Polar bears: The largest land carnivores

Polar bears (Ursus maritimus) are the largest members of the bear family and the biggest land-dwelling carnivores on Earth. These massive animals inhabit the Arctic, where they travel across frozen landscapes and sea ice in search of their main prey, seals.

Scientists believe polar bears developed within the past 500,000 years after a group of brown bears moved north into the Arctic during a warmer period and became geographically isolated. When the climate became colder again, these bears gradually adapted to the harsh Arctic conditions.

Polar bears possess numerous adaptations that allow them to survive in extremely cold environments. Their thick coats and substantial fat reserves help conserve body heat, while small raised structures beneath their paws provide additional traction and help prevent them from sliding across ice.

They are also highly capable swimmers. Their scientific name, Ursus maritimus, means "sea bear," reflecting the species' close dependence on marine environments. Polar bears are unique among bear species because they are classified as marine mammals.

Size & Appearance

When standing on all four legs, polar bears generally measure about 3.5 to 5 feet (1 to 1.5 meters) tall at the shoulder. An adult male can exceed 10 feet (3 meters) in height when standing upright on its hind legs. In 1960, an exceptionally large polar bear killed in Alaska reportedly reached 12 feet (3.7 meters) while standing on its back legs.

Adult males commonly weigh between 770 pounds and more than 1,300 pounds (350 to 600 kilograms). The enormous Alaskan bear recorded in 1960 weighed approximately 2,210 pounds (1,000 kilograms), making it the heaviest polar bear ever documented. Females are considerably smaller, generally weighing between 330 and 650 pounds (150 to 295 kilograms), roughly half the weight of males.

Key Facts

Size: 3.5 to 5 feet (1.5 meters) tall at the shoulder when standing on all fours

Life span: 15 to 18 years

Conservation status: Vulnerable

Although polar bear fur looks white, the individual hairs are actually transparent. Their apparent white coloration results from visible light scattering and reflecting from the clear, hollow hairs. This pale appearance helps the bears blend into snow and ice-covered surroundings.

Depending on the season and lighting, polar bears can sometimes appear yellow, brownish, or gray rather than pure white. Beneath their coat, their skin is black. The dark skin absorbs sunlight and contributes to keeping their bodies warm in the cold Arctic environment.

Polar Bears vs. Kodiak Bears

Polar bears are considered the largest bear species, although Kodiak bears, a particular type of brown bear, can reach dimensions comparable to some polar bears. Kodiak bears live on islands within Alaska's Kodiak Archipelago, where they have remained separated from other brown bear populations for approximately 12,000 years.

These brown bears can grow to more than 10 feet (3 meters) tall when standing on their hind legs and may weigh as much as 1,500 pounds (680 kilograms).

Some sources, including the Alaska Department of Fish and Game, describe Kodiak bears as the largest bears on Earth. Part of this disagreement comes from how the term "largest" is measured. Comparisons can be based on body length, overall weight, average size, or the largest individual ever recorded.

On average, polar bears are taller and heavier. However, an exceptionally large Kodiak bear can exceed the size of an average polar bear.

Where Do Polar Bears Live?

Polar bears inhabit the sea ice and frozen waters of the Arctic, as well as regions surrounding the Arctic Circle. Their range includes Canada, Alaska in the United States, Greenland, Norway, Russia, and occasionally Iceland.

They are not native to Antarctica, despite the fact that both regions are associated with extremely cold climates. Penguins live in Antarctica, while polar bears are found exclusively in the Northern Hemisphere.

Some polar bears remain on permanent sea ice in the Arctic Basin, but most depend on seasonal sea ice that forms around the basin each year. When this temporary ice disappears during summer, polar bears may have to remain on land for several months until freezing temperatures cause the sea ice to return.

Polar bears frequently swim between sea ice and shore while searching for food, looking for mates, or cooling themselves. Their large front paws propel them through the water, while their hind legs act like rudders. They also have partial webbing between their toes, which improves their swimming ability.

Researchers have recorded polar bears swimming for almost 10 consecutive days and covering as much as 427 miles (687 kilometers) in one uninterrupted journey without stopping to rest. Such extended swims can be dangerous and increase the possibility of drowning. As rising temperatures associated with climate change reduce Arctic sea ice, polar bears may be forced to make longer swims more frequently.

What Do Polar Bears Eat?

Polar bears are the most meat-dependent members of the bear family and consume an overwhelmingly carnivorous diet. Ringed seals (Pusa hispida) are their principal prey.

