The family Ursidae, which includes all eight bear species, has a complex and varied dietary profile. While the popular image of a bear often involves hunting large prey, their daily food consumption is far more diverse and dictated by environment. Their diets adapt to local conditions and seasonal availability.
The Omnivore Spectrum
Most bear species are classified as omnivores, meaning their digestive systems process both plant and animal matter. This classification represents a broad spectrum, with specialized diets evolving based on geographic location and resource abundance. A bear’s feeding strategy prioritizes obtaining the most calorically dense food available with the least effort, which is necessary for maintaining their large body mass.
The brown bear often derives up to 90% of its energy from vegetation, roots, and berries during certain times of the year. Conversely, the polar bear is hyper-carnivorous, relying almost entirely on the high-fat content of marine mammals. This range demonstrates that the omnivore label describes a family prioritizing fat and protein when possible but subsisting on plants when necessary.
Defining the Diet of Common Species
American Black Bear
The American Black Bear is the quintessential omnivore, with a diet overwhelmingly composed of plant matter. Over 75% of their food intake consists of grasses, berries, nuts, and roots. Insects like ants and beetle larvae provide a consistent source of protein. They are effective foragers, using their keen sense of smell to locate food and their dexterity to peel bark or tear apart rotten logs for grubs. Animal matter, including small mammals and carrion, typically makes up a small fraction of their diet, consumed only when an opportunity presents itself.
Brown Bear
Brown Bears, including the inland Grizzly and coastal Kodiak bears, exhibit a diet that shifts dramatically with the seasons. In the spring, they focus on high-protein sources, such as scavenging winter-killed animals or preying on vulnerable elk and moose calves. Later in the year, their diet transitions to large amounts of vegetation, including sedges, roots, and berries to build up fat reserves. Coastal populations shift their focus to fish during the annual salmon spawning runs, consuming the most fat-rich parts of the fish, such as the skin and roe.
Polar Bear
The Polar Bear is the only bear species classified as a marine mammal and is an extreme dietary specialist. Their survival depends almost entirely on ringed and bearded seals, which provide the high-fat blubber necessary for insulation and energy in the Arctic environment. Their hunting techniques are specialized for capturing seals on the sea ice, such as waiting patiently at breathing holes. While they have been observed eating items like bird eggs or small rodents when stranded on land, these foods do not contain the caloric density necessary to sustain their body size or meet long-term nutritional needs.
The Role of Small Mammals in Bear Diets
Bears, especially Black and Brown Bears, will eat small mammals, including rabbits and hares, but this is a minor and opportunistic part of their overall diet. Brown bears are adept at digging out burrowing rodents like ground squirrels, marmots, and pikas, which can be a regular food source in some areas. Hares and rabbits are generally too fast and low-yield to justify the energy expenditure of a sustained chase.
Consumption of these lagomorphs often occurs when the bear stumbles upon an easy target, such as a young or injured animal, or if the prey is caught in a vulnerable location. Scavenging a carcass or finding a rabbit confined in a backyard hutch represents a high-reward, low-effort meal that bears readily exploit. These small animals provide a protein boost, but they are not a primary dietary staple that a bear actively hunts daily.
Seasonal Shifts and Opportunistic Feeding
A bear’s decision to consume small, fast prey like a rabbit is understood through seasonal necessity and opportunistic feeding behavior. In the fall, bears enter hyperphagia, a state of excessive hunger where they must consume up to 20,000 calories a day to prepare for winter dormancy. During this time, every available calorie matters, and any easily acquired protein source is valuable for building fat reserves.
Protein is also sought after during the spring, especially by female bears emerging from dens with cubs. Sufficient weight gain and fat storage are necessary for delayed implantation, a process where the fertilized egg will only implant if the mother has achieved a minimum body fat threshold. This biological pressure makes them opportunistic feeders that will not pass up an easy meal if it provides a necessary nutritional boost. Their diet is a flexible response to their environment, prioritizing whatever food is most abundant, accessible, and energy-rich.