What Do Bears Eat? Diet and Foods by Species

Bears are overwhelmingly omnivores, but the family Ursidae spans a dietary spectrum that runs from near-total carnivory in polar bears to near-total herbivory in giant pandas. What any given bear actually eats depends on its species, its habitat, the season, and what happens to be available. A grizzly in coastal Alaska gorging on salmon looks nothing like a sloth bear vacuuming termites from a mound in India, yet both are doing the same thing in evolutionary terms: exploiting whichever food source delivers the most energy for the least effort. The details, species by species, are more surprising than most people expect.

Brown Bears and Grizzlies

Brown bears (including the North American subspecies commonly called grizzlies) are the textbook omnivores. Their diet varies enormously depending on whether they live near the coast or deep in the continental interior. Coastal populations in Alaska and British Columbia draw most of their calories from salmon, while interior populations rely far more on plant foods and, where ungulates like caribou are abundant, on terrestrial meat.

A stable-isotope study spanning North American grizzly populations found that most coastal bears derived the majority of their assimilated carbon and nitrogen from salmon, while interior bears got a much smaller fraction from fish even when salmon runs existed nearby.

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A more recent analysis of grizzly bears in British Columbia confirmed this broad split: dietary niches clustered into either salmon-reliant or plant-reliant categories, with terrestrial meat and landlocked kokanee salmon filling in as supplements regionally. Available salmon biomass was the strongest predictor of which dietary niche a bear fell into.

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When you move inland to places like west-central Alberta, where salmon are absent, grizzlies eat a rotating menu of green vegetation in spring, insects and soft fruits in summer, and hard mast and berries in autumn. Berries are especially critical. Research on those Alberta bears showed that during the late-summer hyperphagic period, fruit allowed grizzlies to optimize the ratio of macronutrients they consumed, maximizing fat gain per unit of energy eaten.

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A separate study of free-ranging European brown bears reached a similar conclusion about autumn diets: the proportions of protein, carbohydrate, and fat selected by wild bears in fall closely matched what captive bears chose when optimizing fat mass gain in feeding experiments.

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American Black Bears

North America’s most widespread bear is also its most flexible eater. Black bears occupy forests from Florida to Alaska, and their diets track whatever a given habitat provides. In eastern hardwood forests, acorns and hickory nuts dominate in autumn. In the Pacific Northwest, berries and salmon share the calendar. In the arid Great Basin of Nevada, the menu looks different again, and the line between wild and human food can blur.

Isotope analysis of black bears in the Sierra Nevada and western Great Basin revealed that both urban and wildland bears used a mix of natural and human-derived foods, with wildland bears leaning more toward wild sources. The median difference in human-food use between urban and wildland bears was only about four percent, though individual bears varied wildly: some wildland bears ate a lot of garbage, and some urban-adjacent bears ate almost none.

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Male black bears in that population also showed isotopic signatures indicating more meat in their diets compared to females, a pattern consistent with what biologists see in other bear populations where larger-bodied males can access protein-rich prey more easily.

Polar Bears

Polar bears sit at the carnivorous extreme of the bear family. They evolved to hunt seals on sea ice, and their entire physiology reflects that specialization. Fatty acid analysis of polar bears in the southern Beaufort Sea estimated that ringed seals made up roughly 46% of their diet, followed by bearded seals at about 20%, seabirds at 17%, bowhead whale (mostly scavenged) at 15%, and beluga whale at just 2%.

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But sea-ice loss is forcing polar bears ashore for longer stretches each year, and what they eat on land tells a different story. A study of polar bear scats during the ice-free season in western Hudson Bay found grasses (mainly Lyme grass) in about 62% of samples, marine algae in 46%, and bird or egg remains in 29%. Caribou showed up in about 10% of scats, seals in roughly 7%, and even other polar bears (from cannibalism) in about 5%.

