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BEHAVIOUR  - Editorial Comment

Editorial Comment

(Editorial Overview Text Replicated on Overall Species page - Ursus maritimus - Polar bear)
  • Polar bears hunt their main prey, seals, mostly by still-hunting, waiting near a breathing hole, usually while lying down, for up to an hour (but for shorter times if sitting or standing). They also stalk seals, crawling slowly until about 15 - 30 m (50 -100 ft) from a basking seal, then making a final rush. Very rarely, seals are hunted while swimming. 
  • Once a seal is killed, the bear will eat the blubber first, starting in the middle of the seal.
  • Washing is considered to be an integral part of feeding behaviour; bears will alternately rinse and lick their paws and face at a pool of water.
  • A bear does not always eat all of its kill; for inexperienced, recently-independent bears, scavenging on kills of older bears is probably important.
  • In summer, in areas where seals are not available, polar bears hunt seabirds such as waterfowl, catching flightless Branta canadensis - Canada geese on land and coming up under birds sitting on the water. They have been found predating various nesting sea birds, eating eggs, chicks and adults.
  • Polar bears also hunt small mammals and some will hunt large ungulates such as Rangifer tarandus - Reindeer and even Ovibos moschatus - Musk ox.
  • When females and their cubs emerge from the maternity den, the female may dig for grasses, sedges and moss near the den in the first weeks while the family remains near the den.
  • Polar bears are attracted to carcasses and congregate at large whale carcasses.
  • Polar bears will scavenge in human rubbish dumps and field camps.

Further information on diet is provided in Polar bear Ursus maritimus - Natural Diet (Literature Reports)

(References are available in detailed literature reports below)

