POLAR BEARS: CHARACTERISTICS, BEHAVIOR AND REPRODUCTION

POLAR BEARS

polar bear in Alaska

Polar bears (Ursus maritimus) are the world's largest land carnivores. They are larger than tigers, lions and other species of bears. They are also the most carnivorous of all bears, primarily eating seals. Other bears feed primarily on berries, acorns and other plant foods. Polar bears inhabit sea ice and coastal waters in the circumpolar regions of the Arctic. They have been seen all over the Arctic, even near the North Pole itself, but mostly the stay close to areas were there are ice flows from which the bears hunt seals.

Polar bear have white- or yellowish fur with black skin and a thick layer of fat. They are more slender than brown bears, with a narrower skull, longer neck and lower shoulder hump. Their teeth are sharper and more adapted to cutting meat. The paws are large and allow the bear to walk on ice and paddle in the water. Polar bears are both terrestrial and pagophilic (ice-living) but are considered marine mammals because of their dependence on marine ecosystems. They are mostly carnivorous and specialized for preying on seals, particularly ringed seals, typically taken by ambush; they bear may stalk prey on the ice or in the water, but prefer to stake out a a breathing hole or ice edge to wait for prey to swim by. These bears primarily feeds on the seal's energy-rich blubber; and sometimes ignore the meat. Polar bears are usually solitary but can be found in groups when on land. During the breeding season, male bears guard females and defend them from rivals. Mothers give birth to cubs in maternity dens during the winter. Young stay with their mother for up to two and a half years. . [Source: Wikipedia]

There are 22,000 to 31,000 polar bears in 19 populations across the Arctic in Canada, Greenland, Alaska, Norway and Russia. They are listed by the International Union for Conservation of Nature (IUCN) as “vulnerable”. In the wild polar bears are estimated to live 25 to 30 years with an average of around 20 years. The age of a polar bear is determined by its teeth. The tooth as cut and the annual rings are counted like the rings of a tree. Annual adult mortality is estimated to be eight to 16 percent. In captivity the oldest recorded lifespan was a female that died at the Detroit Zoo in 1991 at 43 years and 10 months old.

Book: “Lord of the Arctic: A Journey Among the Polar Bears” by Richard C. Davids (Macmillan).

Polar Bear History and Evolution

Polar bears are a relatively new species. It was long thought that they were descendants of brown bears that wandered north and caught seals during ice ages between 500,000 and 200,000 years ago and likely began by scavenging seal carcasses and later learned to hunt them seals by waiting by their breathing holes and attacking them when they surfaced for air. A 2010 study estimated that the polar bear lineage split from other brown bears around 150,000 years ago. DNA studies have show that some brown bears are more closely related to polar bears than they are to other brown bears, particularly the ABC Islands bears of Southeast Alaska. By 125,000 years ago polar bears had evolved into a separate species with a longer snout and smaller. More -jagged teeth better suited for ripping seals to shreds.

polar bear range

Fossils of polar bears are rare. The oldest known fossil is a 130,000- to 110,000-year-old jaw bone, found on Prince Charles Foreland, Norway, in 2004. Mitochondrial DNA studies in the 1990s and 2000s supported the status of the polar bear as a derivative of the brown bear. The fact that polar bears are more genetically close to certain brown bear populations than are some brown bear populations are to other brown bear populations suggests that polar bears have evolved fairly recently from a brown bear ancestor and that brown bear genetic structure is more complicated than previously thought. [Source: Aren Gunderson, Animal Diversity Web (ADW) |=|]

More wide-ranging genetic studies have refuted the idea that polar bears are directly descended from brown bears and found that the two species are separate sister lineages and that genetic similarities between polar bears and some brown bears are the result of interbreeding. A 2012 study estimated the split between polar and brown bears as occurring around 600,000 years ago. A 2022 study estimated the divergence as occurring over one million years ago. Glaciation events over hundreds of thousands of years led to both the origin of polar bears and their subsequent interactions and hybridizations with brown bears. [Source: Wikipedia]

Studies in 2011 and 2012 concluded that gene flow went from brown bears to polar bears during hybridization. In particular, a 2011 study concluded that living polar bear populations derived their maternal lines from now-extinct Irish brown bears. Later studies have clarified that gene flow went from polar to brown bears rather than the reverse. Up to nine percent of the genome of ABC bears was transferred from polar bears, while Irish bears had up to 21.5 percent polar bear origin. Mass hybridization between the two species appears to have stopped around 200,000 years ago.

