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Over the next centuries, several European explorers would mention polar bears and describe their habits.{{sfn|Engelhard|2017|pp=53-66}}{{sfn|Ellis|2009|pp=14–23}} Such accounts became more accurate after the [[Age of Enlightenment|Enlightenment]], and both living and dead specimens were brought back. Nevertheless, some fanciful reports continued, including the idea that polar bears cover their noses during hunts. A relatively accurate drawing of a polar bear is found in [[Henry Ellis (governor)|Henry Ellis]]'s work ''A Voyage to Hudson's Bay'' (1748).{{sfn|Ellis|2009|pp=49, 51–52}} Polar bears were formally classified as a species on the [[Linnaean taxonomy|Linnaean system]] by Constantine Phipps after this 1773 voyage to the Arctic. Accompanying him was a young [[Horatio Nelson]], who was said to have wanted to get a polar bear coat for his father but failed in his hunt.{{sfn|Fee|2019|p=41}} In his 1785 edition of ''[[Histoire Naturelle]]'', [[Georges-Louis Leclerc de Buffon|Comte de Buffon]] mentions and depicts a "sea bear", clearly a polar bear, and "land bears", likely brown and black bears. This helped promote ideas about [[speciation]]. Buffon also mentioned a "white bear of the forest", possibly a [[Kermode bear]].{{sfn|Ellis|2009|p=50}}
Over the next centuries, several European explorers would mention polar bears and describe their habits.{{sfn|Engelhard|2017|pp=53-66}}{{sfn|Ellis|2009|pp=14–23}} Such accounts became more accurate after the [[Age of Enlightenment|Enlightenment]], and both living and dead specimens were brought back. Nevertheless, some fanciful reports continued, including the idea that polar bears cover their noses during hunts. A relatively accurate drawing of a polar bear is found in [[Henry Ellis (governor)|Henry Ellis]]'s work ''A Voyage to Hudson's Bay'' (1748).{{sfn|Ellis|2009|pp=49, 51–52}} Polar bears were formally classified as a species on the [[Linnaean taxonomy|Linnaean system]] by Constantine Phipps after this 1773 voyage to the Arctic. Accompanying him was a young [[Horatio Nelson]], who was said to have wanted to get a polar bear coat for his father but failed in his hunt.{{sfn|Fee|2019|p=41}} In his 1785 edition of ''[[Histoire Naturelle]]'', [[Georges-Louis Leclerc de Buffon|Comte de Buffon]] mentions and depicts a "sea bear", clearly a polar bear, and "land bears", likely brown and black bears. This helped promote ideas about [[speciation]]. Buffon also mentioned a "white bear of the forest", possibly a [[Kermode bear]].{{sfn|Ellis|2009|p=50}}


===Hunting===
===Exploitation===
{{main article|Polar bear hunting}}
{{Further information|Polar bear hunting}}
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Revision as of 17:21, 1 August 2023

This article is about the animal. For other uses, see Polar bear (disambiguation).
"Ice Bear" redirects here. For the We Bare Bears character, see List of We Bare Bears characters § Ice Bear. For other uses, see Ice Bears (disambiguation).

Polar bear
Temporal range: Pleistocene-recent[1]
Sow near Kaktovik, Barter Island, Alaska, United States
CITES Appendix II (CITES)[3]
Scientific classification Edit this classification
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Order: Carnivora
Family: Ursidae
Genus: Ursus
Species:
U. maritimus
Binomial name
Ursus maritimus
Phipps, 1774[4]
Subspecies[5]

†Ursus maritimus tyrannus(?)

Polar bear range
Synonyms

Ursus eogroenlandicus
Ursus groenlandicus
Ursus jenaensis
Ursus labradorensis
Ursus marinus
Ursus polaris
Ursus spitzbergensis
Ursus ungavensis
Thalarctos maritimus

The polar bear (Ursus maritimus) is a large bear native to the Arctic and surrounding areas. It is closely related to the brown bear, and the two species can interbreed. The polar bear is the largest extant species of bear, with adult males weighing 300–800 kg (700–1,800 lb). The species is sexually dimorphic, as adult females are much smaller. The polar bear is white- or yellowish-furred with black skin and a thick layer of fat. It is more slenderly built than the brown bear, with a narrower skull, longer neck and lower shoulder hump. Its teeth are sharper and more adapted to cutting meat. The paws are large and allow the bear to walk on ice and paddle in the water.

Polar bears are both terrestrial and pagophilic (ice-loving) and are considered to be marine mammals due to their dependence on marine ecosystems. They prefer the annual sea ice, but live on land when the ice melts in the summer. They are mostly carnivorous and specialized for preying on seals, particularly ringed seals and bearded seals. Such prey is typically taken by ambush; the bear may stalk its prey on the ice or in the water, but also will stay at a breathing hole or ice edge to wait for prey to swim by. The bear primarily feeds on the seal's energy-rich blubber. Other food includes walruses, beluga whales and some terrestrial foods. Polar bears are usually solitary with large home ranges, but can be found in groups when on land. During the breeding season, male bears guard females and defend them from rivals. Mothers give birth to cubs in a maternity den during the winter, which is also when they hibernate. Young stay with their mother for up to two and a half years.

