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Polar bear

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Polar Bear
Conservation status
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Order: Carnivora
Family: Ursidae
Genus: Ursus
Species: U. maritimus
Binomial name
Ursus maritimus
Phipps, 1774[2]
Polar bear range
Synonyms

Ursus eogroenlandicus
Ursus groenlandicus
Ursus jenaensis
Ursus labradorensis
Ursus marinus
Ursus polaris
Ursus spitzbergensis
Ursus ungavensis
Thalarctos maritimus

The polar bear (Ursus maritimus) is a bear native largely within the Arctic circle encompassing the Arctic Ocean, its surrounding seas and surrounding land masses. It is the world's largest land carnivore and also the largest bear, together with the omnivorous Kodiak bear, which is approximately the same size.[3] An adult male weighs around 350–680 kg (770–1,500 lb),[4] while an adult female is about half that size. Although it is closely related to the brown bear, it has evolved to occupy a narrow ecological niche, with many body characteristics adapted for cold temperatures, for moving across snow, ice, and open water, and for hunting the seals which make up most of its diet.[5] Although most polar bears are born on land, they spend most of their time at sea (hence their scientific name meaning "maritime bear") and can hunt consistently only from sea ice, so spend much of the year on the frozen sea.

The polar bear is classified as a vulnerable species, with 8 of the 19 polar bear subpopulations in decline.[6] For decades, unrestricted hunting[clarification needed] raised international concern for the future of the species; populations have rebounded after controls and quotas began to take effect.[citation needed] For thousands of years, the polar bear has been a key figure in the material, spiritual, and cultural life of Arctic indigenous peoples, and the hunting of polar bears remains important in their cultures.

The IUCN now lists global warming as the most significant threat to the polar bear, primarily because the melting of its sea ice habitat reduces its ability to find sufficient food. The IUCN states, "If climatic trends continue polar bears may become extirpated from most of their range within 100 years."[7] The polar bear was listed as a threatened species under the Endangered Species Act by the United States Department of the Interior in 2008.

Contents

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Naming and etymology

Constantine John Phipps was the first to describe the polar bear as a distinct species.[7] He chose the scientific name Ursus maritimus, the Latin for 'maritime bear',[8] due to the animal's native habitat. The Inuit refer to the animal as nanook,[9] (transliterated as nanuuq in the Inupiaq language,[10]. The Yupik also refer to the bear by nanuuk in Siberian Yupik.[citation needed]) The bear is umka in the Chukchi language. In Russian, it is usually called бе́лый медве́дь (bélyj medvédj, the white bear), though an older word still in use is ошку́й (Oshkúj, which comes from the Komi oski, "bear").[11] In French, the polar bear is referred to as ours blanc ("white bear") or ours polaire ("polar bear").[12] In the Norwegian administered Svalbard archipelago, the polar bear is referred to as Isbjørn ("ice bear").

The polar bear was previously considered to be in its own genus, Thalarctos.[13] However, evidence of hybrids between polar bears and brown bears, and of the recent evolutionary divergence of the two species, does not support the establishment of this separate genus, and the accepted scientific name is now therefore Ursus maritimus, as Phipps originally proposed.[14]

Taxonomy and evolution

Polar bears depend on sea ice as a platform for hunting seals. Large feet and short, sharp, stocky claws are adaptations to this environment.

The bear family, Ursidae, is believed to have split off from other carnivorans about 38 million years ago. The Ursinae subfamily originated approximately 4.2 million years ago. According to both fossil and DNA evidence, the polar bear diverged from the brown bear, Ursus arctos, roughly 150,000 years ago.[15] The oldest known polar bear fossil is a 130,000 to 110,000-year-old jaw bone, found on Prince Charles Foreland in 2004.[15] Fossils show that between ten to twenty thousand years ago, the polar bear's molar teeth changed significantly from those of the brown bear. Polar bears are thought to have diverged from a population of brown bears that became isolated during a period of glaciation in the Pleistocene.[16]

More recent genetic studies have shown that some clades of brown bear are more closely related to polar bears than to other brown bears,[17] meaning that the polar bear is not a true species according to some species concepts.[18] In addition, polar bears can breed with brown bears to produce fertile grizzly–polar bear hybrids,[16][19] indicating that they have only recently diverged and are genetically similar.[20] However, because neither species can survive long in the other's ecological niche, and because they have different morphology, metabolism, social and feeding behaviors, and other phenotypic characteristics, the two bears are generally classified as separate species.[20]

When the polar bear was originally documented, two subspecies were identified: Ursus maritimus maritimus by Constantine J. Phipps in 1774, and Ursus maritimus marinus by Peter Simon Pallas in 1776.[21] This distinction has since been invalidated.

One fossil subspecies has been identified. Ursus maritimus tyrannus—descended from Ursus arctos—became extinct during the Pleistocene. U.m. tyrannus was significantly larger than the living subspecies.[16]

Polar bears investigate the submarine USS Honolulu 280 miles (450 km) from the North Pole.

Population and distribution

The polar bear is found in the Arctic Circle and adjacent land masses. Due to the absence of human development in its remote habitat, it retains more of its original range than any other extant carnivore.[22] While they are rare north of 88°, there is evidence that they range all the way across the Arctic, and as far south as James Bay in Canada. They can occasionally drift widely with the sea ice, and there have been anecdotal sightings as far south as Berlevåg on the Norwegian mainland and the Kuril Islands in the Sea of Okhotsk. It is difficult to estimate a global population of polar bears as much of the range has been poorly studied, however biologists use a working estimate of about 20,000-25,000 polar bears worldwide.[1][23]

There are 19 generally recognized discrete subpopulations.[23][24] The subpopulations display seasonal fidelity to particular areas, but DNA studies show that they are not reproductively isolated.[25] The thirteen North American subpopulations range from the Beaufort Sea south to Hudson Bay and east to Baffin Bay in western Greenland and account for about 70% of the global population. The Eurasian population is broken up into the eastern Greenland, Barents Sea, Kara Sea, Laptev Sea, and Chukchi Sea subpopulations, though there is considerable uncertainty about the structure of these populations due to limited mark and recapture data.

Polar bears play-fighting

The range includes the territory of five nations: Denmark (Greenland), Norway(Svalbard), Russia, US (Alaska) and Canada. These five nations are the signatories of the 1973 International Agreement for the Conservation of Polar Bears, which mandates cooperation on research and conservations efforts throughout the polar bear's range.

Modern methods of tracking polar bear populations have been implemented only since the mid-1980s, and are expensive to perform consistently over a large area.[26] The most accurate counts require flying a helicopter in the Arctic climate to find polar bears, shooting a tranquilizer dart at the bear to sedate it, and then tagging the bear.[26] In Nunavut, some Inuit have reported increases in bear sightings around human settlements in recent years, leading to a belief that populations are increasing. Scientists have responded by noting that hungry bears may be congregating around human settlements, leading to the illusion that populations are higher than they actually are.[26] The Polar Bear Specialist Group of the IUCN takes the position that "estimates of subpopulation size or sustainable harvest levels should not be made solely on the basis of traditional ecological knowledge without supporting scientific studies."[27]

Of the 19 recognized polar bear subpopulations, 8 are declining, 3 are stable, 1 is increasing, and 7 have insufficient data.[6][23]

Habitat

A cub nursing

The polar bear is often regarded as a marine mammal because it spends many months of the year at sea.[28] Its preferred habitat is the annual sea ice covering the waters over the continental shelf and the Arctic inter-island archipelagos. These areas, known as the "Arctic ring of life", have high biological productivity in comparison to the deep waters of the high Arctic.[22][29] The polar bear tends to frequent areas where sea ice meets water, such as polynyas and leads (temporary stretches of open water in Arctic ice), to hunt the seals that make up most of its diet.[30] Polar bears are therefore found primarily along the perimeter of the polar ice pack, rather than in the Polar Basin close to the North Pole where the density of seals is low.[31]

A polar bear.

Annual ice contains areas of water that appear and disappear throughout the year as the weather changes. Seals migrate in response to these changes, and polar bears must follow their prey.[29] In Hudson Bay, James Bay, and some other areas, the ice melts completely each summer (an event often referred to as "ice-floe breakup"), forcing polar bears to go onto land and wait through the months until the next freeze-up.[29] In the Chukchi and Beaufort seas, polar bears retreat each summer to the ice further north that remains frozen year-round.

Biology and behavior

Physical characteristics

Polar bear skeleton

The polar bear is the largest terrestrial carnivore, being more than twice as big as the Siberian Tiger.[32] It shares the title of largest land predator (and largest bear species) with the Kodiak bear.[33] Adult males weigh 350–680 kg (770-1500 lbs) and measure 2.4–3 m (7.9–9.8 ft) in length.[34] Adult females are roughly half the size of males and normally weigh 150–249 kg (330–550 lb), measuring 1.8–2.4 metres (5.9–7.9 ft) in length. When pregnant, however, they can weigh as much as 499 kg (1,100 lb).[34] The polar bear is among the most sexually dimorphic of mammals, surpassed only by the pinnipeds.[35] The largest polar bear on record, reportedly weighing 1,002 kg (2,210 lb), was a male shot at Kotzebue Sound in northwestern Alaska in 1960.[36]

Polar bears have evolved unique features for Arctic life, including furred feet that have good traction on ice.

