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The polar bear (Ursus maritimus) is a bear native to the Arctic. Polar bears and Kodiak bears are the world's largest land carnivores, with most adult males weighing 300-600 kg (660-1320 lb); adult females are about half the size of males. Its fur is hollow and translucent, but usually appears as white or cream colored, thus providing the animal with effective camouflage. Its skin is actually black in color. Its thick blubber and fur insulate it against the cold. The bear has a short tail and small ears that help reduce heat loss, as well as a relatively small head and long, tapered body to streamline it for swimming. A semi-aquatic marine mammal, the polar bear has adapted for life on a combination of land, sea, and ice, and is the apex predator within its range. It feeds mainly on seals, young walruses, and whales, although it will eat anything it can kill. It is the bear species most likely to prey on humans.
The polar bear is a vulnerable species at high risk of extinction. Scientists and climatologists believe that the projected decreases in the polar sea ice due to global warming will reduce their population by two thirds by mid-century. Local long-term studies show that 7 out of 19 subpopulations are declining or already severely reduced. In the USA, the Center for Biological Diversity petitioned to up-list the legal conservation status of polar bears to threatened species in 2005. This petition is still under review.
Size and weight
Polar bears rank with the Kodiak bear as among the largest living land carnivores, and male polar bears may weigh twice as much as a Siberian tiger. Most adult males weigh 350–650 kg (770–1500+ lb) and measure 2.5–3.0 m (8.2–9.8 ft) in length. Adult females are roughly half the size of males and normally weigh 150–250 kg (330–550 lb), measuring 2–2.5 m (6.6–8.2 ft), but double their weight during pregnancy. The great difference in body size makes the polar bear among the most sexually dimorphic of mammals, surpassed only by the eared seals. At birth, cubs weigh only 600–700 g or about a pound and a half. The largest polar bear on record was a huge male, allegedly weighing 1002 kg (2200 lb) shot at Kotzebue Sound in northwestern Alaska in 1960.
Fur and Skin
A polar bear's fur provides camouflage and insulation. Although the fur appears white, in fact the individual hairs are translucent, like the water droplets that make up a cloud; the coat may yellow with age. Stiff hairs on the pads of a bear's paws provide insulation and traction on the ice.
Polar bears gradually molt their hair from May to August; however, unlike other Arctic mammals, polar bears do not shed their coat for a darker shade to camouflage themselves in the summer habitat. It was once conjectured that the hollow guard hairs of a polar bear coat acted as fiber-optic tubes to conduct light to its black skin, where it could be absorbed - a theory disproved by recent studies.
The thick undercoat does, however, insulate the bears: they overheat at temperatures above 10 °C (50 °F), and are nearly invisible under infrared photography; only their breath and muzzles can be easily seen. When kept in captivity in warm, humid conditions, it is not unknown for the fur to turn a pale shade of green. This is due to algae growing inside the guard hairs — in unusually warm conditions, the hollow tubes provide an excellent home for algae. Whilst 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.
The guard hair is 5-15 cm over most of the body of polar bears. However, in the forelegs, males have significantly longer, increasing in length until 14 years of age. The ornamental foreleg hair is suggested as a form of an attractive trait for females, likened to the lion mane.
Though it spends time on land and ice, the polar bear is regarded as a marine mammal due to its intimate relationship with the sea. The circumpolar species is found in and around the Arctic Ocean, its southern range limited by pack ice. Their southernmost point is James Bay in Canada. While their numbers thin north of 88 degrees, there is evidence of polar bears all the way across the Arctic. Population is estimated to be between 20,000 to 25,000.
The main population centers are:
- Wrangell Island and western Alaska
- Northern Alaska
- Canadian Arctic archipelago
- Svalbard-Franz Josef Land
- North-Central Siberia
Tourists watching Polar Bears from a "tundra buggy" near Churchill, Manitoba.The most severe and topically recognized threats to the polar bear are the drastic changes taking place in their natural habitat, which is literally melting away due to global warming. The United States Geological Survey, for example, in November 2006, stated that the Arctic shrinkage in the Alaskan portion of the Beaufort Sea has led to a higher death rate for polar bear cubs.
