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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.

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The polar bear (scientific Latin name Ursus maritimus), also known as white bear or northern bear, is a large mammal of the order Carnivora (meat eaters), family Ursidae (bears). Polar Bears prey on seals.

Polar bears have many adaptations to live in the cold and to catch prey. They have a thick coat of fur on their skin. They also have a thick layer of blubber under the skin. These act as insulators of heat. Polar bears also have stiff hairs under their soles. These not only keep them warm, but also increases the amount of friction and prevents the polar bear from slipping on ice. They have a coat of white fur to camouflage themslves so unsuspecting prey will not notice them. Polar bears also cover their black noses when they sleep in order to further camouflage themselves.

Natural range

It is a circumpolar species found in and around the Arctic Ocean whose southern range limits are determined by pack ice (their southern most point is James Bay, 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:

  • Wrangel Island and western Alaska
  • Northern Alaska
  • Canadian Arctic archipelago
  • Greenland
  • Svalbard-Franz Josef Land
  • North-Central Siberia

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; females, 1.9 to 2.1 m. 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. 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.

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 dispertion 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 is visible.

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 negativly effect 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. 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.

Polar bears do not eat penguins, because their habitats do not overlap. Polar bears live at the North Pole, while those penguins that live in polar regions inhabit the South Pole.

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

Sources

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