Black Bear Biology

Bears crosses a surging river
Bears are good swimmers and will range widely in search of food.

NPS Photo


Before Europeans settled here, the grizzly bear (Ursus arctos) called these parks home. Today this symbol of California is extinct throughout the state; in fact the last known grizzly was killed quite close to Sequoia National Park in 1922. The black bear (Ursus americanus), however, still ranges from the foothills to the high country. Much smaller than the grizzly, male black bears rarely reach 400 pounds (180 kg) here; females may grow to 250 (112.5 kg). Despite their name, black bears can be brown, cinnamon or blonde.

Most black bears spend the winter in dens, typically in the base of a rotted fir tree. Bear cubs are born while their mothers are denning. Although they are tiny, often weighing less than 1/2 pound (.23 kg) at birth, they grow rapidly in their protected, womb-like dens. By the time the one, two or three cubs leave the den with their mother in April, they have gained some 5 pounds (2.25 kg). An adult bear, however, may have lost up to 50% of its weight during denning!

They emerge to seek sustenance from grasses and tender herbs, and whatever carrion they can find. They rely on meadow plants until berries begin to ripen. Bears are members of the order Carnivora, like their closest relatives, the dogs and raccoons, but contrary to what the name suggests, black bears eat relatively little meat. Occasionally bears do kill deer or eat the carrion left over by other predators such as cougars.

Later in the season they tear apart logs for carpenter ants and dig up yellowjacket nests. Autumn's acorns are critical to the bears' efforts to gain weight needed to survive the coming winter. Sometimes in the fall, bears are spotted shaking down acorns from the oak trees. If the winter is warm and the acorn crop plentiful, some bears may remain active, descending from the conifer forest to the oaks below.

Black bears are not usually aggressive, and often escape danger by climbing a tree. But some bears learn to associate people with food, and may lose their instinctive fear of humans. This begins a cycle of unnatural behavior that is dangerous to both bears and humans.

Yearlings, in their first season away from their mother, know the least about finding wild foods and are most vulnerable. They may be the first to become campground bears and the most difficult to return to a natural diet.

These intelligent animals identify food not only by smell, but by appearance -- bags, cans, coolers, and even cars become associated with food. Once one ice chest or car yields food, bears don't hesitate to pry open others to check for our protein-rich, high-calorie food. Because human foods are usually such concentrated sources of protein and calories, bears will select them so long as they take less effort to obtain than berries and acorns. Remember to keep bears wild by never letting a bear get your food and food-related items!!

Last updated: September 17, 2015

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