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Feeding Behaviour

Source Information

  • Most of the annual intake of food is eaten late April to mid-July; during this time there is an abundant source of newly-weaned ringed seal pups, which are 50% fat (by wet weight). (B285.w4)
  • Polar bears hunt Phoca hispida (Phoca - (Genus)) - ringed seal, Erignathus barbatus - Bearded seal, Pagophilus groenlandicus - Harp seal and Cystophora cristata - Hooded seal, and possibly walrus (Odobenus rosmarus). (D244)
    • In spring, about half of the Phoca hispida (Phoca - (Genus)) - ringed seals hunted by polar bears are newborn pups. (D244)
    • Polar bears hunt by still-hunting (77%) and by stalking prey (23%). In winter and early spring, nearly all hunting is still-hunting. Stalking involves crawling on the ice or swimming in leads of water. (D244)
    • In spring, post-parturient female seals and weaned pups appear to be preferred prey. (D244)
    • More of the kill is eaten by a family than by an individual bear. (D244)
    • In summer, following feeding, bears generally washed for about 30 minutes. (D244)
  • For inexperienced, recently-independent bears, scavenging on kills of older bears is probably important. (B406.37.w37)
  • Polar bears scavenging on kills may eat the blubber and the meat. Such food is probably important to subadults which are not yet proficient at hunting, and to those which have had their own kills taken away from them. (J30.53.w3)
  • Unlike Ursus arctos - Brown bear, polar bears generally do not either cache kill or remain with it until it is completely eaten. (J30.53.w3)
    • However, caching of seal carcasses has been observed. (J332.63.w1)
  • Satellite telemetry of female polar bears in the Canadian Arctic has shown that they are most active in the period May to July, when naive seal pups, vulnerable to predation, are most abundant. "Hyperphagia and the large accumulation of body reserves in May-July seems to be crucial to polar bears." (J46.226.w1)
  • Possible tool use - smashing through a seal breathing hole using a block of ice - to assist feeding, has been reported. (B406.37.w37)
  • Polar bears prey mainly on ringed seals Phoca hispida (Phoca - (Genus)) with bearded seals Erignathus barbatus the second most important species of prey. However, they also kill much larger species, including walrus (Odobenus rosmarus) and belugas (Delphinapterus leucas). They are very effective predators of young ringed seals. Quickly eating the blubber layer under the skin first may be important because this contains more than half the total calories of the carcass and young and small bears may be driven from their kills by larger bears. They do not tend to cache their prey. They sometimes show surplus killing - killing more prey than they eat. On land for long periods they will forage on coastal marine and terrestrial plants. They also scavenge at human refuse. In Svalbard, some individuals are good at catching reindeer. Seals are predated mainly by still-hunting. (B490.27.w27)
  • Unpublished data over a 153-day period for two captive polar bears weighing about 200 kg indicated that, given a free choice, they ate about 20 % +/- 2% of their diet as meat, the rest as blubber. (J30.63.w1)
  • Observation of bears in zoos has showed that a polar bear can eat easily eat up to 10% of their own body weight within 30 minutes, and may have a stomach capacity of 15-20% of body weight. (P104.1975.w2) Further information on digestion is provided in Polar bear Ursus maritimus - Detailed Physiology Notes (Literature Reports).
Seals
  • The main food item is Phoca hispida (Phoca - (Genus)) - ringed seal. Other food items include sea birds, and carcasses of stranded marine mammals, reindeer, small land mammals, fish and vegetation. For some individual polar bears, berries are important in the summer and autumn. (B147)
  • Polar bears hunt seals by remaining motionless until a seal emerges from the water, or by stalking the seal on the ice. They also may dig out dens of seals to get the pups. (B147)
  • Polar bears catch Erignathus barbatus - Bearded seal as they surface to breath. Polar bears can detect a seal breathing hole under more than a metre of compacted snow, from nearly one kilometer distance, by smell. (B285.w4)
  • Polar bears stalk their prey; they may swim underwater to reach prey on ice floes. (B180.w4)
  • Polar bears hunt seals at winter breathing holes, in subnivean breeding lairs, and on spring ice where seals haul out. They break through a breathing hole birthing lair and kill by the swipe of a paw or by biting. They also swim under the ice, up to a breathing hole, then catch the seal when it dives. Rarely, polar bears kill seals in open water. (B406.37.w37)
    • A bear engaging in still-hunting of seals will lie on its stomach (90%), sit, or stand near a seal breathing hole, for a mean time of one hour if prone, but only much shorter times if standing or sitting. Adult males will hold position longer than will females with cubs; cubs may interrupt the female, ending the hunt. (B406.37.w37)
    • About 23% of seal hunts involve stalking, with the bear crawling slowly until about 15 - 30 m (50 -100 ft) from a basking seal, then making a final rush. (B406.37.w37)
    • Once the seal is killed the bear may start to eat, or drag it up to 2-3 km inland before feeding. Feeding immediately may be most important for smaller bears to minimise the risk of losing the kill to larger bears. (B406.37.w37)
    • The bear usually skins the carcass to make the blubber accessible, and starts feeding in the centre of the carcass, often eating only the blubber. (B406.37.w37)
    • Washing is considered to be an integral part of feeding behaviour; bears will alternately rinse and lick their paws and face at a pool of water. (B406.37.w37)
  • Where ice permits, polar bears will feed on seals all year. (B406.37.w37)
  • In one study, stalking of basking seals made up 22.65 of hunts (65 of 288 hunts observed). Two methods were used to approach the seal: either lowering the head and creeping in a semi-crouched posture, using any available surface irregularities for cover, or slipping into the water and approaching using channels and polls. the final dash and catch attempt took place from a distance of approximately 15 to 30 metres. In this study, none of 38 "walking stalks" were successful, but in 27 "water stalks" of nine bears, one kill and several near-misses were seen. Another form of aquatic hunting involved the bear going under the ice between breathing holes, surfacing to breath then going under the ice again, finally reaching the seal's own breathing hole, with the apparent aim of surprising the seal by coming up through its breathing hole. (J30.52.w3)
  • Hunting success may be affected by ice conditions; for example, still hunts are more likely to be successful when there are a limited number of holes available for seals to use to surface and breath, rather than when there are many such holes. (J30.52.w3)
  • Once a seal is captured, it is taken away from the water's edge up onto the ice and bitten several times on the back of the upper neck and head, then the bear starts feeding. (J30.52.w3)
    • Occasionally a bear will carry a seal carcass some distance (2-3 km has been observed) before feeding. (J30.52.w3)
    • A 2.5-year-old was seen running around with its catch and periodically shaking or biting it, until the cub's mother noticed, came over, and both fed. (J30.52.w3)
    • While feeding, the bear places one or both forepaws on the carcase, bits into the body and tears it up, starting at about the middle of the body, eating the skin and blubber first. The meat is eaten later. (J30.52.w3)
    • Occasionally a bear will try to cover up the remains of a carcass. (J30.52.w3)
    • Sometimes feeding is interrupted by another bear. (J30.52.w3)
    • If two or more bears feed on one carcass, then after the skin and fat have been eaten it becomes split into two or more pieces. (J30.52.w3)
    • Large pieces of carcass are often left and these are scavenged by other bears. Such scavenging may be important for early-orphaned cubs and for subadults which have left their mother but are not yet proficient hunters. (J30.52.w3)
    • As an integral part of feeding behaviour, polar bears wash their paws and face. (J30.52.w3) See: Polar bear Ursus maritimus - Activity Patterns, Grooming and Navigation Behaviour (Literature Reports) - Self-grooming
  • In the Western Arctic, for kills March to June, nearly all ringed seals killed by bears were under two years of age. (J30.53.w3)
  • During the period late March to April, when Ringed seal pups are born in subnivean birth lairs in the lee of pressure ridges in the sea ice, polar bears hunt extensively along the pressure ridges and break into the lairs. Often, however, the newborn pups are killed in the lair and only partially eaten, or abandoned by the bear. (J30.53.w3)
  • A study of polar bear behaviour when hunting seals found that 30/42 subnivean structures dug into by bears were birth lairs. 15/45 predation attempts produced successful kills. Bears appeared to avoid digging into haul-out lairs of rutting male seals (the have a strong smell and the meat is reported to have an unpleasant taste). Two major hunting behaviours were noted: one hunting behaviour involved the bear digging up practically all the subnivian structures and then waited by a hole for a seal to come up to breath; in other hunts, the bear apparently detected an occupied lair then rushed and jumped on the lair from 50-100 m downwind to pin and kill the seal. An attack was seen in which a bear stalked two hauled-up ringed seals, charged from 80 m and caught one by the hind flippers. In another case, a bear entered the water about 400 m from a hauled-out seal and worked its way towards the seal over 32 minutes (breathing at other seal holes); the seal dove into the water when the bear reached its hole, and the bear failed to catch it. Examined kills included 23 young-of-the-year, six adolescents (one to six years of age), five adults and four of undetermined age. Two of the pups were not eaten at all and only a little fat was taken from a third. In most of the other seals the blubber had been eaten, but one was untouched and two were eaten almost entirely. Bearded seals and walruses are sometimes skinned out by polar bears. It was noted that in the High Arctic the main scavengers were other bears. (J30.58.w6)
  • Phoca hispida (Phoca - (Genus)) - ringed seals, are eaten skin and blubber together; Erignathus barbatus - Bearded seals (which have thick skin) are skinned to reach the blubber. (V.w100)
  • During a study in Radstock Bay, Northwest Territories, Canada, it was noted that two-year-old cubs conducted double the frequency of lying "still hunts" compared to yearlings, and showed a much higher kill rate - not dissimilar to that of adults. It was also noted that in spring cubs of all ages (cub-of-the-year, yearling, two-year-old) showed very little hunting behaviour; this may have been related to the need to dig or pound through 30-60 cm of hard compacted snow drifts to reach seal breathing holes and lairs at this time of the year. Cubs-of-the-year and yearlings generally stayed behind their mothers, watched her movements and imitated them, while two-year-olds ranged up to 1-2 km from the female and chose their own hunting sites. (J30.56.w5)