The polar bear is considered to be a vulnerable species by the International Union for Conservation of Nature (IUCN). Its biggest threats are climate change, pollution and oil/gas development. Climate change has caused a decline in sea ice, giving the polar bear less access to its favoured prey and increasing the risk of malnutrition and starvation. Less sea ice also means that the bears must spend more time on land, increasing conflicts with people. Polar bears have been hunted, both by native and non-native peoples, for their coats, meat and other items. They have been kept in captivity in zoos and circuses and are prevalent in art, folklore, religion and modern culture.

Naming

The polar bear was given its common name by Thomas Pennant in A Synopsis of Quadrupeds (1771). It was historically known as the "white bear" in Europe between the 13th and 18th centuries, as well as "ice bear", "sea bear" and "Greenland bear".[6] The scientific name Ursus maritimus is Latin for "sea bear".[7][8] The bear is called nanook by the Inuit. The Netsilik cultures have different names for bears based on factors such as sex and age: these include adult males (anguraq), single adult females (tattaq), gestating females (arnaluk), newborns (hagliaqtug), large adolescents (namiaq) and hibernating bears (apitiliit).[9]

Taxonomy

Carl Linnaeus classified the polar bear as a type of brown bear (Ursus arctos), labeling it as Ursus maritimus albus-major, articus in his 1758 edition of his work Systema Naturae.[10] Constantine John Phipps formally described the polar bear as a distinct species, Ursus maritimus in 1774, following his 1773 voyage towards the North Pole.[4][11] Due to its adaptations to a marine environment, some have placed the polar bear in its own genus Thalarctos.[12] However Ursus is widely considered to be the valid genus for the species based on the fossil record and the fact that it is interfertile with the brown bear.[12][13]

Different subspecies have been proposed including Ursus maritimus maritimus (Phipps in 1774), U. m. marinus (Pallas 1776).[14] However these are not widely supported and the polar bear is officially considered to be monotypic.[15] One alleged fossil subspecies has been identified, Ursus maritimus tyrannus, which was significantly larger than the living polar bear.[13] However, it may in fact be a large brown bear.[16]

Evolution

The polar bear is one of eight extant species in the bear family Ursidae and of six extant species in the subfamily Ursinae. Ursine bears may have originated around 5 million years ago and show extensive hybridization of species in their lineage. The following cladogram is based on a genetic study by Kumar and collages (2017):[17]

Ursidae

Fossils of polar bears are uncommon and limited to Pleistocene deposits.[13][16] The oldest known fossil is a 130,000- to 110,000-year-old jaw bone, found on Prince Charles Foreland, Norway in 2004.[18][1] Scientists in the 20th century surmised that polar bears directly descended from a population of brown bears, possibly in eastern Siberia or Alaska.[13][16] Mitochondrial DNA studies in the 1990s and 2000s have supported the status of the polar bear as a derivative of the brown bear, finding that some brown bear populations were more closely related to polar bears than other brown bears, particularly the ABC Islands bears.[18][19][20] Lindqvist and collages (2010) estimated that the polar bear linage split from other brown bears around 150,000 years ago.[18]

Polar/brown bear hybrid taxidermy specimen on display at Natural History Museum at Tring in Hertfordshire, England

More extensive genetic studies have found that the two species are in fact separate sister lineages. The genetic similarities between polar bears and some brown bears was found to be the result of interbreeding.[21][22] Hailer and colleges (2012) estimate the split between polar and brown bears occurring around 600,000 years ago.[21] Lan and collages (2022) estimated the divergence occurring even earlier at over one million years ago.[22] Glaciation events over hundreds of thousands of years led to both the origin of polar bears and their subsequent interactions and hybridizations with brown bears.[23]

Studies in 2011 and 2012 concluded that the genetics of brown bears passed into polar bears.[21][24] In particular Edwards and collages (2011) concluded that living polar bear populations derived their matrilines from now extinct Irish brown bears.[24] Later studies have clarified that gene flow went from polar to brown bears rather than the reverse.[23][25][26] Close to 9 percent of the genome of ABC bears resulted from introgression from polar bears,[27] while Irish bears had 20 percent polar bear origin.[25] Mass hybridization between the two species appears to have stopped around 260,000 years ago. Modern hybrids are relatively rare in the wild.[22]

Analysis of the copy number variation in the genes of polar bears compared to brown bears and American black bears shows distinct adaptions. Polar bears have a less diverse array of olfactory receptor genes, a result of there being less odours in their Arctic habitat. With its carnivorous, high fat diet; the species has less copies of the gene involved in making amylase, an enzyme that breaks down starch, and more selection for genes for fatty acid breakdown and a more efficient circulatory system. The bear's thicker coat is the result of more copies of genes involved in keratin creating proteins.[28]

Characteristics

Polar bear skeleton
Skull

The polar bear is both the largest living species of bear and the largest land carnivore, though some brown bear subspecies like the Kodiak bear can rival it in size.[29][30] Males are generally 200–250 cm (6.6–8.2 ft) long with a weight of 300–800 kg (660–1,760 lb). Females are smaller at 180–200 cm (5.9–6.6 ft) with a weight of 150–300 kg (330–660 lb).[5] Sexual dimorphism in the species is particularly high compared to most other mammals.[31] The weight of polar bears fluctuates during the year, as they can bulk up on fat and increase their mass by 50 percent.[29] A fattened, pregnant female can weigh as much as 500 kg (1,100 lb).[32] Adults may stand 130–160 cm (4.3–5.2 ft) tall at the shoulder. The tail is 76–126 mm (3.0–5.0 in) long.[5] The largest polar bear on record, reportedly weighing 1,002 kg (2,209 lb), was a male shot at Kotzebue Sound in northwestern Alaska in 1960. This specimen, when mounted, stood 3.39 m (11 ft 1 in) tall on its hind legs.[33]

