Polar Bear

Appearance

The polar bear is the largest terrestrial carnivore, being more than twice as big as the Siberian tiger. It shares this title with the Kodiak Bear. Adult males weigh 350–680 kg and measure 2.4–3 m in length.

Adult females are roughly half the size of males and normally weigh 150–250 kg, measuring 1.8–2.4 metres in length. When pregnant, however, they can weigh as much as 500 kg. The polar bear is among the most sexually dimorphic of mammals, surpassed only by the pinnipeds. The largest polar bear on record, reportedly weighing 1,002 kg, was a male shot at Kotzebue Sound in northwestern Alaska in 1960. The shoulder height of the polar bear is 130–160 cm.

Compared with its closest relative, the brown bear, the polar bear has a more elongated body build and a longer skull and nose. As predicted by Allen's rule for a northerly animal, the legs are stocky and the ears and tail are small. 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 across in an adult. The pads of the paws are covered with small, soft papillae which provide traction on the ice. 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. The claws are deeply scooped on the underside to assist in digging in the ice of the natural habitat. Research 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. Unlike the brown bear, polar bears in captivity are rarely overweight or particularly large, possibly as a reaction to the warm conditions of most zoos.

The 42 teeth of a polar bear reflect its highly carnivorous diet. The cheek teeth are smaller and more jagged than in the brown bear, and the canines are larger and sharper. The dental formula is 3.1.4.2/3.1.4.3

Polar bears are superbly insulated by up to 10 cm of blubber, their hide and their fur; they overheat at temperatures above 10 °C , and are nearly invisible under infrared photography. 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. The guard hair is 5–15 cm over most of the body. Polar bears gradually moult from May to August, 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.

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. 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.

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

The polar bear is an excellent swimmer and individuals have been seen in open Arctic waters as far as 200 mi from land. With its body fat providing buoyancy, it swims in a dog paddle fashion using its large forepaws for propulsion. Polar bears can swim 6 mph. When walking, the polar bear tends to have a lumbering gait and maintains an average speed of around 3.5 mph. When sprinting, they can reach up to 25 mph.

Naming

Constantine John Phipps was the first to describe the polar bear as a distinct species in 1774. He chose the scientific name ''Ursus maritimus'', the Latin for 'maritime bear', due to the animal's native habitat. The Inuit refer to the animal as ''nanook'' . The Yupik also refer to the bear as ''nanuuk'' in Siberian Yupik. The bear is ''umka'' in the Chukchi language. In Russian, it is usually called бе́лый медве́дь , though an older word still in use is ошку́й . In French, the polar bear is referred to as ''ours blanc'' or ''ours polaire'' . In the Norwegian-administered Svalbard archipelago, the polar bear is referred to as ''Isbjørn''.

The polar bear was previously considered to be in its own genus, ''Thalarctos''. 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.

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. Some estimates of the global population are around 5,000–10,000 in the early 1970s; other estimates were 20,000–40,000 during the 1980s. Current estimates put the global population at between 20,000 and 25,000.

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. Second, controls of harvesting were introduced that allowed this previously overhunted species to recover. Third, the recent effects of climate change have affected sea ice abundance in different areas to varying degrees. Finally, the prediction methods used to predict the decline in the future population of bear bears excluded key forecasting principles and included unquestionable assumptions.

Debate over the listing of the polar bear under endangered species legislation has put conservation groups and Canada's Inuit at opposing positions; the Nunavut government and many northern residents have condemned the U.S. initiative to list the polar bear under the Endangered Species Act. 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.


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. 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. 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.

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. 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. 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. 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. The auction took place in early February 2008. An editorial in ''The New York Times'' said that "these two moves are almost certainly, and cynically, related." 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. On 28 April 2008, a Federal court ruled that a decision on the listing must be made by 15 May 2008; the decision came on 14 May to make the polar bear a protected species.

On 18 July 2011, Charles Monnett, whose work was cited by the U.S. Fish and Wildlife Service in its decision to list the polar bear as threatened under the Endangered Species Act, was suspended from his work at the Bureau of Ocean Energy Management, Regulation and Enforcement. Investigators are reviewing Monnett's research methods as well as the significance he attached to his discovery in 2004 of polar bear carcasses in the Arctic, but supporters argue that the investigation is essentially "a smear campaign" against Monnett.

Upon listing the polar bear under the Endangered species act, the Department of the Interior immediately issued a statement that the listing could not be used to regulate greenhouse gas emissions, although some policy analysts believe that 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. Environmental groups have pledged to go to court to have the Endangered Species Act interpreted in such a way. On 8 May 2009, the new administration of Barack Obama announced that it would continue the policy. The polar bear is only the third species, after the elkhorn coral and the staghorn coral protected under the Endangered Species Act due to climate change. On 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. 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.


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 . 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.

Distribution

The polar bear is found in the Arctic Circle and adjacent land masses as far south as Newfoundland Island. Due to the absence of human development in its remote habitat, it retains more of its original range than any other extant carnivore. 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.

There are 19 generally recognized, discrete subpopulations. The subpopulations display seasonal fidelity to particular areas, but DNA studies show that they are not reproductively isolated. 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.


The range includes the territory of five nations: Denmark , Norway , Russia, the United States and Canada. These five nations are the signatories of the International Agreement on 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. 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. 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. 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."

Of the 19 recognized polar bear subpopulations, eight are declining, three are stable, one is increasing, and seven have insufficient data, as of 2009.

