Polar bear

• 1. Introduction

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  The polar bear is the largest living species of bear, and the largest land carnivore by body mass, with adult males weighing between 300 and 800 kg. In 1960, a male shot at Kotzebue Sound in northwestern Alaska tipped the scales at 1002 kg, the biggest one ever recorded. That size hides a stranger truth: this is not really a land animal. It is classed as a marine mammal, bound to the ocean more than to any forest or plain, and its Latin name, Ursus maritimus, means sea bear. Beneath fur that reads as pure white, the skin underneath is black. It shares a family tree with the brown bear, close enough that the two can still interbreed in the wild, yet different enough that naturalists spent centuries arguing over what to call it. Between 22,000 and 31,000 are thought to survive across the Arctic today, hunted by the people who share its ice for thousands of years, and now losing the ice itself to a warming climate. What turned a bear into an ocean predator, and what happens to it as the frozen ground beneath its paws keeps disappearing?

• 2. Naming And Origins

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  Thomas Pennant gave the animal its common name in 1771, in his book A Synopsis of Quadrupeds. Europeans had called it the white bear for roughly five centuries before that, alongside names like ice bear and Greenland bear, while the Norse used isbjørn and hvitebjørn and the Inuit call it nanook. The Netsilik go further still, with separate words for a bear depending on its sex, age and state, from anguraq for an adult male to apitiliit for one lying dormant.

  Carl Linnaeus first classified the animal in 1758, in his Systema Naturae, but treated it as a variety of brown bear rather than a species in its own right. It took until 1774 for Constantine John Phipps, fresh from a 1773 voyage toward the North Pole, to formally describe it as a distinct species, Ursus maritimus. Even then the debate continued: the naturalist Theodore Knottnerus-Meyer argued its marine adaptations warranted an entirely separate genus, Thalarctos, though the fossil record eventually kept it inside Ursus. Proposed subspecies never held up, and in 1964 the paleontologist Björn Kurtén named a possible extinct one, U. m. tyrannus, from a single ulna fragment roughly 20 percent larger than an ordinary polar bear's; twenty-first century re-examination suggests the bone more likely belonged to a giant brown bear.

  The oldest known polar bear fossil, a jaw bone found on Prince Charles Foreland in Norway in 2004, dates to between 130,000 and 110,000 years ago, evidence of how thin the species' fossil record really is. Genetic studies once suggested direct descent from brown bears in eastern Siberia or Alaska, based on how closely related polar bears were to the ABC Islands brown bears of Southeast Alaska. More extensive work later overturned that: the two are separate sister lineages that repeatedly interbred, with the split now estimated at over a million years ago. Genes flowed from polar bears into brown bears more than the reverse; the ABC Islands bears carry up to 9 percent polar bear ancestry, and now-extinct Irish brown bears carried as much as 21.5 percent. Large-scale hybridization stopped around 200,000 years ago, and wild hybrids remain rare today. The genome still carries the marks of Arctic life: fewer genes for smelling a wide range of odours, fewer copies of the starch-digesting amylase gene to match a diet built almost entirely on fat and meat, and extra copies of the genes that build keratin, the protein behind the bear's dense coat.

• 3. Made For The Arctic

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  Adult males typically measure 200-250 cm long, while females run smaller at 180-200 cm, a gap between the sexes that is unusually wide even by mammal standards, and males also carry proportionally larger heads. A bear's weight shifts through the year: it can pack on enough fat to raise its body mass by 50 percent, and a heavily pregnant female can weigh as much as 500 kg. At the shoulder an adult stands 130-160 cm tall, with a tail of only 76-126 mm, barely visible under the fur.

  Its snout curves into what is sometimes called a Roman nose, one sign that its skull has been reshaped from the brown bear's: narrower, flatter, with a longer neck and a lower shoulder hump. Its 34-42 teeth favour meat over the varied diet of a brown bear, with longer, sharper, more widely spaced canines, though because its prey is usually far smaller than the bear itself, the bite itself is not especially strong. The front paws are broad and hairier than in other bears, for grip on snow and ice, tipped with claws small enough to be sharp and hooked rather than blunt, useful for both snatching prey and hauling the bear's own bulk onto ice.

