Bears are carnivoran mammals of the family Ursidae. They are classified as caniforms, or doglike carnivorans. Although only eight species of bears are extant, they are widespread, appearing in a wide variety of habitats throughout the Northern Hemisphere and partially in the Southern Hemisphere. Bears are found on the continents of North America, South America, Europe, and Asia.
Common characteristics of modern bears include large bodies with stocky legs, long snouts, small rounded ears, shaggy hair, plantigrade paws with five nonretractile claws, and short tails.
While the polar bear is mostly carnivorous, and the giant panda feeds almost entirely on bamboo, the remaining six species are omnivorous with varied diets.
With the exception of courting individuals and mothers with their young, bears are typically solitary animals. They may be diurnal or nocturnal and have an excellent sense of smell. Despite their heavy build and awkward gait, they are adept runners, climbers, and swimmers. Bears use shelters, such as caves and logs, as their dens; most species occupy their dens during the winter for a long period of hibernation, up to 100 days.
Bears have been hunted since prehistoric times for their meat and fur; they have been used for bear-baiting and other forms of entertainment, such as being made to dance. With their powerful physical presence, they play a prominent role in the arts, mythology, and other cultural aspects of various human societies. In modern times, bears have come under pressure through encroachment on their habitats and illegal trade in bear parts, including the Asian bile bear market. The IUCN lists six bear species as vulnerable or endangered, and even least concern species, such as the brown bear, are at risk of extirpation in certain countries. The poaching and international trade of these most threatened populations are prohibited, but still ongoing.
The bear family includes the most massive extant terrestrial members of the order Carnivorans. The polar bear is considered to be the largest extant species, with adult males weighing 350–700 kg (772–1,543 lb) and measuring 2.4–3 metres (7 ft 10 in–9 ft 10 in) in total length. The smallest species is the sun bear, which ranges 25–65 kg (55–143 lb) in weight and 100–140 cm (39–55 in) in length. Prehistoric North and South American short-faced bears were the largest species known to have lived.
The latter estimated to have weighed 1,600 kg (3,500 lb) and stood 3.4 m (11 ft) tall. Body weight varies throughout the year in bears of temperate and arctic climates, as they build up fat reserves in the summer and autumn and lose weight during the winter.
Most bears are opportunistic omnivores and consume more plant than animal matter. They eat anything from leaves, roots, and berries to insects, carrion, fresh meat, and fish, and have digestive systems and teeth adapted to such a diet. At the extremes are the almost entirely herbivorous giant panda and the mostly carnivorous polar bear. However, all bears feed on any food source that becomes seasonally available. For example, Asiatic black bears in Taiwan consume large numbers of acorns when these are most common, and switch to ungulates at other times of the year.
When foraging for plants, bears choose to eat them at the stage when they are at their most nutritious and digestible, typically avoiding older grasses, sedges and leaves.Hence, in more northern temperate areas, browsing and grazing is more common early in spring and later becomes more restricted. Knowing when plants are ripe for eating is a learned behaviour. Berries may be foraged in bushes or at the tops of trees, and bears try to maximize the number of berries consumed versus foliage. In autumn, some bear species forage large amounts of naturally fermented fruits, which affects their behavior.
Smaller bears climb trees to obtain mast (edible reproductive parts, such as acorns). Such masts can be very important to the diets of these species, and mast failures may result in long-range movements by bears looking for alternative food sources. Brown bears, with their powerful digging abilities, commonly eat roots. The panda’s diet is over 99% bamboo, of 30 different species. Its strong jaws are adapted for crushing the tough stems of these plants, though they prefer to eat the more nutritious leaves. Bromeliads can make up to 50% of the diet of the spectacled bear, which also has strong jaws to bite them open.
Brown bear feeding on infrequent, but predictable, salmon migrations in Alaska
The sloth bear, though not as specialised as polar bears and the panda, has lost several front teeth usually seen in bears, and developed a long, suctioning tongue to feed on the ants, termites, and other burrowing insects they favour. At certain times of the year, these insects can make up 90% of their diets.
Some species may raid the nests of wasps and bees for the honey and immature insects, in spite of stinging from the adults. Sun bears use their long tongues to lick up both insects and honey. Fish are an important source of food for some species, and brown bears in particular gather in large numbers at salmon runs.
Typically, a bear plunges into the water and seizes a fish with its jaws or front paws. The preferred parts to eat are the brain and eggs. Small burrowing mammals like rodents may be dug out and eaten.
The brown bear and both species of black bears sometimes take large ungulates, such as deer and bovids, mostly the young and weak.These animals may be taken by a short rush and ambush, though hiding young may be stiffed out and pounced on.The polar bear mainly preys on seals, stalking them from the ice or breaking into their dens. They primarily eat the highly digestible blubber.
Large mammalian prey is typically killed by a bite to the head or neck, or (in the case of young) simply pinned down and mauled. Predatory behaviour in bears is typically taught to the young by the mother.
Bears are prolific scavengers and kleptoparasites, stealing food caches from rodents, and carcasses from other predators. For hibernating species, weight gain is important as it provides nourishment during winter dormancy. A brown bear can eat 41 kg (90 lb) of food and gain 2–3 kg (4.4–6.6 lb) of fat a day prior to entering its den.