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Ecology of the Arctic

polar bear

Polar bear (Ursus maritimus) also called White Bear, Water Bear, Sea Bear, or Ice Bear (Ursus maritimus, formerly Thalarctos maritimus), semiaquatic northern bear, family Ursidae, found throughout Arctic regions, generally on drifting oceanic ice floes. The polar bear is sought for its trophy value and (especially by Eskimo) for its hide, tendons, fat, and flesh; the liver, however, is inedible and often poisonous because of its high vitamin A content. Since 1973 the polar bear has been protected by an international agreement that allows hunting of polar bears only by local populations using traditional weapons. Camouflaged against ice and snow by its whitish fur, the polar bear is a swift and wide-ranging traveler. It swims very well and is often found many miles from land or ice packs. The polar bear stalks and captures its primary prey, the seal, whose southward migrations it may follow as far south as the Gulf of St. Lawrence in Canada and the mouth of the Amur River in Russia. It supplements its diet with fish, seaweed, grass, birds, caribou, and the occasional stranded whale. The male polar bear, which is usually larger than the female, ranges in weight from about 410 to 720 kg (about 900 to 1,600 pounds). It grows to about 1.6 m (5.3 feet) at the shoulder and 2.22.5 m in length (also having a tail of 712 cm [34 inches]). The hairy soles of the polar bear's broad feet protect and insulate it from the cold and also facilitate movement across the ice. An elongated neck supports its relatively small head. The polar bear is usually shy but is dangerous when confronted or attacked. One to four (usually two) cubs are born in winter, in a den of ice or snow, after a gestation period of 240270 days. Cubs weigh about 1 kg at birth and remain with their mother for 10 months to 2 years.

 

polar bear


Polar bear (Ursus maritimus)

 

Polar Bears

Polar Bear Status Report

Polar bears are a potentially threatened species that live in the circumpolar north. They are animals that know no boundaries. They pad across the ice from Russia to Alaska, from Canada to Greenland and on over to Norway's Svalbard archipelago. Biologists estimate their population at 22,000 to 27,000 bears, of which around 15,000 are in Canada. 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. Here is what they encounter in each nation:

 


[ Polar Bear Cubs | Polar Bear I.Q. | Polar Bear Fur | The Sea Bear ]

About the Polar Bear

  • Scientists believe that Ursus maritimus, the "sea bear," evolved about 200,000 years ago from brown bear ancestors.
  • Polar bears are superbly adapted for survival in the Far North.
  • Polar bears are the world's largest land predators. They top the food chain in the Arctic, where they dine primarily on seals.
  • Adult male polar bears weigh from 775 to more than 1,500 pounds. Females are considerably smaller, normally weighing 330 to 550 pounds.
  • Polar bears range throughout the Arctic in areas where they can hunt seals at open leads. The five "polar bear nations" where the ice bears are found include the U. S. (Alaska), Canada, Russia, Denmark (Greenland), and Norway.

Polar Bear Cubs

  • Female polar bears usually have two cubs. Though mating takes place in April or May, the fertile ova are not implanted until the following fall when the mother prepares to go into the den. (This process is known as delayed implantation.)
  • The female polar bear gives birth to her cubs about two months after she enters the den. Newborns are 12 to 14 inches long and weigh little more than a pound.
  • Six out of 10 polar bear cubs die in their first year, victims of starvation, predation or accidents. The high rate is partly due to native hunters, who have been known to kill both mothers and cubs.
  • Although most female polar bears make very good mothers, malnourished or inexperienced sows have been known to kill one or both of their cubs.
  • For at least 20 months, polar bear cubs drink their mother's milk and depend on her for survival. Their mother's success at hunting seals directly influences their own well-being.
  • On at least one occasion, biologists have observed a "natural adoption" among polar bears. In the case in question, a female was tagged with a different set of cubs from those she was accompanying just months before.
  • Females with cubs generally avoid adult male bears, which sometimes attack the young and eat them. Highly protective mother bears are capable of driving off much larger males.
  • Mother polar bears can be so protective of their young that they have been known to rear up and leap at helicopters carrying research scientists. Studies have shown that darted and tagged female bears consistently produce smaller litters and lighter cubs. If tagged in the den area, many pregnant females abandon the site.
  • The world's densest concentration of polar bear birth dens lies off the Siberian coast of Wrangel Island. About 500 have been mapped.
  • Females in the Low Arctic wean their cubs as they approach their second birthday, while those in the High Arctic, where conditions are more demanding, care for their cubs an additional year. Young bears are considered "subadults" until they reach maturity at age five or six.
  • Biologists believe that starvation is the leading cause of death for subadult bears.
  • Those polar bears that manage to survive to adulthood have learned to master the challenges of arctic life. The annual mortality rate of adult bears is surprisingly low--as little as five percent a year.
  • An adult polar bear's only enemies are human hunters and, on rare occasions, other bears.
  • In the wild, adult polar bears live an average of 15 to 18 years, though biologists have tagged a few bears in their early 30s. In zoos, many captive bears live until their mid- to late 30s. One individual in London lived to the ripe old age of 41.

