How Polar Bears Work

The polar bear, or Ursus maritimus (sea bear), probably evolved about 150,000 years ago from brown bears [source: Live Science]. A polar bear can actually mate successfully with a brown bear and the resulting offspring is fertile, which gives more evidence of a relationship between the two. There are a lot more brown bears out there than polar bears, though. Brown bears number more than 200,000 worldwide [source: WWF]. Polar bears only number about 23,000.

Polar bears live only in the Northern Hemisphere – you won't find them at the South Pole. The 23,000 live in 19 separate populations throughout the Arctic, in only five countries: the United States (Alaska), Canada, Russia, Greenland and Norway. About 60 percent of the population lives in Canada.

Life in the Arctic is harsh: The bears live in total darkness between October and February, and the temperature can drop as low as -50 F (-45 C) in winter [source: Polar Bears International]. And that's exactly how they like it.

Polar bears are built for extreme cold. They experience almost no heat loss: Two layers of fur and a blubber layer up to 4.5 inches (11.5 centimeters) thick keep them so well insulated, they'll overheat if they run. The areas that lack this insulation – ears, tail and muzzle – are especially small, minimizing non-insulated surface area.

Polar bears mostly walk slowly, following their favorite prey, the seal, from ice sheet to ice sheet. They need the ice to hunt. In warmer months, when ice sheets get smaller, the bears will walk hundreds of miles to find solid spreads of ice.

Polar bears can walk up to 20 miles (30 kilometers) per day, for several days in a row, relying on tiny bumps on the bottoms of their feet to keep them from slipping on the ice. They'll swim, too, both to cool off after a meal and to bridge the gap between ice sheets when they're following seals. Polar bears use their front paws to paddle and their hind legs to steer (imagine the most powerful doggie paddling ever). They'll go only slightly under the water when they swim, and their nostrils close up when they're submerged. As much as they thrive on the ice, they're strong swimmers. Polar bears have been tracked swimming up to 60 miles (100 kilometers) at a time, and at up to 6 miles per hour (10 kilometers per hour) [source: WWF].

Aside from their dependence on staggering cold, one of the biggest differences between polar bears and other bears is that polar bears don't hibernate. Females go into a sort of semi-hibernation toward end of their pregnancy, but they don't experience the drop in heart rate and body temperature that characterizes real hibernation. They mostly just rest and sleep a lot in the months immediately before and after they give birth.

However, births are declining. Of the 19 polar bear populations, at least five are known to be shrinking dramatically. In at least one area, the creatures are reproducing at just 20 percent of the rate they were two decades ago [source: NBC News].

This serious drop in population is due to climate change, and it has a lot to do with the way polar bears hunt.

In the Arctic, polar bears top the food chain. Both males and females hunt, and their favorite meal is seal, especially a ringed or bearded seal. When hunting's especially good, they'll just eat the seal's fat – which helps build up insulation – and leave the rest behind. The biggest bears can eat 100 pounds (45 kilograms) of blubber in one meal [source: Polar Bears International].

While polar bears prefer seals, they're opportunists. They'll eat anything from beluga whales to walruses [source: Arctic WWF]. The bears can find food on land if they have to, attacking reindeer and raiding birds' nests (bird eggs are a favorite snack), but they aren't well-adapted to hunting on land. Polar bears might even eat garbage generated by humans.

Instead, their strength is on the ice. Polar bears can't swim fast enough to catch a seal in the water and need an ice platform to use their full strength to grab one. But with global temperatures rising, Arctic ice floes melt earlier in the year than they used to, reducing the surface area on which bears can hunt. It also means that when polar bears wander onto land, they can end up stranded because the distance between land and the nearest ice sheet is too far to swim in one shot.

A hunt starts with a scent. Polar bears can smell seals more than half a mile (1 kilometer) away, often by the scent left on their breathing holes [source: Polar Bear International]. In the fall, when the ice is softer, seals cut holes in the ice so they can come up for air when they need to. Polar bears find such breathing holes and wait, sometimes for several days, until a seal comes up for a breath.