Compared to the brown bear, this species has a more slender build, with a narrower, smaller skull, longer neck, and lower shoulder hump.[29] Male polar bears have larger heads than females.[34] The snout profile is curved, resembling a "Roman nose".[35] The more streamlined build of the polar bear is likely an adaption for swimming. The long neck may allow it more easily poke into ice holes and seal dens.[36] They have 34–42 teeth including 12 incisors, 4 canines, 8–16 premolars and 10 molars. The teeth are adapted for a more carnivorous diet than the brown bear, having longer, sharper and more spaced out canines, and smaller, more pointed cheek teeth (premolars and molars).[31][37][36] The species has a large space or diastema between the canines and cheek teeth, which may allow it to better bite into prey.[37][38] Since it normally preys on animals much smaller than it, the polar bear does not have a particularly strong bite.[38]

Polar bears have large paws, with the front paws being broader than the back. They move around by walking or galloping. The feet are hairier than in other bear species, which allows then to walk on snow and sea ice. Walking bears tilt their front paws towards each other. They can run at speeds of up to 20 km/h (12 mph),[39] but typically move at around 5.5 km/h (3.4 mph).[40] When swimming, the broad front paws do the paddling, while the hind legs play a role in steering and diving.[5][41] They can swim at up to 6 km/h (3.7 mph).[42] The claws are small but sharp and hooked, and are used both to snatch prey and climb onto ice.[41][43]

Polar bear jumping on floating ice

The coat consists of dense underfur around 5 cm (2.0 in) long and guard hairs around 15 cm (5.9 in) long.[5] Males have significantly longer hairs on their forelegs, which is thought to attract females, serving a similar function to the lion's mane.[44] The outer surface of the hairs has a scaly appearance, and the guard hairs are hollow, which allows the animals to trap heat and float in the water.[45] The transparent guard hairs forward scatter UV light between the underfur and the skin, leading to a cycle of absorption and re-emission.[46] The fur appears white due to the backscatter of incident light and the absence of pigment.[46][47] Polar bears are pure white after they molt and gain a more yellowish colouration as they are exposed more to the sun. They can also be grayish or brownish.[5] Their light fur provides camouflage in their snowy environment. After emerging from the water, the bear can easily shake itself dry before freezing since the hairs are resistant to tangling when wet.[48] The skin, including the nose and lips, is black and absorbs heat.[5][46] Polar bears have a 5–10 cm (2.0–3.9 in) thick layer of fat underneath the skin,[5] which provides both warmth and energy.[49] Polar bears maintain their core body temperature at about.36.9 °C (98 °F).[50] They risk overheating if they exert themselves too much.[51]

The eyes of a polar bear are located close to the roof of the head, which may allow them to stay out of the water when the animal is swimming at the surface. They are relatively small, which may be an adaption against blowing snow and snow-blindness. They are dichromats, having only two types of cone cells, one for seeing blue-violet and the other for yellow. They have many rod cells which allow them to see at night. The ears are small, allowing them to retain heat and not get frostbitten.[52] They can hear best at frequencies of 11.2–22.5 kHz (26,800–13,300 m).[53] The nasal concha has a large surface area, so more warm air can move through the nasal passages.[35] Their olfactory system is also large and adapted for smelling prey over vast distances.[54] The animal has reniculate kidneys which can efficiently filter out the salt in their food.[55] The polar bear's liver accumulates high concentrations of vitamin A from their prey, making it toxic. High amounts of ito cells prevent the bear from being harmed by the toxicity.[56]

Distribution and habitat

Map of 16 polar bear subpopulations. The colours represent the four major genetic clusters

Polar bears inhabit the Arctic and adjacent areas. Their range includes Greenland, Canada, the US state of Alaska, Russia and the Svalbard Archipelago of Norway.[5][57][58] Polar bears have been recorded just 25 km (16 mi) from the North Pole.[59] The southern limits of their range include James Bay and Newfoundland/Labrador in Canada and St. Matthew Island and the Pribilof Islands of Alaska.[5] They are not permanent residents of Iceland, but have historically been recorded visiting there if they can reach it via sea ice.[60] Due to minimal human development in its remote habitat, it can still be found in much of its original range, more so than any other large carnivore.[61]

Polar bears have been divided into 19 subpopulations labeled the East Greenland (ES), Barents Sea (BS), Kara Sea (KS), Laptev Sea (LVS), Chukchi Sea (CS), northern and southern Beaufort Sea (SBS and NBS), Viscount Melville (VM), M'Clintock Channel (MC), Gulf of Boothia (GB), Lancaster Sound (LS), Norwegian Bay (NB), Kane Basin (KB), Baffin Bay (BB), Davis Strait (DS), Foxe Basin (FB) and the western and southern Hudson Bay (WD and SH) populations.[62][63] A 2022 study has suggested that the bears in eastern Greenland should be divided into north and south.[64] The bears can also be divided into four gene clusters; Southern Canadian, Canadian Archipelago, Western Basin (northwestern Canada west to the Russian Far East) and Eastern Basin (Greenland east to Siberia).[62]

