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NATURAL DIET - Editorial Comment

Editorial Comment

(Editorial Overview Text Replicated on Overall Species page - Ursus maritimus - Polar bear

NATURAL DIET:

QUANTITY EATEN: About 4.4 kg (9.7 lb) of seal may be eaten daily (on average) over the eight months of the winter period, in Hudson Bay. Data from captive bears indicates that given a choice, polar bears will take about 80% of their diet as blubber, 20% as meat.

STUDY METHODS:

  • Polar bear diets have been determined by observation of bears, tracks and carcasses.

(References are available in detailed literature reports below)

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Natural Diet

Source Information

SUMMARY:

General:

  • 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)
  • Ringed seals are the main food; bearded seal are also eaten. (B285.w4)
  • Seals, also fish, birds and eggs, small mammals, carrion, shellfish, crabs, starfish, and some vegetable material - grasses, berries, even algae and fungi. (B180.w4)
  • Mainly seals, also stranded whales, stranded walrus, carrion, human garbage. Rarely herbs, berries and grasses. (B144)
  • The main diet is seals, particularly Phoca hispida (Phoca - (Genus)) - ringed seal. Erignathus barbatus - Bearded seal are also important. Other seals eaten include Pagophilus groenlandicus - Harp seal and Cystophora cristata - Hooded seal. Walrus may be preyed on. Carcasses of whales, walrus Odobenus rosmarus and seals are scavenged. (D244)
  • Ringed seals Phoca hispida (Phoca - (Genus)) are the main prey, bearded seals Erignathhus barbatus are the second most important species of prey. The fatty portions of seals are eaten in preference to muscle and other tissues; more than half the calories available in a seal carcass can be found in the blubber layer under the skin, and this is often eaten first. In Svalbard, Rangifer tarandus - Reindeer are eaten (scavenged and predated). On land in summer, vegetation is eaten, and human refuse also is consumed. Bears also eat bowhead whales (Balaena mysticertus) killed by local Native people in the Beauford Sea. (B490.27.w27)
  • If no other food is available, polar bears will eat small mammals, birds, eggs and vegetation. (D244)
  • Mainly seals, also young walruses, fish and carrion, including that of whales. Some vegetable material, such as seaweed and grass, is also eaten. (B288.w11)
  • Polar bears are more carnivorous than the other bears, eating seals, mainly the ringed seal (Phoca hispida (Phoca - (Genus))) but also fish, sea birds, bird eggs and carrion. Polar bears may congregate to eat a large whale carcass. In autumn, polar bears will eat berries, grass and other vegetable matter. (B399.5.w5)
  • Mainly ringed seal Phoca hispida, also Erignathus barbatus - Bearded seal  and less commonly Pagophilus groenlandicus - Harp seal and Cystophora cristata - Hooded seal. Walrus (Odobenus rosmarus) are sometimes killed, and occasionally belugas (Delphinapterus leucas). Large whales are eaten as carrion. Other foods include small land mammals (e.g. microtine rodents), sea birds, particularly waterfowl, also eggs and chicks, marine invertebrates, and vegetable matter: grasses, sedges, marine algae, broad-leafed herbs (leaves and stems), berries, mosses and seaweed. (B406.37.w37)
    • The main part of the seal eaten is the blubber, which has the highest calorific value; often the meat is not eaten. (B406.37.w37)
    • Females emerging from their maternity den may eat grasses, sedges, mosses, and lichens. (B406.37.w37)
  • In summer polar bears eat some vegetation and carrion, but gain little nutritional value from such items when compared with the value of their main prey (seals). (J30.53.w3)
  • A study on North Twin Island, James Bay, in summer, found that polar bears spent only 2.9-4.9% of their time feeding. When feeding, they fed mainly on crowberries (Empetrum nigrum) and on Branta canadensis - Canada geese. Females with cubs spent the greatest time (4.9%) feeding. (J30.56.w6)
