Polar Bear

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"Polar Bear" is also the name of White Bear Township, Minnesota and a trade name for a type of scuba diver's warm undersuit to be worn under a drysuit.
Polar Bear

Conservation status: Lower risk (cd)

Image:Polar-bear.jpg
Polar Bear
Scientific classification
Kingdom:Animalia
Phylum:Chordata
Class:Mammalia
Order:Carnivora
Family:Ursidae
Genus:Ursus
Species: U. maritimus
Binomial name
Ursus maritimus
Phipps, 1774

The polar bear (Ursus maritimus), also known as white bear or northern bear, is a large bear native to the Arctic. It is the largest land carnivore species. It is the apex predator within its range. It is well-adapted to its habitat: its thick blubber and fur insulate it against the cold, its white color camouflages it from its prey, and it hunts well both on land and in the water.

Contents

Natural range

The Polar Bear is a circumpolar species 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.

Their main population centers are:

The destruction of its habitat on the Arctic ice by 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.[1] There have been no proposals to date to transplant the species to some other environment, such as Antarctica.

Size and weight

They are the world's largest land carnivores. Adult males weigh from 400 to 600 kg (900 to 1300 lb) and occasionally exceed 800 kg (1750 lb). Females are about half the size of males and normally weigh 200–300 kg (450 - 650 lb). Adult males measure 2.4 to 2.6 m (7' 10" to 8' 6"); females, 1.9 to 2.1 m (6' 3" to 6' 11"). At birth, cubs weigh 600 to 700 g. Population estimates range from 16,000 to 35,000, with about 60% in Canada.

Fur and skin

The nose and skin are black. The fur is whiteish in appearance—pure white after molt, yellowish in summer due to oxidation by sun, and sometimes greenish (due to algal growth inside the shaft of hollow guard hairs) in captive bears kept too warm. This fur is good camouflage as well as insulation. The bear is often thought to cover its visible black nose while hunting, though no scientist has observed this. They will, however, cover their muzzles while sleeping, probably for insulation. Stiff hairs grow on the soles of its paws; these insulate and provide traction on ice.

Unlike other arctic mammals, polar bears never shed their coat for a darker shade in the summer. The individual hairs are transparent and unpigmented (like a single water drop in a cloud). The fur is white rather than transparent for the same reasons as clouds, water foam, and cotton (reflection and dispersion of visible light). The fur absorbs ultraviolet light. The hair does not have fiber-optic properties nor does it transmit light or heat to the skin (an urban legend). The coat does however insulate the bears to the point where they overheat at temperatures above 10°C (50°F) and are nearly invisible in the infrared: only their breath and muzzles can be seen.[2]

In July 2005, several polar bears in the Brookfield Zoo turned green as a result of algae growing in their hollow hair tubes. Chicago experienced an extremely hot, humid and dry summer that year. However, the zoo took no action since it has been shown the algae does not negatively affect the bears in any way. The staff believed that exposing the bears to chlorine or bleach would be more harmful than letting the algae run its course. Previously, in February 2004, two polar bears in the Singapore Zoo turned green due to algae growth. A zoo spokesman said that the algae had formed as a result of Singapore's hot and humid conditions. The bears were washed in a peroxide blonde solution to restore their expected colour. A similar algae grew in the hair of three polar bears at San Diego Zoo in the summer of 1979. They were cured by washing the algae away in a salt solution.

Hunting, diet and feeding

It is the most completely carnivorous member of the bear family and the only bear that preys on man as food. It feeds mainly on seals, especially Ringed Seals. Polar bears are excellent swimmers and can often be seen in open waters miles from land. This may be a sign that they have begun aquatic adaptations to better catch their prey. They also hunt very efficiently on land due to their prodigious speed; they are more than capable of outrunning a human. Other prey include beluga whales, walruses and rodents. As a pure carnivore predating upon fish-eating carnivores, the polar bear ingests large amounts of Vitamin A, which is stored in its liver; in the past, humans have been poisoned by eating liver of polar bears.

Phylogeny

The raccoon and bear families are believed to have diverged about 30 million years ago and around 13 million years ago the spectacled bear split from the other ursine bear. The 6 distinct ursine species originated some 6 million years ago. The brown bear and polar bear diverged from a common ancestor around 2 million years ago and crosses between the two species produce fertile hybrids. They only lost their Brown Bear molars between 10 and 20 thousand years ago.

Gallery

Three polar bears investigate the submarine USS Honolulu 280 miles from the North Pole.

Two polar bears sparring near Churchill, Manitoba, Canada.

Polar bear tracks at Svalbard

Mother with cub at Svalbard

A Polar Bear resting.

Tourists watching polar bears from a "tundra buggy" near Churchill, Manitoba

Sources

Wikimedia Commons has more media related to:

External links

Retrieved from "http://en.freepedia.org/Polar_Bear.html"


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