Polar bear

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 cladogram below is based on a 2017 genetic study:[17]

Fossils of polar bears are uncommon.[12][15] 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.[12][15] Mitochondrial DNA studies in the 1990s and 2000s 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 to other brown bears, particularly the ABC Islands bears of Southeast Alaska.[18][19][20] A 2010 study estimated that the polar bear lineage 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 refuted the idea that polar bears are directly descended from brown bears and found that the two species are separate sister lineages. The genetic similarities between polar bears and some brown bears were found to be the result of interbreeding.[21][22] A 2012 study estimated the split between polar and brown bears as occurring around 600,000 years ago.[21] A 2022 study estimated the divergence as 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 gene flow went from brown bears to polar bears during hybridization.[21][24] In particular, a 2011 study concluded that living polar bear populations derived their maternal lines 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] Up to 9 percent of the genome of ABC bears was transferred from polar bears,[27] while Irish bears had up to 21.5 percent polar bear origin.[25] Mass hybridization between the two species appears to have stopped around 200,000 years ago. Modern hybrids are relatively rare in the wild.[22]

Analysis of the number of variations of gene copies in polar bears compared with 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 fewer odours in their Arctic habitat. With its carnivorous, high-fat diet the species has fewer 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 polar bear's thicker coat is the result of more copies of genes involved in keratin-creating proteins.[28]

Polar bears are typically solitary, aside from mothers with cubs and mating pairs.[84] 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.[85][86] They have been recorded forming stable "alliances", travelling, resting and playing together. A dominant 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.[87] Females with dependent offspring tend to stay away from males,[86] but are sometimes associated with other female–offspring units, creating "composite families".[87]

Polar bears are generally quiet but can produce various sounds.[88] Chuffing, a soft pulsing call, is made by mother bears presumably to keep in contact with their young.[89] During the breeding season, adult males will chuff at potential mates.[90] Unlike other animals where chuffing is passed through the nostrils, in polar bears it is emitted through a partially open mouth.[89] Cubs will cry for attention and produce humming noises while nursing.[91] Teeth chops, jaw pops, blows, huffs, moans, growls and roars are heard in more hostile encounters.[90] A polar bear visually communicates with its eyes, ears, nose and lips.[87] Chemical communication can also be important: bears secrete their scent from their foot pads into their tracks, allowing individuals to keep track of one another.[92]

The polar bear is a hypercarnivore,[93] and the most carnivorous species of bear.[35] It is an apex predator of the Arctic,[94] preying on ice-living seals and consuming their energy-rich blubber.[95] The most commonly taken species is the ringed seal, but they also prey on bearded seals and harp seals.[10] Ringed seals are ideal prey as they are abundant and small enough to be overpowered by even small bears.[96] 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 harbour seals.[97] Polar bears, mostly adult males, will occasionally hunt walruses, both on land and ice, though they mainly target the young, as adults are too large and formidable, with their thick skin and long tusks.[98]

Bear feeding on a bearded seal

Besides seals, bears will prey on cetacean species such as beluga whales and narwhals, as well as reindeer, birds and their eggs, fish and marine invertebrates.[99] They rarely eat plant material as their digestive system is too specialized for animal matter,[100] though they have been recorded eating berries, moss, grass and seaweed.[101] In their southern range, especially near Hudson Bay and James Bay, polar bears endure all summer without sea ice to hunt from and must subsist more on terrestrial foods.[102] Fat reserves allow polar bears to survive for months without eating.[103] Cannibalism is known to occur in the species.[104]

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 through 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.[105]

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 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 than 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 the water and wait for prey to come by.[106] This can last hours and when a seal surfaces the bear will try to pull it out with its paws and claws.[107] This tactic is the primary hunting method from winter to early spring.[10]

