Brown bears are omnivores that eat almost anything available, shifting their diet dramatically with the seasons. In spring and early summer, their meals lean heavily toward protein from meat and insects. By fall, they switch to a carbohydrate-rich diet dominated by berries and roots. This seasonal flexibility is what makes brown bears one of the most adaptable large predators on earth.
Spring: Protein After a Long Sleep
When brown bears emerge from their dens between March and May, they’re hungry and drawn to lower elevations where snow is retreating. The first foods available are emerging grasses, sedges, dandelions, clover, and horsetail. Bears also dig up glacier lily bulbs and biscuitroot tubers, using their long claws to excavate starchy calories from the ground.
But plants alone don’t cover the protein deficit after months of hibernation. Bears actively scavenge winter-killed deer, elk, and moose carcasses, and they raid wolf kills. They also become effective predators of newborn ungulates. A study in southcentral Alaska using neck-mounted cameras on brown bears found that ungulates made up over 71% of all observed feeding during the late-May-to-mid-June calving season. Moose calves and caribou calves were the primary targets, and on average each bear was killing roughly one calf per day. Stable isotope analysis of those same bears estimated that terrestrial prey accounted for about 86% of their spring diet.
Not all brown bear populations hunt this aggressively. Inland bears in areas without dense moose or caribou herds rely more on vegetation and carrion. But where young ungulates are abundant, spring is the most carnivorous period of the year.
Summer: Forbs, Insects, and Salmon
As summer progresses, the menu broadens. Bears shift from grasses to leafy plants (called forbs) like dandelion, clover, elk thistle, fireweed, and cow parsnip. They dig for horsetail rootstock in marshy areas and excavate the roots of sweet vetch, yampah, and valerian. Gooseberries, currants, raspberries, and serviceberries start ripening by mid-to-late summer and become increasingly important.
Insects add meaningful protein. Ants are a staple across European and North American populations, and bears will tear apart logs and anthills to reach them. In the Rocky Mountains, some bears climb to alpine elevations to feed on army cutworm moths, which congregate under rocks by the thousands. These moths are extremely high in fat, making them a calorie-dense snack.
For coastal brown bears, summer is when the real feast begins. Pacific salmon start their spawning runs, and bears that live near rivers and streams gorge on them. Adult male brown bears on Kodiak Island consume an estimated 2,788 kilograms of salmon per season, roughly 31 kilograms (68 pounds) per day over a 90-day period. Even smaller subadult females eat around 6 kilograms daily. At peak salmon runs, a single large male may catch and eat 30 salmon in a day.
Fall: Berries and the Race to Gain Weight
Fall triggers hyperphagia, a phase of compulsive eating that prepares bears for hibernation. Adult male coastal brown bears may eat 80 to 90 pounds of food per day during this period, gaining around six pounds daily. The diet flips almost entirely to carbohydrates.
Berries dominate fall feeding. Buffaloberries, chokecherries, hawthorn berries, mountain ash berries, Oregon grape fruits, snowberries, and huckleberries (part of the blueberry family) are all key fall foods. Bear scat in autumn is often visibly full of berry seeds. Bears also dig for calorie-dense roots and bulbs, including oniongrass bulbs (one of the highest-carbohydrate foods in the bear diet), pondweed roots, skunk cabbage roots, bistort, and sweet cicely.
This carbohydrate binge isn’t random. Research on European brown bears confirmed that fall diets are specifically carbohydrate-rich, while spring and summer diets are protein- and fat-dominated. The seasonal shift mirrors what the bear’s body needs: protein for rebuilding muscle after hibernation, then carbohydrates to pack on the fat reserves that will sustain it through winter.
How Location Shapes the Diet
Where a brown bear lives determines what it eats more than almost anything else. Coastal bears with access to salmon runs grow dramatically larger than their inland relatives. The average coastal male in Alaska weighs around 408 kilograms (899 pounds), and some Alaska Peninsula brown bears reach 1,200 pounds. Inland grizzlies, eating a diet heavier in roots, berries, and smaller prey, are typically much lighter.
In the Greater Yellowstone Ecosystem, bears historically relied on cutthroat trout and whitebark pine nuts as major calorie sources. The decline of both, due to introduced lake trout and bark beetle damage, has measurably reduced the protein and energy content of bear diets in that region. When high-quality foods disappear, bears compensate by eating more vegetation, but the nutritional tradeoff is real. Small changes in the availability of nutrient-dense foods like meat, fish, and pine nuts have outsized effects on overall diet quality.
Human Food and Conflict
Brown bears readily exploit human food sources when natural options shrink. Garbage, bird feeders, pet food, fruit trees, livestock feed, and agricultural crops all attract bears. Historically, open garbage dumps in places like Yellowstone supported bears for decades before closures in the late 1960s and early 1970s forced them back to wild foraging.
Habitat disturbances like logging and road building can actually increase berry and green vegetation production in newly opened areas, but they also bring bears into closer contact with people. This overlap is the primary driver of human-bear conflicts and a leading cause of bear deaths. Bears that learn to associate humans with food rarely unlearn it, which is why wildlife managers emphasize securing attractants over any other strategy for coexistence.
The Full Picture
A brown bear’s annual diet is staggeringly varied. Over the course of a year, a single bear might eat grasses, wildflower roots, lily bulbs, ants, moth larvae, moose calves, salmon, clover, dozens of berry species, pine nuts, and the occasional rodent cache it digs from the ground. The proportions shift with every season and every landscape. A coastal Alaskan bear eating 30 salmon a day in July and a Swedish bear flipping rocks for ants in June are the same species, just solving the same problem with different ingredients: consume enough calories to survive six months without eating.