  Underfur about 5 cm deep sits beneath guard hairs roughly 15 cm long, hollow and scaly, which trap heat and help the bear float. Those hairs are also transparent, scattering ultraviolet light forward between the fur and the black skin beneath in a cycle that keeps the animal warm; the coat only looks white from how it scatters ordinary light back out, with no pigment involved. Sun exposure can turn it yellowish, a tint that fades after moulting, and after a swim the hairs resist tangling, letting the bear shake itself dry, while oil in the coat keeps it from freezing solid. Underneath, a fat layer 5-10 cm thick provides both insulation and stored energy, holding the bear's core temperature near 36.9 C.

  The eyes sit near the top of the skull, positioned to stay above the waterline while the bear swims at the surface, and are small enough to guard against snow blindness. Small ears resist frostbite, hearing peaks between 11.2-22.5 kHz, and an oversized nasal cavity and sense of smell are tuned to detect prey across vast distances of ice.

• 4. Life On The Sea Ice

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  Polar bears range across Greenland, Canada, Alaska, Russia and Norway's Svalbard Archipelago, with sightings recorded as close as 25 km from the North Pole. Their range still reaches south to James Bay and Newfoundland and Labrador in Canada and to St. Matthew Island and the Pribilof Islands off Alaska, though Iceland is not permanent territory, only somewhere bears occasionally drift ashore on sea ice. Because so little of this remote ground has been touched by people, the species still occupies more of its original range than any other large land carnivore.

  The bear depends on the annual sea ice covering continental shelves and threading between islands, a zone known as the Arctic Ring of Life for its unusual productivity, and it gravitates toward polynyas and leads, the places where ice meets open water, to find seals. As ice cover shifts through the year the bears travel with it and are pushed onto land each summer once it disappears, sheltering in forests, mountains, rocky ground and along lakeshores. In the Chukchi and Beaufort seas most bears still follow the retreating ice north each year, though since the 1980s a growing share, between 15-40 percent, stays on land instead.

  A bear's home range can span 3500-38000 km2 in a year, and drifting ice can carry it farther still without a deliberate step. On foot it covers an average of 12 km a day, walking or galloping rather than trotting; it can sprint at an estimated 40 km/h but usually cruises near 5.5 km/h. In the water it manages up to 6 km/h, and one study recorded bears swimming for an average of 3.4 days straight, covering 154.2 km and diving for as long as three minutes.

  Adult males, tolerant of each other on land outside the breeding season, have been recorded forming stable "alliances", travelling and resting together, while the rest of the species stays largely solitary apart from mothers with cubs and mating pairs. A dominance hierarchy runs through these gatherings, largest mature males on top, and communication stays mostly quiet: mother bears chuff, a soft pulsing sound, to keep track of their cubs, hostile encounters bring out jaw pops and growls, and every track left in the snow carries scent from glands in the bear's own foot pads, a signature other bears can read long after it has passed.

• 5. Hunting On The Ice

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  Ringed seals make up the bulk of a polar bear's diet, common and small enough that even a young bear can overpower one. Bearded seals and harp seals are taken too, though full-grown bearded seals are large enough to fight free, so adult males have the best odds against them, while hooded, spotted and ribbon seals appear far less often. Adult males occasionally take walruses, usually the young ones, since a full-grown walrus with its thick hide and long tusks is too dangerous to risk. Seals and walruses aside, bears prey on beluga whales, narwhals, reindeer, birds and their eggs, fish and marine invertebrates, and though their digestion is built almost entirely for meat, they have been recorded eating berries, moss, grass and seaweed. Around Hudson Bay and James Bay, where summers leave no sea ice to hunt from, bears lean harder on the land and draw down fat reserves that let them go for months without a real meal; cannibalism has also been documented in the species.

  A hunting bear lowers its head and neck to hide its dark nose and eyes, creeping toward a seal hauled out on the ice before charging at speed to beat it to the hole, sometimes stalking partly through the water with only its nose above the surface until it lunges. In spring, bears hunt seal pups hidden in birth lairs sometimes more than a metre beneath the snow, smashing through the roof with their front feet once they have pinpointed the den by scent, a task that favours the biggest bears. From winter into early spring the more common tactic is simply waiting, motionless, at a breathing hole for hours until a seal surfaces close enough to seize.