Status

As of 2008, the World Conservation Union reports that the global population of polar bears is 20,000 to 25,000, and is declining. In 2006, the IUCN upgraded the polar bear from a species of least concern to a vulnerable species. It cited a "suspected population reduction of >30% within three generations ", due primarily to climate change. 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. The IUCN also cited a "potential risk of over-harvest" through legal and illegal hunting.

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, because at-risk polar bears are often a sign of something wrong with the arctic marine ecosystem.





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. Some estimates of the global population are around 5,000–10,000 in the early 1970s; other estimates were 20,000–40,000 during the 1980s. Current estimates put the global population at between 20,000 and 25,000.

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. Second, controls of harvesting were introduced that allowed this previously overhunted species to recover. Third, the recent effects of climate change have affected sea ice abundance in different areas to varying degrees. Finally, the prediction methods used to predict the decline in the future population of bear bears excluded key forecasting principles and included unquestionable assumptions.

Debate over the listing of the polar bear under endangered species legislation has put conservation groups and Canada's Inuit at opposing positions; the Nunavut government and many northern residents have condemned the U.S. initiative to list the polar bear under the Endangered Species Act. 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.

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. Satiated polar bears rarely attack humans unless severely provoked, whereas hungry polar bears are extremely unpredictable and are known to kill and sometimes eat humans. Polar bears are stealth hunters, and the victim is often unaware of the bear's presence until the attack is underway. Whereas brown bears often maul a person and then leave, polar bear attacks are more likely to be predatory and are almost always fatal. 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, and polar bear zoologist Nikita Ovsianikov has described adult males as having "well-developed friendships." 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. Polar bears have a wide range of vocalisations, including bellows, roars, growls, chuffs and purrs.

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. 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. This kind of social interaction is uncommon; it is far more typical for polar bears to behave aggressively towards dogs.

Habitat

The polar bear is often regarded as a marine mammal because it spends many months of the year at sea. 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. The polar bear tends to frequent areas where sea ice meets water, such as polynyas and leads , to hunt the seals that make up most of its diet. 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.

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. In Hudson Bay, James Bay, and some other areas, the ice melts completely each summer , forcing polar bears to go onto land and wait through the months until the next freeze-up. In the Chukchi and Beaufort seas, polar bears retreat each summer to the ice further north that remains frozen year-round.

Reproduction

Courtship and mating take place on the sea ice in April and May, when polar bears congregate in the best seal hunting areas. A male may follow the tracks of a breeding female for 100 km 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. 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. Partners stay together and mate repeatedly for an entire week; the mating ritual induces ovulation in the female.

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 and often more than doubling her body weight.

Food

The polar bear is the most carnivorous member of the bear family, and most of its diet consists of ringed and bearded seals. 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. Polar bears hunt primarily at the interface between ice, water, and air; they only rarely catch seals on land or in open water.

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

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.

Mature bears tend to eat only the calorie-rich skin and blubber of the seal, whereas younger bears consume the protein-rich red meat. Studies have also photographed polar bears scaling near-vertical cliffs, to eat birds' chicks and eggs. 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.

The polar bear is an enormously powerful predator. It can kill an adult walrus, although this is rarely attempted. A walrus can be more than twice the bear's weight, and has up to three feet long ivory tusks that can be used as formidable weapons. Most attacks on walruses occur when the bear charges a group and either targets the slower moving walruses, usually either young or infirm ones, or a walrus that's injured in the rush of walruses trying to escape. They will also attack adult walruses when their diving holes have frozen over or intercept them before they can get back to the diving hole in the ice. Since attacks on walruses tend to be an extremely protracted and exhausting venture, bears have been known to abandon the hunt after making the initial injury.

Polar bears also have been seen to prey 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. Polar bears very seldom attack full-grown adult whales. 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.

With the exception of pregnant females, polar bears are active year-round, 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. When sea ice is unavailable during summer and early autumn, some populations live off fat reserves for months at a time. 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. 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.

Being both curious animals and scavengers, polar bears investigate and consume garbage where they come into contact with humans. 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. The dump in Churchill, Manitoba was closed in 2006 to protect bears, and waste is now recycled or transported to Thompson, Manitoba.

Evolution

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. The oldest known polar bear fossil is a 130,000 to 110,000-year-old jaw bone, found on Prince Charles Foreland in 2004. 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.

More recent genetic studies have shown that some clades of brown bear are more closely related to polar bears than to other brown bears, meaning that the polar bear is not a true species according to some species concepts. Irish brown bears are particularly close to polar bears. In addition, polar bears can breed with brown bears to produce fertile grizzly–polar bear hybrids, indicating that they have only recently diverged and are genetically similar. 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.

The evolution of the polar bear from the brown bear is an example of peripatric speciation, the process by which an ancestral species gives rise to a daughter species through the evolution of populations located at the margin of the ancestral species' range. The origin of the polar bear therefore rendered the ancestral brown bear a paraspecies, which is paraphyletic species that gave rise to one or more daughter species without itself becoming extinct.

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. 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.


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. 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. 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. 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.

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. 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."
The numbers taken grew rapidly in the 1960s, peaking around 1968 with a global total of 1,250 bears that year.

Cultural

For the indigenous peoples of the Arctic, polar bears have long played an important cultural and material role. Polar bear remains have been found at hunting sites dating to 2,500 to 3,000 years ago and 1,500 year old cave paintings of polar bears have been found in the Chukchi Peninsula. 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.

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. These legends reveal a deep respect for the polar bear, which is portrayed as both spiritually powerful and closely akin to humans. 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. 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.

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. 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. Many of these traditions have faded somewhat in time, especially in light of the total hunting ban in the Soviet Union 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" would not dare to attack a man wearing the tooth of its powerful "big uncle" . 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.