Polar Bear Habitat and Range

Polar bears are native to Arctic regions and the Arctic Ocean. They are holarctic and have a circumpolar distribution (live more or less in a circle around the Arctic). They range throughout the Arctic region surrounding the North Pole. The limits of their range are determined by the ice pack of the Arctic Ocean and the landfast ice (sea ice that remains attached to the coastline) of surrounding coastal areas. Bears have been reported as far south as the southern tips of Greenland and Iceland. [Source: Aren Gunderson, Animal Diversity Web (ADW) |=|]

During the winter, polar bears range along the southern edge of the ice pack or northern edge of ice formed off the coasts of the continents. Pregnant females overwinter on the coastlines where denning habitat is available for young. During the summer, bears remain at the edge of the receding ice pack or on islands and coastal regions that retain landfast ice. Six major populations are recognized based on their geographical location: 1) Wrangel Island, Russia and western Alaska, 2) northern Alaska, 3) the Canadian Arctic archipelago, 4) Greenland, 5) Svalbard-Franz Josef Land in Russia, and 6) Central Siberia.

18 or 19 polar bear populations: East Greenland (ES), Barents Sea (BS), Kara Sea (KS), Laptev Sea (LVS), Chukchi Sea (CS), northern and southern Beaufort Sea (SBS and NBS), Viscount Melville (VM), M'Clintock Channel (MC), Gulf of Boothia (GB), Lancaster Sound (LS), Norwegian Bay (NB), Kane Basin (KB), Baffin Bay (BB), Davis Strait (DS), Foxe Basin (FB) and the western and southern Hudson Bay (WHB and SHB) populations; Bears in and around the Queen Elizabeth Islands proposed as a subpopulation but this is not universally accepted

Polar bears live in polar land and saltwater- marine habitats in tundra and icecap areas. They are typically found at sea level or low elevations, A few denning areas are located on the sides of hills. Polar bears are considered by some to be marine mammals. Their scientists name “Ursus maritimus” means maritime bear. Their preferred habitat is the pack ice, particularly the ice edge and pressure ridges where fractures and refreezing occur and provide the best hunting ground as prey animals such as seals often have breathing holes there. Bears travel as much as 1,000 kilometers (630 miles) north and south, as the ice melts and freezes. During the summer bears often reside on islands or coastlines with landfast ice or drift on ice flows. If they get stranded on land they be forced to endure warm weather and be away from their preferred prey. They can loose a lot of weight in such situations.

Spitsbergen in Norway’s Svalbard islands is far inside the Arctic circle more than 2,000 kilometers north of Norway’s capital Oslo. Ten per cent of the world’s polar bear population is here. As a 15-year-old midshipman, British naval hero Horatio Nelson fought off a polar bear on Spitsbergen after his musket misfired. The Barents Sea region has a population of several thousand bears, around half of which use Svalbard islands for their dens to raise cubs. The animals are concentrated in the icier east and the north of the archipelago. The Norwegian Polar Institute says that some bears based in Svalbard follow the sea ice as it retreats north during the summer melting period to continue hunting, while others will remain on land waiting several months for the ice to return. While the seals are their main source of prey, they are opportunistic hunters who will scavenge from whale carcasses, feed on nesting seabirds and their eggs, and even kill reindeer. Svalbard is one of several places in the Arctic where tourists are given the opportunity to take trips to see polar bears.[Source: Neil Syson, The Sun, August 7, 2011]

Wrangel island is the world’s largest denning ground for polar bears—as many as 400 mothers have been known to land here in winter to raise their young. With climate change making the ice pack much less reliable, polar bears have often sought summertime refuge on the island in recent years as well. Wrangel also supports the largest population of Pacific walruses, and the only snow goose nesting colony in Asia. It is home to snowy owls, muskoxen, arctic foxes, and reindeer as well as massive populations of lemmings and seabirds. And yet, in merciful contrast to the boggy Siberian mainland, there are no mosquitoes. [Source: Hampton Sides, National Geographic, May 2013]

Polar Bear Characteristics

polar bear skeleton

Polar bears range in weight from 150 to 800 kilograms (330 to 1762 pounds) and range in length from 1.8 to 2.5 meters (5.9 to 8.2 feet) and stand up 1.6 meters (5.2 feet) at the shoulder. Sexual Dimorphism (differences between males and females) is present: Female polar bears usually weigh half as much as males. Males reach lengths of 2.5 meters and weigh between 350 and 650 kilograms (880 and 1,300 pounds). Females reach lengths of two meters (6.6 feet) and weigh between 175 and 300 kilograms. A large polar bear standing on its hind legs with its front paws over its head is a high as an African elephant. The next largest terrestrial carnivore after the polar bear is the Kodiak bear. Great White Sharks are about the same size as polar bears. Killer whales and sperm whales—the world’s largest carnivores—are much larger.

