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NATURAL DIET - Editorial Comment

Editorial Comment

(Editorial Overview Text Replicated on Overall Species page - Ursus americanus - American black bear)

NATURAL DIET: 

  • Black bears are omnivorous but primarily vegetarian. 
  • In spring, emerging ground vegetation, catkins and leaf buds are important; hard mast left from the previous fall (autumn) will also be eaten if available, and carcasses may be eaten. In summer and fall, berries and nuts are important. 
  • Animal foods eaten include insects such as ants, crickets and grasshoppers, fish, mammals, birds and reptiles.
  • Black bears will also eat food in human garbage, agricultural crops such as maize (corn), oats, and apples, and honey from apiaries.

QUANTITY EATEN: About 5 - 6 kg (11 - 18 lb) of food is required daily. Tens of thousands of berries and nuts may be eaten daily.

STUDY METHODS: Foods eaten have been determined by analysis of scats, analysis of stomach contents and by observation of foraging bears.

(References are available in detailed literature reports below)

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Natural Diet

Source Information

SUMMARY:
  • Black bears are omnivorous but primarily vegetarian. 
  • In spring, emerging ground vegetation, catkins and leaf buds are important; hard mast left from the previous fall will also be eaten if available, and carcasses may be eaten. In summer and fall, berries and nuts are important. 
  • Animal foods eaten include insects such as ants, crickets and grasshoppers, fish, mammals, birds and reptiles.
  • Black bears will also eat food in human garbage, agricultural crops such as maize (corn), oats, and apples, and honey from apiaries.

General:

  • Bears are omnivorous. The diet of bears varies with the season as different plants flower and fruit. (B392.8.w8)
  • About 75% or more of the diet is vegetable matter, including fruits, berries, nuts, acorns, grass, roots, sapwood and other foods. Insects, fish, rodents, carrion and even large mammals (occasionally) are also eaten. (B147)
  • Omnivorous. Vegetable matter including grasses, herbs, berries, fruits, nuts and seeds, also insects, honey, small vertebrates and carrion; rarely hoofed mammals. (B144)
  • Omnivorous, with most of the diet being vegetable, such as twigs, buds, leaves and roots, nuts, berries and fruit, corn and newly sprouted plants. They also eat honey, honeycombs, larvae and bees, beetles, grubs, ants and crickets, fish and small to medium-sized mammals and other vertebrates. (B180)
  • 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 such as crickets and grasshoppers. In autumn, when fruits and berries ripen, brown bears feed intensively on these. (B399.5.w5)
  • Omnivorous, with vegetable matter central. In spring, new growth vegetation and carcasses. In summer, herbaceous material and fruits. in autumn, berries and mast are most important. Preferred foods are high in protein or carbohydrates and low in terpenes. (D245)
  • Animal material, including mammals, birds, reptiles and insects, is eaten. (D245)
  • They also eat garbage. (D245)
  • Fruit, berries and nuts, shoots, buds, catkins, roots, tubers, insects, some small mammals and young ungulates, fish. (B285.w4)
    • In spring, herbaceous vegetation, young leaves, buds and sometimes carrion of winter-killed ungulates. Also, if available, nuts left from the previous autumn. (B285.w4)
    • In summer, mainly berries and nuts. (B285.w4)
    • In some areas, fish are important in the diet. (B285.w4)
    • Small mammals and caribou in the Labrador tundra. (B285.w4)
  • Omnivorous, with the diet including fruits, nuts, roots, leaves and grass, as well as fish, small rodents, and larger mammals if available. (B288.w11)
  • The importance of different foods in the spring diet may vary. In western Massachusetts, skunk cabbage (Symplocarpus foetidus) was always an important spring food. In springs following an excellent hard mast year, acorns (Quercus rubra) were also important. (J332.86.w2)
  • The diet depends on food availability. In early spring, emerging grasses and sedges, poplar (Populus spp.) catkins and insects, particularly ants, are the main food. Some bears feed on fawns of Odocoileus spp. deer and Alces alces - Moose during the two- to four-week period when these are vulnerable. Mid-May to early June, trembling aspen (Populus tremuloides) leaves are important, with the most nutritious terminal leaves of young trees preferred. In mid-June to early July, berries start to become available (e.g. Frageria spp. strawberries, Amelanchier spp. serviceberries, Prunus pennsylvanica serviceberries) and bears start gaining weight. Through the summer and fall (autumn), other berries and nuts become available. Acorns and beechnuts (Fagus spp.) are important fall foods. (B406.35.w35)
    • Note: Food may be abundant for only eight to ten weeks in late summer and fall or, with a good mast crop of acorns or beechnuts, an extra four to six weeks, but such mast crops only occur about every three or four years. If there is a failure of both summer berries and fall mast, this causes a severe food shortage for bears. (B406.35.w35)
  • Black bears may eat large numbers of crickets and grasshoppers when these are readily available. (J332.18.w1)
  • Black bears will eat garbage. (J332.18.w1)
  • The first foods available in spring in northeastern Minnesota were catkins of aspen and willow, terrestrial and aquatic vegetation, and ants. After this, leaves of quaking aspen and birch, then more shrubs and trees. (D248.w6)
  • Black bears will also eat agricultural crops such as maize (corn), oats, and apples, and honey from apiaries. (V.w98)
  • Black bears will eat field crops (e.g. maize (corn) and oats. (B405.w2)
  • Black bears eat corn (maize), sometimes eat oats, blueberries and apples, and in southern states crops such as soy beans, watermelons and peanuts. (W655.Nov06.w3)
  • A study in western Washington found that in the spring and summer diet the vegetative component was dominated by grasses and sedges, with use of forbs (e.g. horsetail Equisetum arvense, cow parsley Heracleum lanatum, false dandelion Hypochaeris radiacata) increasing from late April to July (as more plants became available). Ingested animal matter was dominated by insects, and more were eaten further into the season; Formicidae were important, but Hymenoptera were also eaten, as well as mammal protein. Based on isotope signatures, their nourishment was 87 +/- 17% plant matter, 13 +/- 17% animal matter. Sapwood (which has a high sugar content and is very attractive to bears in spring) was much more important in the diet of bear in areas without pellet feeders than in areas with pellet feeders [provided to reduce bear damage to conifers]. Where pellet feeders were available, pellets provided 0 - 100% of the diet for individual bears. (J40.65.w2)
  • In Shenandoah National Park, Virginia, in spring the bears ate mainly herbaceous vegetation (62% by volume forbes and raminoides), then squawroot (Canopholis americana) and black cherry and sweet cherry fruits (Prunus serotina and Prunus avium), followed in early and late fall by mainly acorns. When acorns were not available (following defoliation by gypsy moth infestation) the fall foods were various soft masts, pokeweed (Phytolacca americana) berries then grapes (Vitis spp.), also spicebush fruits (Lindena benzoin), and this change in diet appeared not to involve a decline in diet quality (in terms of crude protein, crude fat and crude fibre), despite a drop in acorns from 79% to 13% (early) to 8% (late) of fall diet. Animal foods eaten in spring included bodies and pupae of ants (Formicidae), present in 40% of scats, at 8% volume, and other insects (beetles, termites and unidentified Orthoptera) in 43% of scats at 3% volume, and small amounts of white-tailed deer (Odocoileus virginianus), black bear and other mammal tissues were found. In summer, animal foods were eaten more often and as a greater volume of the diet: ants in 65% of scats (14% volume) and mammals and other invertebrates making up a further 9% of scat volume. Gypsy moths, although abundant, were not eaten. In early fall, beetles were found in 10%, ants in 14% and yellow jackets (Vespidae) in 16% of scats. (J30.73.w1)

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Quantity Eaten

Source Information

SUMMARY: About 5 - 6 kg (11 - 18 lb) of food is required daily. Tens of thousands of berries and nuts may be eaten daily.
  • About 5 - 6 kg (11 - 18 lb) of food is required daily. (B285.w4)
  • Tens of thousands of berries and nuts may be eaten daily. (B285.w4)

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Dietary Study Methods

Source Information

SUMMARY: Foods eaten have been determined by analysis of scats, analysis of stomach contents and by observation.
  • Analysis of scats, observation. (J332.18.w1)
  • Analysis of scats, observation of foraging bears, analysis of stomach contents. (D248.w3)
  • Analysis of scats, stable isotope analysis. (J40.65.w2)

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Authors & Referees

Authors

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

Referee

Ellen Dierenfeld (V.w16), David L. Garshelis (V.w98)

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