Bears belong to the Order Carnivora and the Family Ursidae, but the common idea of them as simple, monolithic predators is far from the truth. While their classification reflects their evolutionary history, their dietary habits are remarkably varied. Whether a bear hunts depends entirely on the species, the environment, and the time of year. Bears exhibit a spectrum of feeding behaviors, ranging from dedicated hunting to intelligent foraging and scavenging, allowing them to thrive across many different biomes.
The Spectrum of Bear Diets
The feeding strategies observed across the eight bear species are best understood by placing them on a spectrum of dietary reliance. At one end is the hypercarnivore, an animal whose diet consists almost exclusively of meat and fat, best exemplified by the Polar Bear. This species relies on a fat-rich diet, with seals often making up the vast majority of its caloric intake, necessary for survival in the nutrient-scarce Arctic.
Most bear species, including the Brown Bear and the American Black Bear, are classified as omnivores, consuming both plant and animal matter. The massive Brown Bear, which includes the Grizzly, has a highly variable diet, consuming everything from grasses and roots to fish and large mammals. Some inland populations derive as much as 80 to 90 percent of their energy from vegetation.
The American Black Bear is a herbivore-leaning omnivore, with a diet predominantly consisting of grasses, berries, and nuts. Animal matter for this species often comes in the form of insects, larvae, or small vertebrates. This adaptability allows bears to exploit seasonal resource pulses.
Active Predation and Hunting Techniques
For the most predatory bears, active hunting involves specialized techniques developed for high-value, high-fat prey. The Polar Bear is a master of still-hunting, waiting patiently and motionless near a seal’s breathing hole, known as an aglu, for hours. Once a seal surfaces to breathe, the bear uses a lightning-fast strike to pull the animal onto the ice.
Polar Bears also crush snow-covered seal lairs, targeting newborn pups during the spring pupping season. They use their immense weight and strength to break through the roof of the den, securing a high-calorie meal with minimal pursuit effort. Their powerful sense of smell allows them to detect seals nearly a kilometer away, even when the prey is hidden beneath compacted snow and ice.
Brown Bears, particularly Grizzly Bears, engage in active predation on large ungulates, though this often focuses on vulnerable individuals. They pursue young-of-the-year, such as moose or elk calves, using their significant speed and power to overcome the smaller, less agile prey. Mature bears may also target adult ungulates, often relying on ambush or lengthy chases to exploit an animal’s exhaustion or injury.
A highly specialized hunting technique is the pursuit of migrating salmon, famously practiced by Brown Bears in coastal areas. Bears stand or wade into rivers and streams, using a combination of pouncing, scooping, or pinning the fish against the river bottom. These bears often exhibit selective consumption, eating only the high-fat portions like the eggs and brain when salmon are highly abundant.
Opportunistic Feeding and Specialized Foraging
The majority of a bear’s diet across most species is acquired through opportunistic feeding and intelligent foraging. This low-risk strategy involves consuming food that requires little energy expenditure to acquire, maximizing the caloric return. Black Bears and inland Brown Bears are particularly skilled at locating and consuming mast crops, which include calorie-dense acorns, nuts, and various berries.
Bears use their robust claws and strength to access food sources hidden beneath the ground or in rotting wood. They flip over large rocks and logs to find insects, grubs, and larvae, which provide a valuable source of protein. Grizzly Bears, with their long, straight claws, are highly efficient at digging up nutrient-rich roots, bulbs, and small burrowing mammals like ground squirrels.
Scavenging is a fundamental component of the bear diet, providing high-protein meals with no hunting cost. Bears readily consume carrion, including animals that have died naturally or kills abandoned by other predators. Due to their dominance and size, Brown Bears frequently displace other predators from a carcass.
Insects form a significant part of the diet for many species, particularly during certain seasons. Grizzly Bears in some regions feed on large aggregations of army cutworm moths that congregate on mountain slopes. Consuming these insects can provide a substantial portion of a bear’s yearly caloric needs.
Seasonal Shifts in Behavior and Energy Needs
The annual cycle of a bear is dominated by preparation for and recovery from winter hibernation, which dictates seasonal shifts in feeding behavior. The intense feeding period in late summer and fall is known as hyperphagia, a biological state where a bear’s appetite goes into overdrive. During this time, bears must consume an extraordinary amount of food to accumulate the necessary fat reserves for denning.
The need to gain weight rapidly drives bears to consume upwards of 20,000 calories each day, causing them to gain 20 to 30 percent or more of their total body weight. The availability of seasonal resources, such as the concentrated protein of a salmon run or the abundance of a successful berry harvest, is crucial. Bears travel long distances and forage incessantly to meet this biological imperative.
The focus during hyperphagia is on fat and carbohydrate-rich foods, which are the most efficient for energy storage. Hunting efforts may increase during the spring when bears emerge from the den, seeking protein-rich ungulates to rebuild muscle mass lost over winter. The most intense feeding effort is concentrated in the fall to ensure survival through the winter and support potential pregnancy.