Facts About Polar Bears: Size, Adaptations, Hunting, Reproduction, and Conservation

Facts about polar bears reveal an animal built entirely around the Arctic environment. The polar bear (Ursus maritimus), whose Latin name means “sea bear,” is the world’s largest land carnivore and the only bear species classified as a marine mammal. Polar bears depend on Arctic sea ice as a hunting platform for nearly all of their food, spending more time at sea than on land. An estimated 22,000 to 31,000 polar bears remain in the wild, distributed across 19 subpopulations spanning five nations: Canada, the United States (Alaska), Russia, Norway (Svalbard), and Denmark (Greenland).

Size and Physical Description

Polar bears are the largest bear species and the largest land-based predator on Earth. Adult males weigh 300 to 800 kilograms and measure 2.2 to 2.5 meters in body length, while females are roughly half the male’s weight at 150 to 300 kilograms.

The size difference between males and females is among the largest of any bear species, driven by competition between males for mating access. A large male can weigh up to 50% more after a successful hunting season than at the start of the next, with most of the additional mass accumulated as fat. Newborn cubs weigh less than one kilogram at birth, among the smallest cub-to-adult size ratios of any placental mammal. The body plan differs from other bears in several specific ways: polar bears have a longer neck, smaller rounded ears, and a narrower, more streamlined skull, all adaptations that reduce heat loss and aid swimming. Feet are large, measuring up to 30 centimeters across, helping distribute weight on thin ice. The footpads are covered in small soft papillae that provide traction on slippery surfaces, and the toes carry partial webbing that assists swimming.

Physical Adaptations for the Arctic

Polar bears have two layers of fur, black skin, and a fat layer up to 11 centimeters thick. These three systems work together to retain body heat so effectively that infrared photography shows almost no heat escaping from a resting bear’s body.

The outer guard hairs are not white but transparent and hollow. Light scatters through the hollow shafts in a way that makes the coat appear white or yellowish, providing camouflage against snow and ice. The guard hairs are also water-repellent, allowing the bear to shake off much of the water immediately after leaving the sea, reducing the time needed to dry. The dense underfur provides additional insulation. Black skin beneath the fur absorbs solar radiation and contributes to warming when the bear is exposed to sunlight. The insulation is so complete that adult males commonly overheat when they run, which is why polar bears almost never sprint at full speed except for very short distances and why still-hunting (motionless waiting) is far more energy-efficient than active pursuit. A polar bear’s body temperature and metabolic rate remain normal at ambient temperatures as low as -37 degrees Celsius as long as wind is absent.

The digestive system is highly adapted for a fat-rich diet. Polar bears absorb approximately 97% of the fat from a seal carcass and 84% of its protein. The stomach can hold up to 20% of the bear’s body weight in a single meal. This efficiency allows bears to build large fat reserves during productive hunting seasons that sustain them through fasting periods lasting weeks or months.

Swimming Ability

Polar bears are powerful and sustained swimmers, using their large front paws to paddle at approximately 10 kilometers per hour while holding the hind legs flat as a rudder. Documented marathon swims include one satellite-tracked female that covered 4,796 kilometers across open Arctic water over multiple legs.

In the water, polar bears rely primarily on their body fat rather than fur for insulation, as wet fur loses most of its insulating value. This is why mother bears avoid swimming with young cubs in spring: cubs lack sufficient fat to stay warm in cold water. Long open-water swims impose a significant metabolic cost. A 2011 study documented a female that swam continuously for nine days across the Beaufort Sea to reach an ice floe, losing 22% of her body weight and her cub in the process. As sea ice retreats further from shore due to climate warming, the frequency and length of these forced open-water swims is increasing across multiple populations.

Diet and Hunting Methods

Ringed seals are the primary prey of polar bears, providing the fat-rich diet the bears depend on for survival. Polar bears are the only bear species that are almost exclusively carnivorous, and their main hunting method is still-hunting: waiting motionlessly at a seal’s breathing hole for hours or days until the seal surfaces.

Ringed seals carve and maintain breathing holes through the sea ice using their claws. Polar bears locate these holes using their sense of smell, which can detect a seal from nearly 1.6 kilometers away and buried under a meter of snow. Once at the hole, the bear waits motionlessly with its nose positioned over the opening. When the seal surfaces, the bear bites the head or neck, hooks it with its claws, and flips it onto the ice in a single rapid motion. This technique, called still-hunting or “lie-and-wait,” is used most consistently in winter and early spring. A second method is stalking: approaching seals resting on ice edges, advancing slowly with the head and neck lowered to conceal the dark nose and eyes. A third method is breaking through snow-covered birthing lairs where ringed seal pups are sheltered in spring. The bear uses its forepaws to smash through the ice ceiling and then reaches in to extract the pup before it can escape.