Sources: Polar Bear by Downs Matthews (Chronicle Books, San Francisco, 1993); Polar Bears by Ian Stirling (University of Michigan Press, Ann Arbor, 1988); Campbell Elliott, regional wildlife manager, Manitoba.


Polar Bear I.Q.

Success at hunting seals may not be measured on a standard I. Q. test, but scientist Alison Ames considers it a sign of the polar bear's brain power.

As part of a study funded by the Universities Federation for Animal Welfare, Ames researched the behavior of captive polar bears in British zoos. She has seen her subjects stack heaps of pipes that they later knock over in elaborate games. She has also watched them smash open ice blocks in order to extract imbedded fish.

Her conclusion: the great white bears are just as smart as apes.

"This is learned behavior and reveals that polar bears are very intelligent animals," Ames told the London Observer. "They are highly cognitive creatures that top the food chain in polar regions. You have to be very clever to do that. Hunting and trapping a seal is no easy matter."

Because of the polar bear's intelligence, Ames favors a move away from the concrete cages of the past. "[Polar bears] respond well to stimulating environments," she says. "They like areas of sand, grass, and hard ground in their enclosures."


Polar Bear Fur

  • Despite what our eyes tell us, a polar bear's fur is not white. Each hair shaft is pigment-free and transparent with a hollow core.
  • Polar bears look white because the hollow core scatters and reflects visable light, much like ice and snow does.
  • When photographed with film sensitive to ultraviolet light, polar bears appear black.

     Early speculation over this discrepancy produced a theory, now widely repeated as fact, that polar bear hair acts like a fiber optic guide to conduct ultraviolet light to the skin.
     In 1998, Daniel W. Koon, a physicist at St. Lawrence University in
Canton, New York, decided to actually test whether or not polar bear hair could efficiently conduct ultraviolet light.
     Koon and a graduate assistant, Reid Hutchins, obtained polar bear hair from the
Seneca Park Zoo in Rochester. Their experiments showed that a one-fifth inch strand of polar bear hair was able to conduct less than a thousandth of a percent of the applied ultraviolet light. With such a high loss rate, meaningful amounts of ultraviolet light cannot be reaching a polar bear's skin.
     Instead, Koon believes the ultraviolet light is absorbed by the keratin making up the hair.

  • In 1979, three polar bears at the San Diego Zoo turned green. Scientists discovered that colonies of algae were growing in the bears' hollow hair shafts.
  • Although the algae in no way harmed the animals, zoo veterinarian Phillip Robinson restored the bears' white fur by killing the algae with a salt solution.
  • The fur on a polar bear cub is whiter than that of adult bears. In older bears, fur colors range from white to almost yellow.
  • Hybrid cubs born to captive polar bears and their close relative, the brown bear, are white at birth but later turn blue-brown or yellow-white.
  • A polar bear is so well-insulated that it experiences almost no heat loss. In addition to its insulating fur, the bear's blubber layer can measure 4.5 inches thick.
  • So effective is the polar bear's insulation that adult males quickly overheat when they run.
  • Because polar bears give off no detectable heat, they do not show up in infrared photographs. (Infrared film measures heat.) When a scientist attempted to photograph a bear with such film, he produced a print with a single spot--the puff of air caused by the animal's breath.

