Polar bear

This article is about the animal. For other uses, see Polar bear (disambiguation). "Ice bear" and "Northern bears" also lead here, and you can find those other uses at Ice Bears (disambiguation) and Northern bears (disambiguation).

The polar bear (Ursus maritimus) is a large bear that lives in the Arctic and nearby areas. It is closely related to the brown bear, and the two kinds can interbreed. The polar bear is the largest living kind of bear and the largest land carnivore by body weight. Adult males can weigh 300 to 800 kilograms (660 to 1,760 pounds). Females are much smaller than males. Scientists call this difference sexually dimorphic.

The polar bear has white or yellowish fur, black skin, and a thick layer of fat that keeps it warm. It is more slender than the brown bear. It has a narrower skull, a longer neck, and a lower shoulder hump. Its sharp teeth are good for cutting meat. Its large paws help it walk on ice and swim through water.

Polar bears can live on both land and ice. This is why they are called pagophilic (ice-living). They are considered marine mammals because they depend on marine ecosystems. They prefer the sea ice that forms each year. In summer, when the ice melts, they live on land. They eat mostly meat and are especially good at hunting ringed seals. They often wait quietly at a breathing hole or at the edge of the ice for prey to swim by. They mainly eat the seal's energy-rich blubber. Other prey includes walruses, beluga whales, and some land animals. Polar bears are usually alone, but they can gather in groups on land. Mothers give birth to cubs in maternity dens during winter. The young stay with their mother for up to two and a half years.

The International Union for Conservation of Nature (IUCN) considers the polar bear a vulnerable species. This means it is at risk of disappearing in the future. The estimated total population is 22,000 to 31,000 animals. Its biggest threats are climate change, pollution, and energy development. Climate change has caused the sea ice to shrink, so polar bears have less access to their favourite prey. This can lead to malnutrition, starvation, and eventually death. With less sea ice, bears must spend more time on land, which increases conflicts with humans.

People have long hunted polar bears, both native and non-native peoples, for their coats, meat, and other items. Polar bears have also been kept in captivity in zoos and circuses. They appear often in art, folklore, religion, and modern culture.

Naming

The polar bear got its common name from Thomas Pennant in A Synopsis of Quadrupeds (1771). In Europe, between the 13th and 18th centuries, people called it the "white bear." It also had other names, such as "ice bear," "sea bear," and "Greenland bear." The Norse called it isbjørn, meaning 'ice bear', and hvitebjørn, meaning 'white bear'.

The Inuit call the bear nanook. The Netsilik people have different names for bears based on their sex and age. For example, adult males are called anguraq, and single adult females are called tattaq. Pregnant females are called arnaluk, and newborns are called hagliaqtug. Large young bears are called namiaq, and bears that are resting through winter are called apitiliit. The scientific name Ursus maritimus is Latin for 'sea bear'.

Taxonomy

Carl Linnaeus first grouped the polar bear as a type of brown bear (Ursus arctos). In the 1758 edition of his book Systema Naturae, he gave it the name Ursus maritimus albus-major, arcticus. Later, Constantine John Phipps described it as its own species, Ursus maritimus, in 1774. He did this after his 1773 voyage towards the North Pole. Some scientists, such as Theodore Knottnerus-Meyer, have put the polar bear in its own genus, Thalarctos, because it is so well suited to life at sea. However, most scientists use the genus Ursus. One reason is the fossil record. Another is that polar bears can breed with brown bears. Other subspecies have been suggested, but these ideas are not supported. So the polar bear is considered monotypic, which means it has no subspecies. In 1964, Björn Kurtén proposed a possible fossil subspecies, U. m. tyrannus, based on a single bone fragment. A later review suggested that this fragment probably came from a giant brown bear.

The polar bear is one of eight living species in the bear family, Ursidae. It is also one of six living species in the subfamily Ursinae. Earlier studies suggested that polar bears came directly from brown bears. Later, more detailed genetic studies showed that the two are separate sister lineages. Their genetic similarities came from interbreeding. Studies estimate that the two species split around 600,000 years ago, or possibly more than one million years ago. Glaciation events, which were periods of ice spreading over the land, lasted hundreds of thousands of years. They helped shape where polar bears came from and how they mixed with brown bears. Studies in 2011 and 2012 found that gene flow went from brown bears to polar bears, but later studies showed it went the other way. Polar bear fossils are uncommon. The oldest known one is a jaw bone, about 110,000 to 130,000 years old. It was found in 2004 on Prince Charles Foreland in Norway.

