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NATURAL DIET - Editorial Comment

Editorial Comment

(Editorial Overview Text Replicated on Overall Species page - Ursus arctos - Brown bear)

NATURAL DIET:

  • Brown bears are omnivorous. The diet varies with area and season, depending on availability. Vegetable foods such as grass, sedges, roots, bulbs and mosses may be important in spring, then succulent forbs, with berries, bulbs and tubers becoming important in summer, and berries, fruits, nuts, acorns and pine seeds in fall. Honey, grain and fungi are also eaten.
  • Considerable animal foods may be eaten. Carcasses of large ungulates may be important in spring. Aggregations of insects may be eaten, salmon are an important seasonal item at salmon rivers. Ground-breeding birds, rodents and various ungulates are eaten, also in some areas Ursus americanus - American black bear; cannibalism also occurs.

QUANTITY EATEN: Little has been published on the amounts eaten by brown bears. A study in the Yukon noted that hyperphagic brown bears ate more than 200,000 berries (of 0.2 g each) per day while gaining weight at 0.4-0.64 kg per day.

STUDY METHODS: Studies have involved scat analysis, examination of feeding sites, direct observation, and stable isotope analysis.

(References are available in detailed literature reports below)

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Natural Diet

Source Information

SUMMARY:
  • Brown bears are omnivorous. The diet varies with area and season, depending on availability. Vegetable foods such as grass, sedges, roots, bulbs and mosses may be important in spring, then succulent forbs, with berries, bulbs and tubers becoming important in summer, and berries, fruits, nuts, acorns and pine seeds in fall. Honey, grain and fungi are also eaten.
  • Considerable animal foods may be eaten. Carcasses of large ungulates may be important in spring. Aggregations of insects may be eaten, salmon are an important seasonal item at salmon rivers. Ground-breeding birds, rodents and various ungulates are eaten, also in some areas Ursus americanus - American black bear; cannibalism also occurs.

General:

NATURAL DIET:

  • Bears are omnivorous. The diet of bears varies with the seas as different plants flower and fruit. (B392.8.w8)
  • "Roots, tubers, forbs, grass, sedges, fruits (berries and nuts), pine seeds, insects, fish, rodents, and ungulates (including livestock)." (B285)
  • Mainly vegetable:
    • In early spring, grasses, sedges, roots, bulbs and mosses. (B147)
    • In late spring, perennial succulent forbs. (B147)
    • In summer and early autumn: berries, also bulbs and tubers. (B147)
    • Insects, fungi and roots may be eaten all year. (B147)
    • Small mammals (mice, ground squirrels, gophers) are dug out of their burrow and eaten. (B147)
    • In the Canadian Rockies, brown (grizzly) bears are quite carnivorous, hunting mountain sheep and goats, elk and moose, and even Ursus americanus - American black bear. (B147)
    • In Alaska, in Mount McKinley National Park, the main diet is vegetation, but carrion is eaten when available and calves of moose and caribou may be caught. (B147)
    • Along the Pacific coasts of Canada, southern Alaska and northeastern Siberia, brown bears feed on salmon in summer, when the salmon are travelling upstream. (B147)
  • Vegetable material including grasses, herbs, fruits, berries, nuts and seeds, also honey, insects, fish, ground-breeding birds, rodents, carrion and hoofed mammals. (B144)
  • Vegetable foods make up most of the diet for much of the year, but these bears will scavenge, kill small mammals, and rob bees' nests. They will take advantage of seasonally available food resources, including insects. Brown bears have been noted feeding on aggregations of ladybirds (Coccinellidae), army cutworm moths (Chorizagrotis auxiliaris) and caddis fly larvae. Brown bears in Tibet and the Himalayas are more active as predators than in much of their range, and even kill buffalo calves. Brown bears also make use of the salmon run. In autumn, when fruits and berries ripen, brown bears feed intensively on these. (B399.5.w5)
  • Omnivorous, with vegetable matter dominant at least seasonally, while animal products are eaten in varied amounts in different parts of the range. (D284.w3)
    • Plants which emerge early in the growing season are important until more nutritious food items become available.
    • Different succulent growing plants, and underground roots, corms and bulbs are used at specific time or in specific habitats when these provide a high protein or general nutrient quality and a relatively low fibre content. 
    • Ants and other insects can be important; insects may assist in meating the bear's amino acid needs. 
    • Fruit is important in all areas, particularly in late summer and autumn when bears need to gain weight rapidly before denning. 
    • In some areas, over-wintered berries are important in spring.
    • Meat (including ungulates, small rodents and fish) may be preferred as a food when available, as it is high in protein and is highly digestible.