Compared with its closest relative, the brown bear, the polar bear has a more elongated body build and a longer skull and nose.[20] As predicted by Allen's rule for a northerly animal, the legs are stocky and the ears and tail are small.[20] However, the feet are very large to distribute load when walking on snow or thin ice and to provide propulsion when swimming; they may measure 30 cm (12 in) across in an adult.[37] The pads of the paws are covered with small, soft papillae (dermal bumps) which provide traction on the ice.[20] The polar bear's claws are short and stocky compared to those of the brown bear, perhaps to serve the former's need to grip heavy prey and ice.[20] The claws are deeply scooped on the underside to assist in digging in the ice of the natural habitat. Despite a recurring Internet meme that all polar bears are left-handed,[38][39] there is no scientific evidence to support this claim.[40] Unlike the brown bear, Polar Bears in captivity are rarely overweight or particularly large, possibly as a reaction to the warm temperatures of most zoos.

The 42 teeth of a polar bear reflect its highly carnivorous diet.[20] The cheek teeth are smaller and more jagged than in the brown bear, and the canines are larger and sharper.[20] The dental formula is:[20]

Dentition
3.1.4.2
3.1.4.3

Polar bears are superbly insulated by up to 10 cm (3.9 in) of blubber,[37] their hide and their fur; they overheat at temperatures above 10 °C (50 °F), and are nearly invisible under infrared photography.[41] Polar bear fur consists of a layer of dense underfur and an outer layer of guard hairs, which appear white to tan but are actually transparent.[37] The guard hair is 5–15 cm (2.0–5.9 in) over most of the body.[42] Polar bears gradually moult from May to August,[43] but, unlike other Arctic mammals, they do not shed their coat for a darker shade to camouflage themselves in the summer conditions. The hollow guard hairs of a polar bear coat were once thought to act as fiber-optic tubes to conduct light to its black skin, where it could be absorbed; however, this theory was disproved by recent studies.[44]

Polar bear diving in a zoo
A polar bear in a synthetic arctic zoo environment.

The white coat usually yellows with age. When kept in captivity in warm, humid conditions, the fur may turn a pale shade of green due to algae growing inside the guard hairs.[45] Males have significantly longer hairs on their forelegs, that increase in length until the bear reaches 14 years of age. The male's ornamental foreleg hair is thought to attract females, serving a similar function to the lion's mane.[46]

The polar bear has an extremely well-developed sense of smell, being able to detect seals nearly 1 mi (1.6 km) away and buried under 3 ft (0.91 m) of snow.[47] Its hearing is about as acute as that of a human, and its vision is also good at long distances.[47]

The polar bear is an excellent swimmer and individuals have been seen in open Arctic waters as far as 200 mi (320 km) from land. With its body fat providing buoyancy, it swims in a dog-paddle fashion using its large forepaws for propulsion.[48] Polar bears can swim 6 miles/hour. When walking, the polar bear tends to have a lumbering gait and maintains an average speed of around 5.5 km/h (3.5 m.p.h.).[48]

Hunting and diet

The long muzzle and neck of the polar bear help it to search in deep holes for seals, while powerful hindquarters enable it to drag massive prey.[49]

The polar bear is the most carnivorous member of the bear family, and most of its diet consists of ringed and bearded seals.[50] The Arctic is home to millions of seals, which become prey when they surface in holes in the ice in order to breathe, or when they haul out on the ice to rest.[49] Polar bears hunt primarily at the interface between ice, water, and air; they only rarely catch seals on land or in open water.[51]

The polar bear's most common hunting method is called still-hunting:[52] The bear uses its excellent sense of smell to locate a seal breathing hole, and crouches nearby in silence for a seal to appear.[49] When the seal exhales, the bear smells its breath, reaches into the hole with a forepaw, and drags it out onto the ice.[49] The polar bear kills the seal by biting its head to crush its skull.[49] The polar bear also hunts by stalking seals resting on the ice: Upon spotting a seal, it walks to within 100 yd (91 m), and then crouches. If the seal does not notice, the bear creeps to within 30 to 40 feet (9.1 to 12 m) of the seal and then suddenly rushes forth to attack.[49] A third hunting method is to raid the birth lairs that female seals create in the snow.[52]

Polar bear at a whale carcass

A widespread legend tells that polar bears cover their black noses with their paws when hunting. This behavior, if it happens, is rare — although the story exists in native oral history and in accounts by early Arctic explorers, there is no record of an eyewitness account of the behavior in recent decades.[48]

Mature bears tend to eat only the calorie-rich skin and blubber of the seal, whereas younger bears consume the protein-rich red meat.[49] Studies have also photographed polar bears scaling near-vertical cliffs, to eat birds' chicks and eggs [53]. For subadult bears which are independent of their mother but have not yet gained enough experience and body size to successfully hunt seals, scavenging the carcasses from other bears' kills is an important source of nutrition. Subadults may also be forced to accept a half-eaten carcass if they kill a seal but cannot defend it from larger polar bears. After feeding, polar bears wash themselves with water or snow.[48]

The polar bear is an enormously powerful predator. It can kill an adult walrus, although it rarely attempts to as a walrus can be more than twice the bear's weight.[54] Polar bears also have preyed on beluga whales, by swiping at them at breathing holes. The whales are of similar size to the walrus and nearly as difficult for the bear to subdue. Most terrestrial animals in the Arctic can outrun the polar bear on land as polar bears overheat quickly, and most marine animals the bear encounters can outswim it. In some areas, the polar bear's diet is supplemented by walrus calves and by the carcasses of dead adult walruses or whales, whose blubber is readily devoured even when rotten.[55]

With the exception of pregnant females, polar bears are active year-round,[56] although they have a vestigial hibernation induction trigger in their blood. Unlike brown and black bears, polar bears are capable of fasting for up to several months during late summer and early fall, when they cannot hunt for seals because the sea is unfrozen.[56] When sea ice is unavailable during summer and early autumn, some populations live off fat reserves for months at a time.[41] Polar bears have also been observed to eat a wide variety of other wild foods, including muskox, reindeer, birds, eggs, rodents, shellfish, crabs, and other polar bears. They may also eat plants, including berries, roots, and kelp, however none of these are a significant part of their diet.[54] The polar bear's biology is specialized to require large amounts of fat from marine mammals, and it cannot derive sufficient caloric intake from terrestrial food.[57][58]

Being both curious animals and scavengers,[54][59] polar bears investigate and consume garbage where they come into contact with humans.[54] Polar bears may attempt to consume almost anything they can find, including hazardous substances such as styrofoam, plastic, car batteries, ethylene glycol, hydraulic fluid, and motor oil.[54][59] The dump in Churchill, Manitoba was closed in 2006 to protect bears, and waste is now recycled or transported to Thompson, Manitoba.[60][61]

Polar bear males frequently play-fight. During the mating season, actual fighting is intense and often leaves scars or broken teeth.

Behavior

Unlike grizzly bears, polar bears are not territorial. Although stereotyped as being voraciously aggressive, they are normally cautious in confrontations, and often choose to escape rather than fight.[62] Fat polar bears rarely attack humans unless severely provoked, whereas hungry polar bears are extremely unpredictable and are known to kill and sometimes eat humans.[55] Polar bears are stealth hunters, and the victim is often unaware of the bear's presence until the attack is underway.[63] Whereas brown bears often maul a person and then leave, polar bear attacks are more likely to be predatory and are almost always fatal.[63] However, due to the very small human population around the Arctic, such attacks are rare.

In general, adult polar bears live solitary lives. Yet, they have often been seen playing together for hours at a time and even sleeping in an embrace,[55] and polar bear zoologist Nikita Ovsianikov has described adult males as having "well-developed friendships."[62] Cubs are especially playful as well. Among young males in particular, play-fighting may be a means of practicing for serious competition during mating seasons later in life.[64] Polar bears have a wide range of vocalisations, including bellows, roars, growls, chuffs and purrs.[65]

In 1992, a photographer near Churchill took a now widely circulated set of photographs of a polar bear playing with a Canadian Eskimo Dog a tenth of its size.[66][67] The pair wrestled harmlessly together each afternoon for ten days in a row for no apparent reason, although the bear may have been trying to demonstrate its friendliness in the hope of sharing the kennel's food.[66] This kind of social interaction is uncommon; it is far more typical for polar bears to behave aggressively towards dogs.[66]

Reproduction and lifecycle

A polar bear swimming

Courtship and mating take place on the sea ice in April and May, when polar bears congregate in the best seal hunting areas.[68] A male may follow the tracks of a breeding female for 100 km (62 mi) or more, and after finding her engage in intense fighting with other males over mating rights, fights which often result in scars and broken teeth.[68] Polar bears have a generally polygynous mating system; recent genetic testing of mothers and cubs, however, has uncovered cases of litters in which cubs have different fathers.[69] Partners stay together and mate repeatedly for an entire week; the mating ritual induces ovulation in the female.[70]

After mating, the fertilized egg remains in a suspended state until August or September. During these four months, the pregnant female eats prodigious amounts of food, gaining at least 200 kg (440 lb) and often more than doubling her body weight.[68]

Maternity denning and early life

Cubs are born helpless, and typically nurse for two and a half years.