  • A summer and autumn study in James Bay and the southwest coast of Hudson Bay, based on scat analysis, found that on the mainland, marine algae were often present, also grasses, particularly Elymus arenarius. Other vegetation eaten included mosses, lichens, mushrooms, rushes, leaves and stems of broad-leaf herbs and shrubs. Animal matter eaten included polar bears, voles (Microtis pennsylvaticus), muskrats Ondatra zibethicus and seals Phoca hispida (Phoca - (Genus)) - ringed seal and Erignathus barbatus - Bearded seal. On islands in James Bay, leaves and stems of shrubs and broadleaved herbs, berries and fruits, particularly Empetrum nigrum, grasses, mosses, lichens, marine algae, mushrooms and sedges were all found in scats. Animal matter remains detected included birds, particularly Clangula hyemalis - Long-tailed duck (found in 34 % of scats, Somateria sp. in 9% and Branta canadensis - Canada goose in 4%, eggshells (5%), mammals (seals in 9%, polar bear in 10% and marine invertebrates, particularly Mytilus edulis (10%) and Strongylocentrotus dreohbachiensis (6%). (J343.28.w1)
  • The main food is the ringed seal. Other seals and walrus (calves and young animals rather than adults) are eaten also. Carcasses of stranded whales (e.g. Bowhead whales Balaena mysticus, and walrus, also are eaten. Minor components of the diet include fish, seabirds, waterfowl and eggs, as well as grass and other vegetation. (J360.3.w1)
  • When a bear kills a seal often it eats mainly the blubber, commonly leaving the meat and, not infrequently, also some of the blubber. If a small seal is killed by a hungry bear, or by a female with one or two cubs, the whole or most of the carcass may be eaten. (J30.53.w3)
  • Polar bears scavenging on kills may eat the blubber and 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)
  • 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 occasionally eat belugas (Delphinapterus leucas) and narwhal (Monodon monoceros). (J343.43.w1)
  • In summer, polar bears sometimes eat 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)
  • On land in summer in western Hudson Bay, 1986 and 1992, 34% of female and 26% of male bears at least 10 km inland fom the coast were found to be feeding on vegetation mainly on berries (Vaccinium uliginosum and Empetrum nigrum). These were eaten mainly by subadults and by adult females. It was considered that this might reduce the weight loss of bears during the summer ice-free period. (J343.46.w1)
  • Polar bears sometimes eat Odobenus rosmarus - Walrus. (J345.8.w4)
  • Polar bears have been observed feeding on Rangifer tarandus - Reindeer. (J344.23.w1)
  • Adult male polar bears sometimes eat juvenile polar bears. (J343.52.w1, J343.55.w1)
  • Polar bears will eat other polar bears and will often eat a bear if they have killed it. (B490.27.w27)
  • Adult males have been seen feeding on adult female polar bears. (J30.64.w1)
  • Further information on feeding is provided in Polar bear Ursus maritimus - Feeding Behaviour (Literature Reports)

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Quantity Eaten

Source Information

SUMMARY: About 4.4 kg (9.7 lb) of seal may be eaten daily (on average) over the eight months of the winter period, in Hudson Bay. Data from captive bears indicates that given a choice, polar bears will take about 80% of their diet as blubber, 20% as meat.
  • In Hudson Bay it has been estimated that each polar bear eats an average of 4.4 kg (9.7 lb) of seal per day over a period of eight months (over winter). (B406.37.w37)
  • 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)

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Dietary Study Methods

Source Information

SUMMARY: Polar bear diets have been determined by observation of bears, tracks and carcasses.
  • Observation of predation on seals. (D244)
  • Observation of predation of birds by polar bears. (J343.59.w2, J435.109.w1 J452.12.w1)
  • Observation of scavenging on carcasses of belugas (Delphinapterus leucas) and narwhal (Monodon monoceros) and predation of beluga calves. (J343.43.w1)
  • Observation of feeding on beluga carcasses. (J435.107.w5)
  • Observations of hunting and feeding on various ungulates. (J343.55.w2, J344.23.w1)
  • Opportunistic observation of kills. (J344.27.w1)
  • Seal kill remains are characterised by bear tracks together with a few patches of blood, and scraps of skin and bones. (P104.1975.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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