Description

The polar bear is the largest living bear and a land carnivore, though some Kodiak bears can be just as big. Males are usually 200 to 250 cm (6.6 to 8.2 ft) long and weigh 300 to 800 kg (660 to 1,760 lb). Females are smaller, at 180 to 200 cm (5.9 to 6.6 ft) and 150 to 300 kg (330 to 660 lb). Males also have bigger heads. Polar bears can add so much fat that their weight rises by 50 percent. The largest polar bear on record, reportedly 1,002 kg (2,209 lb), was a male shot at Kotzebue Sound in northwestern Alaska in 1960.

Compared with the brown bear, the polar bear has a more slender body, a narrower and smaller skull, and a longer neck. Its face has a curved profile, like a "Roman nose". It has 34 to 42 teeth, including 12 incisors, 4 canines, 8 to 16 premolars, and 10 molars. Its long, sharp canines are separated from its cheek teeth by a gap called a diastema, which may help it bite into prey. Its bite is not especially strong, because it usually hunts much smaller animals. Its large paws have hairy soles that keep it warm and help it grip snow and ice. Its small, sharp, hooked claws help it catch prey and climb onto ice.

Its thick coat has dense underfur about 5 cm (2.0 in) long and guard hairs about 15 cm (5.9 in) long. Males have long hairs on their front legs, which may show their fitness to females. The guard hairs are hollow, which helps the bear keep heat in and float. They also forward scatter ultraviolet light to keep it warm. The fur looks white because of the backscatter of incident light, and because it has no pigment. This helps it camouflage itself in snowy places. The fur can look yellowish from sun exposure, but this goes away after the bear moults. It can also look grayish or brownish. Under the skin is a thick layer of fat that provides warmth and energy. The bear keeps its core body temperature at about 36.9 °C (98.4 °F). It can cool off by entering the water and through striated muscle tissue and blood vessels. Its eyes sit near the top of its head and are fairly small, which may help protect them from blowing snow and snow blindness. Polar bears are dichromats, meaning they lack cone cells for seeing mainly green light. However, they have many rod cells to help them see at night. Their small ears help them keep heat in and avoid getting frostbitten. The nasal concha creates a large surface area for warming air. Their large olfactory system helps them smell prey over vast distances. Their reniculate kidneys filter out the salt in their food.

Distribution and habitat

Polar bears live in the Arctic and nearby areas. They are found in Greenland, Canada, Alaska, Russia, and the Svalbard Archipelago of Norway. Some have been seen as close as 25 km (16 mi) from the North Pole. In the south, their range reaches James Bay and Newfoundland and Labrador in Canada, and St. Matthew Island and the Pribilof Islands in Alaska. Polar bears do not live in Iceland all the time, but some have visited when they could reach it over sea ice. Few people live in their remote home, so polar bears can still be found across much of their old range. Scientists have sorted polar bears into at least 18 groups. These include groups in the Barents Sea, Kara Sea, Laptev Sea, Chukchi Sea, the northern and southern Beaufort Sea, Viscount Melville, M'Clintock Channel, Gulf of Boothia, Lancaster Sound, Norwegian Bay, Kane Basin, Baffin Bay, Davis Strait, Foxe Basin, and the western and southern Hudson Bay areas. Some scientists think bears around the Queen Elizabeth Islands form another group, but not everyone agrees. A study from 2022 suggested that bears in southeast Greenland should be seen as a separate group. Polar bears can also be sorted into four gene clusters: Southern Canadian, Canadian Archipelago, Western Basin (from northwestern Canada west to the Russian Far East), and Eastern Basin (from Greenland east to Siberia).

Polar bears depend so much on the ocean that they are considered a marine mammal. They are pagophilic, which means they like ice. They mostly live on yearly sea ice that covers continental shelves and the waters between islands of archipelagos. These areas, called the "Arctic Ring of Life," are very rich in living things. Polar bears often go to places where sea ice meets open water, such as polynyas and leads, to hunt seals. Seals are most of their food. Polar bears move as the ice changes during the year. In summer, when the sea ice melts away, they are forced onto land. On land, they use forests, mountains, rocky areas, lakeshores, and creeks. In the Chukchi and Beaufort seas, most bears follow the summer ice north as it pulls back. However, some bears now stay on land in summer. This has been happening since the 1980s. Some areas have thick multiyear ice that does not fully melt. Bears can stay there all year. But this ice has fewer seals, and the water there has less life in it.