When the ice floes break up in the fall, ending the possibility of hunting, each pregnant female digs a maternity den consisting of a narrow entrance tunnel leading to one to three chambers.[68] Most maternity dens are in snowdrifts, but may also be made underground in permafrost if it is not sufficiently cold yet for snow.[68] In most subpopulations, maternity dens are situated on land a few kilometers from the coast, and the individuals in a subpopulation tend to reuse the same denning areas each year.[22] The polar bears that do not den on land make their dens on the sea ice. In the den, she enters a dormant state similar to hibernation. This hibernation-like state does not consist of continuous sleeping; however, the bear's heart rate slows from 46 to 27 beats per minute.[71] Her body temperature does not decrease during this period as it would for a typical mammal in hibernation.[41][72]

Between November and February, cubs are born blind, covered with a light down fur, and weighing less than 0.9 kg (2.0 lb).[70] On average, each litter has two cubs.[68] The family remains in the den until mid-February to mid-April, with the mother maintaining her fast while nursing her cubs on a fat-rich milk.[68] By the time the mother breaks open the entrance to the den, her cubs weigh about 10 to 15 kilograms (22 to 33 lb).[68] For about 12 to 15 days, the family spends time outside the den while remaining in its vicinity, the mother grazing on vegetation while the cubs become used to walking and playing.[68] Then they begin the long walk from the denning area to the sea ice, where the mother can once again catch seals.[68] Depending on the timing of ice-floe breakup in the fall, she may have fasted for up to eight months.[68]

Cubs may fall prey to wolves or to starvation. Female polar bears are noted for both their affection towards their offspring, and their valiance in protecting them. One case of adoption of a wild cub has been confirmed by genetic testing.[69] Adult male bears occasionally kill and eat polar bear cubs,[73] for reasons that are unclear.[74] In Alaska, 42% of cubs now reach 12 months of age, down from 65% 15 years ago.[75] In most areas, cubs are weaned at two and a half years of age,[68] when the mother chases them away or abandons them. The western coast of Hudson Bay is unusual in that its female polar bears sometimes wean their cubs at only one and a half years.[68] This was the case for 40% of cubs there in the early 1980s; however by the 1990s, fewer than 20% of cubs were weaned this young.[76] After the mother leaves, sibling cubs sometimes travel and share food together for weeks or months.[55]

A female emerging from her maternity den

Later life

Females begin to breed at the age of four years in most areas, and five years in the Beaufort Sea area.[68] Males usually reach sexual maturity at six years, however as competition for females is fierce, many do not breed until the age of eight or ten.[68] A study in Hudson Bay indicated that both the reproductive success and the maternal weight of females peaked in their mid-teens.[77]

Polar bears appear to be less affected by infectious diseases and parasites than most terrestrial mammals.[74] Polar bears are especially susceptible to Trichinella, a parasitic roundworm they contract through cannibalism,[78] although infections are usually not fatal.[74] Only one case of a polar bear with rabies has been documented, even though polar bears frequently interact with Arctic foxes, which often carry rabies.[74] Bacterial Leptospirosis and Morbillivirus have been recorded. Polar bears sometimes have problems with various skin diseases which may be caused by mites or other parasites.

Polar bears rarely live beyond 25 years.[79] The oldest wild bears on record died at the age of 32, whereas the oldest captive was a female who died in 1991 at the age of 43.[80] The oldest living polar bear is Debby of the Assiniboine Park Zoo, who was probably born in December, 1966.[80] The causes of death in wild adult polar bears are poorly understood, as carcasses are rarely found in the species's frigid habitat.[74] In the wild, old polar bears eventually become too weak to catch food, and gradually starve to death. Polar bears injured in fights or accidents may either die from their injuries or become unable to hunt effectively, leading to starvation.[74]

Ecological role

A female nursing a two-year-old cub

The polar bear is the apex predator within its range. Several animal species, particularly Arctic Foxes and Glaucous Gulls, routinely scavenge polar bear kills.[48]

The relationship between ringed seals and polar bears is so close that the abundance of ringed seals in some areas appears to regulate the density of polar bears, while polar bear predation in turn, regulates density and reproductive success of ringed seals.[51] The evolutionary pressure of polar bear predation on seals probably accounts for some significant differences between Arctic and Antarctic seals. Compared to the Antarctic, where there is no major surface predator, Arctic seals use more breathing holes per individual, appear more restless when hauled out on the ice, and rarely defecate on the ice.[48] The baby fur of most Arctic seal species is white, presumably to provide camouflage from predators, whereas Antarctic seals all have dark fur at birth.[48]

Polar bears rarely enter conflict with other predators, though recent brown bear encroachments into polar bear territories have led to antagonistic encounters. Brown bears tend to dominate polar bears in disputes over carcasses,[81] and dead polar bear cubs have been found in brown bear dens.[82] Wolves are rarely encountered by polar bears, though there are two records of wolf packs killing polar bear cubs.[83] Polar bears are sometimes the host of arctic mites such as Alaskozetes antarcticus.[48]

Hunting

Indigenous people

Skins of hunted polar bears in Ittoqqortoormiit, Greenland

Polar bears have long provided important raw materials for Arctic peoples, including the Inuit, Yupik, Chukchi, Nenets, Russian Pomors and others. Hunters commonly used teams of dogs to distract the bear, allowing the hunter to spear the bear or shoot it with arrows at closer range.[84] Almost all parts of captured animals had a use.[85] The fur was used in particular to sew trousers and, by the Nenets, to make galoshes-like outer footwear called tobok; the meat is edible, despite some risk of trichinosis; the fat was used in food and as a fuel for lighting homes, alongside seal and whale blubber; sinews were used as thread for sewing clothes; the gallbladder and sometimes heart were dried and powdered for medicinal purposes; the large canine teeth were highly valued as talismans.[86] Only the liver was not used, as its high concentration of vitamin A is poisonous.[87] Hunters make sure to either toss the liver into the sea or bury it in order to spare their dogs from potential poisoning.[86] Traditional subsistence hunting was on a small enough scale to not significantly affect polar bear populations, mostly because of the sparseness of the human population in polar bear habitat.[88]

History of commercial harvest

In Russia, polar bear furs were already being commercially traded in the 14th century, though it was of low value compared to Arctic Fox or even reindeer fur.[86] The growth of the human population in the Eurasian Arctic in the 16th and 17th century, together with the advent of firearms and increasing trade, dramatically increased the harvest of polar bears.[41][89] However, since polar bear fur has always played a marginal commercial role, data on the historical harvest is fragmentary. It is known, for example, that already in the winter of 1784/1785 Russian Pomors on Spitsbergen harvested 150 polar bears in Magdalenefjorden.[86] In the early 20th century, Norwegian hunters were harvesting 300 bears a year at the same location. Estimates of total historical harvest suggest that from the beginning of the 18th century, roughly 400-500 animals were being harvested annually in northern Eurasia, reaching a peak of 1,300 to 1,500 animals in the early 20th century, and falling off as the numbers began dwindling.[86]

In the first half of the 20th century, mechanized and overpoweringly efficient methods of hunting and trapping came into use in North America as well.[90] Polar bears were chased from snowmobiles, icebreakers, and airplanes, the latter practice described in a 1965 New York Times editorial as being "about as sporting as machine gunning a cow."[90] The numbers taken grew rapidly in the 1960s, peaking around 1968 with a global total of 1,250 bears that year.[91]

Contemporary regulations

Concerns over the future survival of the species led to the development of national regulations on polar bear hunting, beginning in the mid-1950s.[92] In 1973, the International Agreement on the Conservation of Polar Bears was signed by all five nations whose territory is inhabited by polar bears Canada, Denmark (Greenland), Norway (Svalbard), the USSR (now the Russian Federation) and the USA (Alaska).

A Norwegian road sign used on Svalbard to warn about the presence of polar bears.

Also known as the Oslo Agreement, it was a rare case of international cooperation during the Cold War. Biologist Ian Stirling commented, "For many years, the conservation of polar bears was the only subject in the entire Arctic that nations from both sides of the Iron Curtain could agree upon sufficiently to sign an agreement. Such was the intensity of human fascination with this magnificent predator, the only marine bear."[93]

Although the agreement is not enforceable in itself, member countries agreed to place restrictions on recreational and commercial hunting, ban hunting from aircraft and icebreakers, and conduct further research.[94] The treaty allows hunting "by local people using traditional methods," although this has been liberally interpreted by member nations. Norway is the only country of the five in which all harvest of polar bears is banned.

Agreements have been made between countries to co-manage their shared polar bear subpopulations. After several years of negotiations, Russia and the U.S. signed an agreement in October 2000 to jointly set quotas for indigenous subsistence hunting in Alaska and Chukotka.[95] The treaty was ratified in October 2007.[96]

Russia

The Soviet Union banned all harvest of polar bears in 1956, however poaching continued and is believed to pose a serious threat to the polar bear population.[24] In recent years, polar bears have approached coastal villages in Chukotka more frequently due to the shrinking of the sea ice, endangering humans and raising concerns that illegal hunting would become even more prevalent.[97] In 2007, the Russian government made subsistence hunting legal for Chukotka natives only, a move supported by Russia’s most prominent bear researchers and the World Wide Fund for Nature as a means to curb poaching.[97]

Greenland

In Greenland, restrictions for the species were first introduced in 1994 and expanded by executive order in 2005.[24] Until 2005, Greenland placed no limit on hunting by indigenous people. It imposed a limit of 150 for 2006. It also allowed recreational hunting for the first time.[98] Other provisions included year-round protection of cubs and mothers, restrictions on weapons used, and various administrative requirements to catalogue kills.[24]

Canada and the United States

Dogsleds are used for recreational hunting of polar bears in Canada. Use of motorized vehicles is forbidden.