The polar bear is dependent enough on the ocean to be considered a marine mammal.[15][65] It prefers the annual sea ice over continental shelves and between islands of archipelagos. These areas, known as the "Arctic ring of life", have high biological productivity in comparison to the deep waters of the high Arctic.[61][66] The species 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.[67] Polar bears travel in response to changes in ice cover throughout the year. They are forced onto land in summer when the sea ice disappears.[68] Terrestrial habitats used by polar bears include forests, mountains, rocky areas, lakeshores and creeks.[69] In the Chukchi and Beaufort seas, where the sea ice breaks off and floats north during the summer, polar bears generally stay on the ice, though a large portion of the population (15–40%) has been observed spending all summer on land since the 1980s.[70] Some areas have thick multiyear ice that doesn't completely melt and the bears can stay on all year,[71] though this type of ice has less seals and allows for less productivity in the water.[72]

Natural history

Polar bears have wide home ranges. They may independently travel an average of 142,332 km2 (54,955 sq mi) per year, while drifting ice allows them to move even further at 178,040 km2 (68,740 sq mi) per year.[73] Depending on ice conditions, a bear can travel an average of 12 km (7.5 mi) per day.[74] These movements are powered by their energy-rich diet.[49] Polar bears are also capable swimmers. One study found they can swim an average of 154.2 km (95.8 mi) with an average duration of 3.4 days.[75] They can dive for as long as three minutes.[76]

Most polar bears are active year-round. Hibernation occurrs only among pregnant females.[77] Non-hibernating bears typically have a normal 24-hour cycle even during days of all darkness or all sunlight, though cycles less than a day are more common during the former.[78] The species is generally diurnal, being more active early in the day and less so towards the end.[79] Polar bears sleep close to eight hours a day on average.[80] They will sleep in various positions, including curled up, sitting up, laying on one side, on the back with limbs spread, or on the belly with the rump elevated.[40][43] On sea ice, polar bears snooze at pressure ridges where they dig on the sheltered side and lie down. After a snowstorm, a bear may rest under the snow for hours or days. On land, the bears may dig a resting spot on gravel or sand beaches.[40] They will also sleep on rocky outcrops. Adult males require less shelter for sleeping as they are less at risk from other bears.[81]

Social life

Young males play-fighting

Polar bears are typically solitary, aside from mothers with cubs and mating pairs.[82] On land, they are found closer together and gather around food resources. Adult males in particular are more tolerant of each other in land environments and outside the breeding season.[83][84] They have been recorded forming stable "alliances", travelling, resting and playing together. A dominance hierarchy exists among polar bears with the largest mature males ranking at the top. Adult females outrank subadults and adolescents and younger males outrank females of the same age. In addition, cubs with their mothers outrank those on their own.[85] Females with dependent offspring tend to stay away from males,[84] but sometimes associate with other female-offspring units creating "composite families".[85]

Polar bears are generally quiet but can produce various sounds.[86] Chuffing, a soft pulsing call, is made by mother bears presumably to keep in contact with their young.[87] During the breeding season, adult males will chuff at potential mates.[88] Unlike other animals where chuffing is passed through the nostrils, in polar bears it is emitted through a partially open mouth.[87] Cubs will cry for attention and produce humming noises while nursing.[89] Teeth chops, jaw pops, blows, huffs, moans, growls and roars are heard in more hostile encounters.[88] Chemical communication can also be important: bears secret their scent from their foot pads into their tracks which allow individuals to keep track of one another.[90]

Diet and hunting

The polar bear is a hypercarnivore,[91] and the most carnivorous species of bear.[36] It is the apex predator of the Arctic,[92] preying on ice-living seals and consuming their energy-rich blubber.[93] The most commonly taken species is the ringed seal, but they also prey on bearded seals and harp seals.[5] Ringed seals are ideal prey as they are abundant and small enough to be overpowered by even small bears.[94] Bearded seal adults are larger and are more likely to break free from an attacking bear, hence adult male bears are more successful in hunting them. Less common prey are hooded seals, spotted seals, ribbon seals and the more temperate-living harbor seals.[95] Polar bears, mostly adult males, will occasionally hunt walruses, both on land and on ice, though they mainly target the young, as adults are too large and formidable, with their thick skin and long tusks.[96]

Bear feeding on a bearded seal

Besides seals, bears will prey on cetacean species such as beluga whales and narwhals, as well as hoofed mammals, birds and their eggs, fish and marine invertebrates. A small percentage of their diet is plant matter, such as berries, moss, grass and seaweed.[97] The polar bear cannot derive enough energy from such foods, since its digestive system is too specialized for animal matter.[98] In their southern range, especially near Hudson Bay and James Bay, polar bears endure all summer without sea ice to hunt from. Hence they must subsist more on terrestrial foods.[99]

Polar bears hunt their prey in several different ways. When a bear spots a seal hauling out on the sea ice it slowly stalks it with the head and neck lowered, possibly to make its dark nose and eyes less noticeable. As it gets closer, the bear crouches more and eventually charges at a high speed, attempting to catch the seal before it can escape into its ice hole. Some stalking bears need to move through water; traversing though water cavities in the ice when approaching the seal or swimming towards a seal on an ice floe. The polar bear can stay underwater with its nose exposed. When it gets close enough, the animal lunges from the water to attack. Despite popular legend, there is no reliable evidence that polar bears cover their black noses with their paws when hunting.[100]

During a limited time in spring, polar bears will search for ringed seal pups in their birth lairs underneath the ice. Once a bear catches the scent of a hiding pup and pinpoints its location, it approaches the den quietly so as to not alert it. It uses its front feet to smash through the ice and then pokes its head in to catch the pup before it can escape. A ringed seal's lair can be more then 1 m (3.3 ft) below the surface of the ice and thus more massive bears are better equipped for breaking in. Some bears may simply stay still near a breathing hole or other spot near water and wait for prey to come by.[101] This can last hours and when a seal surfaces the bear will try to pull it out with its paws and claws.[102] This tactic is the primary hunting method from winter to early spring.[5]

