My Polar Bear Family And Me

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Clinio Lofton

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Aug 3, 2024, 11:00:56 AM8/3/24

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Polar bears are both terrestrial and pagophilic (ice-living) and are considered to be marine mammals due to their dependence on marine ecosystems. They prefer the annual sea ice but live on land when the ice melts in the summer. They are mostly carnivorous and specialized for preying on seals, particularly ringed seals. Such prey is typically taken by ambush; the bear may stalk its prey on the ice or in the water, but also will stay at a breathing hole or ice edge to wait for prey to swim by. The bear primarily feeds on the seal's energy-rich blubber. Other prey include walruses, beluga whales and some terrestrial animals. 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.

The polar bear is considered to be a vulnerable species by the International Union for Conservation of Nature (IUCN) with an estimated total population of 22,000 to 31,000 individuals. Its biggest threats are climate change, pollution and energy development. Climate change has caused a decline in sea ice, giving the polar bear less access to its favoured prey and increasing the risk of malnutrition and starvation. Less sea ice also means that the bears must spend more time on land, increasing conflicts with people. Polar bears have been hunted, both by native and non-native peoples, for their coats, meat and other items. They have been kept in captivity in zoos and circuses and are prevalent in art, folklore, religion and modern culture.

Carl Linnaeus classified the polar bear as a type of brown bear (Ursus arctos), labelling it as Ursus maritimus albus-major, articus in the 1758 edition of his work Systema Naturae.[8] Constantine John Phipps formally described the polar bear as a distinct species, Ursus maritimus in 1774, following his 1773 voyage towards the North Pole.[4][9] Due to its adaptations to a marine environment, some taxonomists like Theodore Knottnerus-Meyer have placed the polar bear in its genus Thalarctos.[10][11] However Ursus is widely considered to be the valid genus for the species based on the fossil record and the fact that it can breed with the brown bear.[11][12]

Different subspecies have been proposed including Ursus maritimus maritimus and U. m. marinus.[a][13] However these are not supported and the polar bear is considered to be monotypic.[14] One possible fossil subspecies, U. m. tyrannus, was posited in 1964 by Bjrn Kurtn, who reconstructed the subspecies from a single fragment of an ulna which was approximately 20 percent larger than expected for a polar bear.[12] However, re-evaluation in the 21st century has indicated that the fragment likely comes from a giant brown bear.[15][16]

Fossils of polar bears are uncommon.[12][15] The oldest known fossil is a 130,000- to 110,000-year-old jaw bone, found on Prince Charles Foreland, Norway, in 2004.[20][1] Scientists in the 20th century surmised that polar bears directly descended from a population of brown bears, possibly in eastern Siberia or Alaska.[12][15] Mitochondrial DNA studies in the 1990s and 2000s supported the status of the polar bear as a derivative of the brown bear, finding that some brown bear populations were more closely related to polar bears than to other brown bears, particularly the ABC Islands bears of Southeast Alaska.[20][21][22] A 2010 study estimated that the polar bear lineage split from other brown bears around 150,000 years ago.[20]

More extensive 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. The genetic similarities between polar bears and some brown bears were found to be the result of interbreeding.[23][24] A 2012 study estimated the split between polar and brown bears as occurring around 600,000 years ago.[23] A 2022 study estimated the divergence as occurring even earlier at over one million years ago.[24] 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.[25]

Studies in 2011 and 2012 concluded that gene flow went from brown bears to polar bears during hybridization.[23][26] In particular, a 2011 study concluded that living polar bear populations derived their maternal lines from now-extinct Irish brown bears.[26] Later studies have clarified that gene flow went from polar to brown bears rather than the reverse.[25][27][28] Up to 9 percent of the genome of ABC bears was transferred from polar bears,[29] while Irish bears had up to 21.5 percent polar bear origin.[27] Mass hybridization between the two species appears to have stopped around 200,000 years ago. Modern hybrids are relatively rare in the wild.[24]