    (D284.w3)

  • In India: 
    • In spring and early summer, grasses, insects and rodents. (B392.8.w8)
    • In summer, may kill and eat livestock (sheep, goats, ponies).
    • In late summer/autumn, wild and cultivated berries, fruits and nuts, and grain, also grass, roots and tubers. (B392.8.w8)
  • Omnivorous: (B421.w1)
    • Largely vegetable - roots, tubers, bulbs, berries, fruit, nuts (particularly acorns), fungi and grain. (B421.w1)
    • Animal matter eaten includes sheep, other domestic animals, carrion, insects, honey, frogs, small mammals, occasionally large mammals (e.g. deer, boar). (B421.w1)
  • Omnivorous. Plant material such as roots, sprouts, leaves, berries and fungus, also insects, fish, small and large mammals. (B180.w3)
  • Omnivorous, with a largely vegetable diet including roots, tubers and bulbs, fruits, berries and nuts, fungi and grain. Domestic animals, particularly sheep, carrion, insects, frigs, small mammals, birds' eggs, fish and occasionally large wild mammals such as deer and wild pigs are eaten, also honey. (B422.w14)
  • Vegetation: "lush grasses, succulent herbs, tender shoots, flowers, leaves, roots, bulbs, a variety of tubers, mosses, horsetails, willows and many species of berries" also fungi, acorns, pine cones and various nuts. (D243)
  • Insects, larvae and grubs, also birds and eggs. (D243)
  • Small mammals eaten include Spermophilus spp., Marmota - (Genus) spp., Lemmus spp., Synaptomys spp., Dicrostonyx spp., Thomomys spp., Clethrionomys - (Genus) spp., Phenacomys spp., Microtus - (Genus) spp. and Peromyscus spp. (D243)
  • Larger mammals eaten (either as prey or as carrion) include Alces alces - Moose, Rangifer tarandus - Reindeer (caribou), Cervus elaphus - Red deer (North American Elk), Bison bison - Bison, Odocoileus - (Genus) spp. deer and Oreamnos americanus - Mountain goat, Sus scrofa - Wild boar and Ovibos moschatus - Musk ox. (D243)
  • Brown bears eat bulbs and roots of plants, also succulent stems of grasses, insects, small crustaceans, voles (Arvicola spp.), domestic sheep and goats, and carrion. (B425)
  • In a study in Italy the diet was 34.4% fruit, 32.2 % herbs, 15.1 % meat, 14.7 % insects and 2.6 % other. (B425)
  • Fruits, leaves, roots, grass, salmon, other fish, rodents and other small mammals, and sometimes much larger species. (B288.w11)
  • Omnivorous, using protein-rich vegetable matter but also animal matter. Carrion may be important in spring when bears first emerge from the den. The diet varies with area and season, depending on availability. Animal foods include ants, moths, salmon, rodents (Microtus spp. voles, Peromyscus spp. deer mice, northern pocket gophers Thomomys talpoides, Spermatophilus parryuu - arctic ground squirrels) and ungulates - Cervus elaphus - Red deer (North American Elk), Bison bison - Bison, Alces alces - Moose, caribou (Rangifer tarandus - Reindeer). (B406.36.w36)
  • Omnivorous. Availability of high-quality food sources in late summer and during fall (autumn) is particularly important, to allow weight gain prior to hibernation. Body size and productivity of bears with access to fish and/or terrestrial meat sources is higher than those reliant on mainly vegetation year-round. (J30.77.w3)
  • In Norway, scats found near caches of sheep carcasses contained, in addition to sheep remains, blueberries (Vaccinium spp.), other berries, grasses, herbs and mosses. (J332.63.w1)
  • In Plitvice Lakes National Park, Yugoslavia, brown bears were found to eat mainly vegetable material, with 76% of scats containing only vegetable matter, 20% containing vegetable and insect matter, 2% plant and mammal material and 2% plant, mammal and insect material. Remains of at least 21 plant species, two families of insects and at least four mamml species were confirmed. In March to May, the most important components of the diet were herbaceous plants: young grasses, lords and ladies (Arum maculatum) and ferns; these plants contained 80% water and 2-5% crude protein. This is the time of year when plants have the highest protein content. The bears dug for the tuber of lords and ladies, which was the only plant food in spring with a high nitrogen-free