Bear with whale carcass

During walrus hunts, the sight of an approaching polar bear can cause aggregations of walruses to panic and stampede. The bear will look for young that have been crushed or separated during the turmoil.[96] There are reports of bears trying to kill walruses using rocks and pieces of ice.[103] Belugas and narwhals are vulnerable to bear attacks when they are stranded in shallow water or isolated holes in sea ice.[104] When stalking land animals such as reindeer, polar bears will hide in vegetation before an ambush.[105] On some occasions, bears may try to catch prey in open water, swimming underneath a seal or aquatic bird. Seals in particular, however, are more agile than bears in the water.[106] Polar bears rely on raw power when trying to kill their prey, and will employ bites or paw swipes.[91] They have the strength to pull a mid-sized seal out of the water or haul a beluga carcass for quite some distance.[107] Polar bears only occasionally store food for later—burying it under snow—and only in the short term.[108]

Arctic foxes routinely follow polar bears and scavenge scraps from their kills. The bears usually tolerate them but will charge a fox that gets too close when it is feeding. Polar bears themselves will scavenge. Subadult bears will eat remains left behind by others. Females with cubs often defer a carcass to an approaching adult male, though they may be less likely to if they haven't eaten in a long time.[109] Whale carcasses are a valuable food source, particularly on land and after the sea ice melts, and attract several bears.[83] In one area in northeastern Alaska, polar bears have been recorded competing with grizzly bears for whale carcasses. Despite their smaller size, grizzlies are more aggressive and polar bears are more likely to yield to them in confrontations.[110] Polar bears will also scavenge at garbage dumps during ice-free periods.[111] Enough fat reserves allow polar bears to fast for months.[112]

Reproduction and development

Courting male approaching female

Polar bear mating takes place on the sea ice and during spring, mostly between March and May.[5][113][114][82] Males search for estrus females and often travel in twisting directions which reduces the chances of them encountering other males while still allowing them to find females. The movements of females remain linear and they travel more widely.[115] The mating system could be labelled as female defense polygyny, serial monogamy or promiscuity.[114][116]

Upon finding a female, a male will try to isolate and guard her. Courtship can be somewhat aggressive and a male will pursue a female if she tries to run away. It can take days for the male to mate with the female which induces ovulation. After their first copulation, the couple bond. Undisturbed polar bear pairings typically last around two weeks during which they will sleep together and mate multiple times.[117] Competition for mates can be intense and this has led to sexual selection for bigger males. Polar bear males often have scars from fighting.[113][114] A male and female that have already bonded will flee together when another male arrives.[118] A female mates with multiple males in a season and a single litter can have more than one father.[116]

When the mating season ends, the female will build up more fat reserves to sustain both herself and her young. Sometime between August and October, the female constructs and enters a maternity den for winter. Depending on the area, maternity dens can be found in sea ice just off the coastline or further inland, and may be dug underneath snow, earth or a combination of both.[119] The inside of these shelters can be around 1.5 m (4.9 ft) around with a ceiling height of 1.2 m (3.9 ft) while the entrance may be 2.1 m (6.9 ft) and 1.2 m (3.9 ft) wide. The temperature of a den can be much higher than the outside.[120] Females hibernate and give birth to their cubs in the dens.[121] Hibernating bears fast and recycle bodily waste. Polar bears experience delayed implantation and the fertilized embryo does not start development until the fall, between mid-September and mid-October.[122] With delayed implantation, gestation in the species lasts seven to nine months but actual pregnancy is only two months.[123]

Mother nursing her young
Female with cubs

Mother polar bears typically give birth to two cubs per litter. As with other bear species, newborn polar bears are tiny and altricial.[124] The newborns have woolly hair and pink skin, with a weight of around 600 g (21 oz).[5][29] Their eyes remain closed for a month.[125] The mother's fatty milk fuels their growth, and the cubs are keep warm both by the mother's body heat and the den. The mother emerges from the den between late February and early April, and her cubs are well developed and capable of walking with her.[126] At this time they weigh 10–15 kilograms (22–33 lb).[5] A polar bear family stays near the dens for roughly two weeks, during this time the cubs will move and play around while the mother mostly rests. They eventually head out on the sea ice.[127]

Cubs under a year old stay close to their mother. When she hunts, they stay still and watch until she calls them back.[128]. Observing and imitating the mother helps the cubs hone their own hunting skills.[129] After their first year they become more independent and explore. At around two years old, they are capable of hunting on their own, but will return to their mother.[130] The young suckle their mother as she is laying on her side or sitting up.[127] A lactating female cannot conceive and give birth,[131] and cubs are weaned between two and two-and-a-half years.[5] She may simply leave her weaned young or they may be chased away by a courting male.[130] Polar bears reach sexual maturity at around four years for females and six years for males.[132] Females reach their adult size at four or five years of age while males are fully grown at twice that age.[133]

