The polar bear (Ursus maritimus), also known as the white bear, northern bear, sea bear, ice bear or nanuq in some Inuit languages, is a species of bear that is native to the Arctic and the apex predator within its range. Its thick blubber and fur insulate it against the cold. Its fur is white or cream-colored providing camouflage from its prey. The bear has a short tail and small ears that help reduce heat loss, as well as a relatively small head and long, tapered body to streamline it for swimming. The polar bear is a semi-aquatic marine mammal that depends mainly upon the pack ice and the marine food web for survival. It has adapted for life on a combination of land, sea, and ice.

Scientists and climatologists believe that the projected decreases in the polar sea ice due to global warming will have a significant negative impact on of this species within this century.

Size and weight

Polar bears rank with the Kodiak bear as among the largest living land carnivores, and male polar bears may weigh twice as much as a Siberian tiger. There is great sexual dimorphism, with some males reaching more than twice the size of the females. Most adult males weigh 300-600 kg (660-1320 lbs) and measure 2.4-3.0 m (7.9-10.0 ft) in length. Adult females are roughly half the size of males and normally weigh 150-300 kg (330-660 lbs), measuring 1.9-2.1 m (6.25-7 ft). At birth, cubs weigh only 600-700 g or about a pound and a half.

Fur and skin

A Polar Bear resting.A polar bear's fur is white (individual hairs are translucent like the water droplets that make up a cloud) and provides good camouflage and insulation. It may yellow with age. Under the fur, the bear has a black skin, which is visible at the nose, eyes, and mouth. Stiff hairs on the pads of its paws provide insulation and traction on ice.

Unlike other Arctic mammals, polar bears do not shed their coat for a darker shade in the summer. It was once conjectured that the hollow hairs of a polar bear coat acted as fiber-optic tubes to conduct light to its black skin, where it could be absorbed - a theory disproved by recent studies. The thick undercoat does, however, insulate the bears: they overheat at temperatures above 10 °C (50 °F), and are nearly invisible under infrared photography; only their breath and muzzles can be easily seen. When kept in captivity in warm, humid conditions, it is not unknown for the fur to turn a pale shade of green. This is due to algae growing in the guard hairs - in unusually warm conditions, the hollow tubes provide an excellent home for algae. Whilst the algae is harmless to the bears, it is often a worry to the zoos housing them, and affected animals are sometimes washed in a salt solution, or mild peroxide bleach to make the fur white again.

The polar bear is the most carnivorous member of the bear family, and the one that is most likely to prey on humans as food. It feeds mainly on seals, especially ringed seals that poke holes in the ice to breathe, but will eat anything it can kill: birds, rodents, shellfish, crabs, beluga whales, young walruses, occasionally musk oxen or reindeer, and very occasionally other polar bears. Still, reindeer and musk oxen can easily outrun a polar bear, and polar bears overheat quickly: thus the polar bear subsists almost entirely on live seals and walrus calves, or on the carcasses of dead adult walruses or whales. They are enormously powerful predators, but they rarely kill adult walruses, which are twice the polar bear's weight, although this has been known to happen. Humans and larger bears of their own species are the only predators of polar bears.

As a carnivore which feeds largely upon fish-eating carnivores, the polar bear ingests large amounts of vitamin A, which is stored in their livers; in the past, humans have been poisoned by eating the livers of polar bears. Though mostly carnivorous, they sometimes eat berries, roots, and kelp in the late summer.

Polar bear diving in a zoo.Polar bears are excellent swimmers and have been seen in open Arctic waters as far as 60 miles from land. In some cases they spend half their time on ice floes. Their 12 cm (5 in) layer of fat adds buoyancy in addition to insulating them from the cold. 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.

Polar bears are enormous, aggressive, curious, and potentially dangerous to humans. Wild polar bears, unlike most other bears, are barely habituated to people and will quickly size up any animal they encounter as potential prey.

Like other bear species, they have developed a liking for garbage as a result of human encroachment. For example, the dump in Churchill, Manitoba is frequently scavenged by polar bears, who have been observed eating, among other things, grease and motor oil.