Tuesday, November 6, 2012

Scientists have responded

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.[31] 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."[32] HP Compaq HSTNN-I04C Battery

Of the 19 recognized polar bear subpopulations, eight are declining, three are stable, one is increasing, and seven have insufficient data, as of 2009.The polar bear is often regarded as a marine mammal because it spends many months of the year at sea.[33] Its preferred habitat is the annual sea ice covering the waters over the continental shelf and the Arctic inter-island archipelagos. HP Compaq HSTNN-I12C Battery

These areas, known as the "Arctic ring of life", have high biological productivity in comparison to the deep waters of the high Arctic.[27][34] 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.[35] 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.[36] HP Compaq HSTNN-I39C Battery

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.[34] 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.[34] HP Compaq HSTNN-I40C Battery

In the Chukchi and Beaufort seas, polar bears retreat each summer to the ice further north that remains frozen year-round.The polar bear is the largest terrestrial carnivore, being more than twice as large as the Siberian tiger.[37] It shares this title with the Kodiak Bear.[38] Adult males weigh 350–680 kg (770–1500 lbs) and measure 2.4–3 m (7.9–9.8 ft) in length. HP Compaq HSTNN-I44C Battery

The Guinness Book of World Records listed the average male as having a body mass of 386 to 408 kg (850 to 900 lb) and a shoulder height of 133 cm (4.36 ft).[40] Adult females are roughly half the size of males and normally weigh 150–250 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 500 kg (1,100 lb).[39] HP Compaq HSTNN-I44C-A Battery

The polar bear is among the most sexually dimorphic of mammals, surpassed only by the pinnipeds.[41] 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.[40] This specimen, when mounted, stood 339 cm (11.12 ft) tall.[40] The shoulder height of an adult polar bear is 122 to 160 cm (48 to 63 in).[42][40] HP Compaq HSTNN-I44C-B Battery

Compared with its closest relative, the brown bear, the polar bear has a more elongated body build and a longer skull and nose.[25] As predicted by Allen's rulefor a northerly animal, the legs are stocky and the ears and tail are small.[25] 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.[43] HP Compaq HSTNN-I45C Battery

The pads of the paws are covered with small, soft papillae (dermal bumps) which provide traction on the ice.[25] 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.[25] The claws are deeply scooped on the underside to assist in digging in the ice of the natural habitat. HP Compaq HSTNN-I45C-A Battery

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.[44] 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.[25] HP Compaq HSTNN-I45C-B Battery

The cheek teeth are smaller and more jagged than in the brown bear, and the canines are larger and sharper.[25] The dental formula is

Polar bears are superbly insulated by up to 10 cm (3.9 in) of blubber,[43] their hide and their fur; they overheat at temperatures above 10 °C (50 °F), and are nearly invisible under infrared photography.[45] HP Compaq HSTNN-I48C-A Battery

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.[43] The guard hair is 5–15 cm (2.0–5.9 in) over most of the body.[46] Polar bears gradually moult from May to August,[47] but, unlike other Arctic mammals, they do not shed their coat for a darker shade to camouflage themselves in the summer conditions. HP Compaq HSTNN-I48C-B Battery

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.[48]

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.[49] HP Compaq HSTNN-I49C Battery

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.[50]

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 (0.9 m) of snow. HP Compaq HSTNN-I50C-B Battery

Its hearing is about as acute as that of a human, and its vision is also good at long distances.[51]

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.[52] Polar bears can swim 6 mph (9.7 km/h). HP Compaq HSTNN-I54C Battery

When walking, the polar bear tends to have a lumbering gait and maintains an average speed of around 3.5 mph (5.6 km/h).[52] When sprinting, they can reach up to 25 mph (40 km/h).[53]

The polar bear is the most carnivorous member of the bear family, and most of its diet consists of ringed and bearded seals.HP Compaq HSTNN-I64C-5 Battery

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.[54] Polar bears hunt primarily at the interface between ice, water, and air; they only rarely catch seals on land or in open water.[56]

The polar bear's most common hunting method is called still-hunting:[57] The bear uses its excellent sense of smell to locate a seal breathing hole, and crouches nearby in silence for a seal to appear. HP Compaq HSTNN-I65C-5 Battery

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 (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.[54] HP Compaq HSTNN-IB05 Battery

A third hunting method is to raid the birth lairs that female seals create in the snow.[57]

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. HP Compaq HSTNN-IB08 Battery

Mature bears tend to eat only the calorie-rich skin and blubber of the seal, whereas younger bears consume the protein-rich red meat.[54] Studies have also photographed polar bears scaling near-vertical cliffs, to eat birds' chicks and eggs.For subadultbears which are independent of their mother but have not yet gained enough experience and body size to successfully hunt seals, HP Compaq HSTNNIB12 Battery

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.[52]

The polar bear is an enormously powerful predator. It can kill an adult walrus, although this is rarely attempted. HP Compaq HSTNN-IB16 Battery

A walrus can be more than twice the bear's weight,[59] and has up to 3-foot (0.91 m) 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 is injured in the rush of walruses trying to escape. HP Compaq HSTNN-IB18 Battery

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 an attack on a walrus tends to be an extremely protracted and exhausting venture, bears have been known to abandon the hunt after making the initial injury.[60] Polar bears have also been seen to prey on beluga whales, by swiping at them at breathing holes. HP Compaq HSTNN-IB28 Battery

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. HP Compaq HSTNN-IB51 Battery

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,[62] although they have a vestigial hibernation induction trigger in their blood. HP Compaq HSTNN-IB52 Battery

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.[62] When sea ice is unavailable during summer and early autumn, some populations live off fat reserves for months at a time.[45] Polar bears have also been observed to eat a wide variety of other wild foods, HP Compaq HSTNN-IB55 Battery

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.[59] 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. HP Compaq HSTNN-IB62 Battery

Being both curious animals and scavengers,polar bears investigate and consume garbage where they come into contact with humans.[59] Polar bears may attempt to consume almost anything they can find, including hazardous substances such asstyrofoam, plastic, car batteries, ethylene glycol, hydraulic fluid, and motor oil. HP Compaq HSTNN-LB05 Battery

The dump in Churchill, Manitobawas closed in 2006 to protect bears, and waste is now recycled or transported to Thompson, Manitoba.

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.[68] HP Compaq HSTNN-LB08 Battery

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.[61] Polar bears are stealth hunters, and the victim is often unaware of the bear's presence until the attack is underway.[69] Whereas brown bears often maul a person and then leave, polar bear attacks are more likely to be predatory and are almost always fatal.[69] HP Compaq HSTNN-LB0E Battery

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,[61] and polar bear zoologist Nikita Ovsianikov has described adult males as having "well-developed friendships."[68] Cubs are especially playful as well. HP Compaq HSTNN-LB11 Battery

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