Behaviour and ecology

Polar bears may travel across areas from 3,500 km² (1,400 sq mi) to 38,000 km² (15,000 sq mi) in a year. Drifting ice can carry them even further. A bear may travel an average of 12 km (7.5 mi) a day, depending on the ice. They move by walking and galloping, but they do not trot. When they walk, they tilt their front paws towards each other. They can run at speeds of up to 40 km/h (25 mph), but they usually move at about 5.5 km/h (3.4 mph). They are also strong swimmers, reaching 6 km/h (3.7 mph). One study found they can swim for an average of 3.4 days at a time and travel an average of 154.2 km (95.8 mi). They can dive for up to three minutes. They use their broad front paws to paddle and their back legs to steer and dive. Most polar bears are active all year. Only pregnant females go into hibernation. Bears that do not hibernate usually keep a normal 24-hour cycle, even during days of all darkness or all sunlight. The species is generally diurnal, which means it is most active early in the day. Polar bears sleep about eight hours a day on average. They may curl up, sit up, or lie on their backs with their legs spread. On sea ice, they rest at pressure ridges. After a snowstorm, they may rest under the snow for hours or days. Mothers and young bears may sleep on slopes, where they can see another bear coming. Adult males can sleep almost anywhere. Polar bears usually live alone, except for mothers with cubs and mating pairs. However, they gather around food on land. Adult males are more tolerant of each other and have been seen forming stable "alliances". A dominance hierarchy exists, with the largest mature males at the top. Females with young tend to stay away from males. Sometimes they join other groups of females and their young, creating "composite families". Polar bears are generally quiet. Mothers make a soft pulsing call called chuffing to stay in contact with their young. Cubs cry for attention. In more tense encounters, growls and roars can be heard.

The polar bear is a hypercarnivore, which means it eats mostly meat. It is the most carnivorous bear species. It is an apex predator of the Arctic, meaning it sits at the top of the food chain. It hunts ice-living seals and eats their energy-rich blubber. The most commonly taken species is the ringed seal. They also hunt bearded seals and harp seals, and less often hooded seals, spotted seals, ribbon seals and harbour seals. Mostly adult males hunt walruses, usually young ones. Bears also eat cetacean species such as beluga whales and narwhals. They eat reindeer, birds and their eggs, fish and marine invertebrates too. They rarely eat plants, though they have been seen eating berries, moss, grass and seaweed. Their fat reserves let them survive for months without eating. Cannibalism is known to happen. A bear may stalk a seal hauling out on the sea ice, or wait near a breathing hole for prey to come up. In spring, bears search for ringed seal pups in their birth lairs under the ice. They break through the ice with their front feet. Bears may also catch prey in open water, including an aquatic bird. Sometimes they store food for a short time by burying it under snow. Polar bears will scavenge as necrophages when they find food, and young bears often eat what others leave behind. Whale carcasses are a valuable food source. Several bears may feed together on a large beached carrion. In one area of northeastern Alaska, polar bears have competed with grizzly bears for whale carcasses. However, they usually give way to the more aggressive grizzlies. Arctic foxes often follow polar bears to eat scraps. Polar bears will also scavenge at garbage dumps during ice-free periods. Polar bears mate on the sea ice, mostly between March and May. Males look for females in estrus. The mating system can be called polygyny, serial monogamy, or mating with several partners. Competition for mates can be strong, which has led to bigger males being chosen. Between August and October, the female builds and enters a maternity den for winter. She hibernates there and gives birth. Hibernating bears fast and recycle their bodily waste inside their bodies. Polar bears experience delayed implantation, so gestation lasts seven to nine months. The actual pregnancy is only about two months. Newborn cubs are tiny and altricial, which means they depend on their mothers. They have woolly hair and pink skin. Mothers leave the den between late February and early April, and their cubs can walk with them. Cubs stay close to their mothers and learn to hunt by watching and copying. Cubs are weaned between two and two-and-a-half years old. Polar bears can live up to 30 years. Cubs face threats from wolves and adult male bears, which may harm or kill cubs for food. Young bears often struggle to hunt successfully and can become very thin. Polar bears are especially at risk from Trichinella, a parasitic roundworm they can catch by eating other bears.

In 2015, the IUCN Red List labelled the polar bear as vulnerable, because its habitat and population were getting smaller. It estimated the total population at 22,000 to 31,000 bears. The main threats include climate change, pollution and energy development. A 2008 study predicted that two-thirds of the world's polar bears may disappear by 2050, because of the reduction of sea ice. A 2020 study found that a worst-case scenario pathway would lead to most groups disappearing by 2100. An intermediate pathway would still cause some groups to disappear.

