to feed and fatten. Other bears begin losing weight from expending energy to look for digestible food, or perhaps traveling back to their home range to hibernate. Nursing ends. Lethargy begins. The bear's fur more than doubles in insulative value during the fall in preparation for hibernation. Some bears will enter dens in September, especially as their digestible foods disappear.

OCTOBER: Most bears enter dens. Bears now spend some of their precious energy by preparing a different den each year, even when their previous dens would work. They may choose burrows, caves, rock crevices, hollow trees, or depressions under fallen trees or brush piles. These locations provide insulation and also protection from hunters and predators. The entrances are just large enough for the bear to squeeze through, opening into a chamber about 2.5 to 5 feet wide and 2 to 3 feet high. For extra insulation, bears sleep on a nest of leaves, grass and other material that they rake into the den. These nests also help keep the cubs off the cold ground. Hibernation is light.

NOVEMBER: Denning continues for bears that are still out. Hibernation deepens and 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.

DECEMBER: Hibernation continues. Last year's cubs sleep through their first birthday, cozy in the den nest with their warm mother.

For more black bear photos, information and video clips, visit the black bears section of my Web site.