About 500 bears are killed per year by humans across Canada,[99] a rate believed by scientists to be unsustainable for some areas, notably Baffin Bay.[23] Canada has allowed sport hunters accompanied by local guides and dog-sled teams since 1970,[100] but the practice was not common until the 1980s.[101] The guiding of sport hunters provides meaningful employment and an important source of income for native communities in which economic opportunities are few.[26] Sport hunting can bring CDN$20,000 to $35,000 per bear into northern communities, which until recently has been mostly from American hunters.[102]

On 15 May 2008, the U.S. listed the polar bear as a threatened species under the Endangered Species Act and banned all importing of polar bear trophies. Importing products made from polar bears had been prohibited from 1972 to 1994 under the Marine Mammal Protection Act, and restricted between 1994 and 2008. Under those restrictions, permits from the United States Fish and Wildlife Service were required to import sport-hunted polar bear trophies taken in hunting expeditions in Canada. The permit process required that the bear be taken from an area with quotas based on sound management principles.[103] Since 1994, more than 800 sport-hunted polar bear trophies have been imported into the U.S.[104]

Ironically, because of the way polar bear hunting quotas are managed in Canada, attempts to discourage sport hunting would actually increase the number of bears killed in the short term.[26] Canada allocates a certain number of permits each year to sport and subsistence hunting, and those that are not used for sport hunting are re-allocated to Native subsistence hunting. Whereas Native communities kill all the polar bears they are permitted to take each year, only half of sport hunters with permits actually manage to kill a polar bear. If a sport hunter does not kill a polar bear before his or her permit expires, the permit cannot be transferred to another hunter.[26]

The territory of Nunavut accounts for 80% of Canadian kills.[99] In 2005, the government of Nunavut increased the quota from 400 to 518 bears,[105] despite protests from some scientific groups.[106] In two areas where harvest levels have been increased based on increased sightings, science-based studies have indicated declining populations, and a third area is considered data-deficient.[107] While most of that quota is hunted by the indigenous Inuit people, a growing share is sold to recreational hunters. (0.8% in the 1970s, 7.1% in the 1980s, and 14.6% in the 1990s)[101] Nunavut polar bear biologist, Mitchell Taylor, who was formerly responsible for polar bear conservation in the territory, insists that bear numbers are being sustained under current hunting limits.[108] The Government of the Northwest Territories maintain their own quota of 72–103 bears within the Inuvialuit communities of which some are set aside for sports hunters.

In 2010, the 2005 increase was partially reversed. Government of Nunavut officials announced that the polar bear quota for the Baffin Bay region would be gradually reduced from 105 per year to 65 by the year 2013.[109] Environment Canada also banned the export from Canada of fur, claws, skulls and other products from polar bears harvested in Baffin Bay as of January 1, 2010.[109]

Conservation status, efforts and controversies

This map from the U.S. Geological Survey shows projected changes in polar bear habitat from 2001–2010 to 2041–2050. Red areas indicate loss of optimal polar bear habitat; blue areas indicate gain.

As of 2008, the World Conservation Union (IUCN) reports that the global population of polar bears is 20,000 to 25,000, and is declining.[1] In 2006, the IUCN upgraded the polar bear from a species of least concern to a vulnerable species.[110] It cited a "suspected population reduction of >30% within three generations (45 years)", due primarily to global warming.[7] Other risks to the polar bear include pollution in the form of toxic contaminants, conflicts with shipping, stresses from recreational polar-bear watching, and oil and gas exploration and development.[7] The IUCN also cited a "potential risk of over-harvest" through legal and illegal hunting.[7]

According to the World Wildlife Fund, the polar bear is important as an indicator of arctic ecosystem health. Polar bears are studied to gain understanding of what is happening throughout the Arctic, as at risk polar bears are often a sign of something wrong with the arctic marine ecosystem.[111]

Global warming

The IUCN, Arctic Climate Impact Assessment, United States Geological Survey and many leading polar bear biologists have expressed grave concerns about the impact of global warming, including the belief that the current warming trend imperils the survival of the species.[22][112][113][114][115][116]

The key danger posed by global warming is malnutrition or starvation due to habitat loss. Polar bears hunt seals from a platform of sea ice. Rising temperatures cause the sea ice to melt earlier in the year, driving the bears to shore before they have built sufficient fat reserves to survive the period of scarce food in the late summer and early fall.[76] Reduction in sea-ice cover also forces bears to swim longer distances, which further depletes their energy stores and occasionally leads to drowning.[117] Thinner sea ice tends to deform more easily, which appears to make it more difficult for polar bears to access seals.[51] Insufficient nourishment leads to lower reproductive rates in adult females and lower survival rates in cubs and juvenile bears, in addition to poorer body condition in bears of all ages.[22]

In addition to creating nutritional stress, a warming climate is expected to affect various other aspects of polar bear life: Changes in sea ice affect the ability of pregnant females to build suitable maternity dens. As the distance increases between the pack ice and the coast, females must swim longer distances to reach favored denning areas on land.[22] Thawing of permafrost would affect the bears who traditionally den underground, and warm winters could result in den roofs collapsing or having reduced insulative value.[22] For the polar bears that currently den on multi-year ice, increased ice mobility may result in longer distances for mothers and young cubs to walk when they return to seal-hunting areas in the spring.[22] Disease-causing bacteria and parasites would flourish more readily in a warmer climate.[51]

Problematic interactions between polar bears and humans, such as foraging by bears in garbage dumps, have historically been more prevalent in years when ice-floe breakup occurred early and local polar bears were relatively thin.[112] Increased human-bear interactions, including fatal attacks on humans, are likely to increase as the sea ice shrinks and hungry bears try to find food on land.[112][118]

Observations linked to global warming

The effects of global warming are most profound in the southern part of the polar bear's range, and this is indeed where significant degradation of local populations has been observed.[116] The Western Hudson Bay subpopulation, in a southern part of the range, also happens to be one of the best-studied polar bear subpopulations. This subpopulation feeds heavily on ringed seals in late spring, when newly weaned and easily hunted seal pups are abundant.[107] The late spring hunting season ends for polar bears when the ice begins to melt and break up, and they fast or eat little during the summer until the sea freezes again.[107]

Due to warming air temperatures, ice-floe breakup in western Hudson Bay is currently occurring three weeks earlier than it did 30 years ago, reducing the duration of the polar bear feeding season.[107] The body condition of polar bears has declined during this period; the average weight of lone (and likely pregnant) female polar bears was approximately 290 kg (640 lb) in 1980 and 230 kg (510 lb) in 2004.[107] Between 1987 and 2004, the Western Hudson Bay population declined by 22%.[119]

Mothers and cubs have high nutritional requirements, which are not met if the seal-hunting season is too short.

In Alaska, the effects of sea ice shrinkage have contributed to higher mortality rates in polar bear cubs, and have led to changes in the denning locations of pregnant females.[75][120] Recently, polar bears in the Arctic have undertaken longer than usual swims to find prey, resulting in four recorded drownings in the unusually large ice pack regression of 2005.[117]

Pollution

Polar bears accumulate high levels of persistent organic pollutants such as polychlorinated biphenyl (PCBs) and chlorinated pesticides. Due to their position at the top of the food pyramid, with a diet heavy in blubber in which halocarbons concentrate, their bodies are among the most contaminated of Arctic mammals.[121] Halocarbons are known to be toxic to other animals because they mimic hormone chemistry, and biomarkers such as immunoglobulin G and retinol suggest similar effects on polar bears. PCBs have received the most study, and they have been associated with birth defects and immune system deficiency.[122]

The most notorious of these chemicals, such as PCBs and DDT, have been internationally banned. Their concentrations in polar bear tissues continued to rise for decades after the ban as these chemicals spread through the food chain, however the trend seems to have abated, with tissue concentrations of PCBs declining between studies performed in 1989 - 1993 and studies performed in 1996 - 2002.[123]

Sometimes excess heavy metals have also been observed in the polar bear.

Oil and gas development

Oil and gas development in polar bear habitat can affect the bears in a variety of ways. An oil spill in the Arctic would most likely concentrate in the areas where polar bears and their prey are also concentrated, such as sea ice leads.[7] Because polar bears rely partly on their fur for insulation and soiling of the fur by oil reduces its insulative value, oil spills put bears at risk of dying from hypothermia.[56] Polar bears exposed to oil spill conditions have been observed to lick the oil from their fur, leading to fatal kidney failure.[56] Maternity dens, used by pregnant females and by females with infants, can also be disturbed by nearby oil exploration and development. Disturbance of these sensitive sites may trigger the mother to abandon her den prematurely, or abandon her litter altogether.[7]

German stamp depicting Knut and the slogan "Preserve nature worldwide"

Predictions

The U.S. Geological Survey predicts two-thirds of the world's polar bears will disappear by 2050, based on moderate projections for the shrinking of summer sea ice caused by global warming.[51] The bears would disappear from Europe, Asia, and Alaska, and be depleted from the Arctic archipelago of Canada and areas off the northern Greenland coast. By 2080, they would disappear from Greenland entirely and from the northern Canadian coast, leaving only dwindling numbers in the interior Arctic archipelago.[51]

Predictions vary on the extent to which polar bears could adapt to climate change by switching to terrestrial food sources. Mitchell Taylor, who was director of Wildlife Research for the Government of Nunavut, wrote to the US Fish and Wildlife Service arguing that local studies are insufficient evidence for global protection at this time. The letter stated, "At present, the polar bear is one of the best managed of the large Arctic mammals. If all Arctic nations continue to abide by the terms and intent of the Polar Bear Agreement, the future of polar bears is secure.... Clearly polar bears can adapt to climate change. They have evolved and perisisted for thousands of years in a period characterized by fluctuating climate."[108] Ken Taylor, deputy commissioner for the Alaska Department of Fish and Game, has said, "I wouldn't be surprised if polar bears learned to feed on spawning salmon like grizzly bears."[26]

However, many scientists consider these theories to be naive;[26] it is noted that black and brown bears at high latitudes are smaller than elsewhere, because of the scarcity of terrestrial food resources.[107] An additional risk to the species is that if individuals spend more time on land, they will hybridize with brown or grizzly bears.[116] The IUCN wrote:

Polar bears exhibit low reproductive rates with long generational spans. These factors make facultative adaptation by polar bears to significantly reduced ice coverage scenarios unlikely. Polar bears did adapt to warmer climate periods of the past. Due to their long generation time and the current greater speed of global warming, it seems unlikely that polar bear will be able to adapt to the current warming trend in the Arctic. If climatic trends continue polar bears may become extirpated from most of their range within 100 years.[7]

Controversy over species protection

Polar bear at Central Park Zoo, New York City, USA

Warnings about the future of the polar bear are often contrasted with the fact that worldwide population estimates have increased over the past 50 years and are relatively stable today.[124][125] Some estimates of the global population are around 5,000–10,000 in the early 1970s;[126] other estimates were 20,000–40,000 during the 1980s.[29][41] Current estimates put the global population at between 20,000 and 25,000.[24]

There are several reasons for the apparent discordance between past and projected population trends: Estimates from the 1950s and 1960s were based on stories from explorers and hunters rather than on scientific surveys.[127][128] Second, controls of harvesting were introduced that allowed this previously overhunted species to recover.[127] Third, the recent effects of global warming have affected sea ice abundance in different areas to varying degrees.[127] According to WWF data, only 1 out of the 19 polar bear subpopulations is currently known to be increasing; 3 are stable; 8 are declining; and the remaining 7 currently have insufficient data to provide an assessment of population trends.[125]

Debate over the listing of the polar bear under endangered species legislation has put conservation groups and Canada's Inuit at opposing positions;[26] the Nunavut government and many northern residents have condemned the U.S. initiative to list the polar bear under the Endangered Species Act.[129][130] Many Inuit believe the polar bear population is increasing, and restrictions on sport-hunting are likely to lead to a loss of income to their communities.[26][131]

U.S. endangered species legislation

On 14 May 2008 the U.S. Department of the Interior listed the polar bear as a threatened species under the Endangered Species Act, citing the melting of Arctic sea ice as the primary threat to the polar bear.[132] However, the department immediately issued a statement that the listing could not be used to regulate greenhouse gas emissions, saying, "That would be a wholly inappropriate use of the Endangered Species Act. ESA is not the right tool to set U. S. climate policy."[133] However, some policy analysts believe that despite the government's stance, the Endangered Species Act can be used to restrict the issuing of federal permits for projects that would threaten the polar bear by increasing greenhouse gas emissions.[132] Environmental groups have pledged to go to court to have the Endangered Species Act interpreted in such a way.[132] On 8 May 2009, the new administration of Barack Obama announced that it would continue the policy.[134]

While listing the polar bear as a threatened species, the Interior Department added a seldom-used stipulation to allow oil and gas exploration and development to proceed in areas inhabited by polar bears, provided companies continue to comply with the existing restrictions of the Marine Mammal Protection Act.[135] The main new protection for polar bears under the terms of the listing is that hunters will no longer be able to import trophies from the hunting of polar bears in Canada.[135]

The polar bear is only the third species, after the elkhorn coral and the staghorn coral protected under the Endangered Species Act due to global warming. In 4 August 2008, the state of Alaska sued U.S. Interior Secretary Dirk Kempthorne, seeking to reverse the listing of the polar bear as a threatened species, out of concern that the listing would adversely affect oil and gas development in the state.[136] Alaska Governor Sarah Palin said that the listing was not based on the best scientific and commercial data available, a view rejected by polar bear experts.[136]

The ruling followed several years of controversy. On 17 February 2005 the Center for Biological Diversity filed a petition asking that the polar bear be listed under the Endangered Species Act. An agreement was reached and filed in Federal district court on 5 June 2006. Pursuant to that agreement, on 9 January 2007, the US Fish and Wildlife Service proposed to list the polar bear as a threatened species. A final decision was required by law by 9 January 2008, at which time the agency said it needed another month.[137]

On 7 March 2008, the inspector general of the U.S. Interior Department began a preliminary investigation into why the decision had been delayed for nearly two months.[137] The investigation is in response to a letter signed by six environmental groups that U.S. Fish and Wildlife Director Dale Hall violated the agency's scientific code of conduct by delaying the decision unnecessarily, allowing the government to proceed with an auction for oil and gas leases in the Alaska's Chukchi Sea, an area of key habitat for polar bears.[137] The auction took place in early February 2008.[137] An editorial in The New York Times said that "these two moves are almost certainly, and cynically, related."[26][138] Hall denied any political interference in the decision and said that the delay was needed to make sure the decision was in a form easily understood.[137] On 28 April 2008, a Federal court ruled that a decision on the listing must be made by 15 May 2008;[139] the decision came on 14 May.[135]

Canadian endangered species legislation

In Canada, the Committee on the Status of Endangered Wildlife in Canada recommended in April 2008 that the polar bear be assessed as a species of special concern under the federal Species at Risk Act (SARA). A listing would mandate that a management plan be written within five years, a timeline criticized by the World Wide Fund for Nature as being too long to prevent significant habitat loss from climate change.[140]

In culture

This engraving, made by Chukchi carvers in the 1940s on a walrus tusk, depicts polar bears hunting walrus.

Indigenous folklore

For the indigenous peoples of the Arctic, polar bears have long played an important cultural and material role.[85][86] Polar bear remains have been found at hunting sites dating to 2,500 to 3,000 years ago[88] and 1,500 year old cave paintings of polar bears have been found in Chukotka.[86] Indeed, it has been suggested that Arctic peoples' skills in seal hunting and igloo construction has been in part acquired from the polar bears themselves.[86]

The Inuit and Eskimos have many folk tales featuring the bears including legends in which bears are humans when inside their own houses and put on bear hides when going outside, and stories of how the constellation which is said to resemble a great bear surrounded by dogs came into being.[84] These legends reveal a deep respect for the polar bear, which is portrayed as both spiritually powerful and closely akin to humans.[84] The human-like posture of bears when standing and sitting, and the resemblance of a skinned bear carcass to the human body, have probably contributed to the belief that the spirits of humans and bears were interchangeable.[84] Eskimo legends tell of humans learning to hunt from the polar bear. For the Inuit of Labrador, the polar bear is a form of the Great Spirit, Tuurngasuk.[141] The Inuit and Eskimo have a great amount of respect for bears.

Among the Chukchi and Yupik of eastern Siberia, there was a longstanding shamanistic ritual of "thanksgiving" to the hunted polar bear. After killing the animal, its head and skin were removed and cleaned and brought into the home, a feast was held in the hunting camp in its honor. In order to appease the spirit of the bear, there were traditional song and drum music and the skull would be ceremonially fed and offered a pipe.[142] Only once the spirit was appeased would the skull be separated from the skin, taken beyond the bounds of the homestead, and placed in the ground, facing north.[86] Many of these traditions have faded somewhat in time, especially in light of the total hunting ban in the Soviet Union (and now Russia) since 1955.

The Nenets of north-central Siberia placed particular value on the talismanic power of the prominent canine teeth. They were traded in the villages of the lower Yenisei and Khatanga rivers to the forest-dwelling peoples further south, who would sew them into their hats as protection against brown bears. It was believed that the "little nephew" (the brown bear) would not dare to attack a man wearing the tooth of its powerful "big uncle" (the polar bear).[86] The skulls of killed polar bears were buried at specific sacred sites and altars, called sedyangi, were constructed out of the skulls. Several such sites have been preserved on the Yamal Peninsula.[86]

Symbols and mascots

Canada issued Polar Bear stamp.
Coat of arms of the Chukotka Autonomous Okrug in the Russian Federation.

Their distinctive appearance and their association with the Arctic have made polar bears popular icons, especially in those areas where they are native. The Canadian Toonie (two-dollar coin) features the image of a polar bear and both the Northwest Territories and Nunavut license plates in Canada are in the shape of a polar bear. The polar bear is the mascot of Bowdoin College in Maine and the University of Alaska Fairbanks (see also Alaska Nanooks) and was chosen as mascot for the 1988 Winter Olympics held in Calgary.

Companies such Coca-Cola, Polar Beverages, Nelvana, Bundaberg Rum and Good Humor-Breyers have used images of the polar bear in advertising,[143] while Fox's Glacier Mints have featured a polar bear named Peppy as the brand mascot since 1922.

Literature

Polar bears are also popular in fiction, particularly in books aimed at children or young adults. For example, The Polar Bear Son is adapted from a traditional Inuit tale.[144] Polar bears feature prominently in East (also released as North Child) by Edith Pattou, The Bear by Raymond Briggs, and Chris d'Lacey's The Fire Within series. The panserbjørne of Philip Pullman's fantasy trilogy His Dark Materials are sapient, dignified polar bears who exhibit anthropomorphic qualities, and as such feature prominently in the 2007 film adaptation of The Golden Compass.

See also

References

  • Bruemmer, Fred (1989). World of the Polar Bear. Toronto, ON: Key Porter Books. ISBN 1-55013-107-9. 
  • Matthews, Downs (1993). Polar Bear. San Francisco, CA: Chronicle Books. ISBN 0-8118-0050-X. 
  • Hemstock, Annie (1999). The Polar Bear. Manakato, MN: Capstone Press. ISBN 0-7368-0031-X. 
  • Lockwood, Sophie (2006). Polar Bears. Chanhassen, MN: The Child's World. ISBN 1-59296-501-6. 
  • Rosing, Norbert (1996). The World of the Polar Bear. Willowdale, ON: Firefly Books Ltd.. ISBN 1-55209-068-X. 

