The polar bear’s Latin name, Ursus maritimus, literally means “sea bear” and
refers to the animal’s close association with the Arctic waters. The polar bear,
which spends as much time in the ocean as it does on land, is considered to be a
marine mammal. Polar bears are excellent swimmers, and whilst the limit of their
endurance has not been tested, they have been known to swim non-stop for up to
60 miles and reach speeds up to 6 miles per hour. To assist them with this
aquatic feat, the polar bear has large partially webbed forepaws measuring up to
30 cm in diameter. These paws are as remarkable on land as they are in the
water, for the soles contain specialised vacuoles, known as papillae, which act
similarly to suction cups and enable the bear to move upon the surface of an ice
flow without slipping. When the ice is particularly thin, these bears crawl on
their bellies, evenly distributing their weight, and hence avoid falling through
the ice.
Distribution, Population and Range: The current global population of polar bears
is estimated between 22 000 and 27 000 bears, residing in nineteen discrete
populations across Alaska, Canada, Russia, Greenland and Norway. Of this 3-5 000
animals reside in Alaska divided between the Berring Sea population to the west
and the Beaufort Sea population to the north-east. Generally believed to be a
nomadic species, averaging over 6000 km a year, research has shown that polar
bears do in fact have a describable home range. Far greater than the range of
any other species of bear, it is believed that it may extend to an area twice
the size of Icelend! The size of this range is dependent upon the availability
of food, with overlapping ranges occurring in seal abundant regions. Once
weaned, sub-adult bears have been noted to travel up to 1000 km away from their
mother in order to establish an independent home range.
Physical Characteristics: Despite appearing to be white in actual fact the polar
bear’s fur is not. Each hair shaft is pigment-free and transparent with a hollow
core. Polar bears look white because the hollow core scatters and reflects
visible light, in a similar manner to ice and snow. Polar bears often appear to
turn a yellowish hue as they age and some have even been noted to turn green.
When the hairs are examined closely microscopic algae have been identified as
growing inside the hair shaft. When photographed with film sensitive to
ultraviolet light, polar bears appear black.
Keeping Warm: The polar bear has black skin to assist with thermal insulation,
warming the bear. In addition they possess a layer of insulating blubber which
is over 4 inches thick. So effective are these creatures at keeping warm,
despite the cold climate, polar bears are often in danger of overheating
especially when exerting energy during a hunt. Amazing as it may seem, the polar
bears are so adapted to retaining warmth that they don’t detectably radiate heat
and, as a result, do not show up in infra-red photographs!
Diet: Polar bears inhabit areas where the highest concentrations of food can be
found. Polar bears are the only species of bear which are almost exclusively
carnivorous and are the world’s largest land predator. They feed upon ringed and
bearded seals, young walruses and the occasional beluga. They have been known to
eat carrion and, when conditions are extremely harsh, the occasional berry or
leaf!
As an opportunistic hunter, the polar bear experiences cycles of feasting and
fasting, yet surprisingly they do not object to sharing a carcass with other
bears, providing the correct submissive protocol is displayed.
Hibernation: Male polar bears can grow extremely large and weigh up to 600kg.
The females, however, remain much smaller and weigh up to 300kg. The natural
lifespan of a polar bear in the wild is between 15-20 years. Strictly speaking
polar bears do not hibernate as there is no evidence of a marked reduction in
either body temperature or heart rate. Instead the females undergo a period
referred to as ‘denning’. The heart rate will slow and the body temperature
lower, they sleep deeply but they do not experience the difficulty awakening of
truly hibernating bears. Males and sub-adults remain active all year whilst the
pregnant females experience a denning period, selecting a site within a snow
drift alongside a mountain slope.
Family Life: Female polar bears usually have two cubs. Though mating takes place
in April, delayed implantation occurs and the female ova aren’t implanted until
the following autumn when the mother prepares to den. The mother gives birth to
her 500gram cubs two months after entering the den. Sadly, only forty per cent
of the cubs survive their first 12 months, succumbing to predation, inclement
weather and starvation. However, once adult, the polar bear is so well adapted
to its environment that the mortality rate drops to less than 5%. Mother bears
are highly protective and have been known to leap up at research scientists in
their helicopters who have been studying their behaviour. The cubs are dependent
upon the mother’s milk for the first twenty months of life. The polar bear is
renowned for being the most aggressive of all bear species.
Conservation Status: Polar bears are listed on Appendix 2 of CITES, which
implies that they can be traded commercially but only if this trade does not
affect the survival of the species. In 1973, the five nations with polar bear
populations (Canada, Denmark, which governed Greenland, Norway, the U.S., and
the former U.S.S.R.) entered into the International Agreement for the
Conservation of Polar Bears. The US Marine Mammal Protection Act also affords
protection for the species. This makes the polar bear the only species of bear
to have international protection.
Threats: Perhaps the largest threat facing this species of bear is the advent of
global warming. A measurable detrimental effect in the average body size and
reproductive capability of bears has been demonstrated as a direct consequence
of temperature change. The rise in temperature has resulted in prolonged
ice-free periods which have left the polar bear stranded on shore resulting in
severe weight loss. Pregnant females fail to lactate and the mortality rate of
cubs has escalated.
In addition, non-biodegradable chemical pollutants accumulated over the years in
the Arctic region, and have had an adverse effect on the ecosystem. Oil and gas
spills are common occurrences and now, with the environmental policies of new
Bush Administration revealed, the integrity and preservation of the Arctic
National Wildlife Reserve in North-eastern Alaska is under threat. As Defenders
of Wildlife acknowledge this area sustains the most critical onshore denning
habitat of the entire Beaufort Sea polar bear population in the nation. As a
result of oil and gas exploration encroaching into this refuge these bears will
abandon their dens, thus abandoning their young to starvation. To this end
Defenders of Wildlife have launched what is perhaps the world’s largest e-mail
petition to cease this proposal. This petition can be viewed at:
www.savearcticrefuge.org.
We urge you to write to the Bush Administration expressing your outrage at the
proposed oil and gas development in the Arctic National Wilderness Refuge.
References: I am indebted to Polar Bears Alive, a “non-profit organisation
dedicated to the world wide conservation of the polar bear and its arctic
habitat” for much of the information displayed here. Established in 1992 by Dr
Dan Guravich this organisation has provided excellent awareness and education
schemes. Their web-site is excellent and can be viewed at:
www.polarbearsalive.org.
Polar Bears by Downs Matthews (Chronicle Books, San Fransisco,1993); Polar Bears
by Ian Stirling (University of Michigan Press, Ann Arbor, 1988); Polar Bears:
Living with the White Bear, by Nikita Ovsyanikov (Voyageur Press, Stillwater,
MN,1996); Polar Dance by Fred Bruemmer (Images of Nature, Omaha,1997); World of
the Polar Bear by Fred Bruemmer (Key Porter Books, Toronto,1989); Lords of the
Arctic by Richard.C.Davids (Macmillan Publishing, 1982); Daniel. W. Koon, “Is
Polar Bear Hair Fibre Optic?” Applied Optics, Vol.37, page 3198.
|