A polar bear may wait beside a seal's breathing hole, remaining still until the seal surfaces. Bears can also locate seal dens beneath the snow and break through the roof to reach the animals inside.

When seals are abundant and a polar bear is in good physical condition, it may primarily consume the seal's blubber. This fatty tissue provides an extremely concentrated source of calories and helps the bear build and maintain fat reserves between successful hunts.

Polar bears can consume approximately 4.4 pounds (2 kilograms) of fat per day. When seals are difficult to find, they may turn to other sources of food, including walruses, seabirds, fish, and small mammals such as rodents. They may also feed on whale carcasses and other carrion and occasionally consume small quantities of vegetation.

These alternative foods become particularly important when seals are scarce, but seals remain essential for maintaining healthy polar bear populations. As apex predators, polar bears occupy the highest level of their food chain and have no natural predators apart from humans.

Social Behavior and Reproduction

Polar bears are generally solitary animals. The main exception is a mother caring for her cubs. Unrelated bears may occasionally gather together when they have access to a large whale carcass or a garbage site, or when several animals are waiting on land for sea ice to form again.

Polar bears do not normally establish and defend fixed territories. However, individuals may fight over valuable food sources, while males can compete with one another for access to females during the breeding period, which usually occurs between March and June.

Male polar bears locate potential mates by following their scent. After finding a female, the pair may remain together for a week or longer. Following mating, the fertilized eggs do not immediately attach to the female's uterus. Instead, implantation is delayed, usually until September through November.

Including this delayed implantation period, pregnancy can last for approximately seven months. A pregnant female prepares for birth by digging a maternity den inside a snowbank. Unlike most brown and black bears, polar bears do not normally hibernate during winter and generally continue hunting unless conditions become exceptionally severe.

A female polar bear normally gives birth inside her den, most often producing twins during December or January. Newborn cubs are extremely small, generally weighing only about 1.3 pounds (0.6 kilograms).

The cubs grow rapidly by drinking their mother's nutrient-rich milk. By spring, they begin venturing outside the den, although they usually remain close to it during their first 12 days or longer and continue sleeping inside at night.

Young polar bears can remain with their mother for as long as three years while learning essential survival skills. Wild polar bears generally live between 15 and 18 years, although some individuals can survive into their 30s.

One captive polar bear named Debby lived to 42 years old at Assiniboine Park Zoo in Canada. When she died in 2008, she was believed to have been the oldest polar bear in the world.

Are Polar Bears Dangerous to Humans?

Polar bears do not commonly attack people. A 2017 study published in the journal Wildlife Society Bulletin documented 73 confirmed polar bear attacks between 1870 and 2014, including 20 deaths.

The research indicated that nutritionally stressed male polar bears were the most likely individuals to attack humans. Most of the documented attacks were predatory, meaning the bear was attempting to kill a person as a source of food.

The frequency of polar bear attacks increased during the period examined by the study, a trend researchers associated with environmental changes. As Arctic sea ice decreases and retreats farther from shore, polar bears can spend longer periods on land, particularly in places such as Hudson Bay in northeastern Canada.

Geoff York, a study co-author and senior director of conservation at Polar Bears International, explained that the increasing overlap between people and polar bears, together with more bears arriving on land in poor physical condition, can create greater opportunities for conflict.

As the annual sea ice melts, polar bears effectively have to choose whether to remain on the shrinking ice and move farther into Arctic waters or come onto land and search for food there. Bears that remain on shore for longer periods may encounter human settlements and activities. When food becomes scarce, they may also take greater risks in their search for nourishment.

Are Polar Bears Endangered?

Polar bears are classified as vulnerable to extinction by the IUCN Red List of Threatened Species. Climate change represents the greatest long-term threat because rising temperatures are causing the Arctic sea ice on which polar bears depend to shrink.

Other human activities also pose risks. Oil and gas development in the Arctic, for example, can increase the possibility of interactions and conflicts between people and polar bears.

The IUCN estimates that approximately 26,000 polar bears remain in the wild. However, determining their exact population is difficult because the animals occupy remote areas at relatively low densities. Information about some individual polar bear populations is also limited, incomplete, or outdated.

In the United States, polar bears are listed as threatened under the Endangered Species Act and receive protection through the Marine Mammal Protection Act.

Inuit and other Indigenous communities continue to hunt polar bears for food and clothing as part of longstanding cultural traditions, with such hunting subject to regulations. Inuit communities have traditionally referred to polar bears as "Nanuq" and have viewed them as intelligent, powerful animals with qualities that are almost human.