Bear

I

Introduction

Bear, large carnivorous mammal closely related to pandas, raccoons, and dogs. Bears are distinguished from other carnivore families by having heavy bodies, a short tail and short, rounded ears, plantigrade feet (both heel and sole touching the ground, as in human beings), and a hind foot with five toes. They also lack the shearing carnassial teeth common to most carnivores; the crushing molars of bears are believed to be an adaptation for eating plants. Although 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 may also graze on vegetation; grizzly bears eat grasses, herbs, berries, and nuts, as well as living or dead animals.

II

Kinds and Habitats

Bears occupy a diversity of habitats, but human encroachment has squeezed them primarily into mountain, forest, and Arctic wildernesses. The animals occur on all continents except Africa, Antarctica, and Australia. (Crowther’s bear of northern Africa’s Atlas Mountains is believed to be extinct.)

The Arctic coastal areas of northern countries are the home of the polar bear, the only semiaquatic bear. It is also known as the ice bear in some languages because of its preference for sea ice for hunting; the bottoms of its paws are furry to provide traction on the slippery ice.

Brown bears have been successful in the plains and forests of the North Temperate Zone. Their range is dangerously reduced in most of North America, although they are surviving (but hunted) in Alaska and western Canada. Variants include the largest bear, the Kodiak of Alaska, which weighs up to 780 kg (1,700 lb) and is as much as 3 m (10 ft) long. The closely related grizzly (meaning “grey”) is named after its white-tipped fur. Remnant populations of European brown bears live in scattered mountain regions.

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

The Asiatic black bear, also known as the moon bear, lives in the mountain ranges of south-eastern Asia. It has a black, shaggy coat and a pronounced white “v” on its chest. The upper lip is usually white.

The sun bear, which occurs from China to Sumatra and Borneo, 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 climbs trees.

Ranging through the tropical forests of India and Sri Lanka is the sloth bear, named after its usually slow movements. It 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 of the Andes, extending into Ecuador, is named after the yellow facial markings on its shaggy black coat. The muzzle, throat, and chest are usually cream-coloured.

III

Behaviour and Life Cycle

Bears have a lifespan of 15 to more than 30 years in the wild. They possess a keen sense of smell, and although detailed knowledge of the acuteness of their vision and hearing awaits further study, they are probably comparable to those of dogs. The winter torpor of some species has not usually been called hibernation, although recent studies suggest that black, brown, and polar bears are true hibernators, 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 temperature of bears 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 a while.

A female bear typically gives birth to one to four cubs after a gestation period of three to nine months. The cubs are born very small (for example, about 300 g, or 10 oz, among black bears) and require maternal care for two or three years. Even when feeding independently, yearling bears need protection against older males, which are known to kill and eat them. Females have evolved methods to protect the young by chasing them up trees or by attacking other animals that approach too closely; they can run rapidly when necessary. Because of this, increased human intrusions into wilderness areas—especially in the United States—has led to retaliation, in which people get mauled, and an eventual decline in the numbers of bears. Another cause of conflict is that competition for natural foods leads bears to discover and exploit new food sources provided by human beings. In agricultural areas, stored grain, livestock, beehives, and various crops are raided. Bears in national parks develop new feeding patterns based on campers’ food and refuse. Some bears learn how to release food hung up on cables, break branches off trees, and open locked cars.

Learning plays a large role in a cub’s ability to obtain food. Its relatively slow development and long tie with its mother allow it to observe the mother’s skills and to remember sites and experiences. Even the mostly herbivorous spectacled bear must learn when and where to find the most nutritious parts of plants in each season. Less fussy feeders such as the 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 eaten to provide energy reserves for hibernation.

Communication among bears depends on a signalling system effective for such widely dispersed animals, because a bear may need to move 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 communication signposts. Although there is little firm data on the function of marking behaviour in bears, smelling such sites could provide other bears with information about the range’s occupant. Large resident males chase off subordinates, so the signposts could elicit fear and avoidance by intruders and provide a basis for territoriality.

IV

Evolution

Fossilized remains of a considerable number of bears and bear-like animals have been found that date from the Miocene Epoch, up to 23.3 million years ago. Apparently the bears evolved from an extinct group of carnivores known as the cynodonts. The best-known extinct bear is the cave bear, whose remains have been found in caves throughout Eurasia and North America. Larger than the Kodiak, it probably went to the caves for occasional shelter.