The American black bear, Ursus americanus, is frequently perceived as a forest vegetarian because it spends so much time foraging for plants. This perception does not reflect the biological necessity of their full diet. Black bears are classified as opportunistic omnivores, meaning their diet is highly flexible and includes both plant and animal matter. While they have a digestive system similar to that of carnivores, their survival relies on consuming a wide variety of food sources. This adaptive strategy allows them to thrive across diverse habitats by seeking the right balance of carbohydrates, fats, and protein throughout the year.
The Dominant Role of Plant Matter
Plant-based foods constitute the vast majority of a black bear’s annual caloric intake, often making up 85% to 95% of their diet by volume because these items are the most abundant and easiest to acquire. Bears possess the dexterity and foraging intelligence to seek out a complex menu of plant components.
A significant portion of this vegetation comes from mast, divided into two categories. Hard mast includes energy-dense nuts and seeds, such as acorns, hickory nuts, and beechnuts, which are important for fat storage. Soft mast consists of fleshy fruits and berries, providing necessary carbohydrates and sugars during the summer months. Examples include:
- Blueberries
- Raspberries
- Wild cherries
- Apples
Black bears also consume herbaceous material, especially in the spring, for a quick source of nutrients. They graze on:
- Grasses
- Clover
- Dandelions
- Skunk cabbage
They also use their long claws and powerful forearms to dig for roots, bulbs, and tubers, extracting underground storage organs that provide starches and sugars. Although bears appear herbivorous due to this heavy dependence on plants, the nutritional profile of vegetation is often low in protein and fat. This nutritional gap must be filled by animal sources to ensure proper growth and maintenance.
Essential Animal Protein Sources
Animal matter provides the concentrated protein and fat necessary for black bears, even though it represents a smaller percentage of their total annual food volume. Since they are not efficient pursuit predators, bears rely on opportunistic methods to secure these items, often using their keen sense of smell to locate hidden meals.
Insects are a primary source of animal protein. Bears rip apart rotten logs and overturn rocks to consume colonies of ants and their larvae, which are rich in protein and fat. They also seek out bee and wasp nests, tolerating stings to access the nutritious larvae, pupae, and honeycombs.
Vertebrates are consumed when the opportunity arises. Carrion, or the remains of dead animals, is readily scavenged, especially in early spring. Bears also prey on vulnerable young animals, such as deer fawns and elk calves. Black bears near water sources may incorporate fish into their diet. In regions where anadromous fish like salmon spawn, bears congregate to scoop them out of rivers, providing a concentrated source of fat and protein before winter.
Seasonal and Geographic Dietary Shifts
The black bear’s diet is highly dynamic, shifting throughout the year in response to resource availability and changing metabolic needs. This adaptability allows the species to occupy such a vast range across North America. The seasonal cycle begins in spring when bears emerge from dens having lost significant body weight.
During spring scarcity, the diet is dominated by newly sprouted grasses, forbs, and carrion. Protein intake is higher as bears rebuild muscle mass. They also seek out vulnerable newborn ungulates, such as fawns.
Summer brings an abundance of soft mast, shifting the diet heavily toward berries and fruits. Bears supplement this high-sugar intake with insects to maintain protein levels. This combination supports milk production for females nursing cubs.
The most intense feeding period, known as hyperphagia, occurs in the fall as bears prepare for hibernation. Their appetite increases dramatically, requiring the consumption of up to 20,000 kilocalories per day. Their focus is almost exclusively on high-fat, high-carbohydrate foods like hard mast (acorns and nuts) to rapidly accumulate fat reserves.
Geographic location introduces variation. Inland populations rely heavily on a successful hard mast crop for fall energy. Conversely, black bears in the Pacific Northwest access spawning salmon, which provides a high-fat protein source that alters their local feeding habits.