Sources: Lords of the Arctic by Richard C. Davids (Macmillan Publishing, 1982); Polar Bears by Ian Stirling (University of Michigan Press, Ann Arbor, 1988); Daniel W. Koon, "Is Polar Bear Hair Fiber Optic?", Applied Optics, Vol 37, page 3198.


The Sea Bear

  • The polar bear's Latin name, Ursus maritimus, or "Sea Bear," refers to the animal's close association with the Arctic's chilly waters.
  • Alone among bears, the polar bear is considered a marine mammal.
  • Polar bears are often seen along open leads, where they hunt seals, as well as on the pack ice.
  • Polar bears spend as much time on the ice as they do on land.
  • Polar bears are champion swimmers. They have been known to swim more than 60 miles without a rest.
  • The polar bear's swimming limit is not known.
  • Polar bears have been clocked swimming as fast as six miles per hour.
  • A polar bear's forepaws are partially webbed to assist it in swimming. The massive size of the forepaws help as well. Each measures up to 12 inches in diameter.
  • Polar bears are skilled divers. They easily swim from one ice floe to the next.
  • When a polar bear emerges from the water, it shakes water from its fur like a dog.
  • A polar bear also wrings water from its fur by dragging itself across the ice.
  • Polar bears have excellent underwater vision. They can spot food up to 15 feet away.
  • The polar bear's fat layer, which is three to four inches thick, not only protects it from the cold, but adds to its bouyancy in the water.


Polar bears live year round near arctic waters hunting seal and other animals, rarely coming on land except on islands and rocky points.  In winter they hunt along the Arctic shelfs looking for tasty seals, fish, and even humans!  Their white coats provide camouflage in the ice and snow which make them almost invisible as they stalk their prey. 

Picture

Polar Bear
Photo William Fitzhugh

In winter, when they are far from land they search for breathing holes made by seals.  When the seal comes up for air, the polar bear will kill it and flip it out of the water with a single blow of its great clawed paw! Polar bears are very dangerous, and grow to a huge size and weigh as much as small automobile (1000 pounds). They have longer legs than other bears and large furry feet. These big feet help to distribute their weight as they walk on thin ice in the arctic waters. Polar bears are strong swimmers and can stay submerged for two minutes at a time. Their fur is made of hollow hairs which trap air and help to insulate them in the frigid waters.  Picture

Polar Bear
Photo Corel

In November polar bears retire to dens dug out of the snow or permafrost. The females remain until the spring when they emerge with one or two cubs who stay with them for the next year and a half. The males spend a shorter time in the dens and may be seen out and about at any time of the year.

19th Century Naturalist
Edward Nelson Recounts:

"The Eskimo of Saint Lawrence Island and the American coast are well supplied with firearms which they use when bear-hunting.  In winter, north of the straits, the bears often become thin and very savage from lack of food.

A number of Eskimo on the Alaskan coast show frightful scars obtained in contests with them in winter.  One man, who came on board the Corwin, had the entire skin and flesh torn from one side of his head and face including the eye and ear, yet had escaped and recovered. One incident was related to me which occurred near Point Hope during the winter of 1880-'81. Men went out from Point Hope during one of the long winter nights to attend to their seal nets, which were set through holes in the ice.  While at work near each other, one of the men heard a bear approaching over the frosty snow, and having no weapon but a small knife, and the bear being between him and the shore, he threw himself upon his back on the ice and waited.  The bear came up and for a few moments smelled about the man from head to foot, and finally pressed his cold nose against the man's lips and nose and sniffed several times; each time the terrified Eskimo held his breath until, as he afterwards said, his lungs nearly burst. The bear suddenly heard the other man at work, and listening for a moment he started towards him at a gallop, while the man he left sprang to his feet and ran for his life for the village and reached it safely.  At midday, when the sun had risen a little above the horizon, a large party went out to the spot and found the bear finishing his feast upon the other hunter and soon dispatched him.  Cases similar to this occur occasionally al1 along the coast where the bear is found in winter."

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