Analysis of the number of variations of gene copies in polar bears compared with brown bears and American black bears shows distinct adaptions. Polar bears have a less diverse array of olfactory receptor genes, a result of there being fewer odours in their Arctic habitat. With its carnivorous, high-fat diet the species has fewer copies of the gene involved in making amylase, an enzyme that breaks down starch, and more selection for genes for fatty acid breakdown and a more efficient circulatory system. The polar bear's thicker coat is the result of more copies of genes involved in keratin-creating proteins.[30]

Polar bears inhabit the Arctic and adjacent areas. Their range includes Greenland, Canada, Alaska, Russia and the Svalbard Archipelago of Norway.[10][57][58] Polar bears have been recorded as close as 25 km (16 mi) from the North Pole.[59] The southern limits of their range include James Bay and Newfoundland and Labrador in Canada and St. Matthew Island and the Pribilof Islands of Alaska.[10] They are not permanent residents of Iceland but have been recorded visiting there if they can reach it via sea ice.[60] Due to minimal human encroachment on the bears' remote habitat, they can still be found in much of their original range, more so than any other large land carnivore.[61]

Polar bears have been divided into at least 18 subpopulations labelled 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.[62][56] Bears in and around the Queen Elizabeth Islands have been proposed as a subpopulation but this is not universally accepted.[56] A 2022 study has suggested that the bears in southeast Greenland should be considered a different subpopulation based on their geographic isolation and genetics.[63] Polar bear populations can also be divided into four gene clusters: Southern Canadian, Canadian Archipelago, Western Basin (northwestern Canada west to the Russian Far East) and Eastern Basin (Greenland east to Siberia).[62]

Polar bears may travel areas as small as 3,500 km2 (1,400 sq mi) to as large as 38,000 km2 (15,000 sq mi) in a year, while drifting ice allows them to move further.[72] Depending on ice conditions, a bear can travel an average of 12 km (7.5 mi) per day.[73] These movements are powered by their energy-rich diet.[48] Polar bears move by walking and galloping and do not trot.[74] Walking bears tilt their front paws towards each other.[41] They can run at estimated speeds of up to 40 km/h (25 mph)[75] but typically move at around 5.5 km/h (3.4 mph).[76] Polar bears are also capable swimmers and can swim at up to 6 km/h (3.7 mph).[77] One study found they can swim for an average of 3.4 days at a time and travel an average of 154.2 km (95.8 mi).[78] They can dive for as long as three minutes.[79] When swimming, the broad front paws do the paddling, while the hind legs play a role in steering and diving.[10][41]

Most polar bears are active year-round. Hibernation occurs only among pregnant females.[80] Non-hibernating bears typically have a normal 24-hour cycle even during days of all darkness or all sunlight, though cycles less than a day are more common during the former.[81] The species is generally diurnal, being most active early in the day.[82] Polar bears sleep close to eight hours a day on average.[83] They will sleep in various positions, including curled up, sitting up, lying on one side, on the back with limbs spread, or on the belly with the rump elevated.[42][76] On sea ice, polar bears snooze at pressure ridges where they dig on the sheltered side and lie down. After a snowstorm, a bear may rest under the snow for hours or days. On land, the bears may dig a resting spot on gravel or sand beaches.[84] They will also sleep on rocky outcrops.[85] In mountainous areas on the coast, mothers and subadults will sleep on slopes where they can better spot another bear coming.[83] Adult males are less at risk from other bears and can sleep nearly anywhere.[85]

Polar bears are generally quiet but can produce various sounds.[90] Chuffing, a soft pulsing call, is made by mother bears presumably to keep in contact with their young.[91] During the breeding season, adult males will chuff at potential mates.[92] Unlike other animals where chuffing is passed through the nostrils, in polar bears it is emitted through a partially open mouth.[91] Cubs will cry for attention and produce humming noises while nursing.[93] Teeth chops, jaw pops, blows, huffs, moans, growls and roars are heard in more hostile encounters.[92] A polar bear visually communicates with its eyes, ears, nose and lips.[89] Chemical communication can also be important: bears secrete their scent from their foot pads into their tracks, allowing individuals to keep track of one another.[94]