Polar Bear
Order: Carnivora
Family: Ursidae
Genus and Species: Ursus maritimus
Supremely adapted to ice floes and frozen shores, the polar bear—the largest land carnivore and most carnivorous bear—ranges widely across the Arctic wilderness, seeking seals and other prey.
Physical Description: The polar bear is one of the world's few all-white animals. Only its eyes, nose pad, and lips are black; although beneath its white fur, its skin is also black. The bear's white coat, which helps it blend with its icy environs, is thick, and covers a thick fat layer. These two adaptations enable polar bears to survive harsh Arctic winters that average -30 degrees Fahrenheit. Partially webbed feet assist in swimming, which polar bears can do for long distances. Like other bears, the polar bear relies on a keen sense of smell to sniff out prey. Its large body size helps it conserve heat, while its long neck helps it view its open habitat, both while on land and while swimming. Polar bears put their sharp claws to good use when grabbing prey and loping across the slippery ice.
Size: Male polar bears are much larger than females. Adult males grow eight to almost nine feet long, while females grow to about six feet long. Males weigh 800 to 1,400 pounds, whereas females are about half the male's weight, at from 440 to 650 pounds. On two legs, a large male polar bear may stand ten feet or, rarely, taller.
Geographic Distribution: Polar bears range across the frozen top of the Northern Hemisphere. They are found in the northernmost reaches of Alaska, Canada, Russia, on Norway's far-flung Svalbard Islands, and along the coasts of Greenland. They reach their southern limit in Canada's Hudson Bay.
Status: An estimated 21,000 to 28,000 polar bears roam across large distances of the Arctic. While not considered endangered, some isolated populations are vulnerable to pollution, and possibly to the effects of global warming.
Habitat: Most polar bears live on ice where it meets open water. There they find their most important prey—seals. Some polar bears live at least part of the year on actual land, after winter ice and snow melt. Unlike other bears, they inhabit habitats virtually free of vegetation.
Natural Diet: Polar bears primarily hunt seals—especially ringed seals (Phoca hispida), but also bearded (Erignathus barbatus), harp (Phoca groenlandica), and hooded seals (Cystophora cristata). On occasion, they also attack larger animals, such as walrus (Odobenus rosmarus) and beluga whales (Delphinapterus leucas), and eat carrion. Small animals and vegetation, if available, supplement their diets during food shortages.
Reproduction: The polar bear is a slow breeder. Most females reach breeding age at four or five years, and usually do not breed more than once every two or three years. Males take longer to mature, about six years, but often begin mating as late as ten years due to stiff competition with other males for mates. Breeding occurs from March to June, when one male may mate with several females. One to three cubs are born in November or January, after the female digs a den in the ice (rarely on land). Mother and cubs remain in their den until late March or April. Cubs stay with their mother for two years or a bit longer.
Life Span: Polar bears live up to 25 years in the wild; The oldest zoo polar bear lived 41 years.
Behavior: Aside from courting adults and females with young, polar bears generally live alone. In some areas, such as walrus colonies, they may scavenge and feed together, but they hunt alone. The bears sniff out seals and catch them when they surface at breathing holes in the ice, stalk them when they rest on the ice, and break into their ice dens. Food availability and the seasonal ebb and flow of ice keep them on the go. They wander widely, and can cover more than 40 miles a day. Polar bears frequently swim from one ice floe to the next, paddling at about six miles per hour with their front paws. When necessary, they can stay under water up to two minutes.
A Few Polar Bear Neighbors:
Seals and walruses: These marine mammals keep a wary eye out for polar bears, which hunt them. These two haul out onto the ice or shore, but hunt fish under water.
Snow geese (Anser caerulescens): These white geese with black wingtips breed in the far north and spend their winters far to the south along North America's coasts. In winter, you can see thousands at coastal refuges from New Jersey south to North Carolina.
Arctic fox (Alopex lagopus): A small, usually all-white, canid that scavenges at polar bear kills, and also hunts small animals, including baby seals.
Snowy owl (Nyctea scandiaca): All white except for some black speckling, the snowy owl hunts lemmings and other small creatures.
Fun Facts:
Some polar bears living in Alaska are suspected of "commuting" to and from Siberia via floating ice floes.
A polar bear can sniff out seal breathing holes from more than half a mile away.
While in their birthing dens, female polar bears live off their fat reserves—without any food—for up to eight months.
Polar bears' attempts to catch prey succeed only about two percent of the time. Even with plenty of seals around, a bear may catch a seal only every four to five days.
Polar bears likely evolved from a light-colored population of brown bears.
By Howard Youth
ZooGoer 28(2) 1999.
Copyright 1999 Friends of the National Zoo.
All rights reserved.
