Brown bears, found across vast regions of Eurasia and North America, have a remarkably diverse diet. They are classified as omnivores, consuming both plant and animal matter. This broad approach allows them to adapt to a wide range of habitats and food availability. Their opportunistic feeding habits enable them to thrive by utilizing whatever sustenance is accessible.
The Broad Spectrum of Their Diet
Brown bears exploit different food sources based on availability. Their omnivorous diet is influenced by what is abundant in their surroundings, not a strict preference for plants or animals. This flexibility helps them survive across diverse ecosystems. They consume the greatest variety of foods among all bear species, constantly exploring potential sources. Their jaw structure is well-suited for processing a wide range of items.
Key Plant-Based Foods
Despite their powerful build, brown bears often derive a significant portion of their energy from plant matter, sometimes up to 90% in certain regions. They consume a variety of plants including berries, nuts, roots, tubers, grasses, flowers, and fungi. Berries like blueberries, raspberries, and huckleberries are important in late summer and fall. Acorns and pine cones also provide essential carbohydrates.
Brown bears use their long, strong claws to dig for roots, bulbs, and tubers such as glacier lilies and dandelions. These underground foods are important in spring when other sources are scarce. Grasses, shoots, and sedges are also consumed, particularly in the spring, though they are less nutritious.
Key Animal-Based Foods
Animal-based foods provide brown bears with essential protein and fats. They regularly consume insects, including ants, grubs, and beehive larvae, often tearing apart rotten logs or digging in soft earth. In some areas, army cutworm moths can be a significant food source, with bears consuming tens of thousands daily during summer.
Fish, especially spawning salmon, are an important part of the diet for coastal brown bear populations, such as those in Alaska. Bears often target the fat-rich parts of salmon, like the skin, brain, and roe.
Brown bears also hunt small mammals such as rodents, marmots, ground squirrels, hares, and pikas. They can detect active burrows and dig them out to access prey. Carrion, or dead animals, is another important food source, particularly in spring when winter-killed ungulates become available. While they primarily scavenge, brown bears may also prey on vulnerable animals like elk, moose, or deer calves. They may occasionally take larger ungulates.
Seasonal and Regional Dietary Shifts
A brown bear’s diet changes throughout the year and across different geographic locations, reflecting food availability. In spring, after emerging from hibernation, their diet primarily consists of winter-provided carrion, grasses, shoots, and roots, as more nutritious options are still developing. As spring progresses into summer, bears shift to consuming green vegetation and a variety of insects.
During late summer and autumn, fruits and berries become increasingly important, providing the high-energy carbohydrates necessary for bears to build fat reserves before winter hibernation. In regions with abundant fish, like coastal Alaska, salmon runs in late summer and fall allow bears to gain substantial weight. Regional variations are pronounced; for instance, inland grizzlies in areas like Yellowstone National Park may rely more on ungulates and insects, while bears in Scandinavia consume significant amounts of berries and sometimes ungulate calves or even domestic sheep.