Polar Bear
Ursus maritimus
Polar Bear (Ursus maritimus): The Sea-Ice Bear
The polar bear (Ursus maritimus) is the largest of the eight bear species and lives on Arctic sea ice, where it hunts seals. Its fur looks white, but the hairs are pigment-free and its skin is black.
- Habitat
- Arctic sea ice, especially ice edges and leads; coasts in summer
- Size
- Males 350 to 600+ kg; females 150 to 290 kg
- Diet
- Mainly ringed and bearded seals; also walrus, birds, carrion
- Range
- Circumpolar Arctic: Canada, USA, Russia, Norway, Greenland
- Conservation
- Vulnerable (IUCN 2015); about 26,000 bears
- Lifespan
- About 25 to 30 years in the wild
Habitat & range
Polar bears live around the North Pole, on the pack ice of the Arctic Ocean and the landfast ice along its coasts. The edge of the ice limits their range, and they move hundreds of kilometres north and south as the ice melts and refreezes. They are found in five countries: Canada, the United States (Alaska), Russia, Norway and Greenland. Canada has about two-thirds of the world's polar bears. The IUCN Polar Bear Specialist Group recognises 20 subpopulations. The newest, in Southeast Greenland, was described in 2022: these bears are genetically distinct and hunt from freshwater glacier ice when there is little sea ice. Greenland recognised the subpopulation in 2023 and the specialist group in 2024. The scientific name Ursus maritimus, given in 1774, means 'maritime bear'.
Diet & hunting
Polar bears are the most carnivorous of all bears. Their main prey are ringed seals, and they also take bearded, harp and hooded seals, walruses, seabirds and their eggs, and scavenge whale and seal carcasses. Their usual method is still-hunting: the bear waits beside a seal's breathing hole in the ice until the seal comes up to breathe. They also stalk seals resting on the ice, creeping up low or approaching through channels of open water. When hunting is good, a bear may eat only a seal's skin and blubber and leave the rest for other bears and Arctic foxes. Polar Bears International reports that a polar bear can eat more than 45 kg of blubber in one sitting. Where the sea ice melts completely in summer, bears have to come ashore and live mostly off their fat reserves until the ice returns.
Body & adaptations
Adult males normally weigh 350 to more than 600 kg and females 150 to 290 kg. Compared with a brown bear, a polar bear has no shoulder hump, a relatively small head and a longer neck. Its paws can measure up to 30 cm across; the forepaws work as paddles when swimming, and small bumps called papillae on the black footpads, plus fur between the toes, give grip on ice. The fur is not actually white. Each hair is pigment-free and transparent, and the coat looks white because it scatters and reflects light. Underneath, the skin is black. In summer the fur can look yellowish. Two layers of fur hold in heat so well that adult males can overheat when they run. A popular idea that the hairs act like optical fibres, carrying sunlight to the skin, was tested and rejected in 1998.
Conservation
The IUCN Red List classifies the polar bear as Vulnerable (2015 assessment), with an estimated 26,000 bears (95% confidence interval 22,000 to 31,000). The assessors found loss of Arctic sea ice from climate change to be the most serious threat, with a median probability of about 71% that the global population declines by more than 30% over three generations. A 2020 study in Nature Climate Change estimated how long polar bears can fast before cub survival and adult survival fall sharply. With high greenhouse gas emissions, it projected that falling reproduction and survival would put all but a few high-Arctic subpopulations at risk by 2100. In the United States, the polar bear has been listed as threatened since 2008.
Fun facts about Polar Bear
- Polar bear cubs weigh only about 0.5 to 0.6 kg at birth, inside a snow den, and leave it in spring weighing roughly 10 to 15 kg.
- A GPS-collared female in the Beaufort Sea swam 687 km without stopping over nine days in 2008. She lost 22% of her body mass and her yearling cub.
- Satellite-collared polar bears can travel more than 3,000 km in a month, and some have home ranges larger than 600,000 square kilometres.
- Polar bears evolved from brown bear ancestors, likely between about 343,000 and 479,000 years ago, and the two species can still interbreed.
Polar Bear vs Grizzly Bear
At Alaska's whale bone piles the smaller grizzlies usually push polar bears off the food; the polar bear's strengths are on the sea ice and in the water.
These two bears really do meet. Grizzlies have recently become more common on the Arctic islands of western Canada, and near Kaktovik on Alaska's Beaufort Sea coast both species come each autumn to feed on the bowhead whale remains that Inupiat whalers leave on the beach. By size alone the polar bear should win, since it is the largest bear species. But a study of 137 encounters at the Kaktovik bone pile found the opposite: grizzlies were socially dominant. In most encounters a grizzly simply walked up and the polar bear gave way, and in about half of them the polar bears were displaced from the food. Polar bears were much less aggressive toward grizzlies than toward other polar bears. On land, at a shared carcass, the grizzly wins.
Read more about Grizzly Bear.
Common questions about Polar Bear
Is polar bear fur really white?
No, it only looks white. Each hair is pigment-free and transparent, and the coat appears white because it scatters and reflects light (Polar Bears International). The skin underneath is black, and the fur can look yellowish in summer (ADW). The popular claim that the hairs pipe sunlight to the skin like optical fibres does not hold up: measurements show almost no light travels along a hair (Koon 1998).
How many polar bears are left in the world?
About 26,000, with a 95% confidence range of 22,000 to 31,000, according to the IUCN Red List assessment that lists the species as Vulnerable (Wiig et al. 2015). They live in 20 recognised subpopulations, the newest in Southeast Greenland (PBSG 2024), and about two-thirds are in Canada (Polar Bears International).
How far can a polar bear swim?
Hundreds of kilometres. In 2008 a GPS-collared female in the Beaufort Sea swam 687 km without stopping over nine days. She lost 22% of her body mass and her yearling cub (Durner et al. 2011). A study of 20 collared females found 50 swims longer than 50 km between 2004 and 2009, averaging 154 km, and swimming appeared to become more frequent over the study (Pagano et al. 2012).
Would a polar bear beat a grizzly bear?
Not at a shared carcass, it seems. Polar bears are the largest bear species (Polar Bears International), yet in 137 encounters at a whale bone pile near Kaktovik, Alaska, the smaller grizzlies were dominant. Most often a grizzly simply approached and the polar bear gave way, and polar bears were displaced from the food about half the time (Miller et al. 2015).
Can polar bears and grizzly bears have cubs together?
Yes. Wild hybrids, sometimes called pizzly or grolar bears, have been confirmed in the Canadian Arctic. A genetic study traced eight of them to one female polar bear that mated with two grizzlies: four first-generation hybrids, plus four cubs that one hybrid daughter had with the same grizzly males (Pongracz et al. 2017). Hybrids can be fertile (ADW).
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