When a polar bear spots a seal coming up for air, it gets down on all fours, delicately putting each paw on the ice to keep silent. The bear then makes a shallow dive through the hole to grab the seal with its claws. Those sharp, 2-inch claws grip the seal extremely well. Still, seals sometimes get away. Polar bears have been known to express frustration when they lose their prey, pounding the ice or throwing blocks of it in a sort of tantrum. When the hunt is successful, a bear will share a kill with others as long as they beg properly: keeping low, circling the kill and occasionally nudging the hunter with their noses.

After eating, polar bears always clean up, which is why their fur stays so white. They need to stay dry and fluffy to maintain their body heat. They bathe in water during the summer and snow during the winter, using their tongues to clean their paws and cubs. After a good meal and a bath, they'll often take a nap, for much the same reason: Their survival depends on energy conservation. After any kind of exertion, they'll often lie down and go to sleep for an hour or so. Like humans, a polar bear's full "night's rest" lasts for about eight hours, although it's as likely to take place during the day as at night. The bears spend most of their time in 24-hour darkness and 24-hour light depending on the season, so time of day is largely irrelevant

Life on the ice is pretty routine for a polar bear, unless it's a pregnant one.

As with most animals, polar bears mate in the spring. Scientists aren't sure how sexually mature males find females who are ready to mate. Brown bear females seem to leave a scent trail for males to follow. This could also be the case with polar bears.

Females usually mate successfully for the first time between the ages of 6 and 8. They only have about five litters in their lifespan, which is one of the lowest reproduction rates among mammals. Females only mate every few years, so males must compete fiercely for a female to mate with. When male bears fight over a female, the challenger will lower his head, put his ears back and open his mouth wide, roaring and bearing teeth. Polar bears seldom fight to the death for mating rights; the weaker bear usually submits after an injury.

Female polar bears don't really go into heat the way some other mammals do. They're induced ovulators, which means that it's intercourse itself that causes their ovaries to release an egg. Ovulation doesn't happen immediately, and it may take several tries before a successful mating occurs. Once mated, the couple stays together for about a week before separating. Polar bears aren't monogamous animals – a strong male might impregnate several females in one season [source: Polar Bears International].

Like most aspects of polar-bear life, the pregnancy process is about energy conservation. A pregnant female feeds heavily in the spring to build up her fat reserves and prepare for a maternity rest in the fall. In the maternity den, only the cubs eat, consuming their mother's high-fat breast milk for their first months of life.

In late fall, the female digs a cave in a snowdrift, either on a mountainside very close to sea ice or on the sea ice itself. This den is protected from the wind, and provides a secure place to sleep. In early winter, the female gives birth after an approximate eight-month gestation period [source: Polar Bears International]. However, it only takes four months for the unborn cub to actually develop. During the first four months of pregnancy, the embryo is stagnant in the uterus while the mother gains the weight (about 450 pounds or 200 kilograms) she'll need to ensure its development and proper feeding after birth.

There are typically two cubs per litter, and they're surprisingly small. A cub weighs about a pound (2 kilograms) at birth and measures about a foot (30 centimeters) long. It's also blind, toothless and lacking insulation, with only very short, thin fur. Polar bear cubs have no chance of survival without their mother. The family stays in the maternity den until early spring, and the mother doesn't drink, eat or defecate during that time. All she does is protect and feed her young. Even after they leave the den, cubs stay with their mom until they're about 2 years old, learning to hunt, clean themselves and survive in the harshest of habitats.

Like many mothers in the animal kingdom, a polar bear will kill anyone or anything that comes near her young. Polar bears are predators, pure and simple. So what happens when they get stuck on land, with people around? There might be trouble – but as we'll find out, polar bears seldom go looking for a fight with a human.

Modern zoos around the world keep polar bears, often trying to emulate their natural habitats as much as possible. A zoo is pretty much the only place where it's safe for a human to get anywhere near a polar bear.

