Behavior

Little is known about the behavior in the wild of half of the ursid species, mostly due to their remote geographical distribution. These include the spectacled bear, Asiatic black

A sun bear (Helarctos malayanus) showing its long tongue, in Cambodia. (Photo by Terry Whittaker/Photo Researchers, Inc. Reproduced by permission.)

The giant panda (Ailuropoda melanoleuca) bases 99% of its diet on bamboo. (Photo by Hans Reinhard/OKAPIA/Photo Researchers, Inc. Reproduced by permission.)

A sun bear (Helarctos malayanus) showing its long tongue, in Cambodia. (Photo by Terry Whittaker/Photo Researchers, Inc. Reproduced by permission.)

The giant panda (Ailuropoda melanoleuca) bases 99% of its diet on bamboo. (Photo by Hans Reinhard/OKAPIA/Photo Researchers, Inc. Reproduced by permission.)

bear, sun bear, and sloth bear. In general, however, bears overall are solitary animals except during mating season or in mother-cub groupings. Occasionally among brown bears, siblings will stay near one another for a year or two after they leave their mother. Although additional research is needed for substantiation, some reports indicate that sloth bears may form social units, and that male sun bears may remain with the mother after she gives birth.

Bears generally maintain home ranges, with the males' ranges frequently overlapping with those of the females. Black bears mark their territories with scent markings or long scratches clawed into trees. Unusually, male panda bears sometimes do their scent marking while standing on their hands. In black bears and several other species, the ranges of male bears may also overlap, but since the ranges are often very large and bears rarely see one another, the overlaps present little opportunity for territorial conflicts. Even when bears come together at one feeding site, such as brown or black bears at a salmon stream, individual bears maintain their personal space and share the resource. When bears approach one another too closely, temporary dominance hierarchies may form, with the largest males mounting short-lived aggressive displays, including growls, and occasional charges to maintain a small feeding territory. During breeding season, males generally compete for females, but the male-female bonds typically only last one or two weeks.

Kodiak bears (Ursus arctos middendorffi) fight over a fishing site at McNeil River, Alaska, USA. (Photo by Erwin and Peggy Bauer. Bruce Coleman, Inc. Reproduced by permission.)

With their large, plantigrade feet and stout limbs, bears are often pictured as lumbering animals that always move slowly and deliberately. They can, however, move very quickly when necessary. Black bears, for example, can run at speeds of 30 mph (50 kph), and polar bears are fast enough to catch caribou on the Arctic tundra. Even the somewhat awkward-moving sloth bear can outrun a human over short distances. Most bears are also accomplished tree climbers. The sun bear has perfected climbing, quickly scaling trees in search of honey and other food items, and even fashioning resting/ feeding platforms out of broken branches high up in the trees. Polar bears and adult brown bears (with the exception of some populations in Europe) do not climb, but both are good swimmers. Other bears, like the Asiatic black bear, can also swim. With their large and slightly webbed front feet, polar bears are particularly adept swimmers and divers, and reportedly are able to swim across open-water expanses of up to 100 mi (65 km).

Ursids tend to be crepuscular (mainly active at dawn and dusk) or nocturnal animals, although some extend their active periods into the daytime. Polar bears are an example. While they are most active at night and at dawn, they are frequently seen hunting during the day.

Although ursids do not technically hibernate, many cooler-climate bears do enter winter dormancy, during which the respiratory and heart rates drop, but the body temperature dips only slightly. In the black bear, for instance, their body temperature drops from about 100°F (38°C) to 88-93°F (31-34°C). The Asiatic black bear is an exception: Its body temperature declines precipitously to just 37-45°F (3-7°C). It is during the winter dormancy that female ursids give birth. As she sleeps, the young suckle and grow. Among the cooler-climate species, both males and females become dormant, except in the polar bears, where only pregnant females enter winter sleep. During the winter, bears are capable of awakening, and occasionally leave their winter dens, which may be burrows, hollow logs, or tunnels in the snow and ice. Warm-climate bears, including sun, sloth, and spectacled bears, do not enter winter sleep. Although most brown bears and Asiatic black bears "hibernate," those from warmer climates frequently skip winter dormancy and remain active all year.

Pregnancy And Childbirth

Pregnancy And Childbirth

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