The body of a polar bear is large and stocky, similar to that of a brown bear, except it lacks the shoulder hump. Compared to other bears, polar bears have long necks, relatively small heads and a sloping profile. The head of an average-size, 375-kilograms male is half a meter (16 inches) long and a 25 centimeters wide.

Polar hair is clear not white. The scattering of light makes it appear white. On the snow polar bears are white on white. Often the only thing that gives them away is their black nose. The fur can be yellowish in the summer due to oxidation or may even appear brown or gray, depending on the season and light conditions. Some zoo polar bears become green after algae grows in their hollow hair.

Polar Bear Adaptions for Cold, Ice and Water

To retain heat polar bears have dense clear fur that scatters light. Their skin is black which absorbs the sun's rays. Their long snout warms air before it passes to their lungs. To stay warm polar bears even have fur on their feet, which also helps give them traction while walking on ice and snow. Their liver is so high in Vitamin A it is toxic to humans. Females have four functional mammae. Aren Gunderson, Animal Diversity Web (ADW) |=|]

Polar bear spend most of their time at sea, either in the water or on ice flows. They have been recorded swimming for more than a week straight and covering over 650 kilometers (400 miles). Despite the fact that polar bears have been recorded swimming 100 miles at a stretch in the open sea, they are generally slow and vulnerable in the water. Polar bears have a plantigrade gait (walking on the soles of the feet, like a human or a bear). They have been clocked running at 35mph.

ringed seal

Like almost all mammals polar bears are endothermic (use their metabolism to generate heat and regulate body temperature independent of the temperatures around them), heterothermic (having a body temperature that fluctuates with the surrounding environment) and homoiothermic (warm-blooded, having a constant body temperature, usually higher than the temperature of their surroundings). |=|

The paws of polar bears are about 20 centimeters (8.5 inches) wide. Their huge paws act like snow shoes on the ice and snow and serve as flippers when they are swimming and as clubs when hunting seals. On the bottom of heir feet are papillae: small bumps that give them traction on ice. Polar bears roam over wide areas and can swim long distances. The bears rely on the marine sea ice environment for their survival, using the ice for hunting and breeding. They can keep their eyes open and close their nostrils under water and stay submerged for two minutes.

Polar Bear Prey

Polar bear are the most carnivorous of all bears, primarily eating seals, although in some regions their diet includes kelp, grasses, berries, leaves, carrion, fish eggs, sea birds, small mammals and garbage from nearby settlements. For some unknown reason some polar bears like to feed on antifreeze. Unlike brown bears that bury their uneaten carcasses to be eaten later, polar bears leave partly eaten carcasses in the ice that are scavenged by foxes, ravens and other bears.

The primary prey of polar bears is ringed seals (Pusa hispida). They also hunt bearded seals (Bearded seals), harp seals (Pagophilus groenlandicus), hooded seals (Cystophora cristata), walruses and fish. They scavenge on carrion of seals, walruses, and whales and may outright kill wahles from time to time. In the summer, they may consume some vegetation but gain little nutrition from it. Bears often leave a kill after consuming only the blubber. The high caloric value of blubber relative to meat is important to bears for maintaining an insulating fat layer and storing energy for times when food is scarce. [Source: Backpacker, magazine, Aren Gunderson, Animal Diversity Web (ADW) |=|]

Polar bears have been observed hunting two-ounce voles in the tundra grass and cocking their heads and placing their ears to the round to listen to the animal's squeaking. At the other side of the size spectrum an ecologist told National Geographic that he saw 40 or so beluga whales trapped by ice gathering around a small hole in the ice. It was eight miles to open water, too far for the whales to swim. Twenty five polar bears gathered at one hole and feasted on the whales. Some bears were twice their normal size and had eaten so much they didn’t need t eat for an entire year.