extract. In summer, cultivated oats and summer fruits (Prunus avium - Wild cherry and Rubus fruticosus - Bramble) were important, with consumption of oats peaking August and early September. Oat ears have a high crude protein content (11%) and were found in 70% of summer scats, making up 12% of diet volume. In autumn, the diet was mainly fruits, especially plums, pears and apples, which made up 53% of scat volume, and nuts, which made up 33% of scat volume. Bears climbed trees to reach fruit and nuts before these dropped, as shown by claw marks visible on hazel and plum trees. Before denning, they fed heavily on beechnuts. Mammals eaten included deer and small mammals. In the autumn, the bears showed intensive digging for small mammals. Bears occasionally took carcasses and garbage from baiting pints and garbage dumps around the boundaries of the park. (J345.7.w2)
  • In Croatia, in spring and summer major food sources included broad-leaved garlic (Allium ursinum), lords and ladies (Arum maculatum) and, at permanent feeding sites, carron and corn. Additionally, grasses, clovers and sorrels were eaten. In summer, the main plant foods were wild angelica (Angelica silvestris) and stinking aposeris (Aposeris foetida), with oats also eaten. In late summer, fruits of raspberry (Rubus idaeus), bramble (Rubus fruticosus), common buchthorn (Rhannus cathartica) and blueberry (Vaccinium myrtillus) were most important. In fall, beech nuts were important. (J345.10.w3)
  • Brown bears have widely varying diets, from mainly herbivorous to diets including much animals protein. In general, they use mainly vegetable matter immediately after den emergence in spring, although in some areas animal protein sources such as frogs, caddis flies, fish roe or ungulate carrion may be important at this time. (D283.w5)
    • A study of northern interior Canadian grizzly bears in the Yukon noted that green vegetation was eaten in spring (April to May), particularly roots of Hedysarum alpinum (alpine sweetvetch), Salix spp. (willow) catkins, grasses and other green vegetation. Two cases were observed of bears eating carrion of Alces alces - Moose (killed by spring snow-slides). In summer (June-July), they ate willow catkins and grasses; dry bearberries were eaten in some areas. Later, as soapberries became available (July 15-25), these were eaten. Additionally, scat analysis showed that roots of Hedysarum, wasps, and carrion were eaten. In fall (August to October), bears continued eating soapberries and, where available intensively, other berries (e.g. crowberries, blueberries (Vaccinium spp.) and bearberries. Roots were also eaten. In late September and October ground squirrels (Spermophilus undulatus) were eaten also. (D283.w5)
    • Note: feeding habits may be affected by previous experience: bears may show preference for some foods even with other highly nutritious foods available (e.g. gorging on berries before taking fresh meat, or fish), and may not take some foods (e.g. garbage, fish) when they become available, but continue using foods they are used to. (D283.w5)
  • In Yellowstone National Park, protein foods used include cutthroat trout (Oncorhynchus clarki, formerly Salmo clarki) and ungulates such as elk (Cervus elaphus - Red deer (North American Elk)). (J345.8.w7, J345.8.w)
  • Brown bears sometimes kill and eat Ursus americanus - American black bear. (D274, J435.107.w3)
  • Large male brown bears sometimes kill and eat brown bear cubs, yearlings and occasionally even adult females. (D243, J435.107.w1)
  • An adult male and an adult female grizzly bear travelling together were observed killing and eating five Ovibos moschatus - Musk ox calves; the fifth calf was not eaten by the bears. (J435.107.w4)
  • Grizzly bears are known to search for and prey on the young of several ungulates species - caribou (Rangifer tarandus - Reindeer), Alces alces - Moose, and Cervus elaphus - Red deer (North American Elk). (J435.107.w4)
  • In North America, brown bears sometimes eat Ursus americanus - American black bear. In Alaska, an incident of predation by a grizzly bear on a denned adult black bear was recorded. (J435.107.w3)
