[PDF] The Polar Bear System 2: Still Potent!
"I will never forget my 'first' polar bear. Today, it still drives me to do all we can to secure a future for these true icons on ice. Working for WWF has given me the amazing opportunity to work alongside leading polar bear scientists and Inuit who have generously shared their wealth of traditional knowledge."
[PDF] The Polar Bear System 2: Still potent!
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With less sea ice, polar bears are forced to stay longer on land. This is increasingly bringing them into contact with local people in Arctic villages and towns, leading to bears and people being injured or killed in self-defense.
These powerful predators typically prey on seals. In search of this quarry they frequent areas of shifting, cracking ice where seals may surface to breathe air. They also stalk ice edges and breathing holes. If the opportunity presents itself, polar bears will also consume carcasses, such as those of dead whales. These Arctic giants are the masters of their environment and have no natural enemies.
Females den by digging into deep snow drifts, which provide protection and insulation from the Arctic elements. They give birth in winter, usually to twins. Young cubs live with their mothers for some 28 months to learn the survival skills of the far north. Females aggressively protect their young, but receive no help from their solitary male mates. In fact, male polar bears may even kill young of their species.
Because of expected habitat loss caused by climate change, the polar bear is classified as a vulnerable species. For decades, large-scale hunting raised international concern for the future of the species, but populations rebounded after controls and quotas began to take effect.[12] For thousands of years, the polar bear has been a key figure in the material, spiritual, and cultural life of circumpolar peoples, and polar bears remain important in their cultures. Historically, the polar bear has also been known as the "white bear".[13] It is sometimes referred to as the "nanook", based on the Inuit term nanuq.[14]
Constantine John Phipps was the first to describe the polar bear as a distinct species in 1774 in his report about his 1773 expedition towards the North Pole.[4][2] He chose the scientific name Ursus maritimus, the Latin for "maritime bear",[15] due to the animal's native habitat. The Inuit refer to the animal as nanook (transliterated as nanuq in the Inupiat language).[16][14] The Yupik also refer to the bear as nanuuk in Siberian Yupik.[17] In the Chukotko-Kamchatkan languages of Alyutor and Koryak, the name of the polar bear is umqa, while in the related Chukchi, it is umqə.[18] In Russian, it is usually called бе́лый медве́дь (bélyj medvédj, 'white bear'), though an older word still in use is ошку́й (Oshkúj, which comes from the Komi oski, "bear").[19] In Quebec, the polar bear is referred to by the french terms ours blanc ('white bear') or ours polaire ('polar bear').[20] In Norwegian, one of the primary languages of the Svalbard archipelago,[21] the polar bear is referred to as isbjørn ('ice bear') or kvitbjørn ('white bear').[22]
The polar bear was previously considered to be in its own genus, Thalarctos.[23] 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.[2]
The bear family, Ursidae, is thought to have split from other carnivorans about 38 million years ago.[24] The subfamily Ursinae originated approximately 4.2 million years ago.[25] The oldest known polar bear fossil is a 130,000 to 110,000-year-old jaw bone, found on Prince Charles Foreland in 2004.[26] Fossils show that between 10,000 and 20,000 years ago, the polar bear's molar teeth changed significantly from those of the brown bear.[27] Polar bears are thought to have diverged from a population of brown bears that became isolated during a period of glaciation in the Pleistocene[5] from the eastern part of Siberia (from Kamchatka and the Kolym Peninsula).[27]
The evidence from DNA analysis is more complex. The mitochondrial DNA (mtDNA) of the polar bear diverged from the brown bear, Ursus arctos, roughly 150,000 years ago.[26] Further, some clades of brown bear, as assessed by their mtDNA, were thought to be more closely related to polar bears than to other brown bears,[28] meaning that the brown bear might not be considered a species under some species concepts, but paraphyletic.[29] The mtDNA of extinct Irish brown bears is particularly close to polar bears.[30] A comparison of the nuclear genome of polar bears with that of brown bears revealed a different pattern, the two forming genetically distinct clades that diverged approximately 603,000 years ago,[31] although the latest research is based on analysis of the complete genomes (rather than just the mitochondria or partial nuclear genomes) of polar and brown bears, and establishes the divergence of polar and brown bears at 400,000 years ago.[32]
When the polar bear was originally documented, two subspecies were identified: the American polar bear (Ursus maritimus maritimus) by Constantine J. Phipps in 1774, and the Siberian polar bear (Ursus maritimus marinus) by Peter Simon Pallas in 1776.[36] This distinction has since been invalidated.[37][38][39] One alleged fossil subspecies has been identified: Ursus maritimus tyrannus, which became extinct during the Pleistocene. U.m. tyrannus was significantly larger than the living subspecies.[5] However, recent reanalysis of the fossil suggests that it was actually a brown bear.[1]
With the discovery of a southeast Greenland population in 2022,[43][44] there are 20 generally recognized, discrete subpopulations of polar bears.[41][45] The subpopulations display seasonal fidelity to particular areas, but DNA studies show that they are not reproductively isolated.[39] The 14 North American subpopulations range from the Beaufort Sea south to Hudson Bay and east to eastern Greenland and account for about 54% of the global population.[46]
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.[49] The Polar Bear Specialist Group of the IUCN Species Survival Commission 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."[50]
The polar bear is a marine mammal because it spends many months of the year at sea.[52] However, it is the only living marine mammal with powerful, large limbs and feet that allow them to cover kilometres on foot and run on land.[53] 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.[40][54] 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.[55] Freshwater is limited in these environments because it is either locked up in snow or saline. Polar bears are able to produce water through the metabolism of fats found in seal blubber,[56] and 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.[57]
Compared with its closest relative, the brown bear, the polar bear has a more elongated body build and a longer skull and nose.[35] As predicted by Allen's rule for a northerly animal, the legs are stocky and the ears and tail are small.[35] 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.[67] The pads of the paws are covered with small, soft papillae (dermal bumps), 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.[35] The claws are deeply scooped on the underside which assists 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.[68] 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.[citation needed]
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 3.1.4.23.1.4.3.[35]
The polar bear has an extremely well developed sense of smell, being able to detect seals nearly 1.6 km (1 mi) away and buried under 1 m (3 ft) of snow. Its hearing is about as acute as that of a human, and its vision is also good at long distances.[76]
The polar bear is an excellent swimmer and often will swim for days.[77] One bear swam continuously for 9 days in the frigid Bering Sea for 700 km (400 mi) to reach ice far from land. She then travelled another 1,800 km (1,100 mi). During the swim, the bear lost 22% of her body mass and her yearling cub died.[78] With its body fat providing buoyancy, the bear swims in a dog paddle fashion using its large forepaws for propulsion. Polar bears can swim at 10 km/h (6 mph). When walking, the polar bear tends to have a lumbering gait and maintains an average speed of around 5.6 km/h (3.5 mph).[79] When sprinting, they can reach up to 40 km/h (25 mph).[80]