Ursus maritimus

Description

Well adapted to aquatic life, the polar bear's long neck and narrow skull give it a streamlined appearance, and its large, flat, oar-like front feet allow it to swim with ease; in fact, individual polar bears have been observed swimming in open water as far as 200 miles from the nearest land (although those bears likely got that far out by riding floating ice).

Polar bears are also well adapted for the Arctic conditions in which they live. Their fur is thicker than that of any other bear, and it even covers their feet, providing both warmth and traction. The fur is actually colorless, it looks white because it refracts sunlight; the skin, however, is black, allowing it to absorb the sun's heat. Believe it or not, polar bears are so well insulated that it is actually possible for them to get overheated during the Arctic summer.

The polar bear is 8-10 feet long, up to 5.3 feet tall at the shoulder, and weighs 550-1700 pounds (males are larger than females).

Distribution and Habitat

Polar bears are found throughout the Arctic, with 19 separate geographical subpopulations known. They are highly dependant on the pack ice there, since they spend much of their time hundreds of miles from land. The most important habitats for polar bears are the edges of pack ice, where currents and wind interact with the ice, forming a continually melting and refreezing matrix of ice patches. These are the areas of greatest seal abundance and accessibility.

Diet

The most carnivorous member of the bear family, the polar bear feeds primarily on ringed and bearded seals. The polar bear can smell a seal on the ice from up to 20 miles away, can detect an air hole from up to a mile away, and can even smell a seal that has buried itself in the snow. A very patient hunter, a polar bear will wait hours for a seal to emerge from an air hole. Polar bears will feed on walrus and whale carcasses, birds, and even vegetation and kelp, but only if they are having difficulty getting seals.

Reproduction

Polar bears breed from late March through May. Males and females go their separate ways after mating. If mating is successful, the female embarks on a feeding binge that lasts into the fall, at which time she enters a den, where she will give birth to 1-4 cubs sometime between November and the end of January. The cub(s) only weigh about a pound at birth, but will reach a weight of 20-30 pounds by the time they emerge from the den in March or April, thanks to the high fat content of the mother's milk; at 35% fat, polar bear milk is the richest milk in the bear family. The cub(s) remain remain with the mother for about 2-2.5 years, at which time they can hunt for themselves. Females reach sexual maturity at 5-6 years, males at 10-11 years, and polar bears have an average lifespan of about 25 years in the wild.

Scientific Classification

phylum Chordata
subphylum Vertebrata
class Mammalia
order Carnivora
family Ursidae
genus & species Ursus maritimus

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