  Walruses are hunted differently: a bear provokes a herd into a stampede and picks off young animals crushed or separated in the chaos, with accounts of bears hurling rocks or ice at them. Belugas and narwhals become vulnerable when stranded in shallow water or trapped at an isolated breathing hole, and kills generally rely on raw strength, a bite or a paw swipe, strong enough to drag a beluga carcass a considerable distance or haul a mid-sized seal straight out of the water.

  Subadults, the least successful hunters, often survive on what others leave behind, and in northeastern Alaska polar bears have even been seen losing beached whale carcasses to more aggressive grizzly bears despite being the larger animal. Arctic foxes trail polar bears for the same reason, scavenging scraps from a kill until they wander too close and get charged off.

• 6. Mating, Motherhood And Mortality

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  Mating happens on the sea ice, mostly between March and May. Males track females in estrus along twisting paths that cut the odds of meeting rival males, while females move in straighter, wider-ranging lines. Once a male finds a female he isolates and guards her, and it can take days of pursuit before mating actually occurs, an act that induces ovulation and bonds the pair, who often stay together about two weeks if undisturbed. Competition for mates is fierce enough to have favoured larger males over time, and grown males frequently carry scars from fights; a female typically mates with more than one male each season, and a single litter can end up with more than one father.

  Once mating ends, a pregnant female builds fat reserves through the rest of the season, then digs a maternity den sometime between August and October, in coastal sea ice or further inland, carved from snow, earth or both, roughly 1.5 m wide with a 1.2 m ceiling. There she hibernates, fasting and recycling her own bodily waste, while a fertilized embryo that has waited since mating finally begins developing between mid-September and mid-October, stretching total gestation to seven to nine months even though real pregnancy lasts only about two.

  Litters usually number two cubs, born blind and nearly hairless at around 600 g, eyes staying shut for a month. Fed on fat-rich milk and warmed by the den and their mother's body, cubs are ready to walk by the time she emerges, sometime between late February and early April, weighing 10-15 kg. The family lingers near the den for about two weeks before heading onto the sea ice.

  For their first year, cubs freeze in place to watch whenever their mother hunts, learning entirely by imitation before she calls them back, and by around age two a cub can hunt alone. Weaning happens between two and two and a half years, after which the mother may leave her grown cub or a courting male may drive it off; females reach sexual maturity around age four, males not until six, fully grown only by roughly twice that age.

  A polar bear can live to 30, a lifespan long enough to absorb the loss of cubs along the way. Some die in the den or the womb if their mother is not in good condition, others starve if she cannot kill enough; adult male bears sometimes kill cubs to bring a mother back into estrus, and a mother who cannot outrun an approaching male may fight him at the risk of her own life. Subadults fare worst of all, independent but still poor hunters, often losing kills to larger bears and left to scavenge underweight, while the species as a whole is especially prone to the parasitic roundworm Trichinella, picked up through cannibalism.

• 7. A Warming World

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  In 2015 the International Union for Conservation of Nature listed the polar bear as vulnerable, citing a decline in area of occupancy, extent of occurrence and quality of habitat. The species is split into at least 18 recognized subpopulations, and in 2021 the IUCN's Polar Bear Specialist Group judged four of them, including the Barents Sea and Chukchi Sea populations, as likely stable, two more as likely increasing, and three, including the Southern Beaufort Sea and southern and western Hudson Bay populations, as likely in decline; the remaining ten lacked enough data to judge.

  A 2008 study, based on expected sea ice loss, predicted two-thirds of the world's polar bears could vanish by 2050, leaving only a single surviving population within 50 years. A 2020 study modeled a worst-case pathway in which most subpopulations disappear entirely by 2100. Not every projection agrees: a 2025 study warned the 2020 modeling leaned too heavily on Hudson Bay data, citing earlier research that found Chukchi Sea bears notably more resilient to shrinking ice than their Beaufort Sea neighbors, while a 2026 study of Svalbard's bears found some able to fatten up on less ice-dependent prey and survive extended ice-free stretches.

