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BEAR,
any of seven genera of large mammals constituting the family
Ursidae. Bears include the largest members of the order Carnivora
and are closely related to pandas, raccoons, and dogs. They 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 humans), and a hind foot with five toes. They also
lack the shearing teeth common to most carnivores; the crushing
molars of bears are believed to be an adaptation for a plant diet.
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; the grizzly eats grasses, herbs, berries, and
nuts as well as living or dead animals.
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 North Africa’s
Atlas Mountains is believed to be extinct.)
The Arctic coast areas of northern countries are the home
of the polar bear (Thalarctos maritimus), the only
marine 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 furred for traction.
Brown bears (Ursus arctos) have been successful
in the plains and forests of the North Temperate Zone. Their range
is dangerously reduced in the lower U.S., but they are surviving
and hunted in Alaska and western Canada. Variants include the largest
bear, the Kodiak of Alaska, which weighs up to 780 kg (1700 lb)
and is as much as 3 m (10 ft) long. The closely related grizzly
is named for its white-tipped fur. Remnant populations of European
brown bears live in scattered mountain regions.
The North American black bear (Ursus americanus)
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) color phases found in western North America.
The Asian black bear (Selenarctos thibetanus),
also known as the moon bear, is found in mountain ranges of Southeast
Asia. It has a black, shaggy coat and a pronounced white V on its
chest. The upper lip is usually white.
The sun bear (Helarctos malayanus), 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 (Melursus ursinus), named for its
usually slow movements. The 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 (Tremarctos ornatus)
of the Andes, extending into Ecuador, is named for the yellow facial
markings on its shaggy black coat. The muzzle, throat, and chest
are usually cream colored.
Bears have a life span of 15 to more than 30 years in the
wild. They possess a keen sense of smell, and although detailed
knowledge of their vision and hearing abilities awaits further study,
they are probably comparable to those of dogs. Although the winter
torpor of some species usually has not been called hibernation,
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 six 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 from 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 lead to
human maulings, retaliation, and an eventual decline in bear numbers.
Another cause of conflict is that competition for natural foods
leads bears to discover and exploit new food sources grown by humans.
In agricultural areas, stored grain, livestock, beehives, and other
crops are raided. Bears in public parks develop new feeding patterns
based on camper food and garbage. Some bears learn how to release
cable-suspended food, break tree limbs, 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. Feeding generalists 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 important for energy reserves for hibernation.
Communication among bears depends on a signaling 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 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 elicit fear and avoidance by intruders and
provide a basis for territoriality.
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 Carnivora 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.
Conservation of wide-ranging generalist carnivores is difficult
because of the large areas of relative wilderness needed to sustain
them. The challenge is more difficult with bears, because their
olfactory ability permits detection of new odors over large distances.
Drawn as if by magnets to these odors, they lose in the inevitable
resulting conflicts with humans. Better knowledge and management
of such indirect impacts on bears may lessen the adverse effects
of mineral and fuel exploration and development, but concerted efforts
are needed in many parts of the world.