Notes

  1. ^ a b c Schliebe et al. (2008). Ursus maritimus. IUCN Red List of Threatened Species. Retrieved on 5 January 2010.
  2. ^ Phipps, John (1774). A voyage towards the North Pole undertaken by His Majesty's command, 1773 /by Constantine John Phipps.. London :Printed by W. Bowyer and J. Nicols, for J. Nourse. p. 185. http://www.biodiversitylibrary.org/page/628763. Retrieved 8 September 2008. 
  3. ^ "Polar bear, (Ursus maritimus)" (PDF). U.S. Fish and Wildlife service. http://www.fws.gov/endangered/factsheets/polar_bear.pdf. Retrieved 9 September 2009. "Appearance. The polar bear is the largest member of the bear family, with the exception of Alaska’s Kodiak brown bears, which equal polar bears in size."  (Overview page)
  4. ^ Kindersley, Dorling (2001,2005). Animal. New York City: DK Publishing. ISBN 0-7894-7764-5. 
  5. ^ Gunderson, Aren (2007). "Ursus Maritimus". Animal Diversity Web. University of Michigan Museum of Zoology. http://animaldiversity.ummz.umich.edu/site/accounts/information/Ursus_maritimus.html. Retrieved 27 October 2007. 
  6. ^ a b IUCN Polar Bear Specialist Group, 2009.15th meeting of PBSG in Copenhagen, Denmark 2009: Press Release Retrieved on 10 January 2010.
  7. ^ a b c d e f g h Schliebe et al. (2008). Ursus maritimus. 2006. IUCN Red List of Threatened Species. IUCN 2006. www.iucnredlist.org. Retrieved on 9 May 2006. Database entry includes a lengthy justification of why this species is listed as vulnerable.
  8. ^ Kidd, D.A. (1973). Collins Latin Gem Dictionary. London: Collins. ISBN 0-00-458641-7. 
  9. ^ The Marine Mammal Center
  10. ^ The Arctic Sounder
  11. ^ Этимологический Словарь - Piotr Czerwinski → Oshkuy
  12. ^ Grand Quebec
  13. ^ This combines the Ancient Greek words thalassa/θαλασσα 'sea', and arctos/αρκτος 'bear' and also, with reference to Ursa Major, 'northern' or 'of the north pole'Liddell, Henry George and Robert Scott (1980). A Greek-English Lexicon (Abridged Edition). United Kingdom: Oxford University Press. ISBN 0-19-910207-4. 
  14. ^ "IUCN Red List: Ursus maritimus". http://www.iucnredlist.org/apps/redlist/details/22823/0/full. Retrieved 15 February 2008. 
  15. ^ a b Lindqvist, Charlotte; Schuster, Stephan C.; Sun, Yazhou; Talbot, Sandra L.; Qi, Ji; Ratan, Aakrosh; Tomsho, Lynn P.; Kasson, Lindsay et al. (2010). "Complete mitochondrial genome of a Pleistocene jawbone unveils the origin of polar bear". PNAS 107 (11): 5053–5057. doi:10.1073/pnas.0914266107. .
  16. ^ a b c DeMaster, Douglas P.; Stirling, Ian (8 May 1981). Ursus Maritimus. 145. American Society of Mammalogists. 1–7. doi:10.2307/3503828. OCLC 46381503. http://links.jstor.org/sici?sici=0076-3519(19810508)2%3A145%3C1%3AUM%3E2.0.CO%3B2-D. Retrieved 21 January 2008. 
  17. ^ Lisette P. Waits, Sandra L. Talbot, R.H. Ward and G. F. Shields (April 1998). "Mitochondrial DNA Phylogeography of the North American Brown Bear and Implications for Conservation". Conservation Biology. pp. 408–417. http://www.cnrhome.uidaho.edu/documents/Waits%20et%20al%201998%20cb.pdf&pid=78496&doc=1. Retrieved 1 August 2006. 
  18. ^ Marris, E. (2007). "Linnaeus at 300: The species and the specious". Nature 446 (7133): 250–253. doi:10.1038/446250a. .
  19. ^ Schliebe, Scott; Evans, Thomas; Johnson, Kurt; Roy, Michael; Miller, Susanne; Hamilton, Charles; Meehan, Rosa; Jahrsdoerfer, Sonja (21 December 2006) (PDF). Range-wide Status Review of the Polar Bear (Ursus maritimus). Anchorage, Alaska: U.S. Fish and Wildlife Service. http://alaska.fws.gov/fisheries/mmm/polarbear/pdf/Polar_Bear_%20Status_Assessment.pdf. Retrieved 31 October 2007. 
  20. ^ a b c d e f g h i Stirling, Ian (1988). "The First Polar Bears". Polar Bears. Ann Arbor: University of Michigan Press. ISBN 0-472-10100-5. 
  21. ^ Rice, Dale W. (1998). Marine Mammals of the World: Systematics and Distribution. Special Publications of the Society for Marine Mammals. 4. Lawrence, Kansas: The Society for Marine Mammalogy. ISBN 1-891276-03-4. 
  22. ^ a b c d e f g h Derocher, Andrew E.; Lunn, Nicholas J.; Stirling, Ian (April 2004). "Polar Bears in a Warming Climate". Integrative and Comparative Biology 44 (2): pp. 163–176. doi:10.1093/icb/44.2.163. http://icb.oxfordjournals.org/cgi/content/full/44/2/163. Retrieved 12 October 2007. 
  23. ^ a b c d Polar Bears and Conservation and "Polar Bear FAQ". Polar Bears International. http://www.polarbearsinternational.org/faq/. Retrieved 14 July 2009. 
  24. ^ a b c d e Compiled and edited by Jon Aars, ed (June 2005). "Status of the Polar Bear" (PDF). Proceedings of the 14th Working Meeting of the IUCN/SSC Polar Bear Specialist Group. 32. Polar Bears, Nicholas J. Lunn and Andrew E. Derocher. Gland, Switzerland: IUCN. pp. 33–55. ISBN 2-8317-0959-8. http://pbsg.npolar.no/docs/PBSG14proc.pdf. Retrieved 15 September 2007.  See also HTML excerpts: population status reviews and Table 1 summarizing polar bear population status per 2005.
  25. ^ Paetkau, S.; Amstrup, C.; Born, E. W.; Calvert, W. (October 1999). "Genetic structure of the world's polar bear populations" (PDF). Molecular Ecology (Blackwell Science) 8 (10): pp. 1571–1584. ISSN 1471-8278. http://www.biology.ualberta.ca/faculty/andrew_derocher/uploads/abstracts/Paetkau_et_al_1999.pdf. Retrieved 17 November 2007. 
  26. ^ a b c d e f g h i j k Campbell, Colin; Lunau, Kate (25 January 2008). "The war over the polar bear: Who's telling the truth about the fate of a Canadian icon?". Maclean's. http://www.macleans.ca/science/environment/article.jsp?content=20080123_5242_5242&page=1. Retrieved 9 March 2008. 
  27. ^ Compiled and edited by Jon Aars, ed (June 2005). "Press Release" (PDF). Proceedings of the 14th Working Meeting of the IUCN/SSC Polar Bear Specialist Group. 32. Polar Bears, Nicholas J. Lunn and Andrew E. Derocher. Gland, Switzerland: IUCN. pp. 61–62. ISBN 2-8317-0959-8. http://pbsg.npolar.no/docs/PBSG14proc.pdf. Retrieved 19 April 2008. 
  28. ^ Stirling, Ian (1988). "Introduction". Polar Bears. Ann Arbor: University of Michigan Press. ISBN 0-472-10100-5. 
  29. ^ a b c d Stirling, Ian (1988). "Distribution and Abundance". Polar Bears. Ann Arbor: University of Michigan Press. ISBN 0-472-10100-5. 
  30. ^ Stirling, Ian (January 1997). "The importance of polynyas, ice edges, and leads to marine mammals and birds". Journal of Marine Systems (Elsevier) 10 (1-4): pp. 9–21. doi:10.1016/S0924-7963(96)00054-1. 
  31. ^ Matthews, p. 15
  32. ^ Davids, Richard C.; Guravich, Dan (1982). "Lords of the Arctic". Lords of the Arctic: A Journey Among the Polar Bears. New York: MacMillan Publishing Co., Inc.. ISBN 0-02-529630-2. 
  33. ^ "Polar bear, (Ursus maritimus)" (PDF). U.S. Fish and Wildlife service. http://www.fws.gov/endangered/factsheets/polar_bear.pdf. Retrieved 22 March 2008. "Appearance. The polar bear is the largest member of the bear family, with the exception of Alaska’s Kodiak brown bears, which equal polar bears in size."  (Overview page)
  34. ^ a b Hemstock, p. 4
  35. ^ Perrin, William F.; Bernd Würsig, J. G. M. Thewissen (2008). Encyclopedia of Marine Mammals (2 ed.). San Diego, CA: Academic Press. p. 1009. http://books.google.ca/books?id=2rkHQpToi9sC&pg=PA1009&lpg=PA1009&dq=polar+bear+sexually+dimorphic&source=bl&ots=hCixMz68As&sig=evEUSfMPY2yMqmVP3qJPuZjs6Hs&hl=en&ei=43cfSuKOCJa8swPBy7GQBA&sa=X&oi=book_result&ct=result&resnum=4#PPA1009,M1. 
  36. ^ Wood, G.L. (1981). The Guinness Book of Animal Records. p. 240. 
  37. ^ a b c Lockwood, pp. 10 - 16
  38. ^ "Are polar bears left-handed or right-handed?". September 2006. http://www.blurtit.com/q497068.html. Retrieved 25 November 2007. 
  39. ^ "Bear Facts: Myths and Misconceptions". 2007. http://www.polarbearsinternational.org/bear-facts/myths-and-misconceptions/. Retrieved 25 November 2007. 
  40. ^ Researchers studying polar bears have failed to find any evidence of left-handedness in all bears and one study of injury patterns in polar bear forelimbs found injuries to the right forelimb to be more frequent than those to the left, suggesting, perhaps, right-handedness. "Fractures of the Radius and Ulna secondary to possible Vitamin 'D' deficiency in Captive Polar Bears (Ursus maritimus)". http://www.polarbearsinternational.org/pbhc/fractures.htm. Retrieved 25 November 2007. 
