The polar bear (Ursus maritimus) is a bear native to the Arctic. It is the world's largest land carnivore, with most adult males weighing 300-600 kg (660-1320 lbs); adult females are about half the size of males. Its fur is hollow and translucent but usually appears as white or cream coloured, thus providing the animal with effective camouflage, however 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. Some scientists and climatologists believe that the projected decreases in the polar sea ice due to global warming will have a significant negative impact on of this species within this century. Despite these predictions, the actual data shows that as the earth has warmed, the total global population of polar bears has increased, and not shrunken. In 2005, Mitch Taylor, a Canadian authority on polar bears, stated, "We’re seeing an increase in bears that’s really unprecedented, and in places where we’re seeing a decrease in the population it’s from hunting, not from climate change." In a 2007 article, H. Sterling Burnett wrote, "Since the 1970s, while much of the world was warming, polar bear numbers increased dramatically, from roughly 5,000 to 25,000 bears."
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 300–600 kg (660–1320 lb) and measure 2.4–3.0 m (7.9–10.0 ft) in length. When standing upright, an adult male can stand up to 3.35 m (11.5 ft). That is about as tall as an elephant. Adult females are roughly half the size of males and normally weigh 150–300 kg (330–660 lb), measuring 1.9–2.1 m (6.25–7 ft). The great difference in body size makes the polar bear the second most sexually dimorphic of mammals, following the eared seals . At birth, cubs weigh only 600–700 g or about a pound and a half. The largest polar bear was a huge male, alledgedly weighing 1002 kg (2200 lb) shot at Kotzebue Sound in northwestern Alaska in 1960.
A polar bear's fur is white (individual hairs are transparent, like the water droplets that make up a cloud) and provides good camouflage and insulation. It may yellow with age. The fur acts as miniature greenhouses, and turns sunlight into heat, which is absorbed by the bear's black skin. Stiff hairs on the pads of its paws provide insulation and traction on 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 of most 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.
The raccoon and bear families are believed to have diverged about 30 million years ago. The spectacled bear split from other bears around 13 million years ago. The six distinct ursine species originated some 4 million years ago. According to both fossil and DNA evidence, the polar bear diverged from the brown bear roughly 200 thousand years ago; fossils show that between 10 and 20 thousand years ago the polar bear's molar teeth changed significantly from those of the brown bear.
Polar bears have, however, bred with brown bears to produce fertile grizzly–polar bear hybrids, suggesting that the two are close relatives. But neither species can survive long in the other's niche, and with distinctly different morphology, metabolism, social and feeding behaviors, and other phenotypic characters, the two bears are generally classified as separate species.
In a widely cited paper published in 1996, a comparison of the DNA of various brown bear populations showed that the brown bears of Alaska's ABC islands shared a more recent common ancestor with polar bears than with any other brown bear population in the world. Also to see how the bear species once split yet are still connected, polar bears still have HIT (hibernation induction trigger) in their blood, but they also utilize this to hibernate as the brown bear does. They may occasionally enter a dormant state referred to as "denning" (pregnant females in particular), though their body temperature does not decrease during this period as it would for a typical mammal in hibernation.
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. Still, reindeer and musk oxen can easily
outrun a polar bear, and polar bears overheat quickly: thus the
polar bear subsists almost entirely on live seals and walrus
calves, or on the carcasses of dead adult walruses or whales.
They are enormously powerful predators, but they rarely kill
adult walruses, which are twice the polar bear's weight,
although this has been known to happen. Humans and Orcas 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; in the past, humans have been poisoned by eating the livers of polar bears. 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 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.
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.
Like other bear species, they have developed a liking for garbage as a result of human encroachment. For example, the dump in Churchill, Manitoba is frequently scavenged by polar bears, who have been observed eating, among other things, grease and motor oil..
The 2004 National Geographic study found no cases of cubs being born as triplets, a common event in the 1970s, and that only one in twenty cubs were weaned at eighteen months, as opposed to half of cubs three decades earlier.
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.
Although some local populations of polar bears have been shrinking, their total global population has been growing. , . Between the 1970s and 2007, the total global population of polar bears increased from 5,000 to 25,000. On the west coast of Hudson Bay in Canada, for example, there were an estimated 1200 polar bears in 1987, and 950 in 2007.
In February 2005 the environmental group, Center for Biological Diversity, with support from American senator Joe Lieberman, petitioned the United States Fish and Wildlife Service (FWS), part of the Department of the Interior to use the Endangered Species Act and list the bears as a threatened species.
Under United States law the FWS was required to respond to the petition within 90 days, but in October 2005 after no reply had been received the Center for Biological Diversity threatened to sue the United States Government. On 14 December 2006 the Center for Biological Diversity along with Greenpeace and the Natural Resources Defense Council filed a lawsuit in California.
On December 27, 2006, the United States Department of the Interior in agreement with the three groups proposed that polar bears be added to the endangered species list, the first change of this type to be attributed to global warming. It will take up to a year to make the final determination. The Natural Resources Defense Council contends that though it is "a big step forward" the proposal fails to identify global warming pollution as the cause of rising Arctic temperatures and vanishing sea ice. In addition, it says the proposal offered by Dr. Rosa Meehan, Supervisor of the U.S. Fish and Wildlife Service, does not designate any of the land discussed as the kind of habitat that is essential for the polar bear's survival as "critical habitat" that could help the bear recover.
The World Conservation Union had already given polar bears threatened status in May 2006.
The most immediate 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 loss of sea ice in the Alaskan portion of the Beaufort Sea has led to a higher death rate for polar bear cubs.
The Harvard University Gazette said:
The BBC reported:
There is also some concern over pollution in addition to the
normal natural problems the bears might face. 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.
The bears sometimes have problems with various skin diseases with dermatitis caused sometimes by mites or other parasites. The bears are especially susceptible to Trichinella, a parasitic roundworm they contract by eating infected seals. Sometimes excess heavy metals have been observed, as well as ethylene glycol (antifreeze) poisoning. Bears exposed to oil and petroleum products lose the insulative integrity of their coats, forcing metabolic rates to dramatically increase to maintain body heat in their challenging environment. Bacterial Leptospirosis, rabies and morbillivirus have been recorded. Interestingly, the bears are thought by some to be more resistant than other carnivores to viral disease. The pollutant effect on the bears' immune systems, however, may end up decreasing their ability to cope with the naturally present immunological threats it encounters, and in such a challenging habitat even minor weaknesses can lead to serious problems and quick death.
Polar bears have been made both controversial and famous for their distinctive white fur and their habitat. Companies like Coca-Cola, Polar Beverages, Nelvana, Bundaberg Rum and Good Humor-Breyers have used images of this bear in logos. The first has consistently displayed the bears as thriving near penguins, though the animals naturally live in opposite hemispheres. The Canadian 2-dollar coin (right) features the image of a polar bear. The panserbjřrne of the fantasy trilogy His Dark Materials are polar bears with human-level intelligence. The TV series Lost has featured polar bears on a mysterious tropical island where they are portrayed as fearsome beasts. Also, a polar bear was chosen as mascot for the 1988 Winter Olympics held in Calgary, Canada. The Polar Bear is the mascot of Bowdoin college.
This Polar Bear Page is Copyright The Animal Web Guide © 2004 - 2009 Chuck Ayoub