Bear with whale carcass

Bears hunt walrus groups by provoking them into stampeding and then look for young that have been crushed or separated from their mothers during the turmoil.[98] There are reports of bears trying to kill or injure walruses by throwing rocks and pieces of ice on them.[108] Belugas and narwhals are vulnerable to bear attacks when they are stranded in shallow water or stuck in isolated breathing holes in the ice.[109] When stalking reindeer, polar bears will hide in vegetation before an ambush.[73] 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.[110] Polar bears rely on raw power when trying to kill their prey, and will employ bites or paw swipes.[93] They have the strength to pull a mid-sized seal out of the water or haul a beluga carcass for quite some distance.[111] Polar bears only occasionally store food for later—burying it under snow—and only in the short term.[112]

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 they are feeding. Polar bears themselves will scavenge. Subadult bears will eat remains left behind by others. Females with cubs often abandon a carcass when they see an adult male approaching, though are less likely to if they have not eaten in a long time.[113] Whale carcasses are a valuable food source, particularly on land and after the sea ice melts, and attract several bears.[85] 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 likely to yield to them in confrontations.[114] Polar bears will also scavenge at garbage dumps during ice-free periods.[115]

Courting male approaching female

Polar bear mating takes place on the sea ice and during spring, mostly between March and May.[10][116][117][84] Males search for females in estrus and often travel in twisting paths 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.[118] The mating system can be labelled as female-defence polygyny, serial monogamy or promiscuity.[117][119]

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.[120] Competition for mates can be intense and this has led to sexual selection for bigger males. Polar bear males often have scars from fighting.[116][117] A male and female that have already bonded will flee together when another male arrives.[121] A female mates with multiple males in a season and a single litter can have more than one father.[119]

Polar bear cubs

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.[122] The inside of these shelters can be around 1.5 m (4.9 ft) wide with a ceiling height of 1.2 m (3.9 ft) while the entrance may be 2.1 m (6.9 ft) long and 1.2 m (3.9 ft) wide. The temperature of a den can be much higher than the outside.[123] Females hibernate and give birth to their cubs in the dens.[124] Hibernating bears fast and internally 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.[125] With delayed implantation, gestation in the species lasts seven to nine months but actual pregnancy is only two months.[126]

Mother polar bears typically give birth to two cubs per litter. As with other bear species, newborn polar bears are tiny and altricial.[127] The newborns have woolly hair and pink skin, with a weight of around 600 g (21 oz).[10][29] Their eyes remain closed for a month.[128] The mother's fatty milk fuels their growth, and the cubs are kept 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.[129] At this time they weigh 10–15 kilograms (22–33 lb).[10] 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.[130]

Cubs under a year old stay close to their mother. When she hunts, they stay still and watch until she calls them back.[131] Observing and imitating the mother helps the cubs hone their hunting skills.[132] After their first year they become more independent and explore. At around two years old, they are capable of hunting on their own.[133] The young suckle their mother as she is lying on her side or sitting on her rump.[130] A lactating female cannot conceive and give birth,[134] and cubs are weaned between two and two-and-a-half years.[10] She may simply leave her weaned young or they may be chased away by a courting male.[133] Polar bears reach sexual maturity at around four years for females and six years for males.[135] Females reach their adult size at 4 or 5 years of age while males are fully grown at twice that age.[136]

Polar bears can live up to 30 years.[10] The bear's long lifespan and ability to consistently produce young offsets cub deaths in a population. Some cubs die in the dens or 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 can eat better in the coming year. Cubs will eventually starve if their mothers cannot kill enough prey.[137] Cubs also face threats from wolves[138] and adult male bears. Males kill cubs to bring their mother back into estrus but also kill young outside the breeding season for food.[104] A female and her cubs can flee from the slower male. If the male can get close to a cub, the mother may try to fight him off, sometimes at the cost of her life.[139]

Subadult bears, who 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, their kill will likely 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.[140] Polar bears are especially susceptible to Trichinella, a parasitic roundworm they contract through cannibalism.[141]

Hunter with polar bear slain with bow and arrow in Alaska (1924)