  • Grizzly bears with caribou (Rangifer tarandus - Reindeer) calving herds available include caribou in their diet both as carrion and as prey. (J345.7.w4)
  • In central Sweden, ants, which were abundant (30.5-38.5 tonnes per bear), formed an important part of the diet, being found as 12% of scat volume in spring, 16% in summer and 4% in autumn (fall). The most preferred species was the carpenter ant (Camponotus herculeanus). Of the mound-building, red forest ants, Formica aquilonia/polyctena complex ants were preferred compared with Formica exsecta and Formica lugubris. (J30.77.w2)
  • A study in Slovenia found that ants were present in 85% of scats and made up an average of 25% of the ingested dry mass in summer. Despite a relatively low biomass of ants available, 1% of those available in Sweden (135 g/hectare of beech forest, versus 9,600 g/hectare for ants in central Sweden, and almost no large ant colonies), bears ate about 50% of the amounts of ants they ate in Sweden, appearing to be a sought-after food source. (J30.81.w1)
  • A study using stable isotope analysis showed that grizzly bears inhabiting the Columbia river drainage prior to 1931 had 33-90% of their metabolised carbon and nitrogen coming from salmon. For brown bears on Chicanof and Admiralty Islands, most individuals feed on salmon in the late summer and fall (autumn), but a subpopulation (despite geographically having access to spawning salmon) does not use salmon; this data from stable isotopes confirmed telemetry data which had indicated this subpopulation. (J30.74.w2)
  • Bears make use of insect aggregations, such as army cutworm moths, ladybirds, grasshoppers and caddis flies, where available. (J30.69.w1)
    • In the Shoshone National Forest (in the Yellowstone ecosystem), between 15 June and 15 September 1981-1989, bears were seen, at known or suspected alpine talus sites (scree slopes), mainly at >3350 m, on south (four sites),west (seven), north (six) and east (one) facing slopes, of >30 degrees. They were feeding nearly exclusively on invertebrates, particularly army cutworm moths (Euxoa auxiliaris). At these sites, subadult females appeared underrepresented, and there was a tendency for females with cubs-of-the-year to be underrepresented. Females with young appeared to decrease from June to September while the proportion of subadults increased. Most bears used a given site only in one year, but one bear used the same site for six years. Bears dug 10-60 cm (usually 15-50 cm) deep to get the moths. The researchers noted that moths in these areas tended to be both abundant and lethargic. If more than one bear used a site they were 40-200 m apart except for paired subadults and suspected mating adults. The bears also bedded at or near the feeding sites, in the open scree or bed 28 cm deep in open tundra . Most beds were shaded by a cliff or boulder, usually shallow (<10 cm deep), shaped from scree or rocky soil, and were found in close-set clusters of 3-11. Bears were seen climbing cliff slopes, "apparently to bed in clefts". The timing of the bears' activity on the sites coincided with the presence of the moths in the mountains. Bear scats collected from the sites contained moths, graminoides (Graminales), and debris, with small amounts of pine seeds (Pinus albicaulis), clover (Trifolium spp.), deer hair (Odocoileus hemionus) and ants (Formicidae). It was noted that in the National Forest fleshy fruits are scarce and the mian food used by bears for fattening during hyperphagia is whitebark pine seeds, usually available only after the third week in August at altitudes > 2425 m, therefore the insect aggregations are used by dominant bears. It was noted that insect aggregations are used also in the Mission Mountains, but there they are used more by subordinate or security conscious bears, versus by lone adults; fleshy fruits are more available in the Mission Mountains in August and September at moderate to low elevations. (J30.69.w1)
  • Brown bears sometimes eat soil. Deliberate geophagy was observed in grizzly bears in Yellowstone, peaking in March to May and August to October, at times when much meat and mushrooms were being eaten. (J345.11.w2)

