A Year in the Life of a Black Bear

NOTE: This description is for black bears in cold northern climates. Bears in warmer areas have a slightly different year. See Journey North's Facts About Black Bears.

What Happens Each Month?
JANUARY: Cubs are born in dens. Mother licks the blind and nearly hairless cubs clean, and keeps them warm. After giving birth, the mother tends to the cubs' needs. Snug in the den she eats their feces and moves into position so cubs can easily nurse. Cubs 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 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: Snow usually melts and 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. It's mating season. 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.

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 enter dens in September, especially as their digestible foods disappear.

Photo courtesy of North American Bear Center

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: Hibernation deepens. 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.

What is Hibernation?

Hibernation is the way bears conserve energy through the season when their food supply disappears. Dr. Lynn Rogers explains: "New knowledge of hibernation processes has led biologists to redefine mammalian hibernation as simply a specialized seasonal reduction of metabolism concurrent with the environmental pressures of food unavailability and low environmental temperatures."

"Black bears, once considered not true hibernators because of their high body temperature in winter, are now known to be highly efficient hibernators. They sleep for months without eating, drinking, urinating, or defecating. Hibernators with lower body temperatures, such as chipmunks, woodchucks, and ground squirrels, cannot do this. These other mammals must awaken every few days, raise their temperatures to over 94 degrees F, move around in their burrows, and urinate. Some of them must also eat and defecate. Black bears, however, develop far more insulative pelts and have lower surface-to-mass ratios than the smaller hibernators. As a result, the bears' body heat is lost very slowly, enabling them to cut their metabolic rate in half and still make it through winter, maintaining temperatures above 88 degrees--within 12 degrees of their normal summer temperature. This, in turn, means that a black bear can react to danger faster than most other hibernators whose body temperatures may be less than 40 degrees."

Summer With Blackheart and Her Cubs
In January 2001, Dr. Lynn Rogers told Journey North about a good summer for one of his study bears, whom he calls Blackheart:
"I have a neat bear in her den near here with two big cubs that became friends with me last year. The bear is Blackheart. She had a good year last year. The good times started with an outbreak of tent caterpillars in June. She liked them more than any other food. She and her little cubs went wherever there were a lot of caterpillars and climbed the aspen and birch trees to get them. When the caterpillars made cocoons, the bears turned over rocks and tore open logs to get ant pupae. In July, berries ripened. Their favorites were juneberries, cherries, wild sarsaparilla berries, and blueberries. In August, a great food--hazelnuts--ripened and was abundant. The cubs grew like mad. There aren't many oaks in this north country, so bears can't eat acorns here like they do farther south. When the nuts and berries become scarce in September, bears here look for hornet nests to tear apart and eat the hornet larvae. They don't like getting stung by the adult hornets, but they keep wiping the hornets off their noses and keep at the hornet nest until they find the brood comb with the larvae. Then they run off, shake the hornets out of their fur, and look for the next nest.

"Blackheart entered her den in October, but hikers disturbed her in November and she took her cubs to a different den."