Polar bears were hunted as early as 8,000 years ago, as indicated by archaeological remains at Zhokhov Island in the East Siberian Sea. The oldest graphic depiction of a polar bear shows it being hunted by a man with three dogs. This rock art was among several petroglyphs found at Pegtymel in Siberia and dates from the fifth to eighth centuries. Before access to firearms, native people used lances, 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.[162] Bears were harvested for the fur, meat, fat, tendons, bones and teeth.[163][164] The fur was worn and slept on, while the bones and teeth were made into tools. For the Netsilik, 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.[165]

Skins of hunted bears in Greenland

Norsemen in Greenland traded polar bear furs in the Middle Ages.[166] Russia traded polar bear products as early as 1556, with Novaya Zemlya and Franz Josef Land being important commercial centres. Large-scale hunting of bears at Svalbard 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 on the island. From the 1870s to the 1970s, around 22,000 of the animals were hunted in total. Over 150,000 polar bears in total were either killed or captured in Russia and Svalbard, 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 19th century and early 20th century.[167] In the mid-20th century, countries began to regulate polar bear harvesting, culminating in the 1973 agreement.[152]

Polar bear meat was commonly eaten as rations by explorers and sailors in the Arctic. Its taste and texture have been described both positively and negatively. Some have called it too coarse with a powerful smell, while others praised it as a "royal dish".[168] The liver was known for being too toxic to eat. This is due to the accumulation of vitamin A from their prey.[169] Polar bear fat was also used in lamps when other fuel was unavailable.[168] Polar bear rugs were almost ubiquitous on the floors of Norwegian churches by the 13th and 14th centuries. In more modern times, classical Hollywood actors would pose on bearskin rugs, notably Marilyn Monroe. Such images often had sexual connotations.[170]

Road sign warning about the presence of polar 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.[171] They are attracted to the smell of human-made foods, particularly at garbage dumps and may be shot when they encroach on private property.[172] In Churchill, Manitoba, local authorities maintain a "polar bear jail" where nuisance bears are held until the sea ice freezes again.[173] Climate change has increased conflicts between the two species.[171] Over 50 polar bears swarmed a town in Novaya Zemlya in February 2019, leading local authorities to declare a state of emergency.[174]

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 defence of the young. In comparison to brown and American black bears, attacks by polar bears were more often near and around where humans lived. This may be due to the bears getting desperate for food and thus more likely to seek out human settlements. As with the other two bear species, polar bears are unlikely to target more than two people at once. Though popularly thought of as the most dangerous bear, the polar bear is no more aggressive to humans than other species.[175]

Visitors observing polar bears underneath a plexiglass 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.[176] It is one of the few marine mammals that can reproduce well in captivity.[177] They were originally kept only by royals and elites. The Tower of London got a polar bear as early as 1252 under King Henry III. In 1609, James VI and I of Scotland, England and Ireland were given two polar bear cubs by the sailor Jonas Poole, who got them during a trip to Svalbard.[178] At the end of the 17th century, Frederick I of Prussia housed polar bears in menageries with other wild animals. He had their claws and canines removed to perform mock fights. Around 1726, Catherine I of Russia gifted two polar bears to Augustus II the Strong of Poland, who desired them for his animal collection.[179] Later, polar bears were displayed to the public in zoos and circuses.[180] In early 19th century, the species was exhibited at the Exeter Exchange in London, as well as menageries in Vienna and Paris. The first zoo in North America to exhibit a polar bear was the Philadelphia Zoo in 1859.[181]

Polar bear exhibits were innovated by Carl Hagenbeck, who replaced cages and pits with settings that mimicked the animal's natural environment. In 1907, he revealed a complex panoramic structure at the Tierpark Hagenbeck Zoo in Hamburg consisting 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 in Munich 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. Similar naturalistic and "immersive" exhibits were opened in the early 21st century, such as the "Arctic Ring of Life" at the Detroit Zoo and Ontario's Cochrane Polar Bear Habitat.[182][183] Many zoos in Europe and North America have stopped keeping polar bears due to the size and costs of their complex exhibits.[184] In North America, the population of polar bears in zoos reached its zenith in 1975 with 229 animals and declined in the 21st century.[185]