  41. ^ a b c d e Stirling, Ian (1988). Polar Bears. Ann Arbor: University of Michigan Press. ISBN 0-472-10100-5. 
  42. ^ Uspenskii, S. M. (1977). The Polar Bear. Moscow: Nauka. 
  43. ^ Kolenosky G. B. 1987. Polar bear. pp. 475–485 in Wild furbearer management and conservation in North America (M. Novak, J. A. Baker, M. E. Obbard, and B. Malloch, eds.). Ontario Fur Trappers Association, North Bay, Ontario, Canada.
  44. ^ Koon, Daniel W. (1998). "Is Polar Bear Hair Fiber Optic?". Applied Optics (Optical Society of America) 37 (15): pp. 3198–3200. doi:10.1364/AO.37.003198. PMID 18273269. http://www.opticsinfobase.org/abstract.cfm?URI=ao-37-15-3198. 
  45. ^ In unusually warm conditions, the hollow tubes provide an excellent home for algae. While the algae is harmless to the bears, it is often a worry to the zoos housing them, and affected animals are sometimes washed in a salt solution, or mild peroxide bleach to make the fur white again.
  46. ^ Derocher, Andrew E.; Magnus Andersen, and Øystein Wiig (October 2005). "Sexual dimorphism of polar bears" (PDF). Journal of Mammalogy 86 (5): 895–901. doi:10.1644/1545-1542(2005)86[895:SDOPB]2.0.CO;2. http://www.biology.ualberta.ca/faculty/andrew_derocher/uploads/abstracts/Sexual%20dimorphism%20of%20polar%20bears%202005.pdf. 
  47. ^ a b Rosing, pp. 20-23
  48. ^ a b c d e f g h Stirling, Ian (1988). "Behavior". Polar Bears. Ann Arbor: University of Michigan Press. ISBN 0-472-10100-5. 
  49. ^ a b c d e f g Matthews, pp. 73-88
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  52. ^ a b Hemstock, pp. 24-27
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  60. ^ Lunn, N. J.; Stirling, Ian (1985). "The significance of supplemental food to polar bears during the ice-free period of Hudson Bay". Canadian Journal of Zoology (Toronto: NRC Research Press) 63 (10): pp. 2291–2297. doi:10.1139/z85-340. 
  61. ^ Eliasson, Kelsey (May 2004). "Hudson Bay Post - Goodbye Churchil Dump". http://www.polarbearalley.com/churchill-dump.html. Retrieved 9 June 2008. 
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  64. ^ Matthews, p. 95
  65. ^ Bear Behaviour and Activities from Gary Brown's The Great Bear Almanac, Lyons & Burford, Publishers, 1993
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  67. ^ Why Didn't the Wild Polar Bear eat the Husky? The National Institute for Play
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  69. ^ a b Carpenter, Tom (November/December 2005). "Who's Your Daddy?". Canadian Geographic (Ottawa: The Royal Canadian Geographic Society): 44–56. 
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  73. ^ Derocher, AE and Wiig, Oe; Infanticide and Cannibalism of Juvenile Polar Bears (Ursus maritimus) in Svalbard Arctic [Arctic]. Vol. 52, no. 3, pp. 307-310. Sep 1999
  74. ^ a b c d e f "Polar bears in depth: Survival". Polar Bears International. http://www.polarbearsinternational.org/polar-bears-in-depth/survival/page1/. Retrieved 20 October 2008. 
  75. ^ a b Regehr, Eric V.; Amstrup, Steven C.; Stirling, Ian (2006). written at Anchorage, Alaska (PDF). Polar Bear Population Status in the Southern Beaufort Sea. Reston, Virginia: U.S. Geological Survey. Open-File Report 2006-1337. http://pubs.usgs.gov/of/2006/1337/pdf/ofr20061337.pdf. Retrieved 15 September 2007. 
  76. ^ a b Stirling, Ian; Lunn, N. J.; Iacozza, J. (September 1999). "Long-term Trends in the Population Ecology of Polar Bears in Western Hudson Bay in Relation to Climatic Change" (PDF). Arctic 52 (3): pp. 294–306. ISSN 0004-0843. http://pubs.aina.ucalgary.ca/arctic/Arctic52-3-294.pdf. Retrieved 11 November 2007. 
  77. ^ Maternal success appeared to decline after this point, possibly because of an age-related impairment in the ability to store the fat necessary to rear cubs. Derocher, A.E.; Stirling, I. (1994). "Age-specific reproductive performance of female polar bears (Ursus maritimus)". Journal of Zoology 234 (4): 527–536. doi:10.1111/j.1469-7998.1994.tb04863.x. http://md1.csa.com/partners/viewrecord.php?requester=gs&collection=ENV&recid=3794443&q=Ursus+maritimus+reproduction&uid=792151267&setcookie=yes. Retrieved 15 February 2008. 
  78. ^ Larsen, Thor; Kjos-Hanssen, Bjørn (October 1983). "Trichinella sp. in polar bears from Svalbard, in relation to hide length and age". Polar Research (Oslo: Norwegian Polar Institute) 1 (1): pp. 89–96. doi:10.1111/j.1751-8369.1983.tb00734.x. 
  79. ^ Hemstock, pp. 29-35
  80. ^ a b Wrigley, Robert E. (Spring 2008). "The Oldest Living Polar Bear" (PDF). Polar Bears International Newsletter. Polar Bears International. http://www.polarbearsinternational.org/rsrc/files/pbispring08.pdf. Retrieved 9 June 2008. 
  81. ^ adn.com | front : Polar bears, grizzlies increasingly gather on North Slope
  82. ^ "ABC News: Grizzlies Encroaching on Polar Bear Country". Abcnews.go.com. http://abcnews.go.com/Technology/DyeHard/Story?id=582243&page=3. Retrieved 10 October 2009. 
  83. ^ Wolf (Canis lupus) Predation of a Polar Bear (Ursus maritimus) Cub on the Sea Ice off Northwestern Banks Island, Northwest Territories, Canada. ARCTIC VOL. 59, NO. 3 (SEPTEMBER 2006) P. 322– 324
  84. ^ a b c d Stirling, Ian (1988). "The Original Polar Bear Watchers". Polar Bears. Ann Arbor: University of Michigan Press. ISBN 0-472-10100-5. 
  85. ^ a b Lockwood, pp 6-9
  86. ^ a b c d e f g h i j k Uspensky, Savva Mikhailovich (1977). Белый Медведь (tr: Belyi Medved') - (in Russian). Moscow: Nauka. 
  87. ^ As a carnivore which feeds largely upon fish-eating carnivores, the polar bear ingests large amounts of vitamin A, which is stored in their livers. The resulting high concentrations cause Hypervitaminosis A,Rodahl, K.; Moore, T. (July 1943). "The vitamin A content and toxicity of bear and seal liver". The Biochemical Journal (London: Portland Press) 37 (2): pp. 166–168. ISSN 0264-6021. http://www.pubmedcentral.nih.gov/picrender.fcgi?artid=1257872&blobtype=pdf. Retrieved 11 November 2007. 
  88. ^ a b Lockwood, pp. 31-36
  89. ^ "Polar Bear Management". Government of the Northwest Territories. http://wildlife.enr.gov.nt.ca/NWTWildlife/bears/PolarBear/management.htm. Retrieved 14 March 2008. 
  90. ^ a b Bruemmer, pp. 93-111
  91. ^ "Proceedings of the 2nd Working Meeting of Polar Bear Specialists". Polar Bears. Morges, Switzerland: IUCN. February 1970. http://pbsg.npolar.no/Meetings/PressReleases/02-Morges.htm. Retrieved 24 October 2007. 
  92. ^ Norway passed a series of increasingly strict regulations from 1965 to 1973, and has completely banned hunting since then. The Soviet Union banned all hunting in 1956. Canada began imposing hunting quotas in 1968. The U.S. began regulating in 1971 and adopted the Marine Mammal Protection Act in 1972.
  93. ^ Stirling, Ian Foreword in Rosing, Norbert (1996). The World of the Polar Bear. Willowdale, ON: Firefly Books Ltd.. ISBN 1-55209-068-X. 
  94. ^ International Agreement on the Conservation of Polar Bears, 15 November 1973, Oslo
  95. ^ "U.S. and Russia Sign Pact To Protect the Polar Bear". New York Times. 17 October 2000. http://query.nytimes.com/gst/fullpage.html?res=980DE3DD1F3FF934A25753C1A9669C8B63. Retrieved 12 April 2008. 
  96. ^ "US-Russia Polar Bear Treaty Ratified". ScienceDaily. 18 October 2007. http://www.sciencedaily.com/releases/2007/10/071014202952.htm. Retrieved 12 April 2008. 
  97. ^ a b Steven Lee Myers (16 April 2007). "Russia Tries to Save Polar Bears With Legal Hunt". New York Times. http://www.nytimes.com/2007/04/16/world/europe/16polar.html?_r=1&oref=slogin. Retrieved 12 April 2008. 
  98. ^ The Humane Society of the United States "Hitting Polar Bears When They Are Down"
  99. ^ a b Lunn, N. J.; et al. (June 2005). "Polar Bear Management in Canada 2001-2004". in Compiled and edited by Jon Aars (PDF). Proceedings of the 14th Working Meeting of the IUCN/SSC Polar Bear Specialist Group. 32. Polar Bears, Nicholas J. Lunn and Andrew E. Derocher. Gland, Switzerland: IUCN. pp. 101–116. ISBN 2-8317-0959-8. http://pbsg.npolar.no/docs/PBSG14proc.pdf. Retrieved 15 September 2007. 