Birds

  • In summer, polar bears have been observed hunting and eating eggs, chicks and adults of sea birds such as glaucous gull Larus hyperboreus (Larus (Genus)), little auk (Alle alle - Dovekie), thick-billed murres, Uria lomvia (Uria (Genus)) and geese (B406.37.w37, J343.59.w2, J435.109.w1 J452.12.w1)
  • A study on North Twin Island, James Bay, in summer, found that Branta canadensis - Canada geese were one of the main foods taken, although the bears spent only 2.9-4.9% of their time feeding. Females with cubs spent the greatest time (4.9%) feeding. (J30.56.w6)
  • A summer study on islands in James Bay found that remains of sea ducks, particularly Clangula hyemalis - Long-tailed duck and Somateria sp. were found in scats too frequently to just be the result of scavenging. It was noted that polar bears have been seen stalking and killing Branta canadensis - Canada geese, which were also found in scats. It was considered probable that some bears have learned to catch ducks (probably during the moult) or the open sea. Polar bears have been observed swimming underwater and surfacing under single seabirds or flocks of seabirds on the surface. Eggs appear not to be taken commonly and polar bears have been seen walking through a nesting Anser caerulescens - Snow goose colony without the birds being disturbed, but they are taken sometimes, as indicated by their feathers found 5% of scats in this study, and a polar bear on Baffin Island was noted to have its stomach full of eider eggs when it was killed. (J343.28.w1)
  • Polar bears swim among sea birds and catch them while they sit on the water. (B147)
  • Polar bears stalk and kill Branta canadensis - Canada geese on land while they are flightless. (B406.37.w37)
  • Polar bears have been observed predating at island colonies of thick-billed murres, Uria lomvia (Uria (Genus)) in the Northwest Territories, Canada, during summer. (J435.109.w1)
  • Polar bears have been seen digging out nests in a little auk (Alle alle - Dovekie) colony and eating eggs, chicks and adults, in a colony in Frans Josef Land, during August. (J452.12.w1)
  • A polar bear was observed unsuccessfully chasing adult Branta leucopsis - Barnacle goose) during their flightless period (moult) and then plundering the nest of a glaucous gull Larus hyperboreus (Larus (Genus)), taking three nestlings. (J343.59.w2)
  • Some polar bears have learned to dive then come up underneath birds while they are on the water; this may be most successful in stormy weather when the sea is "roiled and murky". (B406.37.w37)

