Only a small portion of the diet of bears consists of animal matter, and then primarily in the form of colonial insects and beetles. Most vertebrates are consumed in the form of carrion. Black bears are not active predators and feed on vertebrates only if the opportunity exists. The diet of black bears is high in carbohydrates and low in proteins and fats. Consequently, they generally prefer foods with high protein or fat content, thus their propensity for the food and garbage of people.
Bears feeding on a protein-rich food source show significant weight gains and enhanced fecundity.
Spring, after the bears' emergence from winter dens, is a period of relative food scarcity. Bears tend to lose weight during this period and continue to subsist partly off of body fat stored during the preceding fall. As summer approaches, a variety of berry crops become available. Summer is generally a period of abundant and diverse foods for black bears, enabling them to recover from the energy deficits of winter and spring. The sexes coexist briefly during the mating season, which generally peaks from June to mid-July.