Polar Bear
\nThe
Polar Bear (
Thalarctos maritimus or
Ursus maritimus) is a large
mammal of the order
Carnivora, family
Ursidae. It is a
circumpolar species found in and around the
Arctic Ocean. It is the world's largest land
carnivore. Adult males weigh from 400 to 600 kilograms and occasionally exceed 800 kilograms. Females are about half the size of males and normally weigh 200 to 300 kilograms. Adult males measure 240 to 260 centimeters and females 190 to 210 centimeters. At birth, cubs weigh 600 to 700 grams.
The Polar Bear is instantly recognisable by its
white coat. Unlike other
arctic mammals it never sheds this coat for a darker colour in
summer. The
hair is not actually
pigmented white; it is unpigmented and hollow, like white hair in
humans.
An interesting feature of the coat is that it appears
black when photographed with
ultraviolet light. A number of people have suggested that this is because the hairs channel the light to the black
skin of the bear to help it stay warm during the cold, sunless
winters. Measurements show, however, that the hairs strongly absorb
violet and ultraviolet rays. This is why Polar Bear's pelt often appears
yellow. More colourful Polar Bear have occasionally been reported. In February 2004, two Polar Bears in a Signapore zoo appeared to turn green as a result of
algae growing in their hollow hair tubes. 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.
Polar bears are wonderfully insulated; to the point where they overheat at temperatures above 50°F (10°C). Their insulation is so effective that when viewed with infrared (heat) camera they are barely visible. Only the pads of their feet emit detectable heat.
It is the most completely carnivorous member of the
bear family and feeds mainly on
sealss. Polar Bears are superb
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 man.\nAs a pure carnivore predating upon
fish-eating carnivores, the Polar Bear ingests large amounts of
vitamin A, which ends up stored in its
liver: in the past, arctic explorers have been poisoned by eating Polar Bear liver.
Polar Bears are currently threatened, not mainly by
hunting, but by habitat loss caused by
global warming; for example, the area of
ice covering
Hudson Bay in Northern Canada in winter is shrinking, limiting their access to
seal prey. The sensitivity of the survival rates of the bears to global temperature is attested to by the population bulge in the cohort of bears born during the transient cooling that followed the eruption of
Mount Pinatubo in
1991.
A Polar Bear is depicted on
Canada's $2
toonie coin.
References
\n*Singapore's Green Polar Bears - News report from cnews\n*
Polar Bears International - Polar Bear conservation group homepage
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