Mortality

Polar bears can live up to 30 years.[5] The bear's long lifespan and ability to consistently produce young each year offsets cub deaths. Some cubs die in the dens or in the womb if the female is not in good condition. Nevertheless, the female has a chance to produce a surviving litter the next spring if she is able to eat better in the coming year. Cubs will eventually starve if their mothers can't kill enough prey.[134] Cubs also face threats from wolves[135] and adult male bears. Males kill cubs to bring their mother back into estrus, but also kill young outside the breeding season for food.[136] A female and her cubs can flee from the slower male when he is farther away. If the male is able to get close, the mother defends the cubs, potentially at the cost of her life.[137]

Subadult bears, which are independent but not quite mature, have a particularly rough time as they are not as successful hunters as adults. Even when they do succeed, there is a chance their kill will be stolen by a larger bear. Hence subadults have to scavenge and are often underweight and at risk of starvation. At adulthood, polar bears have a high survival rate, though adult males suffer injuries from fights over mates.[138] Polar bears are especially susceptible to Trichinella, a parasitic roundworm they contract through cannibalism.[139]

Conservation status

Main article: Polar bear conservation
Map from the U.S. Geological Survey shows projected changes in polar bear habitat from 2001 to 2010 and 2041 to 2050.

In 2015, the IUCN Red List categorized the polar bear as vulnerable due to "decline in area of occupancy, extent of occurrence and/or quality of habitat". It estimated the total population to be between 22,000 to 31,000, and the current population trend as unknown. Threats to polar bear populations include climate change, pollution and oil/gas development.[2]

In 2021, the IUCN/SSC Polar Bear Specialist Group labeled four subpopulations (Barents and Chukchi Sea, Foxe Basin and Gulf of Boothia) as "likely stable", two (Kane Basin and M'Clintock Channel) as "likely increased" and three (Southern Beaufort Sea, Southern and Western Hudson Bay) as "likely decreased" over specific time periods between the 1980s and 2010s. The remaining ten did not have enough data.[63] A 2016 study projected a likely decline in polar bear numbers of more than 30 percent over three generations due to the reduction of sea ice. The study concluded that declines of more than 50 percent are much less likely.[140] A 2012 review suggested that polar bears may become regionally extinct in southern areas by 2050 if trends continue, leaving the Canadian Archipelago and northern Greenland as strongholds.[141]

The key danger from climate change is malnutrition or starvation due to habitat loss. As polar bears hunt seals on the sea ice, rising temperatures cause the ice to melt earlier in the year, driving the bears to shore before they have built sufficient fat reserves to survive the period of scarce food in the late summer and early fall. Thinner sea ice tends to break more easily, which appears to make it more difficult for polar bears to access seals. Insufficient nourishment leads to lower reproductive rates in adult females and lower survival rates in cubs and juvenile bears. Lack off access to seals also causes bears to find food on land which increases the risk of conflict with humans.[61][141]

Polar bear swimming. The loss of sea ice has lead to more open water and more pressure on the bears to swim great distances.

Reduction in sea-ice cover also forces bears to swim longer distances, which further depletes their energy stores and occasionally leads to drowning. Increased ice mobility may result in less stable site for dens or longer distances for mothers travelling to and from dens on land. Thawing of permafrost would lead to more fire-prone roofs for bears denning underground, while less snow would lead to more cave-ins or reduced insulation.[61][141] Maximum corticosteroid-binding capacity of corticosteroid-binding globulin in polar bear serum correlates with stress in polar bears, and this has increased with climate warming.[142] Disease-causing bacteria and parasites would flourish more readily in a warmer climate.[141]

Oil and gas development also affects polar bear habitat. The Chukchi Sea Planning Area of northwestern Alaska, which has had many drilling leases, was found to be an important site for non-denning female bears.[143] Oil spills are also a risk. A 2018 study found that ten percent or less of prime bear habitat in the Chukchi Sea is vulnerable to a potential spill, but could harm nearly 40 percent of the polar bear population at full reach.[144] Polar bears accumulate high levels of persistent organic pollutants such as polychlorinated biphenyl (PCBs) and chlorinated pesticides, due to their position at the top of the ecological pyramid. Many of these chemicals have been internationally banned due to the recognition of their harm on the environment. Traces of them have slowly dwindled in polar bears but still persist and have even increased in some populations.[145]

Polar bears receive some legal protection in all the countries they inhabit. The species has been labeled as 'threatened' under the US Endangered Species Act since 2008,[146] while the Committee on the Status of Endangered Wildlife in Canada listed it as of 'Special concern' since 1991.[147] In 1973, the Agreement on the Conservation of Polar Bears was signed by all five nations with polar bear populations, Canada, Denmark (Greenland), Russia (then USSR), Norway and the US. This banned most harvesting of polar bears, allowing indigenous hunting using traditional methods, and promoted preservation of bear habitat.[148] CITES lists the species under Appendix II,[3] which allows regulated trade.[149]

Relationship with humans

Polar bears have coexisted and interacted with circumpolar peoples for millennia.[150] "White bears" are mentioned as commercial items in the Japanese writing Nihon Shoki in the seventh century. It is not clear if these were polar bears or white-coloured brown bears.[151] During the Middle Ages, Europeans considered white bears to be a novelty and were more familiar with brown and black-coloured bears.[152] An early written account of the polar bear in its natural environment is found in the 13th century anonymous Norwegian text Konungs skuggsjá, which mentions that "...the white bear of Greenland wanders most of the time on the ice of the sea, hunting seals and whales and feeding on them" and says the bear is "...as skillful a swimmer as any seal or whale".[153]

Nelson and the bear, by Richard Westall (1773)