A 1999 study by scientists from the Canadian Wildlife Service of polar bears in the Hudson Bay showed that global warming is threatening polar bears with starvation. Rising temperatures cause the sea-ice from which the bears hunt to melt earlier in the year, driving them to shore weeks before they have caught enough food to survive the period of scarce food in the late summer and early fall and leading to a 21% decline in the local subpopulation.
There is a photographically confirmed case from the beginning of the 20th century of a Svalbard polar bear drifting on ice as far south as the northern coast of the Norwegian mainland. It was found and killed near the village of Berlevag. More recent sightings in Berlevag, including one in the summer of 2005, remain unconfirmed.
Polar bears are enormous, aggressive, curious, and potentially dangerous to humans. Wild polar bears, unlike most other bears, are barely habituated to people and will quickly size up any animal they encounter as potential prey. Males are normally solitary except for mating season, and females are usually social towards one another.
Hunting, diet and feeding
The polar bear is the most carnivorous member of the bear family, and the one that is most likely to prey on humans as food. It feeds mainly on seals, especially ringed seals that poke holes in the ice to breathe, but will eat anything it can kill: birds, rodents, shellfish, crabs, beluga whales, young walruses, occasionally muskox or reindeer, and very occasionally other polar bears. Its biology is specialized to digest fat from marine mammals and cannot derive much nutrition from terrestrial food. Most animals can easily outrun a polar bear on the open land or in the open water, and polar bears overheat quickly: thus the polar bear subsists almost entirely on live seals and walrus calves taken at the edge of sea-ice in the winter and spring, or on the carcasses of dead adult walruses or whales. They live off of their fat reserves through the late summer and early fall when the sea-ice is at a minimum.They are enormously powerful predators, but they rarely kill adult walruses, which are twice the polar bear's weight, although such an adult walrus kill has been recorded on tape. Humans are the only predators of polar bears. 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 make the liver poisonous to humans, causing Hypervitaminosis A.Though mostly carnivorous, they sometimes eat berries, roots, and kelp in the late summer.
Polar bears are excellent swimmers and have been seen in open Arctic waters as far as 60 miles (100 km) from land. In some cases they spend half their time on ice floes. Their 12 cm (5 in) layer of fat adds buoyancy in addition to insulating them from the cold. 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.
Like other bear species, they have developed a liking for garbage as a result of human encroachment. But unlike other animals, they have an affinity for hydrocarbons, presumably derived from their taste for animal fat. For example, the dump in Churchill, Manitoba was frequently scavenged by polar bears, who have been observed eating, among other things, grease and motor oil. To protect the bears, the dump was closed in 2006. Garbage is now recycled or transported to Thompson, Manitoba.
Food pollution is a concern to polar bear health.Reduced cub survival has been reported in connection with PCBs, as well as reports of organochlorines affecting the endocrine system and immune systems with lower immunoglobulin G seen with increasing PCB levels.The lipophilic PCBs are considered a serious threat to marine mammals generally and to their food web, quickly concentrating into fat and blubber. These and related compounds are known in mammals (including humans) to cause such things as abortion, still births, alteration of the menstrual cycle, poor growth and survival of young, carcinogenicity, immunotoxicity, and even outright lethality. Other classes of organohalogens have been found in polar bears, such as PCDDs, PCDFs, TCPMe and TCPMeOH. Hermaphroditic polar bears have now been observed in less pristine areas. While some countries now ban some of these substances, they are still produced in others, and still end up all over the entire planet including the formerly pristine Arctic. Even after the use of these chemicals is stopped, they continue to accumulate up the food chain, including in marine mammals and humans, for some time to come.