Polar Bears on the Hunt

Polar bears have two-inch claws and teeth designed to catch and hold slippery prey. Compared with omnivorous brown bears, carnivorous polar bears have more jagged cheek teeth and larger, sharper canines. .Polar bear hunt seals mostly from ice flows. They wait for coastal waters to freeze on then live a solitary life of seal hunting. The bears often ignore the meat and gorge themselves on the fat, which they need for energy. Polar bears hunt seals mainly using two methods: by stalking seals from land or underneath ice after they have emerged at breathing holes; or by waiting patiently near the seal's breathing hole and biting its head as it surfaces for air.

The favorite polar bear prey is ring seal pups that are born in the spring in little caves hollowed out of snow drifts by their mothers above their breathing holes in the sea ice. The seals are well hidden but the bears can locate the pups with their amazing sense of smell. The polar bears kill the pups with a bite to the head. The 25-kilogram pups are almost half fat.

When a bear sees a seal basking out of the water it will use a stalking technique to get close, then make an attempt at catching it. One stalking technique is crouching and staying out of sight while creeping up on the seal. Polar bears are so strong they can reach inside a hole in the ice, kill while it is in the water the seal with a single, crushing bite and then pull it out of the water using its strong neck and shoulder muscles. Sometimes polar bears break through the ice with their paws to catch seals and fish.

Another technique is to swim through any channels or cracks in the ice until it is close enough to catch the seal. Using this technique a bear may actually dive under the ice and surface through the breathing hole in order the surprise the seal and eliminate its escape route. Feeding usually occurs immediately after the kill has been dragged away from the water. Polar bears consume the skin and blubber first. After feeding, polar bears will wash themselves by licking and rinsing their fur. [Source: Aren Gunderson, Animal Diversity Web (ADW) |=|]

Polar Bear Behavior

Polar bears are terricolous (live on the ground), natatorial (equipped for swimming), diurnal (active during the daytime), motile (move around as opposed to being stationary), nomadic (move from place to place, generally within a well-defined range), engage in hibernation (the state that some animals enter during winter in which normal physiological processes are significantly reduced, thus lowering the animal’s energy requirements) and solitary. [Source: Aren Gunderson, Animal Diversity Web (ADW) |=|]

Polar bears have been observed sliding down hills, playing in snow banks, and napping with their heads in their paws. They have also been seen playing with tires and putting them around their neck. In Alaska polar bears have been observed punching out the lights on an airstrip one by one. Polar bears sometimes play with dogs, other times they kill and eat them. The same is true with humans. Polar bears have been observed grieving the dead. Males play fight in October when they gather together to wait for the ice to free up enough to begin hunting. Females carefully watch their cubs if a male approaches. When given a chance, males will eat polar bear cubs.

Aren Gunderson wrote in Animal Diversity Web: Polar bears are solitary. The exceptions to this are when a mother is caring for her cubs and when males and females are paired during mating. Bears may also come into competition with one another when a seal kill attracts other bears looking to scavenge. In instances where bears encounter each other, the smaller bear will tend to run away. A female with cubs, however, will charge males that are much larger to protect her young or a kill that they are feeding on. Polar bears are inactive most of the time (66.6 percent), either sleeping, lying, or waiting (still hunting). The rest of their time is spent traveling (walking and swimming; 29.1 percent), stalking prey (1.2 percent), or feeding (2.3 percent). Polar bears are excellent swimmers, they may range widely in search of food and sightings as far south as Maine, in the United States, have been documented.

Photographer Martin Gregus, Jr. Spent more than a months with polar bears in Manitoba, Canada and gave them names. Jason Bittel wrote in National Geographic: The more Gregus studied the bears, the more he learned of their personalities. There was the persistent cub he named Hercules. He lost a leg yet managed to survive his first two summers. An enormous female, Wanda, seemed to be feared by other bears but spent her days doing yoga-like stretches in the fireweed. Another female, Wilma, appeared to be so comfortable with Gregus that she’d nurse her cubs, Pebbles and Bamm-Bamm, close enough for him to hear their purring. Athena liked to lounge with her three-legged cub, Hercules, whod had already survived two dummers. Gregus can’t say for sure how the limb was lost, but he suspects an encounter with wolves may be the cause. The bears’ den is in wolf territory. Gregus also witnessed behaviors he’d rarely seen before, such as bears grazing on plants and hunting tern chicks by chasing them into the surf. [Source: Jason Bittel, National Geographic, August 9, 2022]

Polar bears sense and communicate with touch, sound and chemicals usually detected by smelling. Polar bears have a keen sense of smell that can pick up particles per million several kilometers away. Like other bear species, polar bears and use their sensitive lips and whiskers to explore objects. They vision and hearing are adequate but not so keen. They make a "chuffing" sound as a form of greeting.