Performing polar bear at the 1973 Nationaal Songfestival in the Netherlands

Polar bears have been trained to perform in circuses. Bears in general, being large, powerful, easy to train and human-like in form, were widespread in circuses, 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 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 involved tightropes, balls, roller skates and motorcycles. One of the most famous polar bear trainers in the second half of the twentieth century was the East German Ursula Böttcher, whose small stature contrasted with that of the large bears. Starting in the late 20th century, most polar bear acts were retired and the use of these bears for the circus is now prohibited in the US.[186]

Several captive polar bears gained celebrity status in the late 20th and early 21st century, notably Knut of the Berlin Zoological Garden, who was rejected by his mother and had to be hand-reared by zookeepers. Another bear, Binky of the Alaska Zoo in Anchorage, became famous for attacking two visitors who got too close.[187][188] Captive polar bears may pace back and forth, a stereotypical behaviour. In one study, they were recorded to have spent 14 percent of their days pacing.[189] Gus of the Central Park Zoo was prescribed Prozac by a therapist for constantly swimming in his pool.[190] To reduce stereotypical behaviours, zookeepers provide the bears with enrichment items to trigger their play behaviour.[191] Zoo polar bears may appear green due to algae concentrations.[192]

Ivory carving of a swimming polar bear from the Dorset culture, northern Canada

The coat of arms of Greenland

Polar bears have prominent roles in Inuit culture and religion. The deity Torngarsuk is sometimes imagined as a giant polar bear. He resides underneath the sea floor in an underworld of the dead and has 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 goddess Nuliajuk who was responsible for their creation, along with other sea creatures. It is believed that shamans 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 skins. In Inuit astronomy, the Pleiades star cluster 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.[193]

Nordic folklore and literature have also featured polar bears. In The Tale of Auðun of the West Fjords, written around 1275, a poor man named Auðun spends all his money on a polar bear in Greenland, but ends up wealthy after giving the bear to the king of Denmark.[194] 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 Icelandic 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.[195] 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 seducing women.[196]

Drawings of polar bears have been featured on maps of the northern regions. Possibly the earliest depictions of a polar bear on a map is the Swedish 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). Polar bears have also been filmed for cinema. An Inuit polar bear hunt was shot for the 1932 documentary Igloo, while the 1974 film The White Dawn filmed a simulated stabbing of a trained bear for a scene. In the film The Big Show (1961), two characters are killed by a circus polar bear. The scenes were shot using animal trainers instead of the actors. In modern literature, polar bears have been characters in both children's fiction, like Hans Beer's Little Polar Bear and the Whales and Sakiasi Qaunaq's The Orphan and the Polar Bear, and fantasy novels, like Philip Pullman's His Dark Materials series. In radio, Mel Blanc provided the vocals for Jack Benny's pet polar bear Carmichael on The Jack Benny Program.[197] The polar bear is featured on flags and coats of arms, like the coat of arms of Greenland, and in many advertisements, notably for Coca-Cola since 1922.[198]

As charismatic megafauna, polar bears have been used to raise awareness of the dangers of climate change. Aurora the polar bear is a giant marionette created by Greenpeace for climate protests.[199] The World Wide Fund for Nature has sold plush polar bears as part of its "Arctic Home" campaign.[200] Photographs of polar bears have been featured in National Geographic and Time magazines, including ones of them standing on ice floes, while the climate change documentary and advocacy film An Inconvenient Truth (2006) includes an animated bear swimming.[199] Automobile manufacturer Nissan used a polar bear in one of its commercials, hugging a man for using an electric car.[201] To make a statement about global warming, in 2009 a Copenhagen ice statue of a polar bear with a bronze skeleton was purposely left to melt in the sun.[202]