  100. ^ Freeman, M.M.R.; Wenzel, G.W. (March 2006). "The nature and significance of polar bear conservation hunting in the Canadian Arctic". Arctic 59 (1): pp. 21–30. ISSN 0004-0843. 
  101. ^ a b Wenzel, George W. (September 2004). "3rd NRF Open Meeting" (PDF). http://www.nrf.is/Open%20Meetings/Yellowknife_2004/Wenzel.pdf. Retrieved 3 December 2007. 
  102. ^ "Nunavut hunters can kill more polar bears this year". CBC News. 10 January 2005. http://www.cbc.ca/story/canada/national/2005/01/10/polar-bear-hunt050110.html. Retrieved 15 September 2007. 
  103. ^ "Bear Facts: Harvesting/Hunting". Polar Bears International. http://www.polarbearsinternational.org/bear-facts/hunting/. Retrieved 14 March 2008. 
  104. ^ The Humane Society of the United States "Support the Polar Bear Protection Act"
  105. ^ CBC News, 10 January 2005, "Nunavut hunters can kill more polar bears this year"
  106. ^ CBC News, 4 July 2005, "Rethink polar bear hunt quotas, scientists tell Nunavut hunters"
  107. ^ a b c d e f Stirling, Ian; Derocher, Andrew E. (Fall 2007). "Melting Under Pressure: The Real Scoop on Climate Warming and Polar Bears" (PDF). The Wildlife Professional (Lawrence, Kansas: The Wildlife Society) 1 (3): pp. 24–27, 43. http://www.biology.ualberta.ca/faculty/andrew_derocher/uploads/abstracts/Stirling_Derocher_Wildlife_Professional_PB_climate_2007.pdf. Retrieved 17 November 2007. 
  108. ^ a b Taylor, Mitchell K. (6 April 2006) (PDF). Review of CBD Petition. Letter to the U.S. Fish and Wildlife Service. http://www.ff.org/centers/csspp/pdf/200701_taylor.pdf. Retrieved 8 September 2007. 
  109. ^ a b George, Jane (April 2010). "Nunavut hunters still enraged over bear quotas". http://www.nunatsiaqonline.ca/stories/article/8976_nunavut_hunters_still_enraged_over_bear_quotas/. Retrieved 4 April 2010. 
  110. ^ "Release of the 2006 IUCN Red List of Threatened Species reveals ongoing decline of the status of plants and animals". World Conservation Union. http://www.iucn.org/en/news/archive/2006/05/02_pr_red_list_en.htm. Retrieved 1 February 2006. 
  111. ^ WWF: A Leader in Polar Bear Conservation . Retrieved 29 June 2009, from WFF - Polar Bear Web site: http://www.worldwildlife.org/species/finder/polarbear/polarbear.html#
  112. ^ a b c Stirling, Ian; and Claire L. Parkinson (September 2006). "Possible Effects of Climate Warming on Selected Populations of Polar Bears (Ursus maritimus) in the Canadian Arctic" (PDF). Arctic 59 (3): 261–275. ISSN 0004-0843. http://neptune.gsfc.nasa.gov/publications/pdf/pubs2006/Stirling%20-%20Possible%20Effects%20of%20Climate%20Warming.pdf. Retrieved 15 September 2007. 
  113. ^ Stirling, Ian; N.J. Lunn, John Iacozza, Campbell Elliott and Martyn Obbard (March 2004). "Polar Bear Distribution and Abundance on the Southwestern Hudson Bay Coast During Open Water Season, in Relation to Population Trends and Annual Ice Patterns" (PDF). Arctic 57 (1): 15–26. ISSN 0004-0843. http://umanitoba.ca/ceos/files/publications_pdf/058.pdf. Retrieved 15 September 2007. 
  114. ^ Barber, D.G.; J. Iacozza (March 2004). "Historical analysis of sea ice conditions in M'Clintock Channel and the Gulf of Boothia, Nunavut: implications for ringed seal and polar bear habitat." (PDF). Arctic 57 (1): 1–14. ISSN 0004-0843. http://goliath.ecnext.com/coms2/gi_0199-263435/Historical-analysis-of-sea-ice.html. 
  115. ^ T. Appenzeller and D. R. Dimick, "The Heat is On," National Geographic 206 (2004): 2-75. cited in Flannery, Tim (2005). The Weather Makers. Toronto, Ontario: HarperCollins. pp. 101–103. ISBN 0-00-200751-7. 
  116. ^ a b c Arctic Climate Impact Assessment (2004). Impact of a Warming Arctic: Arctic Impact Climate Assessment. Cambridge: Cambridge University Press. ISBN 0 521 61778 2. OCLC 56942125. http://amap.no/workdocs/index.cfm?dirsub=%2FACIA%2Foverview. . The relevant paper is Key Finding 4
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  118. ^ Mitchell Taylor, a former polar bear researcher for the Nunavut government, believes that arctic warming has been caused by natural phenomena and is not a long-term threat to the polar bear. After his retirement, he was not re-appointed to the international Polar Bear Specialist Group (PBSG), giving rise to speculation that he was excluded from the group because of his views on global warming. According to the PBSG chair, appointments to the PBSG are given to scientists who are currently active in polar bear research, and that as a retired researcher Taylor did not qualify. (References: Booker, Christopher (27 June 2009). "Polar bear expert barred by global warmists". The Daily Telegraph (London). http://www.telegraph.co.uk/comment/columnists/christopherbooker/5664069/Polar-bear-expert-barred-by-global-warmists.html. Retrieved 12 August 2009. 
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  120. ^ The proportion of maternity dens on sea ice has changed from 62% between the years 1985–1994, to 37% over the years 1998–2004. The Alaskan population thus now more resembles the world population, in that it is more likely to den on land.Fischbach, A. S.; Amstrup, S. C.; Douglas, D. C. (October 2007). "Landward and eastward shift of Alaskan polar bear denning associated with recent sea ice changes". Polar Biology (Berlin: Springer) 30 (11): pp. 1395–1405. doi:10.1007/s00300-007-0300-4. 
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  123. ^ Verreault, Jonathan; Muir, Derek C.G.; Norstrom, Ross J.; Stirling, Ian; Fisk, AT; Gabrielsen, GW; Derocher, AE; Evans, TJ et al. (December 2005). "Chlorinated hydrocarbon contaminants and metabolites in polar bears (Ursus maritimus) from Alaska, Canada, East Greenland, and Svalbard: 1996-2002" (PDF). Science of The Total Environment (Shannon, Ireland: Elsevier) 351-352: pp. 369–390. doi:10.1016/j.scitotenv.2004.10.031. PMID 16115663. http://www.biology.ualberta.ca/faculty/andrew_derocher/uploads/abstracts/Verreault%20et%20al%20STOTEN%202005.pdf. Retrieved 17 November 2007. 
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  128. ^ Bruemmer, p. 101. In an meeting of the five circumpolar nations on 6 September 1965, estimates of the worldwide population ranged from 5,000 to 19,000. "The truth was, no one knew... Scientific research had been sketchy and knowledge of the polar bear was based largely on stories brought back by explorers and hunters."
  129. ^ "Nunavut MLAs condemn U.S. proposal to make polar bears threatened species". CBC News. 4 June 2007. http://www.cbc.ca/canada/north/story/2007/06/04/nu-pbear.html. Retrieved 15 September 2007. 
  130. ^ "Inuit reject U.S. Polar Bear Proposal". CBC News. 21 June 2007. http://www.cbc.ca/canada/north/story/2007/06/21/polar-bears.html. Retrieved 15 September 2007. 
  131. ^ Northern Research Forum. Polar Bear as a Resource. A position paper presented for the 3rd NRF Open Meeting in Yellowknife and Rae Edzo, Canada. September 15–18, 2004
  132. ^ a b c Hassett, Kevin A (23 May 2008). "Bush's polar bear legal disaster". National Post. http://www.nationalpost.com/opinion/story.html?id=533276. Retrieved 7 June 2008. 
  133. ^ Quotation from Interior Secretary Dirk Kempthorne, in Hassett, Kevin A (23 May 2008). "Bush's polar bear legal disaster". National Post. http://www.nationalpost.com/opinion/story.html?id=533276. Retrieved 7 June 2008. 
  134. ^ U.S. to keep Bush administration rule on polar bears, McClatchy Newspapers, 8 May 2009
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  136. ^ a b Joling, Dan (5 August 2008). "Alaska sues over listing polar bear as threatened". Globe and Mail. http://www.theglobeandmail.com/servlet/story/RTGAM.20080805.wpolarbears0805/BNStory/International/. Retrieved 29 August 2008. 
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  138. ^ Editorial (15 January 2008). "Regulatory Games and the Polar Bear". New York Times. http://www.nytimes.com/2008/01/15/opinion/15tue2.html. Retrieved 20 October 2008. 
  139. ^ Biello, David (30 April 2008). "Court Orders U.S. to Stop Keeping Polar Bear Status on Ice". Scientific American News. http://www.sciam.com/article.cfm?id=court-orders-polar-bear-announcement. Retrieved 8 June 2008. 
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