Polar bears mate in April/May over a one week period needed to induce ovulation. The fertilized egg then remains in a suspended state until August or September. During this time, the females then eat prodigial amounts in preparation for pregnancy, doubling their body weight or more. In October they dig a maternity den in a snow drift and enter a dormant state similar to hibernation. Cubs are born in December without awakening the mother. She remains dormant while nursing her cubs until the family emerges from the den in March. Cubs are weened at two or three years of age and are separated from their mother. Sexual maturity typically comes at the age of four, but may be delayed by up to two years.
In the 1990's less than 20% cubs in the Western Hudson Bay were weaned at eighteen months, as opposed to 40% of cubs in the early 1980's.
In Alaska, the United States Geological Survey reports that 42 percent of cubs now reach 12 months of age, down from 65 percent 15 years ago. In other words, less than two of every three cubs that survived 15 years ago are now making it past their first year.
The USGS has also published research which purports that the percentage of Alaskan polar bears that den 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.
The World Conservation Union listed polar bears as a vulnerable species, one of three sub-categories of threatened status, in May 2006. Their latest estimate is that 7 out of 19 subpopulations are declining or already severely reduced. The United States Geological Survey forecasts that 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. 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.
Global warming has already had an impact on polar bear population health and size. Recent declines in polar bear numbers can be linked to the retreat of sea ice and its formation later in the year. Ice is also breaking up earlier in the year, forcing bears ashore before they have time to build up sufficient fat stores, or forcing them to swim long distances, which may exhaust them, leading to drowning. The results of these effects of global warming have been thinner, stressed bears, decreased reproduction, and lower juvenile survival rates.
Because of the inaccessibility of the arctic, there has never been a comprehensive global survey of polar bears, making it difficult to establish a global trend. The earliest preliminary estimates of the global population were around 5,000-10,000 in the early 1970s, but this was revised to 20,000-40,000 in the 1980s. Part of this increase may indicate recovery as a result of conservation measures implemented in the early 1970s, but it is principally a revised estimate based on a growing base of data. Current estimates bound the global population between 20,000-25,000. Long-term studies of local populations of polar bears show they have been shrinking in the Western Hudson Bay and Baffin Bay areas, and are under stress in the Southern Beaufort Sea area. In the Western Hudson Bay in Canada, for example, there were an estimated 1200 polar bears in 1987, and 950 in 2007.
The need for species protection has been disputed by two professionals: H. Sterling Burnett and Mitchell K. Taylor. Burnett, a Senior Fellow of the right-wing advocacy group National Center for Policy Analysis, has claimed that the total global population of polar bears increased from 5,000 to 25,000 between the 1970s and 2007. Mitchell Taylor, the Nunavut Government Manager of Wildlife Research, wrote a letter to the U.S. Fish and Wildlife Service arguing that local studies are insufficient evidence for global protection at this time. The views of these two people have received much attention from the media, although their views are refuted by a majority of arctic scientists.
Hunters from around the arctic have harvested hundreds of be polar bears annually since at least the 18th century. The harvest grew rapidly in the 1960's, peaking around 1968 with a global total of 1250 bears that year. Although the polar bear was not deemed endangered at the time, the growing threat encouraged countries to regulate polar bear hunting around that time. Norway passed a series of increasingly strict regulations from 1965 to 1973. Canada began imposing hunting quotas in 1968. The U.S. began regulating in 1971 and adopted the Marine Mammal Protection Act in 1972. In 1973 the International Agreement on the Conservation of Polar Bears (known as the Oslo Agreement among experts) was signed by the five nations whose Arctic territory is inhabited by polar bears: U.S., Canada, Norway, Denmark (via its territory Greenland) and Russia (then the Soviet Union). Although the agreement is not enforceable in itself, member countries agreed to place restrictions on recreational and commercial hunting, completely ban hunting from aircraft and icebreakers), and conduct further research. The treaty allows hunting "by local people using traditional methods," although this has been liberally interpreted by member nations. All nations except Norway allow hunting by the Inuit, and Canada and Denmark allow trophy hunting by tourists.
Many environmental and animal protection groups fear that global warming will have a tremendous impact on the viability of polar bear populations and fear that continued trophy hunting will have further negative consequences.
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