Protected from cold by a thick fur coat and a
layer of blubber, the polar bear hunts seals in
open areas in the Arctic sea ice.Astrong swimmer,
the polar bear uses its large front paws as paddles.
Its white fur blends in with the ice and
snow as it stalks or still-hunts seals. Ringed seals
are the polar bear's primary food, but it also
consumes bearded seals, and occasionally walruses,
belugas, narwhals, musk oxen, and carrion
(dead terrestrial and marine mammals). Although
largely carnivorous, when on land the polar bear
may eat grasses, kelp, berries, and lichens. Males
and nonpregnant females do not make dens or
hibernate, but spend the winter hunting on the
sea ice. The polar bear evolved from the terrestrial
brown bear about 100,000 to 200,000 years ago. In
captivity, polar bears and brown bears have interbred
and produced fertile offspring. This shows a
high degree of genetic relatedness. In nature,
however, these two species are geographically
isolated fromone another and would rarely meet.
Swimming in icy water among the ice floes of
the Arctic, quietly stalking a resting seal, then killing
it with a crushing blow of its forepaw, the polar
bear is an impressive example of an animal's
ability to adapt to and live in one of the harshest
environments on earth.
Physical Characteristics of Polar Bears
Male polar bears are up to five feet high at the shoulder while on all fours and up to ten feet long. When standing on its hind legs, a male can be eleven feet tall. Adult males are generally much bigger than females: 1,100 to 1,770 pounds for males, 330 to 770 pounds for females. Like other bears, polar bears are plantigrade. Mating takes place in late March to late May. This is the only time that the male is with the female. Other than family groups of females with their cubs, polar bears are solitary. Pregnant females dig snow or earth dens in which they will give birth to one to three cubs in late November to early January. The mother's milk is very rich, with an average fat content of 33 percent. The cubs, which weigh 1 to 1.5 pounds at birth, grow quickly and weigh 22 to 33 pounds when they emerge from the den with their mother in late February to early May. Polar bear cubs usually leave their mother at 2.5 years of age, at which time the mother is ready to breed again. Therefore, the female usually gives birth every third year.
By the 1960's, polar bear populations were in serious decline due to sport hunting. In 1967, the five "polar bear nations" (the United States, Canada, Denmark, Norway, and the Soviet Union) limited hunting to the Inuit (Eskimo) people. By 2001, polar bears had recovered, and there were twenty thousand to forty thousand in the world. A 1999 study by longtime polar bear biologist Ian Stirling and his colleagues shows that polar bears at Hudson Bay are 10 percent thinner and have 10 percent fewer cubs than they did twenty years ago. In 1999, the ice on Hudson Bay melted three weeks earlier than it did twenty-five years earlier. Polar bears must wait for ice to form each fall to hunt ringed seals, their main food source. Hudson Bay polar bears fast six to eight months each year and then hunt seals intensively during the ice season. The three-week reduction of hunting time has not yet resulted in significant decline of the polar bear population, but is expected to do so if the climate trend continues.
Genus and species: Ursus maritimus
Geographical location: Northern marine areas of Alaska, Canada, Greenland, Norway*s Svalbard Archipelago, and Russia
Habitat: The sea ice and adjacent land areas of the circumpolar Arctic
Gestational period: About eight months
Life span: Up to thirty-two years in the wild, over forty years in captivity
Special anatomy: Fur, hide, and blubber providing effective insulation from the extreme arctic cold; white fur providing camouflage against the backdrop of ice and snow and greatly aiding in stalking seals; large paws used for paddling in water and which act like snowshoes on thin ice; pads of the feet covered with small, soft papillae that improve traction on ice; small ears and tail to reduce heat loss and a large body mass to conserve heat
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