Over the next centuries, several European explorers would mention polar bears and describe their habits.[154][155] Such accounts became more accurate after the Enlightenment, and both living and dead specimens were brought back. Nevertheless, some fanciful reports continued, including the idea that polar bears cover their noses during hunts. A relatively accurate drawing of a polar bear is found in Henry Ellis's work A Voyage to Hudson's Bay (1748).[156] Polar bears were formally classified as a species on the Linnaean system by Constantine Phipps after this 1773 voyage to the Arctic. Accompanying him was a young Horatio Nelson, who was said to have wanted to get a polar bear coat for his father but failed in his hunt.[11] In his 1785 edition of Histoire Naturelle, Comte de Buffon mentions and depicts a "sea bear", clearly a polar bear, and "land bears", likely brown and black bears. This helped promote ideas about speciation. Buffon also mentioned a "white bear of the forest", possibly a Kermode bear.[157]

Exploitation

Further information: Polar bear hunting
Eskimo hunter with polar bear slain with bow and arrow (1924)
Skins of hunted bears in Greenland

Polar bears were hunted as early as 8,000 years ago, as indicated by archeological remains at Zhokhov Island. The oldest graphic depiction of a polar bear shows it being hunted by a man with three dogs. This rock art was among several polygraphs found at Pegtymel and dates to the fifth to eighth centuries. Prior to access to firearms, native people used lances and bows and arrows, and hunted in groups accompanied by dogs. Though hunting typically took place on foot, some people killed swimming bears from boats with a harpoon. Polar bears were sometimes killed in their dens. Killing a polar bear was considered a rite of passage for boys in some cultures. Native people respected the animal and hunts were subject to strict rituals.[158] Bears were harvested for the fur, meat, fat, tendons, bones and teeth.[159][160] The fur was worn and slept on, while the bones and teeth were made into tools. For the Netslik, the individual who finally killed the bear had the right to its fur while the meat was passed to all in the party. Some people kept the cubs of slain bears.[161]

Norsemen in Greenland traded polar bear furs in the Middle Ages.[162] In Russia, Novaya Zemlya and Franz Josef Land were important commercial centres for polar bear products, the former starting all the way back in 1556. Large scale hunting of bears at Svaland occurred since at least the 18th century, when no less than 150 bears were killed each year by Russian explorers. In the next century, more Norwegians were harvesting the bears. From the 1870s to the 1970s, around 22,000 of the animals were hunted. Over 150,000 polar bears in total were either killed or captured in both Russia and Svaland, from the 18th to the 20th century. In the Canadian Arctic, bears were harvested by commercial whalers especially if they could not get enough whales. The Hudson's Bay Company is estimated to have sold 15,000 polar bear coats between the late 19 century and early 20th century.[163] In the mid 20th century, countries begin to regulate polar bear harvesting, culminating in the 1973 agreement.[148]

Polar bear meat was commonly eaten as rations by explorers and sailors in the Arctic. Its taste and texture has been described both positively and negatively. Some have called it too coarse with a powerful smell, while others praised it as a "royal dish".[164] The liver was known for being too toxic to eat.[56] Polar bear fat was also used for lamps when they ran out of fuel.[164] Polar bear rugs were historically popular and by the 13th and 14th centuries, they were almost ubiquitous on the floors of Norwegian churches. In more modern times, Hollywood actors would pose on bearskin rugs, notably Marilyn Monroe. Such images often had sexual connotations.[165]

Conflicts

Further information: Bear danger and Bear attack
Road sign warning about the presence of bears. The Norwegian text translates into "Applies to all of Svalbard".

When the sea ice melts, polar bears, particularly subadults, conflict with humans over resources on land.[166] They are attracted to the smell of human-made foods, particularly at garbage dumps and may be shot when they encroach on private property.[167] In Churchill, Manitoba, local authorities maintain a "polar bear jail" where nuisance bears are held until the sea ice freezes again.[168] Climate change has increased conflicts between the two species.[166] Over 50 polar bears swarmed a town in Novaya Zemlya in February 2019, leading local authorities to declare a state of emergency.[169]

From 1870 to 2014, there were an estimated 73 polar bear attacks on humans, which led to 20 deaths. The majority of attacks were by hungry males, typically subadults, while female attacks were usually in defense of young. In comparison to brown and American black bears, attacks by polar bears were more often near and around were humans lived. This may be due to the bears being more desperate for food and thus more likely to seek out human settlements. As with the other two bear species, polar bears are more likely to target no more than two people at once. Despite its reputation, the polar bear is generally not more aggressive than other bears.[170]

Captivity

Visitors observing polar bears underneath a glass tunnel at the Detroit Zoo

The polar bear was a particularly sought after species for exotic animal collectors due to being relatively rare and remote living, and its reputation as a ferocious beast.[171] They were originally kept only by royals and elites. In 1609, James I was given two polar bear cubs by sailor Jonas Poole, who got them during a trip to Svalbard.[172] At the end of the 17th century, Frederick I of Prussia housed them in menageries with other wild animals. He had them declawed and defanged to perform mock fights. Around 1726, Catherine I of Russia gifted two polar bears to Augustus II the Strong, who desired them for his animal collection.[171] Over time, polar bears were being displayed to the public in zoos and circuses.[173] In the early 19th century, the species would be exhibited at the Tower of London and the Exeter Exchange and a menagerie in Vienna.[174]