Polar Bears in the Different Seasons

Polar bears stuff themselves with seals from April to early July, when there are ice platforms from which to hunt seals. An impregnated female may increase her body weight by 50 percent or more, building 12.5 centimeters (five inches) layers of fat around her rump and thighs. Except for nursing or pregnant females polar bears generally do not hibernate in the winter like other bears. Most of the dens that do exist are found in Russia. Females go to their dens. Scientist are not sure where the males and non-breeding females go. During rough Arctic storms, polar bears sometimes build temporary snow shelters. Some bears follow have seasonal migration routes between Norway and Russia

In the summer, polar bears sleep, wander around, try to conserve energy in what is sometimes called walking hibernation. Scientist are studying the bears unique metabolism to find treatments for obesity and bone and kidney problems. Males and nonbreeding females go out to sea after the ice freezes over. Pregnant females stay ashore. Bears need ice floes as a platform to hunt seals. During the summer, when the sea ice has melted, the bears are unable to hunt and sometimes fast the entire summer—eating almost nothing until the sea ice starts to form once again in autumn. During the summer polar bears can not tolerate long exertions. Scientist can easily track them down on foot as they don’t travel far. It is suspected that the bears have to jump in the water periodically to cool off. In the winter the bears can run and run; scientists had difficulty tracking them even with a snow mobile.

“You always see polar bears on ice and snow,” says photographer Martin Gregus, Jr., who photographed bears in Manitoba, Cananda “But it’s not like they stop living in the summertime.” In this part of the Arctic, everything’s flat, Gregus says. That means even a small boulder can provide a better view — if a bear hasn’t succumbed to sleep, that is. The bears, including Veronica often stood on this rock, scouring the area for seals to eat or bear. Beans and Aurora poke their heads above the blooming fireweed. Summer in the Arctic is vividly colorful. “All of these pictures show bears that are fat, healthy, and playful,” Gregus says. So although from a global perspective everything may be going wrong for polar bears, “obviously something’s going right here...These bears are really thriving and adapting to the environment,” Gregus says. [Source: Jason Bittel, National Geographic, August 9, 2022]

Polar Bear Mating, Reproduction and Denning

Polar bears are polygynous (males have more than one female as a mate at one time) and employ delayed implantation (a condition in which a fertilized egg reaches the uterus but delays its implantation in the uterine lining, sometimes for several months). Polar bears engage in seasonal breeding. Females breed yearly, usually from March to June. Delayed implantation extends gestation up to to 265 days from 195 days. The number of offspring ranges from one to 4, with the average number being two.

The Polar bears mating system has been described as sequentially polygynous. Male and female breeding pairs remain together for a short time during the females’s three-day estrus period. Sometimes male polar bears fight for access to mates. Describing one battle. John Eliot wrote in National Geographic, "They faced nose-to-nose, mouths open, they reared up and wrestled with their front legs wrapped around each other. They pummeled hard with their paws but did not draw blood with their claws. Finally one of them lay submissively on his back, punching the bear above with his front paws while rear legs gyrated wildly. After 15 minutes they called time-out."

Females become impregnated in the spring but because of delayed implantation the eggs don't begin to develop until the fall. Pregnant females stay ashore in the winter in dens they have dug in the earth during the summer and autumn. The denning areas often cover more than a thousand square miles and are riddled with dens that bears have used for centuries. The dens are oriented towards the south and east away from the prevailing winds. Pregnant females establish a winter den on land dug into the snow usually within eight kilometers of the coast in October or November.

The cubs are born in the mother's den between November and January. She remains in hibernation nursing her cubs until April. While they are in their dens the heart rate of the female bears drops from 60 beats a minute to 30 beats minute. Females often fast for eight months of the year, six of them in her den in the winter and two in the summer when there is no ice to hunt seals. After a mother gives birth and nurses her young she might lose up to 45 percent of her body weight.

