Mammals - Polar Bear
 Region:
Americas
Class: Mammalia
Order: Carnivora
Family: Ursidae
Genus: Ursus
Scientific Name: Ursus maritimus
Description: In comparison to other bears, the polar bear
are equipped with longer legs and neck, the ears are relatively
short, the nose is more “roman”, the cheek teeth
are sharper and more edged and the canine teeth are more
prominent. The rhinarium (nose-pad) and tongue are black,
the eyes brown. The soles of the feet are bordered with
dense fur and the claws are shorter but sharper. Polar
bears differ in size throughout their range. Males are
approximately one third larger than females.
Distribution: The polar bear is circumpolar in distribution,
inhabiting all Arctic seas and coastlines. It is found
on the pack-ice off the Alaskan coast north of Bering
Strait, off the coasts of Greenland and along the Eurasian
Arctic coast from Spitsbergen to Wrangell Island. Rare
stragglers reach Iceland. Individual bears have been seen
on the frozen Arctic Ocean as far as latitude 88 degrees
north, only 2 degrees from the North Pole. In Canada they
are found along the arctic coasts from Alaska to Labrador
and from the tip of James Bay to northern Ellesmere Island.
Polar bears do roam as far as 150 kilometres inland into
the coniferous forests, where they live very differently
from the polar bears which belong to the high Arctic.
Habitat: Frequent the southern broken edge of the arctic
ice pack. They avoid solidly frozen sea ice and the open
seas. Some live inland in coniferous forest areas in summer
months.
Food: The ringed seal is by far the most important prey.
Polar bears also eat the bearded seal, harp seal and hooded
seal. Young walrus are sometimes taken. During the summer
months it feeds upon the shoreline carrion, fish, mussels,
crabs, starfish and the eggs and nestling young of waterfowl
and cliff-dwelling birds. It also grazes on kelp, grasses
and eats mushrooms, crowberries and lemmings.
Skin/Color/Coat: Polar bears are considered the largest
land carnivores in the world, matched perhaps only by
the kodiak brown bear. Their pelage is thick, coarse and
long. The guard hairs are shiny, almost glossy, oily and
waterproof, and have hollow shafts. Polar bears are pure
white in winter; in summer and autumn, the coat is thinner
and has yellow wash or is almost a golden colour. Polar
bears moult annually between the end of May and August.
Reproduction and Development: Normally solitary animals
outside the breeding season, polar bears mate in midsummer.
Females breed between the ages of 3 and 7 at two to four
year intervals. The gestation period is 195 - 265 days,
including a period of delayed implantation. Females retreat
to their winter dens to give birth to 1-4 cubs, which
takes place between late November and early January. The
newborns are small (30 cm long), blind and almost naked
and weigh less than 1 kg. Growth is very quick. At 2 months
they weigh about 5 kg and move about the den. Their eyes
open at 6 weeks. By mid-March to early April, when the
den is opened, the cubs weigh about 10 kg and are surprisingly
strong. The cubs suckle for 9 months, occasionally one
year. They are very dependent on their mother and stay
with her for 2 years. At that time they weigh 90 - 180
kg and are half grown. Female polar bears are polyandrous.
The males fight among themselves for the female’s
attention and a couple will pair off for a period of a
few days to two weeks
Adaptations: On land a shuffling walk may be increased
to a rolling gallop of 40 km/h. the polar bears can outrun
caribou over a short distance. They are often seen standing
high on their hind legs, stretching their neck in order
to scan the landscape. On thin ice, the polar bear will
spread its legs to distribute its mass. Its thickly padded
and furred soles allow the bear to move quietly as well
as providing good traction. The claws are used to dig
into icy slopes and to grip its prey. The polar bear is
a strong swimmer, paddling with its forefeet only and
trailing its hind feet. It can stay submerged for 2 minutes
and swim at a speed of approximately 6.4 km/h, often covering
long distances.Insulation: The polar bear has a thick
layer of sub-cutaneous fat, very dense underfur with several
layers of glossy guard hair on the outside. Their pelt
is much thicker in winter and provides excellent insulation.
The fat layers also add to buoyancy in the water. Water
is shed easily from the oily waterproof fur. The ears
are small and furry with a heavy network of blood vessels
to keep them warm and conserve heat. The tail is short
and rounded. Colouration: The creamy white coat allows
the bear to be inconspicuous when hunting seal. The colourless
hair is hollow and picks up the colour of its surroundings.
Polar bears are the only Arctic species in which all individuals
stay white year round. Skin and tongue are black . Hunting:
Polar bears will stand or lie by the seal’s blowhole
in the ice for hours; they may swim towards seals resting
on the ice flows with only their nose showing above the
water. They will dive quietly, then swim up to the ice
edge and jump out on the seal, and will also crawl towards
a sunbathing seal using every piece of raised ice to conceal
the approach. Senses: Polar bears have good eyesight.
Their eyes have inner eyelids that keep the glare of the
sun on snow and ice from blinding them. They keep their
eyes open under water. They also have a keen sense of
smell, however, their sense of hearing is dull. Denning:
Polar bears of both sexes occupy dens for shelter. There
appear to be 3 main types of winter refuges: maternity
dens, temporary dens and winter shelters. Temporary dens
are generally excavated by single bears and are occupied
for periods of a single day or two, to up to three to
four months. The bears use them to escape the bad weather
and as resting places. Maternity dens are occupied by
pregnant females not only as a safe place to give birth
to her cubs, but as well as a place of protection for
the cubs during their first few months. Topographic factors
influence the den sites. In Canadian core areas, dens
frequently occur on south-facing slopes where northerly
prevailing winds create the best drifts, where the wind-chill
is least and insulation (received solar radiation) is
greatest. Polar bears do not always, or even ordinarily
hibernate in winter – especially the males –
though the degree of inactivity may depend on the weather,
the state of the ice pack, and the fat reserves of the
bear. The lethargy displayed by bears while in the den
enables them to rest and conserve their vital fat reserves.
During this time, the body temperature of the polar bear
decreases by a few degrees from normal and the respiration
rates are markedly reduced.
Threats: Extensive hunting, started in 17th century. Protective
measures were taken in 1960 through an international agreement
(Canada, former USSR and Norway) to protect the bears
in part of their range. Exploitation of minerals and fossil
fuels in the Arctic pose a continuous threat. Research
to identify the effects of Arctic development on the bear
population continues. Native people may legally hunt them.
Follow up on tagged polar bears throughout the Arctic
confirm the theory that they occur in separate populations
with limited exchange between them. Polar bears may be
one of the animals most threatened by global warming.
They depend entirely on sea ice as a platform from which
to hunt seals. If the ice does not form or forms too late
in the season many polar bears could starve.
Status: Conservation Dependent
References: Banfield, A.W.; Mammals of Canada, 2nd edition,
1981 Forsyth, Adrian. Mammals of the Canadian Wild, 1985.
Larsen; The World of the Polar Bear Canadian Wildlife
Service Report; Denning Habits of the Polar Bear, Smithonian,
February, 1978 Stirling, Ian. Polar Bears. Ann Arbor:
The University of Michigan Press, 1988. Whitfield, Dr.
Philip,The Simon & Schuster Encyclopedia of Animals
, 1998. |
|
|