Whales, walrus etc.

  • Polar bears opportunistically prey on walrus, beluga Delphinapterus leucas, narwhal Monodon monoceros, waterfowl and seabirds. (B285.w4)
  • Polar bears have been reported to attack Delphinapterus leucas - Beluga whale occasionally. (D244)
  • Eight polar bears were seen feeding on stranded belugas (Delphinapterus leucas) and narwhal (Monodon monoceros). A large (presumed male) bear was seen preying on beluga calves successfully by leaping off a floating ice pan; a female and cub were seen scavenging the remains of the beluga calf carcasses. (J343.43.w1)
  • During studies near Point Barrow, Alaska, USA, two occurrences were seen of polar bears feeding on belugas, Delphinapterus leucas. On one occasion an adult male bear was seen eating a beluga carcass on sea ice. On another occasion two bears were seen at the site of a beluga carcass. Signs such as bloody tracks on the ice, and the fact that beluga carcasses generally sink, indicated the whales were probably killed by the bears. Another study had shown that bears eat the blubber and muscle of belugas. (J435.107.w5)
  • Polar bears will scavenge carcasses of whales, walrus Odobenus rosmarus and seals. (D244)
    • Since prey often is not fully eaten by the bear which caught it, scavenging may be important. (D244)
  • Particularly in summer, polar bears are attracted to carcasses and large numbers (up to 40) have been found at a single whale carcass. (B406.37.w37)
  • In the central Canadian High Arctic, where walrus movements are severely restricted in the winter due to only limited areas of open water for breathing and haulout holes, both successful and unsuccessful attacks by polar bears on walrus were observed. (J345.8.w4)
  • Polar bears scavenge carcasses of whales and walrus, and many of bears may be seen near a single large carcass. (J360.3.w1)

Other polar bears

Ungulates

  • A female polar bear and cubs were observed stalking and chasing caribou (Rangifer tarandus - Reindeer) (unsuccessfully). (J343.55.w2)
  • Polar bears have been seen chasing Ovibos moschatus - Musk ox, and one has been reported killing a musk ox on sea ice. (J343.55.w2)
  • Polar bears sometimes prey on Rangifer tarandus - Reindeer; this occurs in winter/early spring, when the reindeer may be weakened, making them easier prey. The bears also often scavenge reindeer carcasses. (J344.23.w1)

Vegetation

  • When females and their cubs emerge from the maternity den, the female may dig for grasses, sedges and moss near the den in the first weeks while the family remains near the den. (B406.37.w37)
  • Polar bears sometimes forage for food in soil, kelp, sand, grass and snow. (B407.w4)
  • Polar bears have been seen apparently bringing up seaweed from the bottom, eating it, then diving again for more weed. (J30.52.w3)
  • A study on North Twin Island, James Bay, in summer, found that crowberries (Empetrum nigrum) were one of the main foods taken, although the bears spent only 2.9-4.9% of their time feeding. Females with cubs spent the greatest time (4.9%) feeding. (J30.56.w6)
  • In summer, polar bears feed on grass and other vegetation. (J360.3.w1)

Garbage

  • Polar bears scavenge human rubbish dumps and field camps for food. (B406.37.w37)
  • A study along the western coast of Hudson Bay, Canada, including observation of bears at the Churchill dump, 1981-1983, indicated that bears which fed at the dump were significantly heavier than those which did not, but did not show any reproductive (number of cubs) or survival advantage of this behaviour. Adult males did not feed at the dump even if the had done so as cubs or subadults. (J30.63.w2)

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Authors & Referees

Authors

Dr Debra Bourne MA VetMB PhD MRCVS (V.w5)

Referee

Andrew Derocher (V.w100), Ellen Dierenfeld (V.w16)

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