Grizzly bears, a subspecies of the brown bear, are adaptable omnivores with diverse diets. They consume a wide array of food, thriving in various North American ecosystems. Their diet changes significantly with the season and resource availability. This flexibility is crucial for their survival and building fat reserves for hibernation.
Diverse Food Sources
Grizzly bears eat both plants and animals, with a significant portion being plant-based. They forage for vegetation, including grasses, sedges, and forbs like dandelions and clover. Roots and tubers, like horsetails, are excavated using their powerful claws and shoulder muscles. Berries, such as huckleberries, buffaloberries, and strawberries, provide essential sugars for energy.
Insects, including ants, grubs, and army cutworm moths, contribute protein to their diet. In regions with accessible waterways, fish, particularly salmon and trout, become a significant food source during spawning runs. Grizzlies also consume small mammals like ground squirrels, marmots, and voles, often dug from their burrows. Carrion, such as winter-killed moose and elk or carcasses left by other predators, is readily consumed.
Seasonal Dietary Changes
A grizzly bear’s diet shifts yearly based on food availability and metabolic needs. In spring, as they emerge from hibernation, bears often feed on newly sprouted grasses, roots, and any carrion from winter kills that become exposed. They also seek early-season insects and young shoots of plants like dandelions and clover. This period focuses on replenishing energy after months of inactivity.
During the summer months, as plant life flourishes, berries become a prevalent part of their diet. Insects, such as moths and various grubs, continue to be consumed, offering protein. In areas with salmon runs, fish become a high-protein, calorie-dense food source.
As fall approaches, grizzly bears enter a period known as hyperphagia, characterized by intense eating to build fat reserves for the upcoming winter hibernation. Their diet during this time becomes very calorie-dense, often including abundant high-fat nuts, a variety of berries, and continued consumption of fish where available. During hyperphagia, a bear might consume up to 20,000 calories per day, gaining several pounds daily to prepare for months without food.
Opportunistic Foraging
Grizzly bears exhibit highly opportunistic and adaptable foraging behaviors, rarely being selective about their food sources. Their resourcefulness allows them to exploit almost any nutritious item they encounter. They are skilled scavengers, readily consuming carrion and even human-sourced food if accessible.
Their powerful sense of smell, estimated to be many times greater than a bloodhound’s, enables them to locate buried roots, small mammals, or carrion from significant distances. With their long, curved claws and muscular shoulder hump, grizzlies are adept at digging for roots, tubers, and burrowing animals. This intelligence and flexibility in finding and acquiring food allows them to thrive across diverse environments.