When a seal is caught and food is plentiful, polar bears preferentially consume the fat and skin first, leaving the leaner meat for scavengers such as Arctic foxes, ravens, and smaller bears. Fat delivers more than twice the caloric density of protein per gram and is absorbed more completely. During lean periods or when stranded on land in summer, polar bears may eat bird eggs, vegetation, berries, kelp, and carcasses of large marine mammals, but these terrestrial food sources cannot meet the caloric demands of the bears’ metabolic requirements and function only as supplements during unavoidable fasting periods.

Reproduction and Cub Development

Polar bear breeding occurs on the sea ice in spring, typically between April and May. Cubs are born in midwinter in maternity dens, where the mother fasts completely for the entire denning period, sustaining herself and her cubs solely on stored fat.

Pregnant females excavate maternity dens in late autumn by digging into deep snowdrifts on land near coastlines. The den consists of a tunnel leading to a chamber, where the insulating properties of snow maintain a temperature near 0 degrees Celsius even when external temperatures drop to -40. Inside the den, the mother’s body temperature drops to 31 to 35 degrees Celsius, a controlled reduction that reduces metabolic rate and extends fat reserves, similar to hibernation but without the full metabolic shutdown seen in other hibernating species. Cubs, usually twins, are born in December or January weighing approximately 0.5 kilograms. They are blind, nearly hairless, and entirely dependent on their mother. The mother produces milk containing approximately 31 to 36% fat, among the richest milk of any bear, enabling rapid cub growth. By the time the family leaves the den in March or April, cubs weigh 10 to 15 kilograms.

The family spends one to two weeks near the den site while cubs adjust to outdoor conditions, then begins the walk to the sea ice where the mother resumes hunting. Cubs remain with their mother for approximately 28 months, learning seal detection, breathing hole identification, and hunting technique. Males play no role in raising young and may kill cubs if encountered. Females breed every two to four years. Most females first reproduce at four to eight years of age, and males, though sexually mature at similar ages, typically do not successfully breed until eight to ten years due to competition from larger adults. Longevity in the wild is 25 to 30 years.

Range and Sea Ice Dependence

Polar bears are found only in the Arctic, distributed across the sea ice of Canada, Alaska, Russia, Norway, and Greenland. Their entire existence depends on sea ice as a hunting platform, mating area, and travel corridor.

Polar bears do not hold fixed territories. Instead, they follow seasonal sea ice expansion and contraction across enormous home ranges. Males in prairie-like Arctic habitat can cover 7 to 50 square kilometers, while individual females have been satellite-tracked traversing thousands of kilometers in a single year. The bears concentrate along the edges of sea ice near polynyas (open water surrounded by ice) and leads (cracks in the ice), where seals must surface frequently to breathe. These areas, known as the Arctic Ring of Life, represent the most productive sea ice habitat because of the biological richness of the underlying water column. In summer, when sea ice melts and retreats, bears in southern subpopulations such as Hudson Bay are forced ashore and must fast until freeze-up in autumn. Hudson Bay has historically been ice-free for roughly four months; that period has extended by an average of three weeks since 2000.

Conservation Status and Climate Threats

The IUCN classifies the polar bear as Vulnerable. The U.S. government listed the species as Threatened in 2008. The primary driver of population decline is loss of sea ice habitat due to climate change, which reduces hunting opportunities, increases fasting periods, and forces longer and more dangerous open-water swims.

Three of 19 subpopulations are assessed as likely declining, with Southern Beaufort Sea, Southern Hudson Bay, and Western Hudson Bay showing documented decreases in body condition, cub survival, and overall population size. A 2008 modeling study predicted that two-thirds of the world’s polar bears could disappear by 2050 under a high-emission scenario. A 2020 study found that a worst-case climate pathway would eliminate most subpopulations by 2100, while even an intermediate pathway would result in some subpopulation losses within the same period. Beyond climate change, polar bears also accumulate persistent organic pollutants including PCBs and chlorinated pesticides at the top of the Arctic food chain, with documented effects on hormone function and immune response. Oil and gas development in the Chukchi and Beaufort seas intersects with key polar bear habitat, and oil spills at full reach could affect up to 40% of the polar bear population. Polar bears have no natural predators as adults; their survival depends entirely on the persistence of sea ice.