Essay/Term paper: Polar bears

Essay, term paper, research paper:  Science

Polar bears are big, white bears (sometimes darker fur) that live in
very cold regions like around the artic poles. There are 21,000 to 28,000
Polar bears alive that are known. Polar bears swim in water and are
carnivores, they eat fish . Polar bears feed mainly on ringed seals and
bearded seals. Depending upon their location, they also eat harp and hooded
seals and eat carcasses of beluga whales, walruses, narwhals, and Bowhead
whales.
A polar bears' stomach can hold up to 15% to 20% of its body weight. It
can use 84% of the protein and 97% of the fat it eats.
Polar bears need about 2 kg (4.4 lb.) of fat per day to survive. A
ringed seal weighing 55 kg (121 lb.) could provide up to eight days of
energy for a polar bear. On cold days polar bears curl up and cover their
muzzle area. During the winter, some polar bears leave their dens and find
other places to stay warm. They may use these shelters for several months at
a time.
Polar bears generally walk with a steady, clumsy walk. The front paws
swing towards the sides with each step, landing slightly pigeon-toed. The
head swings from side to side. The walk has a four-beat pattern, first the
right front foot touches the ground, then the left back foot, then the left
front foot, and lastly, the right back foot.
Humans may encounter polar bears wherever human and polar bear habitats
come together. Polar bear attacks occur most often at sites of human camp
where they fish and hunt or in towns close by polars' habitat. Compared to
other bears, polar bears are more willing to consider humans as prey. Most
likely the person attacked is killed, unless the polar bear is killed first.
Polar bears can live up to 20 to 30 years, but only a few of the polar
bears live past 15 to 18 years. The oldest known polar bear in the Arctic
lived 32 years. And the oldest polar bear in a zoo lived 41 years.
Adult polar bears have no natural predators. Males sometimes kill other
males competing for mates. Males rarely kill females protecting cubs. Cubs
less than one year old sometimes are prey to adult male polar bears and
other meat eaters, such as wolves. Newborn cubs may be killed by mothers
that are hungry.
Polar bears have been hunted for thousands of years. Evidence of human
polar bear hunts have been found in 2,500- to 3,000-year-old ruins. Arctic
people have hunted polar bears for food, clothing, bedding, and
religious-sacrifice purposes. Hunting of polar bears for hides began as
early as the 1500s. Kills increased a lot in the 1950s and 1960s when
hunters began using snowmobiles, boats, and airplanes to hunt polar bears.
Public concern about this type of hunting led to an international agreement
in 1973 banning the use of aircraft or large motor boats for polar bear
hunts. Hunting is the greatest single cause of polar bear deaths.
Today, polar bears are hunted by native Arctic people mostly for food,
clothing, souvenirs and sale of furs. Polar bears are also killed in defense
of people or their land. Hunting is government-regulated in Canada,
Greenland, and the United States. Though hunting is now illegal in Norway
and Russia.
There are environmental factors, too. Oil spills from tankers
threaten polar bears. A polar bear's fur loses its insulation when covered
with oil. And oil spills could contaminate polar bear food sources.
The presence of toxic chemicals in polar bears may have long-term effects on
their health. Toxic chemicals from worldwide industrial businesses are
carried to the Arctic by air, rivers, and oceans. Arctic animals in higher
food chain levels get larger amounts of toxic chemicals in their tissues
than those below them. Polar bears, at the top of the food chain, develop
the highest levels of all.
Human-made toxic chemicals such as polychlorinated biphenyls (PCBs),
dichlorodiphenyltrichloroethane (DDT), and chlordanes are present in the
Arctic. These chemicals have been found in really high levels in the tissues
of polar bears. Scientists continue to watch the levels of toxic chemicals
in polar bears to determine their long-term effects. Radionuclides, from
nuclear waste dumping in the Russian Arctic, may have effects on polar
bears, and the Arctic ecosystem as a whole.
Starvation is the greatest threat to young polar bears. Babies are not
good enough at hunting, and often are chased from prey by larger adults.
Older, weaker bears also are vulnerable to starvation.
As in any animal population, a variety of diseases and parasites can be
responsible for polar bear illnesses. Polar bears are especially unprotected
to the parasitic worm Trichinella, which they contract by feeding on
infected seals. Trichinella larvae are in various parts of the polar bear's
body, usually muscle tissue. If enough larvae is in one area, such as the
heart, the tissue becomes very damaged. Death may occur.
The scientific classification of polar bears is:

Order = Carnivora
The scientific order Carnivora includes bears, dogs, cats, raccoons,
otters, weasels, and their relatives. All carnivores have well developed
claws and a pair of cheek teeth for cutting hard foods.

Family = Ursidae
All bears belong to this family. The family is divided into three
subfamilies, Ursinae (black bears, brown bears, polar bears, sloth bears,
and sun bears), Tremarctinae (spectacled bears), and Ailuropodinae (giant
pandas).


Genus species = Ursus maritimus.
There are five other species in the genus Ursus: brown bears, American
black bears, Asiatic black bears, sun bears, and sloth bears. Species can be
distinguished by size, build, color, and habitat.


Fossil Record
The oldest known polar bear fossil is less than 100,000 years old.
Polar bears probably developed during the Pleistocene era from an ancestral
brown bear. Polar bears and brown bears are still closely related; when
cross-bred, they make fertile offspring.