See also: Brown bear Ursus arctos - Feeding Behaviour (Literature Reports)

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Quantity Eaten

Source Information

SUMMARY: Little has been published on the amounts eaten by brown bears. A study in the Yukon noted that hyperphagic brown bears ate more than 200,000 berries (of 0.2 g each) per day while gaining weight at 0.4-0.64 kg per day.
  • A study of northern interior Canadian grizzly bears in the Yukon found that in autumn (fall), feeding entirely on soapberries weighing about 0.2 g per berry, each bear would eat more than 200,000 berries per day to gain weight at a rate of 0.4-0.64 kg/day. (B490.26.w26, D283.w2)
  • In feeding trials of captive bears with salmon and white-tailed deer, maximum daily intake reached > 40 kg/day for salmon and about 18 kg/day for deer. On a percentage body weight basis, intake was proportionately highest in smaller bears than in larger bears and varied from about 7% to 24% for deer and 12-25% for salmon. (J30.77.w)

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Dietary Study Methods

Source Information

SUMMARY: Studies have involved scat analysis, examination of feeding sites, direct observation, and stable isotope analysis.
  • Analysis of scats found near cached sheep carcasses. (J332.63.w1)
  • Direct observation, finding blood on the muzzle, locating radio-collared bears feeding on caribou. (J345.7.w4)
  • Direct observation. (J435.107.w3)
  • Analysis of scats and examination of feeding sites. (J345.7.w2)
  • Direct observation of bears feeding, and analysis of scats. (D283.w5)
  • Note: care must be taken when using faecal analysis to estimate the proportions of the diet made up from different food types. since there is considerable variation in the amount of food required to produce 1 mL of fecal output (from 0.16 to 40.8 g dry matter), depending on the type of food. Suggested correction factors to allow for this include: 0.16-0.35 for vegetation, 0.51-1.84 for berries, 0.35-1.40 for roots, 0.91-1.25 for insects, 1.54 for pine nuts, 1.54-12.5 for mammals (varying depending on the proportion of poorly-digested materials such as skin, hair and bones eaten), and 40.8 for fish such as trout. (J59.24.w2)
  • Direct observation of foraging, and scat analysis have been used to study bear diets. (J30.74.w2)
  • Stable isotope analysis can be used to determine the diet. Carbon isotopes indicate whether the diet was terrestrial or marine, wile analysis of nitrogen isotopes can provide information on whether the diet was herbivorous or carnivorous (15N is enriched relative to 14N at each step up a food chain). Different tissues collected at one time can be used to provide information from different time periods, depending on turnover rates: plasma indicates the diet in the week before sampling, rbc indicate the diet in the 2-3 months before sampling, hair indicates the diet during the midsummer to fall (period of hair growth) and collagen, which has a low turnover rate, indicates yearly or lifetime diet. (J30.74.w2)
  • Stable isotope analyses. (J30.77.w3)

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Authors & Referees

Authors

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

Referee

Ellen Dierenfeld (V.w16), Djuro Huber (V.w101), Chuck Schwartz (V.w105)

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