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Researchers have linked nutritional stress from these longer ice-free periods to an increase in cannibalism. Observations in the southern Beaufort Sea suggested that prolonged time without access to their primary prey may drive some bears to kill and eat others.

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Why the Polar Bear Skull Cannot Chew Like a Grizzly’s

Polar bears diverged from brown bears relatively recently, and their skulls reflect a rapid evolutionary shift toward grabbing slippery prey rather than grinding tough plant material. Finite element modeling comparing polar bear and brown bear skulls of similar size found that while their jaw muscles generate comparable bite forces, the polar bear skull is structurally weaker. Peak stresses in the polar bear cranium during molar bites reached up to four times those in the brown bear model, meaning the polar bear skull deforms much more when trying to process hard or tough foods.

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The differences were most pronounced for bites using the post-canine teeth, where food is actually chewed. A polar bear can easily shear blubber and swallow chunks of seal fat, but its skull is poorly suited to crushing bones or grinding vegetation. This helps explain why polar bears stuck on land cannot simply switch to a grizzly-like diet of roots and berries when the ice disappears.

For comparison, extinct cave bears evolved in the opposite direction. Analysis of cave bear skulls shows they lost their three most anterior premolars and developed broader molar surfaces, features associated with a heavily plant-based diet.

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Isotopic evidence, though, complicates the picture. Bone collagen from a Romanian cave site showed that many of its cave bears had higher nitrogen isotope values than associated herbivores, indicating an omnivorous or even partly carnivorous diet, suggesting that cave bears could adjust what they ate depending on local conditions.

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Giant Pandas

Giant pandas are the most extreme dietary specialists in the bear family, eating almost exclusively bamboo. What makes this remarkable is that their bodies never really adapted for it. Pandas retain the short, simple digestive tract of a carnivore and lack the genes needed to produce cellulose-digesting enzymes.

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Their gut bacteria confirm this mismatch: microbial community analysis has shown that the panda gut microbiome looks more like that of a carnivore than an herbivore, both in bacterial composition and functional potential.

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To compensate for poor digestion efficiency, pandas eat enormous quantities. A wild adult may consume 12 to 38 kilograms of bamboo per day, cycling between shoots, leaves, and stems depending on the season. Shoots, available mainly in spring and summer, are nutritionally richer and easier to digest; stems, eaten more in winter, are tougher and less nutritious. Pandas will occasionally eat meat, fish, or eggs if the opportunity arises, but these events are rare enough to be footnotes in a bamboo-dominated existence.

Sloth Bears and Sun Bears

The two smallest mainland Asian bears have converged on insect-heavy diets, though in different proportions. Sloth bears are myrmecophagous specialists, meaning they are built to eat ants and termites. Their long, curved claws rip open mounds, and a gap in their front teeth lets them form a vacuum tube with their lips to suck insects out. A systematic review of sloth bear feeding ecology across the Indian subcontinent confirmed that ants, termites, and fleshy fruits are dietary staples, with seasonal and habitat-level variation shaping how much of each they eat.

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Sun bears, the smallest of all bear species, take a different approach depending on what the forest offers. In the tropical rainforests of Borneo, sun bear diets swing dramatically with fruit availability. During mass fruiting events, which occur irregularly and are linked to El Niño cycles, nearly 100% of their diet was fruit. During the lean intermast periods, sun bears shifted to a mostly insectivorous diet. Researchers documented sun bears feeding on 115 fruit species spanning 30 plant families, with figs serving as a key fallback food when other fruit was scarce.

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Spectacled Bears

The spectacled (or Andean) bear is South America’s only living bear species and one of the most herbivorous bears after the giant panda. A study in Peru confirmed 83 different foods in their diet, including insects, rodents, corn, berries, bamboo hearts, cactus species, tree fruits, and at least 22 species of bromeliads. Bromeliads, particularly their starchy hearts, are the dominant food during months when fruit is not available. From about February to July, when fruit ripens, spectacled bears shift their movements to reach those preferred food sources.

