Polar Bear

Quick Take

• Polar bears are built to survive brutal Arctic cold, but their bodies face a surprisingly opposite problem that forces them to stay slow. Explore their body adaptations →
• The polar bear may not be the species everyone thinks it is, and the evidence changes how scientists classify it entirely. See how scientists classify them →
• In head-to-head encounters, the planet's largest land carnivore doesn't always come out on top, and the winner might just surprise you. See who wins these encounters →
• Some experts put a hard deadline on wild polar bears surviving, and that timeline is far shorter than most people realize. Check the extinction timeline →

Polar bears are the largest land carnivores on Earth, built to thrive in the harsh Arctic. Roaming the sea ice, they hunt seals almost exclusively for food, making them deeply dependent on frozen waters. As that ice shrinks, the polar bear has become a powerful symbol of a changing Arctic.

Classification and Scientific Name

Ursus maritimus (“maritime bear”) was first described in 1774 by Constantine John Phipps. Inuit people call it Nanook, and Norwegian names are isbjørn (‘ice bear’) or kvitbjørn (‘white bear’).

The polar bear was once believed to be its own separate species, but recent evidence has shown that it actually descended from the brown bear. The accepted scientific name for the polar bear is now Ursus maritimus.

The polar bear is a large species of bear that is found inhabiting the ice fields in the Arctic Ocean. It is the biggest species of bear in the world (except the Kodiak brown bears found in Alaska, which can reach similar sizes), with males typically weighing between 600 and 1,200 pounds, though the largest individuals can exceed 1,700 pounds. Thought to be closely related to the brown bear, the polar bear’s name actually means “sea bear,” as they not only spend a great deal of time close to the coast but are also strong and capable swimmers that have been spotted up to 100 miles from the closest ice or land.

They are, however, being severely affected by global warming as the ice that they rely so heavily on is disappearing fast, which has led to the polar bear becoming a strong symbol of the effects of climate change. Polar bear populations have also fallen across the Arctic Ocean due to hunting, pollution, and drilling for oil and gas, leading to them being listed as a threatened species.

Evolution

The Ursidae family has evolved over millions of years. The oldest known polar bear fossil is a 130,000 to 110,000-year-old jaw bone found on Prince Charles Foreland in 2004. This suggests that the polar bear diverged from a population of brown bears during the Pleistocene period when Siberia was covered by glaciers. It is believed that this isolation led to changes in the molar teeth of polar bears between 10,000 and 20,000 years ago, which further differentiated them from their brown bear ancestors.

Nuclear DNA analysis suggests polar bears diverged from brown bears, Ursus arctos, approximately 400,000–600,000 years ago. Some clades of brown bear mtDNA are more closely related to polar bears than to other brown bears. Irish bears’ (now extinct) mtDNA is particularly close. Nuclear genome comparison revealed distinct clades approximately 603,000 years ago, but a recent complete genome analysis revised this date to 400,000 years ago.

However, the two species have mated intermittently for all that time, most likely coming into contact with each other during warming periods, when polar bears were driven onto land, and brown bears migrated northward. Most North American brown bears derive between 3 percent and 8 percent of their genetic material from polar bears, but one population, the ABC Islands bears, has between 5 percent and 10 percent polar bear genes, indicating more frequent and recent mating.

Polar bears can breed with brown bears to produce fertile hybrids, suggesting their genetic similarity persists despite morphological and behavioral differences. Thus, the two species remain classified as separate.

Anatomy and Appearance

Adult polar bears typically measure more than six feet in length and weigh around half a ton. Females, though, are much lighter than their male counterparts, who are almost double their weight. Polar bears are one of the few large mammals found in such hostile conditions and have adapted well to their life on the ice. Their fur is thick and dense and is made up of a warm undercoat with longer guard hairs on top that are clear, hollow tubes that trap warmth from the sun and transmit it directly down to their black skin, which then absorbs the welcome heat.

The polar bear has a strong and muscular body, broad front paws that help when paddling in the water, and fur on the bottom of its feet that not only helps to keep them warm but also gives the polar bear extra grip when moving about on the ice. They have very long necks in comparison to other bear species, which enables their head to remain above the water when swimming. They also have more elongated muzzles and smaller ears than their relatives.

The largest polar bear ever recorded weighed 2,209 pounds (1,002 kg). It stood 11 feet 1 inch tall on its hind legs and was discovered in Alaska in 1960. While polar bears are the largest bear species, in documented altercations that pit polar bears vs. grizzly bears, it has normally been the grizzly that stands its ground while the polar bear flees.

Distribution and Habitat

Polar bears are found on the icy coasts that surround the North Pole and as far south as Hudson Bay. Around 60% of polar bears can be found in northern Canada, with the remaining individuals distributed throughout Greenland, Alaska, Svalbard, and Russia, where they tend to be found relatively close to the ocean, roaming vast distances across the ice fields. Polar bear populations have fallen drastically throughout their natural range, with the biggest threat to this enormous carnivore being global warming.

Although polar bears are accustomed to seasonal changes in the Arctic Circle, the summer ice melt is happening earlier and more rapidly year by year, meaning that polar bears have less time to hunt on the ice before it disappears. Their precarious habitats are also affected severely by human encroachment in the forms of hunting, growing settlements, and the release of chemical pollutants into the water.