The biggest danger from climate change is habitat loss. Polar bears hunt seals on sea ice. However, warmer weather melts the ice earlier, pushing bears to shore before they have stored enough fat. Melting permafrost, bacteria and parasites add to the problems, and so do oil spills. Polar bears also accumulate harmful chemicals such as persistent organic pollutants, polychlorinated biphenyl (PCBs) and pesticides. This happens because they sit at the top of the ecological pyramid.

Polar bears are protected by law in all the countries where they live. The US Endangered Species Act has listed the species as threatened since 2008. The Committee on the Status of Endangered Wildlife in Canada has listed it as 'Special concern' since 1991. In 1973, five nations signed the Agreement on the Conservation of Polar Bears. This agreement banned most hunting and protected bear habitat. The Convention on International Trade in Endangered Species of Wild Fauna lists the species under Appendix II, which allows regulated trade.

Relationship with humans

Polar bears have lived alongside circumpolar peoples for thousands of years. A seventh-century Japanese book, Nihon Shoki, mentions "white bears," but it is not clear whether these were polar bears. In the Middle Ages, Europeans knew brown and black bears better. The first known written account of polar bears in nature is in the 13th-century Norwegian text Konungs skuggsjá. Later descriptions became more accurate after the Enlightenment, though some made-up ideas continued. Henry Ellis's 1748 work included a fairly accurate drawing. Horatio Nelson was a young sailor on an 1773 Arctic voyage. He tried to catch a polar bear for his father's coat, but he failed. In 1785, Comte de Buffon described a "sea bear" in his Histoire Naturelle. This helped spread ideas about speciation.

Further information: Bear hunting

Polar bears were hunted at least 8,000 years ago. Remains found at Zhokhov Island in the East Siberian Sea show this. Native peoples hunted them with spears, bows and arrows, and dogs. In some cultures, killing a polar bear was a rite of passage for boys. People used the bears for their fur, meat, and bones. Later, traders sold polar bear products, and large numbers of bears were hunted at Novaya Zemlya, Franz Josef Land, and Svalbard. The Hudson's Bay Company sold thousands of polar bear coats between the late 1800s and early 1900s. In the mid-20th century, countries began to set rules for hunting.

Explorers and sailors sometimes ate polar bear meat, though people did not all agree on how it tasted. The liver was considered too toxic to eat because it has a lot of vitamin A. By the 13th and 14th centuries, polar bear rugs were common in Norwegian churches. Later, Hollywood actors such as Marilyn Monroe posed on bearskin rugs.

Further information: Bear danger and Bear attack

When sea ice melts, polar bears can come into contact with people, especially near garbage dumps. In Churchill, Manitoba, local workers keep a "polar bear jail." Nuisance bears are held there until the sea ice freezes again. Climate change has made these meetings more common. In February 2019, many polar bears swarmed a town in Novaya Zemlya. Some people have been hurt by polar bears, and some have died. Even so, polar bears are no more aggressive toward people than other bear species, even though they are often thought of as the most dangerous.

Animal collectors wanted polar bears for a long time, and royalty were among the first to keep them. The Tower of London received a polar bear under King Henry III in 1252. Polar bears were later shown in zoos and circuses. Carl Hagenbeck changed zoo design by replacing cages with settings that looked more like the bears' natural home. Many zoos have since stopped keeping polar bears because their exhibits are expensive. Circuses helped change the polar bear's image from a fearsome monster to something more funny. Performing bears included those trained by Wilhelm Hagenbeck's circus and by East German trainer Ursula Böttcher. Starting in the late 20th century, most polar bear acts were stopped, and the US does not allow their use in circuses. Some captive bears became famous. One was Knut of the Berlin Zoological Garden, who was hand-raised by zookeepers after his mother rejected him. Captive bears may also pace back and forth, a stereotypical behaviour. To help them, zookeepers give them toys and objects to play with.

Further information: Cultural depictions of bears

Polar bears have important roles in Inuit culture and religion. The deity Torngarsuk is sometimes imagined as a giant polar bear. The goddess Nuliajuk was linked to the creation of polar bears. Polar bears appear in Nordic folklore and literature, and they have been drawn on maps and paintings. Today, polar bears are often used to raise awareness of the dangers of climate change. Groups such as Greenpeace and the World Wide Fund for Nature use them this way. Photographs of polar bears have appeared in National Geographic and Time. The bear is also a popular symbol in advertising, including for Coca-Cola since 1922.