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.
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
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 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 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
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
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
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?
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
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."