Nature Wallpapers: January 2007

The polar bear (Ursus maritimus), also known as the white bear, northern bear, or sea bear, is native to the Arctic. It is one of the two largest land carnivore species and the apex predator within its range. It is well-adapted to its habitat: its thick blubber and fur insulate it against the cold and its translucent fur (which appears white or cream-coloured) camouflages it from its prey. The polar bear rivals the Kodiak bear as the largest four-footed carnivore on Earth and can live up to 25 years. Unlike other arctic mammals, polar bears never shed their coat for a darker shade in the summer. It was originally hypothesized that the hollow hairs of a polar bear coat acted as fiber optic tubes to conduct light to the black polar bear skin, where it could be absorbed. However, a number of recent studies have demonstrated that this is not true. This thick undercoat does, however, insulate the bears to the point where they overheat at temperatures above 10°C (50°F) and are nearly invisible under infrared photography; only their breath and muzzles can be seen. Growing through the undercoat is a relatively sparse covering of hollow guard hairs about 6 inches long. These guard hairs are stiff, shiny and erect, and stop the undercoat from matting when wet. Water is easily shaken off before it can freeze. The bear also rolls in snow to shed moisture from the coat.

The polar bear's entire body is furred, even the bottom of its paws. That helps prevent bears from slipping on the ice. The polar bear is classified as a marine mammal. Its feet are partially webbed for swimming, and its fur is water-repellent. A formidable predator, it has extremely sharp claws. The polar bear hunts well on land and on the sea ice, as well as in the water.

Polar bears are excellent swimmers and have been seen in open arctic waters as far as 60 miles from land. Recently, polar bears in the arctic have undertaken longer than usual swims to find prey, resulting in four recorded drownings in the unusually large ice pack regression of 2005.

They also hunt very efficiently on land due to their prodigious speed; they are more than capable of outrunning a human. Still, caribou and musk oxen can easily outrun a polar bear, and polar bears overheat quickly: thus the polar bear subsists almost entirely on seals and on walrus calves or adult carcasses. Polar bears are enormous, aggressive, curious, and extremely dangerous to humans. It is best to remember that wild polar bears, unlike most other bears, are often barely habituated to people and will quickly size up any animal they encounter as potential prey. A polar bear should never be approached and if one is spotted, it is best to retreat slowly on foot, preferably to an indoor location, or move away in a vehicle.

Males are 8 to 11 feet long and weigh 500 to 1,100 pounds but can reach as much as 1,500 pounds. Females are smaller, measuring 6 to 8 feet long, and weigh from 350 to 600 pounds, occasionally reaching 700 pounds.

Their range is limited by the availability of sea ice that they use as a platform to hunt seals, the mainstay of their diet. The destruction of its habitat on the Arctic ice, which has been attributed to global warming, threatens the bear's survival as a species; it may become extinct within the century. Signs of this have already been observed at the southern edges of its range.

The polar bear is a circumpolar species sometimes regarded by authorities as a marine mammal found in and around the Arctic Ocean whose southern range limits are determined by pack ice (their southernmost point is James Bay in Canada). While their numbers thin north of 88 degrees, there is evidence of polar bears all the way across the Arctic. Population estimates are generally just over 20,000.

Polar bears have been made both controversial and famous for their distinctive white fur and their habitat. Companies like Coca-Cola, Polar Beverages, Nelvana, Bundaberg Rum and Good Humor-Breyers have used images of this bear in logos. The first has consistently displayed the bears as thriving near penguins, though the animals naturally live in opposite hemispheres. The Canadian 2-dollar coin (right) features the image of a polar bear. The panserbjørne of the fantasy trilogy His Dark Materials are polar bears with human-level intelligence.The TV series Lost has featured polar bears on a mysterious (and, strangely, tropical) island.

In April 2006, the first, and to date only, grizzly-polar bear hybrid found in the wild was killed by a sport hunter at Banks Island, Northwest Territories, Canada. A DNA test conducted by Wildlife Genetics International in British Columbia confirmed that it was a hybrid, with the mother a polar bear and the father a grizzly. You can see pictures and read about hybrids here.