The American black bear, Ursus americanus, is the most widespread bear species in North America. It is an opportunistic omnivore whose varied diet changes constantly based on local availability. The black bear’s ability to consume a wide spectrum of food sources, from tender spring grasses to calorie-dense fall nuts, allows it to maintain a broad geographic distribution. Their feeding habits focus on maximizing energy intake from whatever resources are present in their environment.
The Foundation: Plant-Based Primary Foods
Plant matter forms the vast majority of the black bear’s diet, often accounting for approximately 90% of its food intake. This vegetative portion provides the bulk and primary energy source for the bear’s daily maintenance during the active months. In the spring, after emerging from their dens, black bears seek out succulent growth like grasses, forbs, leaves, and flowers, which are high in protein and easily digestible.
As the summer progresses, the diet shifts to soft mast, including a wide variety of fruits and berries such as blueberries, raspberries, elderberries, and black cherries. These small fruits are consumed in enormous quantities, with a bear capable of eating tens of thousands of berries in a single day. Late summer and fall bring concentrated calorie sources in the form of hard mast, like acorns, hickory nuts, and walnuts. These nuts are rich in fats and carbohydrates, which are required for the bear to build up its winter fat reserves.
Opportunistic Protein and Insect Sources
While the bulk of their diet is plant-based, animal protein and fat are consumed for their high nutritional density. Insects are a favored source of this protein, as black bears are efficient at locating and consuming ant larvae, grubs, and the pupae of wasps and bees. They use their powerful limbs and claws to tear apart logs and overturn rocks to access these colonies, often tolerating stings to reach the honey and larvae.
Meat consumption is opportunistic rather than through large-game predation. Bears readily consume carrion, using their acute sense of smell to locate deceased animals like deer from great distances. Active predation is limited to vulnerable, young animals, such as white-tailed deer fawns or elk calves, caught during their first few weeks of life. Black bears also hunt small mammals, raid bird nests, and catch fish during seasonal runs.
Seasonal Eating Cycles and Hyperphagia
The black bear’s diet is governed by an annual cycle of food availability, culminating in a period of intense feeding known as hyperphagia. This biological imperative begins in late summer and continues through the fall, driving the bear to consume calories to prepare for winter hibernation. During this time, the bear’s primary goal is fat storage, which fuels gestation and nursing for females during the denning period.
During hyperphagia, a black bear will spend up to 20 hours a day foraging and may consume up to 20,000 calories daily. This gorging can result in a bear gaining 20% to nearly 100% of its body weight, sometimes adding 3 to 5 pounds per day. Their focus shifts to calorie-dense hard mast, which provides the fat required to enter the den in optimal condition. Female bears must achieve a specific fat threshold to ensure the implantation of the fertilized embryo.
Managing Human-Provided Food Sources
The caloric demand of hyperphagia, coupled with an acute sense of smell, is the primary driver of conflicts between black bears and humans. Anthropogenic food sources, which include garbage, pet food, birdseed, and barbecue grease, are attractive because they offer a high concentration of calories with minimal foraging effort. When bears access these sources, they become habituated, losing their natural fear of humans and associating people and homes with food.
This food-conditioning is detrimental to bears, as human food often contains materials like plastic packaging and metal that can cause internal damage. The high sugar content can lead to tooth decay and abscesses. The consequences of this behavior frequently lead to the bear being labeled a “nuisance,” often resulting in relocation or, in extreme cases, euthanasia.
To prevent this, property owners must “bear-proof” their environment by securing all attractants. This involves storing garbage in bear-resistant containers until the morning of collection, removing bird feeders between April and November, and cleaning outdoor grills immediately after use.