Polar Bear Cubs and Mothers

Polar bear young are altricial, meaning they are relatively underdeveloped at birth. Cubs are born with their eyes closed; they have a good coat of fur and weigh about 0.6 kilograms. Parental care is provided exclusively by female. There is an extended period of juvenile learning. The age in which young are weaned ranges from 24 to 36 months. On average males and females reach sexual or reproductive maturity three to six years.[Source: Aren Gunderson, Animal Diversity Web (ADW) |=|]

A healthy female delivers about five litters in her lifetime. Polar bear cubs are born around New Year's Day. Their fine hair is almost invisible. They open their eyes after around 10 days (compared to 40 days for black bears). The cubs stay in their den with their mother until April when the cubs emerge from the den weighing 10 to 15 kilograms. (22 to 33 pounds) and the mother begins hunting seals. The dens are often relatively far inland, a few days walk from the sea.

Polar bear milk is richer than the milk of other bears. It is about 30 percent fat. One scientist tried a bit of polar bear milk said, "Not bad. It tastes like nuts. But its very rich." Cubs need their mothers for warmth and food. If anything happens to their mother, cubs usually die within a few days from exposure, starvation or are eaten by other bears. When threatened mother polar bears leap into the water and their cubs cling to their fur and tail and are pulled to safety.

When mother polar bears emerge from their dens they have fasted and eight months and her hungry cubs may be three months old. Most females keep their young with them for two and a half years. Some wean their cubs a year earlier so they can breed every two years instead of the normal three years. Frequent wrestling matches help polar bear cubs develop hunting and fighting skills.The mortality rate for cubs is estimated to be 10-30 percent.

Nomadic and largely solitary males play no role in childrearing. They can be dangerous and females with cubs usually go out of their way to avoid them. If there are three cubs, the strongest and most persistent one often feeds at the expense of the others. Mothers tend to ignore the rivalry for food. Runts very rarely survive more than a few months. When it is time for young bears to become independent either the mother herself or an adult male chases the offspring away.

Pizzly Bears and Grolars

When a polar bear (Ursus maritimus) and a grizzly bear (Brown bears horribilis) mate, they can create hybrids called "pizzly" or "grolar" bears. According to Live Science: Although rare in nature, these pizzly bear hybrids are starting to spread across the Arctic due to climate change. Starving polar bears are heading farther south to find more food, while the warming world is allowing adaptable grizzlies to expand northward. This movement is leading to more interactions between the two species and more mating. [Source: Patrick Pester, Live Science, October 25, 2023]

In 2006, Roger Kuptana, an Inuit tracker from the Northwest Territories, Canada guided an American hunter who shot a pizzly == the first documented case of a grizzly-polar hybrid in the wild. Associated Press reported: Territorial officials seized the bear’s body and a DNA test from Wildlife Genetics International, a lab in British Columbia, confirmed the hybrid was born of a polar bear mother and grizzly father. “It’s something we’ve all known was theoretically possible because their habitats overlap a little bit and their breeding seasons overlap a little bit,” said Ian Stirling, a biologist with the Canadian Wildlife Service in Edmonton, Alberta. “It’s the first time it’s known to have happened in the wild.” He said the first person to realize something was different about the bear — shot and killed last month on the southern end of Banks Island in the Beaufort Sea — was Kuptana. “These guides know their animals and they recognized that there were a number of things that didn’t look quite right for a polar bear,” Stirling told The Associated Press. The bear’s eyes were ringed with black, its face was slightly indented, it had a mild hump to its back and long claws. Stirling said polar bears and grizzlies have been successfully paired in zoos and that their offspring are fertile, but there had been no documented case in the wild. [Source: Beth Duff-Brown, Associated Press, May 12, 2006]

Adam Popescu wrote in Washington Post: Textbooks say these two species aren’t supposed to inhabit the same environments. Polar bears are marine mammals; grizzlies are terrestrial. But as the Arctic warms, sea ice is shrinking and the tundra is expanding. And the bears’ disparate populations are meeting, mating and creating a new breed that’s capable of reproducing. Bears sharing both species’ DNA have been recorded several times over the past decade. So why are these two species linking up? It’s called flexible mate choice: The bears are mating with the best possible partners as opposed to not mating at all, and they’re mating because they share relatively close territories and the same branches of the same evolutionary tree. [Source: Adam Popescu, Washington Post, May 23, 2016]

Image Sources: Wikimedia Commons

Text Sources: Animal Diversity Web animaldiversity.org ; National Geographic, Live Science, Natural History magazine, David Attenborough books, New York Times, Washington Post, Los Angeles Times, Smithsonian magazine, Discover magazine, The New Yorker, Time, BBC, CNN, Reuters, Associated Press, AFP, Lonely Planet Guides, Wikipedia, The Guardian, Top Secret Animal Attack Files website and various books and other publications.

Last updated June 2025