Behavior and Lifestyle

The polar bear is a solitary animal that can not only run at speeds of up to 25mph, but its strong ability to swim at 6mph makes it a true apex predator within its environment. These semi-aquatic mammals can hunt both on the ice and in the water and have been known to swim vast distances across the open ocean in search of food. Polar bears are able to dive under the water to catch their prey, which they do by keeping their eyes open and holding their breath for up to three minutes.

On land, they tend to hunt using two main techniques: they either stalk and then chase their prey or sit waiting next to a breathing hole for many hours before ambushing the seal as it emerges. Eating seals is vital to the survival of the polar bear as they are able to provide it with a high-energy meal. During the short Arctic summer, however, polar bears are forced further north as the ice recedes, and they have to feed on other animals further inland.

Reproduction and Life Cycles

Polar bears tend to breed in the spring between April and May, with the gestation period then varying considerably (depending on the health of the female) due to a period of delayed implantation. Up to 9 months later, the female gives birth to between 1 and 3 cubs in a den that she has dug into the snow or ground. The cubs weigh just over one pound when they are newborns and are hairless and cannot see. Females enter their dens towards the end of autumn and don’t emerge with their cubs until the harsh winter conditions have turned into spring.

although polar bear cubs begin eating solid food when they are around 5 months old, they are not weaned until they are between two and three years old. Cubs are known to commonly play-fight with other cubs, which involves wrestling and chasing, along with baring their teeth and even biting one another, but without causing harm. These games are critical for polar bear cubs to learn how to fight and therefore defend themselves successfully once they leave their mother and live on their own.

Diet and Prey

The polar bear is the largest carnivorous mammal on land and must hunt regularly to ensure that it is well-fed and maintains its insulating layer of fat to keep it warm. The skins and blubber of ringed seals make up the bulk of the polar bears’ diet, as they often leave the remaining meat, which provides an important source of food for other animals, such as Arctic foxes. Although seals are their primary source of food, polar bears also eat birds, berries, fish, and reindeer (particularly during the trickier summer months), along with the occasional walrus. The carcasses of large marine mammals, including seals, walruses, and even whales, also provide a regular food source; polar bears are said to have such a keen sense of smell that they can detect carcasses from a considerable distance. Polar bears are also known to break into underground seal dens to hunt the pups inside them.

Predators and Threats

Because the polar bear is an enormous and ferocious predator, there are no animals that prey on it in its surrounding environment. They tend to have the most trouble with other polar bears, and females will protect their cubs fiercely from males that may be trying to harm them.

Humans are by far the biggest threat to the dwindling polar bear population, having hunted them relentlessly from their arrival in the Arctic in the 1600s until international hunting bans were enacted in the mid-1970s. Along with the receding ice fields that are crucial to the survival of the polar bear caused by climate change, they are also heavily affected by drilling for oil and gas, increased shipping activity, and rising levels of industrial chemicals that pollute the water.

The polar bear has a relatively slow rate of reproduction, which means that populations are not only shrinking rapidly, but they are not growing quickly enough to sustain themselves. Some experts claim that the polar bear could be extinct from the wild in the next 30 years.

Interesting Facts and Features

Before the harsh winter conditions fully arrive, female polar bears dig dens in the snow, where they hibernate through these hostile months, give birth to their cubs, and only emerge in the spring. These dens are known to be up to forty degrees warmer than the outside, but males seem to prefer to be active all year round. Polar bears have a layer of blubber under their skin which can be up to 4 inches thick and helps to keep them warm. They are, in fact, so well insulated that polar bears must move slowly for the majority of the time so that they don’t overheat.

Polar bears shed their fur in the summer, meaning that they seem at their whitest at the beginning of autumn. By the spring, their coats appear to be more yellow in color, a color change thought to be partly due to oils found in seal skins.

Relationship with Humans

Before the 1600s, when the European, Russian, and American hunters arrived in the heart of the Arctic Circle, only native people really knew anything about them. Polar bears were mercilessly hunted until 1973, when an international agreement put an end to such uncontrolled hunting. Even today, native people are still allowed to hunt the polar bear for traditional uses, but the biggest threat to polar bears is the rapidly melting ice shelf. Global warming caused by people is thought to be reducing the ice so quickly, in fact, that some say that the southern limit of their range at Hudson Bay will have no ice at all by 2080.

Polar bears are known to be aggressive towards humans, with reported attacks still occurring, including the most recent and famous incident in Svalbard, when several teenagers and their expedition leaders were attacked by a polar bear in their camp.

Conservation Status and Life Today

Today, the polar bear has been listed on the IUCN Red List as a species that is Vulnerable in its natural environment. Although international hunting bans have prevented such a high level of hunting, conservation efforts within the Arctic Circle prove to be hard, with the very thing polar bears need to survive is disappearing more every year. Increased levels of industrial activity in their natural environment also cause declines in the quality of their remaining habitats. There are estimated to be between 20,000 and 25,000 polar bears left roaming close to the North Pole, with the majority of these found in northern Canada.