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Polar Bear

Ursus maritimus

Description
Evolution
Distribution and Abundance
Life History
Relationships with People

Formerly it was believed that polar bears migrated freely all across the Arctic, but modern research suggests that there are actually a number of more or less distinct populations. Russian and American are investigating the possibility that Beringian bears comprise a single group which during winter is distributed from Wrangel Island south along the Asian coast and in the central Bering Sea as far as St. Mathew Island. In summer, those wintering in the Bering Sea return to the north with the retreat of pack ice. Beringian bears seldom mingle with another population found in the Beaufort Sea east of Pt. Barrow, Alaska.

In 1981 the IUCN Polar Bear Specialist Group agreed that the world population was between 20,000 and 40,000. As of 1988 the most accepted estimate for the Alaska populations was 3,000-5,000.

Ringed seals are the bears' principal prey. They also hunt bearded seals and occasionally the more dangerous walrus. Normally solitary hunters, they have an impressive range of strategies, learn quickly, and show immense patience, power and speed. It has been calculated that their caloric needs require one ringed seal every six and a half days. Arctic foxes live on the sea ice in winter by scavenging polar bear kills.

Since their prey is available year-round, polar bears do not hibernate like brown bears, except pregnant females, who spend about five months in dens to give birth to their cubs. The female must greatly increase her weight, mostly in fat, to carry off a successful pregnancy and denning. The cubs, usually two, are born in December or January, weighing only 0.5 to 0.9 kilograms (one to one and a half pounds). By the time the family breaks out of the den in March or April the cubs weigh 10-15 kilograms (25-30 pounds). Cubs generally remain with their mother for two and a half years. Females are therefore able to bear young only every three years. This low rate of reproduction is balanced by a long life and low rates of natural mortality.

Moving in autumn from drifting ice to suitable denning sites requires a remarkable and little understood navigational ability. An important denning area for the Beringia population is on Wrangel Island. Denning also occurs on the northeastern coast of Alaska, although a majority of the Beaufort population dens on sea ice.

Polar bears have a preeminent place in Eskimo cultural and spiritual life. The spiritual guardians of shamans were usually polar bears, and it was believed that the spirits of people and bears sometimes interchanged. Killing a bear was a major event, requiring ceremonial propitiation of its spirit. Sometimes it was the bear who killed the person, for the predator-prey relationship went both ways.

For information when traveling in bear country.