The polar bear's body is long and streamlined, with a long neck and small head. Adult males are 7 to 9 1⁄2 ft (210–290 cm) long, stand 4 to 4 1⁄2 ft (122–137 cm) at the shoulder, and weigh 700 to 1,600 lbs (320–730 kg). Females are somewhat smaller. The extremely dense fur appears yellowish white but is in fact unpigmented. Unlike other bears, polar bears have hairy soles, which help them grip the ice. They may attain a running speed of 25 mi (40 km) per hr on ice.
Polar bears are omnivorous, but feed chiefly on marine animals such as seals and young walruses. Quite fearless, they will stalk any animal, including humans. They take advantage of carcasses left by hunters, and in summer eat vegetation on the shore. If food is scarce, their physiology can slow to a state known as walking hibernation.
Except for a brief courtship in summer, polar bears are solitary. Males and nonpregnant females are thought to wander all winter. A pregnant female makes a winter den in the snow; two tiny, helpless cubs are born in January and nursed in the den until March. They usually remain with the mother for about a year and a half, while learning to hunt.
Polar bears have been extensively hunted, especially by Eskimos, for fur, flesh, and ivory, and they have declined greatly in numbers. Although extremely dangerous to humans, they do well in captivity. In recent years, changes in sea ice cover in the Arctic appears to have placed some populations of polar bears under stress, and has led the U.S. government to list the bear as threatened. Polar bears can crossbreed in the wild and in captivity with grizzly bears. Polar bears are classified in the phylum Chordata, subphylum Vertebrata, class Mammalia, order Carnivora, family Ursidae.
See study by A. E. Derocher (2012).
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