bears

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Bear, any of several species of a large carnivorous mammal, related to giant pandas, lesser pandas, raccoons, and dogs. A bear is distinguished from members of the other carnivore families by its heavy body; short tail; short, rounded ears; and plantigrade feet (both heel and sole touch the ground, as in humans) with five clawed toes. It also lacks the shearing teeth common to most carnivores; the crushing molars of a bear are believed to be an adaptation for a plant diet. Although all bears are classified as carnivores, the different species vary widely in their feeding habits. For example, the polar bear feeds almost exclusively on seals and other animals, but it may also graze on vegetation; the grizzly eats grasses, herbs, berries, and nuts as well as living or dead fish and other animals.

II HABITATS AND SPECIES

Bears occupy a wide range of habitats, but human encroachment has squeezed them primarily into mountain, forest, and arctic wilderness areas. These animals occur on all continents except Africa, Antarctica, and Australia. (Crowther's bear of North Africa's Atlas Mountains is believed to be extinct.)

The Arctic coast areas of northern countries are the home of the polar bear, the only marine bear. It is also known as the ice bear in some languages because of its preference for hunting on sea ice. The bottoms of its paws are furred for traction.

The Brown bear has lived successfully in the plains and forests of the North Temperate Zone. While its range is dangerously reduced in the lower United States, this bear survives and is hunted in Alaska and western Canada. The largest brown bear, the Kodiak of Alaska, weighs up to 780 kg (1700 lb) and is as much as 3 m (10 ft) tall. The closely related grizzly is named for its white- or silver-tipped fur. Remnant populations of European brown bears live in scattered mountain regions on that continent.

The American black bear varies in color from pure white (Kermode's bear of the coast of British Columbia) to the pure black, bluish, blonde, and reddish-brown (cinnamon) found in western North America.

The Asiatic black bear, also known as the moon bear, is found in mountain ranges of Southeast Asia. It has a black, shaggy coat with a pronounced white V shape on its chest. The upper lip is usually white.

The Malayan sun bear, found from China to Indochina, has a short black coat with an irregular white or yellow mark on the chest and a light muzzle. Like all but the largest bears, it is a tree climber.

Ranging through the tropical forests of India and Sri Lanka is the sloth bear, named for its usually slow movements. This bear has a long snout and mobile lips, which are used to suck up termites. The long, shaggy black coat commonly has a white mark on the chest.

The spectacled bear found in the Andes mountains and Ecuador, is named for the yellow facial markings on its shaggy black coat. The muzzle, throat, and chest are usually cream colored.

III BEHAVIOR AND LIFE CYCLE

Bears have a life span of 15 to more than 30 years in the wild. All species possess a keen sense of smell, which is much more developed than their hearing or eyesight. Recent studies suggest that black, brown, and polar bears are true hibernators (see hibernation), going without food or elimination of metabolic wastes for three to five months (and as long as seven months in northern Alaska). Compared to rodent hibernators, however, the body temperature of a hibernating bear remains higher, although the heart rate drops from 45 to only 10 beats per minute. In warm winter periods, a hibernating bear may revive and leave its den for brief periods.

A female bear typically gives birth to one to four cubs six to nine months after mating. The longer gestation results from delayed implantation of the fertilized egg to time the birth to coincide with the beginning of hibernation. The vulnerable newborns receive additional warmth and protection sharing close quarters with their mother during hibernation. The cubs are born very small-about 300 g (about 10 oz) among black bears-and require maternal care for two or three years. Even after a yearling bear starts to feed independently, it needs protection from older males, which will kill and eat cubs. Females have evolved methods to protect their young by chasing them up trees or by attacking other animals that approach too closely; a bear can run rapidly when necessary. This maternal instinct, when met with increased human intrusions into wilderness areas, occasionally leads to human maulings.

Another cause of conflict is competition for food, which leads bears to discover and exploit food grown by humans. In agricultural areas, livestock, beehives, stored grain and other crops are raided. Bears in public parks develop new feeding patterns as begging or scavenging through human trash replaces natural hunting skills. Some bears learn how to release cable-suspended food, break tree limbs, and open locked cars. When humans are perceived as the source of food, bears may attack if they are denied the food they have come to rely upon.

Learning plays a large role in a cub's ability to obtain food. Its relatively slow development and prolonged tie with its mother enable a cub to observe and replicate the mother's skills. Even the predominantly herbivorous spectacled bear must learn when and where to find the most nutritious parts of plants in each season. Omnivorous black and brown bears survive by remembering from year to year where and when to return to salmon runs, rich patches of ripe berries, and other concentrated foods important for energy reserves for hibernation.

Communication among bears depends on a signaling system that is effective over long distances, because a bear may travel as much as 150 km (90 mi) to exploit the changing seasonal foods in its home range. Bears appear to sense and avoid each other at a distance. Within a home range, trees may be clawed, bitten, and rubbed to serve as communicating signposts. Although little firm data exist on the function of marking behavior in bears, smelling such sites could provide other bears with information about the range's occupant. Large resident males disperse subordinates, so the signposts could cause intruders to avoid the area and provide a basis for territoriality.

IV EVOLUTION

Fossilized remains of a considerable number of bears and bearlike animals have been found that date from the Miocene epoch. Apparently the bears evolved from an extinct group of carnivores known as the cynodonts. The best-known extinct bear is the cave bear, found in cave deposits throughout Eurasia and North America. Larger than the Kodiak, the cave bear probably went to the caves for occasional shelter.

V CONSERVATION

Conservation of these wide-ranging generalist carnivores is difficult because large areas of relative wilderness are needed to sustain them. This challenge is made more difficult by the keen sense of smell of bears, which allows them to detect new odors over large distances. When drawn to these odors that result from human activity, a bear loses the inevitable resulting conflicts with humans. Mineral and oil and gas exploration and development also have adverse effects on bear habitats.

Scientific classification: Bears make up the family Ursidae. The polar bear is classified as Ursus maritimus; the brown bear as Ursus arctos; the American black bear as Ursus americanus; the Asiatic black bear as Ursus thibetanus; the sun bear as Helarctos malayanus, although some sources classify it as Ursus malayanus; the sloth bear as Melursus ursinus, although some sources classify it as Ursus ursinus; and the spectacled bear as Tremarctos ornatus.