Polar bear exhibits were innovated by Carl Hagenbeck, who replaced cages and pits with settings that mimic the animal's natural environment. In 1907, he revealed a complex panorama structure at the Tierpark Hagenbeck Zoo. It consisted of exhibits made of artificial snow and ice separated by moats. Different polar animals were displayed on each platform, giving the illusion of them living together. Starting in 1975, Hellabrunn Zoo housed its polar bears in an exhibit which consisted of a glass barrier, a house, concrete platforms mimicking ice floes and a large pool. Inside the house were maternity dens, and rooms for the staff to prepare and store the food. The exhibit was connected to an outdoor yard for extra room.[175] In 2001, the Detroit Zoo opened its "Arctic Ring of Life" exhibit, which cost $15 million dollars to build.[176] The exhibit has a plexiglass tunnel underneath the water allowing for a more immersive experience for the guests.[177] Many zoos in Europe and North America have stopped keeping polar bears due to the costs of their exhibits.[178]

Performing polar bear at the 1973 Nationaal Songfestival

Polar bears have historically been trained to perform in circuses. Bears in general were popular in circuses as they were large, strong, easy to train and had human-like characteristics, and the white coat of polar bears made them particularly attractive. Circuses helped change the polar bear's image from a fearsome monster to something more comical. Performing polar bears were being used in 1888 by Circus Krone in Germany and later in 1904 by the Bostock and Wombwell Menagerie in England. Circus director Wilhelm Hagenbeck trained up to 75 polar bears to slide into a large tank through a chute. He began performing with them in 1908 and they had a particularly well-received show at the Hippodrome in London. Other circus tricks performed by polar bears included tightrope walking, ball bouncing, roller-skating and motorcycle riding. One of the most famous polar bear trainers post-WWII was East German Ursula Böttcher, whose small stature contrasted with that of the large bears. Starting in the late 20th century, polar bear acts were being retired and the use of these bears for the circus is now prohibited in the US.[179]

Several captive polar bears were given celebrity status, notably Knut (2006–2011) of the Berlin Zoological Garden, who was rejected by his mother and had to be hand-reared by zookeepers. Another bear, Binky (1975–1995) of the Alaska Zoo in Anchorage, became famous for attacking two visitors who got too close.[180] Captive polar bears may pace back and forth, a stereotypical behaviour. In one sample, zoo polar bears were found to have spent 14 percent of their days pacing.[181] Gus (1985–2013) of the Central Park Zoo was prescribed Prozac by a therapist for constantly swimming in his pool.[182] To reduce stereotypical behaviours, zookeepers provide the bears with enrichment items to trigger their play behaviour.[183] Zoo polar bears may appear green due to algae concentrations.[184]

Cultural significance

Further information: Cultural depictions of bears
Model of a swimming polar bear from the Dorset culture, northern Canada
The coat of arms of Greenland

Polar bears have had prominent roles in Inuit culture and religion. The deity Torngarsuk was sometimes imagined as a giant polar bear. He resided underneath the sea floor in an underworld of the dead and had power over sea creatures. Kalaallit shamans would worship him through singing and dancing and were expected to be taken by him to the sea and consumed if he considered them worthy. Polar bears were also associated with the goddness Nuliajuk who was responsible for their creation, along with other sea creatures. It was believed that shaman could reach the moon or the bottom of the ocean by riding on a guardian spirit in the form of a polar bear. Some folklore involves people turning into or disguising themselves as polar bears by donning their skins or the reverse, with polar bears removing their own skins. Polar bears also feature in Inuit astronomy, where the Pleiades constellation is conceived of as a polar bear trapped by dogs while Orion's Belt, the Hyades and Aldebaran represent hunters, dogs and a wounded bear respectively.[185]

Nordic and Icelandic folklore and literature has also featured polar bears. In The Tale of Auðun of the West Fjords, a poor man named Auðun spends all his money on a polar bear in Greenland, but ends up rich after giving the bear to the king of Denmark.[186] In the 14th century manuscript Hauksbók, a man named Odd kills and eats a polar bear that killed his father and brother. In the story of The Grimsey Man and the Bear, a mother bear nurses and rescues a farmer stuck on an ice floe and is repaid with sheep meat. 18th century writings mention the legend of a "polar bear king" known as the bjarndýrakóngur. This beast was depicted as a polar bear with "ruddy cheeks" and a unicorn-like horn, which glows in the dark. The king could understand when humans talk and was considered to be very astute.[187] Two Norwegian fairy tales, East of the Sun and West of the Moon and White-Bear-King-Valemon involve white bears turning into men and sleeping with women.[188]

Polar bear drawings have historically been featured on maps of the northern regions. Possibly the earliest depictions of a polar bear on a map is the Carta marina of 1539, which has a white bear on Iceland or "Islandia". A 1544 map of North America includes two polar bears near Quebec. Notable paintings featuring polar bears include François-Auguste Biard's Fighting Polar Bears (1839) and Edwin Landseer's Man Proposes, God Disposes (1864). A real polar bear hunt was filmed for the 1932 documentary Igloo. In The Big Show (1961), two people are killed by a circus polar bear. The scenes were shot using animal trainers instead of the actors. The 1974 film The White Dawn features a polar bear being speared but it was simulated and the trained bear was unharmed. In the His Dark Materials fantasy novels, armour-clad polar bears perform ritualized combat bouts. In the The Jack Benny Program, Benny has a pet polar bear named Carmichael.[189] The polar bear is featured on the coat of arms of Greenland, and in many advertisements, notably for Coca-Cola.[190] The bear is considered to be a powerful symbol for the dangers of climate change and has been used to raise awareness.[191]

See also

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