Brown bears (Ursus arctos) are adaptable animals found across diverse Northern Hemisphere landscapes. Their ability to thrive in various environments stems from their flexible, omnivorous diet. These large mammals consume both plant and animal matter, and are known for opportunistic foraging, utilizing whatever food sources are abundant. This dietary versatility allows them to adjust their eating habits to shifting availability throughout the year and across different geographic regions.
An Omnivorous Appetite
Brown bears consume a wide array of foods. Plant matter constitutes a significant portion of their diet, sometimes making up to 90% of their food energy. This includes vegetation such as grasses, sedges, and forbs, particularly in spring. They also consume roots, tubers, and bulbs, which they skillfully dig up using their long, strong claws. Berries like blueberries, huckleberries, raspberries, and elderberries are highly favored when in season, alongside nuts, seeds, and fungi.
Brown bears also actively seek out and consume animal matter. Insects are a common dietary component, with bears eating ants, grubs, and larvae found in beehives. Fish, especially salmon during their spawning runs, are a substantial protein source for many populations. Smaller mammals such as rodents, including marmots, ground squirrels, mice, and voles, are also prey. Larger prey like elk, deer, moose calves, and caribou are hunted, though a significant portion of their meat intake often comes from scavenging carrion, particularly winter-killed animals available in spring.
A Menu Driven by Season
The diet of brown bears undergoes shifts throughout the year, influenced by seasonal food availability. As bears emerge from hibernation in spring, their diet largely consists of easily accessible green vegetation and carrion. They graze on new shoots, grasses, sedges, and forbs, and scavenge carcasses of animals that did not survive the winter. This early season intake helps them regain some of the weight lost during their denning period.
Moving into summer, their diet diversifies with ripening fruits and an increase in insect populations. Berries become increasingly important, providing essential carbohydrates. In areas with fish populations, summer also marks the beginning of fish runs, offering a high-protein food source.
By late summer and into fall, brown bears enter hyperphagia, characterized by intense feeding to build fat reserves for hibernation. They prioritize high-calorie foods such as abundant berries, nuts, and, for many populations, large quantities of spawning salmon. This critical period of weight gain directly impacts their survival through the winter.
Regional Dining
The specific diet of a brown bear is highly dependent on its geographical location, reflecting the unique resources available in different ecosystems. In coastal regions, such as parts of Alaska and British Columbia, brown bears exhibit a strong reliance on aquatic resources. Salmon forms a major part of their diet, especially during spawning season, where bears can consume dozens of fish per day. They also forage for shellfish like crabs and clams along beaches and estuaries.
Inland forest and mountain regions, such as Yellowstone National Park, present a different menu. Here, brown bears consume various plant materials like berries, roots, and pine nuts, particularly whitebark pine seeds. They also hunt ungulates such as elk and bison, often targeting calves or scavenging carcasses. Insects, including army cutworm moths, can contribute significantly to their caloric intake.
In northern tundra or arctic regions, where vegetation is sparse and large ungulate herds are present, bears may rely more heavily on caribou and muskoxen, along with small rodents and specialized tundra plants. These regional differences highlight brown bears’ adaptability to local food opportunities.