With sea ice melting, polar bears are frequently forced to move onto land in the warmer months. More polar bears on land – looking for sustenance where their natural prey is absent – means more interactions with humans, and more attacks. Polar bears don't seek out confrontations, but if they're really hungry or feel threatened, they'll kill – and eat – a human without a second thought.

If you're traveling in polar bear territory, you should be mentally prepared for a potential encounter. The best way to avoid these animals is to keep attractants, like garbage, food, animal remains, soap, propane canisters – really, anything that smells – tightly sealed and in a place where no creatures can detect them. This bit of advice alone can keep you from coming face to face with a hungry (read: potentially aggressive) bear [source: BearSmart].

If you do stumble into a polar bear, don't panic. Stop moving. Assess the situation. Is the animal curious? Is it behaving in a predatory way? Or is it stressed and defensive? If the animal doesn't know you're there or seems unconcerned with your presence, simply slowly back away.

If the bear approaches, it may be trying to figure out what sort of being you are, exactly. And that's when you should raise your arms, begin speaking in calm, low tones, all for the purpose of making it clear to the bear that you're a human and not some sort of tasty two-legged prey. If all else fails, you may have to deploy bear spray to halt a bear attack. This potent spray is statistically proven to work better than firearms in many cases [source: Outside].

Still, attacks are extremely rare, and they're always by a bear that's either starving or provoked [source: Polar Bears International]. The town that hosts the most polar bears in the world, Churchill, Manitoba, has had two people killed by polar bears in 300 years [source: Polar Bears International]. The first attack took place after several teenagers came upon a bear and started throwing rocks at it. The second attack was on a man who had meat in his pockets and happened to come upon a hungry bear.

Throughout the animal's range – (including Canada, U.S., Russia, Norway, Russia and Greenland), researchers documented just 73 attacks by non-captive polar bears from 1870 to 2014. Of those attacks, 20 proved fatal [source: USGS]. Fatal encounters in North America are much more likely to involve black or brown bears, which are more numerous and have a much wider range, and thus, are more likely to encounter humans [source: KTUU].

Although the thought of a polar bear attack is scary, wildlife advocates are far more fearful about the potential impacts of climate change on this species' ecosystem. Global warming is causing distinct changes to the bear's habitat.

Namely, warming temperatures are melting Arctic sea ice, at rate of roughly 4 percent per decade [source: Carbon Brief]. Less sea ice means fewer hunting grounds for bears, which rely almost entirely on their seal stalking abilities to survive, sitting for hours on a piece of ice waiting for a seal to appear. Warmer conditions mean the ice forms later in winter and melting earlier in spring, so bears experience dwindling access to their primary food source. Some are forced to roam farther to find food, a startling development for animals that already spend about half of their waking hours hunting.

The extra energy they expend searching for sustenance sometimes takes a serious toll on bear nutrition and health. Scientists have documented bears losing significant body mass during these long hunting expeditions. In some cases, bears starve to death because they're simply unable to catch any seals [source: National Geographic].

But the news may not be all bad. "Although most of the world's 19 populations have returned to healthy numbers, there are differences between them," the World Wildlife Fund said in 2019. It noted that four populations were in decline due to climate-related stress, two were increasing, five were stable and eight had missing or outdated information.

In 2008, the U.S. listed polar bears as a threatened species under the Endangered Species Act [source: WWF]. In Canada, officials are still convinced that populations are stable and have opted to keep polar bears listed as a species of special concern, rather than escalating its status to threatened.

"In this community of scientists, it’s been known for some time that the international polar bear campaigns and their implicit story of the threat that the bear will go extinct are problematic," wrote Arctic Today in 2018. "The scientific guardians of the 19 populations of polar bear in the Arctic are connected through the Polar Bear Specialist Group under the UN’s International Union for Conservation of Nature, IUCN, and they never said that the polar bear will go extinct."

But even if the polar bear is not going extinct, that doesn't mean that polar bears are completely safe. It means that the story needs to be told differently, emphasizing the areas where polar bears are vulnerable as well as the stressing the climate change damage to the Arctic Circle in general and addressing the concerns of the people who live in that region as well.