  A 2024 study found that leaning harder on terrestrial food during longer ice-free periods likely will not sustain Hudson Bay's bears, putting subadults at particular risk; the underlying problem is that rising temperatures push sea ice to melt earlier each year, forcing bears ashore before they can build fat reserves for the lean months of late summer and early fall. Thinner ice also breaks apart more easily, making seals harder to reach, and the resulting malnutrition lowers reproductive rates in females and survival odds for cubs. Longer swims drain energy and raise drowning risk, while less stable ice complicates safe denning and warmer, wetter conditions raise the risk of den collapse and of disease-causing parasites thriving.

  The Chukchi Sea Planning Area off northwestern Alaska, heavily leased for drilling, is important habitat for female bears that do not den there, and a 2018 study estimated a spill at full reach could touch nearly 40 percent of the entire polar bear population. Sitting atop the Arctic food chain, bears also accumulate high levels of persistent pollutants such as PCBs, chemicals banned internationally decades ago that have slowly declined in bear tissue overall but risen in some populations. Legal protection now covers polar bears in every country they inhabit, from the US, which listed the species as threatened in 2008, to the 1973 Agreement on the Conservation of Polar Bears, signed by Canada, Denmark, Norway, the then-Soviet Union and the US, which banned most commercial harvesting while still permitting indigenous hunting by traditional methods.

• 8. Bears And People

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  The 13th-century Norwegian text Konungs skuggsjá offers the earliest known written account of the animal in the wild, describing how 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 calling it as skillful a swimmer as any seal or whale. Centuries later, a young Horatio Nelson joined Constantine Phipps's Arctic voyage hoping to bring his father a polar bear coat, and came home empty-handed.

  Archaeological remains on Zhokhov Island in the East Siberian Sea show the species was hunted as early as 8,000 years ago, long before anyone wrote a word about it, and rock art at Pegtymel in Siberia, dating from the fifth to eighth centuries, depicts a hunter and three dogs bringing one down. In some cultures, killing a polar bear marked a boy's passage into manhood. Trade followed: Norsemen carried polar bear furs out of Greenland in the Middle Ages, and Russia was trading polar bear products by 1556. At Svalbard, Russian explorers killed no fewer than 150 bears a year from the 18th century onward, and roughly 22,000 more were taken there between the 1870s and the 1970s; across Russia and Svalbard combined, more than 150,000 bears were killed or captured between the 18th and 20th centuries. The Hudson's Bay Company alone is estimated to have sold 15,000 polar bear coats between the late 19th and early 20th centuries. The liver was long known to be too toxic to eat, poisoned by the vitamin A the bears accumulate from their prey, while the fat fueled lamps and the pelts covered the floors of Norwegian churches by the 13th and 14th centuries; Marilyn Monroe was among the Hollywood stars later photographed posing on a bearskin rug.

  Where sea ice now melts each summer, bears drift toward towns, and in Churchill, Manitoba, authorities keep a so-called polar bear jail to hold nuisance animals until the ice returns. In February 2019, more than 50 polar bears swarmed a town on Novaya Zemlya, prompting local authorities to declare a state of emergency. Between 1870 and 2014, an estimated 73 polar bear attacks on humans caused 20 deaths.

  Captive polar bears have a long royal history: the Tower of London kept one from 1252, under King Henry III, and in 1609 the sailor Jonas Poole gave two cubs, caught at Svalbard, to James VI and I. The zookeeper Carl Hagenbeck later reinvented how bears were displayed, opening a panoramic exhibit of artificial snow and ice at his Hamburg Tierpark in 1907, and circuses embraced the animal too: Wilhelm Hagenbeck trained as many as 75 polar bears to slide down a chute into a tank, starting in 1908, in a show that drew crowds at London's Hippodrome. Individual bears have become celebrities in their own right, among them Knut of the Berlin Zoological Garden, hand-reared by keepers after his mother rejected him, and Gus of the Central Park Zoo, prescribed the antidepressant Prozac for compulsively swimming laps in his pool.

  In Inuit belief, the deity Torngarsuk is sometimes imagined as a giant polar bear living beneath the sea floor, ruling over sea creatures, while the Pleiades star cluster is pictured as a polar bear cornered by dogs. Modern culture has turned the same animal into a warning: the 2006 documentary An Inconvenient Truth included an animated bear swimming through open water, and in 2009 an ice sculpture of a polar bear with a bronze skeleton was deliberately left in Copenhagen to melt in the sun, a monument built to disappear.