The American black bear, Ursus americanus, is the most common and widespread bear species in North America. Regarding cannibalism, the answer is a qualified affirmative: the species rarely consumes its own kind. While not a typical behavior, the consumption of bear tissue occurs under two distinct scenarios. These uncommon events reveal the complex behavioral and ecological pressures governing the lives of these large omnivores.
The Black Bear’s Primary Diet
Black bears are classified as opportunistic omnivores, adapting their diet to the seasonal availability of food sources. Despite belonging to the order Carnivora, their diet consists of an estimated 85% plant matter, including grasses, roots, berries, and nuts.
The remaining portion of their diet is animal matter, primarily composed of insects and carrion. They occasionally prey on vulnerable small mammals or the neonates of ungulates like deer and elk, particularly in the spring. This flexible feeding strategy allows black bears to thrive in diverse environments. During the fall, they enter hyperphagia, feeding voraciously to build the fat reserves necessary for winter dormancy.
Infanticide: Predation on Young
The most active form of bear-on-bear consumption is infanticide, which is driven primarily by reproductive strategy rather than simple hunger. This behavior is overwhelmingly perpetrated by adult male bears, or boars, targeting the young cubs of a female, or sow. The male’s motivation for killing the cubs is to induce the mother to re-enter estrus sooner than she naturally would. A sow will not mate while she is nursing her young, a period that can last for over a year.
By eliminating her dependent offspring, the male removes the barrier to immediate reproduction, allowing him to potentially sire a new litter. This sexually selective infanticide serves to maximize the male’s genetic fitness. Though consumption of the cub’s carcass may sometimes follow the killing, the initial predatory act is rooted in reproductive competition.
This behavior profoundly impacts the survival rates of cubs and is a major source of mortality in bear populations. Females with cubs are highly protective, fiercely defending their young against infanticidal males. They may also alter their movements and home range use to avoid areas frequented by large males.
Scavenging and Opportunistic Consumption
Separate from the reproductive drive of infanticide is the opportunistic consumption of already deceased conspecifics. Black bears are effective scavengers with an acute sense of smell, detecting carrion from long distances. If a black bear encounters the carcass of another bear, regardless of the cause of death, it may consume the remains.
This behavior is purely nutritional, reflecting the bear’s general opportunistic feeding strategy for high-protein food sources. The consumption of a bear carcass is scavenging, which is distinct from active predation. It is a practical response to the availability of meat that requires no energy expenditure for the kill. The bear utilizes this resource like the remains of any other animal it did not kill.