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Recent field research in high-elevation puna grasslands has shown that spectacled bears are surprisingly selective about which bromeliads they eat. When given a choice between two species of Puya bromeliads, bears were nearly three times more likely to forage on one species over another, and they also preferred denser patches with more available plants.

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This selectivity matters for conservation: if bears depend on particular bromeliad species in particular densities, habitat degradation that reduces those patches can squeeze bears out even if other vegetation remains.

Asiatic Black Bears

Asiatic black bears range from Iran to Japan, and their diets follow a seasonal rotation that tracks plant phenology closely. A review of dietary studies across their range found a consistent pattern: bears eat mostly green vegetation in spring (sprouts, young leaves, flowers), shift toward insects and soft fruits in summer, and pivot to hard mast like acorns and chestnuts in autumn.

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In years when acorn crops fail, Asiatic black bears are more likely to raid crops or enter villages, a dynamic that drives much of the human-bear conflict across their range in Japan and Korea.

How Bear Diets Shape Ecosystems

Bears are not just consumers. They redistribute nutrients across landscapes in ways that affect entire ecosystems. The most studied example involves salmon-eating bears. When a brown bear drags a salmon carcass into the forest, it deposits marine-derived nitrogen and phosphorus in riparian soils, fertilizing streamside vegetation.

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These carcass remnants also feed scavengers from eagles to beetles, and the nutrient pulse benefits trees measurably enough that researchers have mapped growth rings in streamside conifers back to salmon run years.

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Fruit-eating bears play a different ecological role: seed dispersal. A study in the Canadian Rocky Mountains estimated that half of the seeds defecated by berry-eating bears were deposited at least 1.1 kilometers from where the bear ate, with some traveling up to 7 kilometers. The seed shadows covered areas up to about 150 square kilometers. Passage through the bear gut also stripped away germination-inhibiting compounds in the berry pulp, boosting germination rates from less than 1% for intact whole berries to nearly 29% for seeds freed from pulp.

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What Happens When Bears Eat Human Food

Access to human food is not just a nuisance issue; it changes bear biology. A study of free-ranging black bears in Colorado found that bears that ate more human food hibernated for shorter periods, and those shorter hibernation bouts were associated with accelerated telomere loss, a marker of cellular aging.

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Hibernation appears to slow cellular aging, so when calorie-rich garbage shortens that dormant period, bears may age faster at the cellular level. The bears eating human food were heavier, which sounds like a benefit, but the long-term cost in biological wear may outweigh the short-term caloric gain.

This finding reframes the familiar advice to secure trash cans and bird feeders. It is not only about preventing property damage or dangerous encounters. Chronic access to human food can alter the basic physiology of local bear populations, potentially reducing lifespans even in bears that never have a direct conflict with people. The isotope work from Nevada reinforced this point: individual variation in human-food use was enormous, meaning that even in relatively wild areas, a single unsecured dumpster can reshape the diet of bears living kilometers away.

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The Gut Microbiome Factor

One puzzle in bear biology is how bears in different habitats can reach similar body conditions while eating completely different foods. Part of the answer involves the gut microbiome. Research comparing brown bears across three Alaskan national parks, where diets ranged from predominantly salmon and marine species to seasonal vegetation and mammals, found that gut microbial communities differed meaningfully between populations and appeared to help bears extract nutrition from whichever diet was locally available. Despite dramatic differences in what they ate, the bears achieved comparable body conditions.

Giant pandas offer the flip side of this story. Their gut microbiome is poorly suited to their actual diet, resembling a carnivore’s microbial community despite processing nothing but bamboo. Seasonal shifts in which bamboo parts are available drive large swings in the panda gut flora, which may partially explain why pandas must eat such vast quantities to meet their energy needs.

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In bears generally, the gut appears to be one of the underappreciated engines of dietary flexibility, helping omnivorous species bridge the gap between what they happen to find and what their bodies need.