The grizzly bear (Ursus arctos horribilis) is a powerful apex predator in North America. As an omnivore with a highly varied menu, questions often arise about the limits of its consumption, specifically whether it preys upon or consumes its own kind. The central question is direct: Does cannibalism occur within grizzly bear populations?
Defining Cannibalism and the Direct Answer
In a biological context, cannibalism is defined as the consumption of all or part of another individual of the same species (a conspecific). This behavior is a documented, though infrequent, occurrence in grizzly bears. Cannibalism can involve active predation, where a bear kills another for consumption, or opportunistic scavenging of an already deceased conspecific. Both scenarios fit the definition, but the motivations are distinct.
Systematic reviews show that conspecific consumption is most frequently associated with two main drivers: infanticide and conspecific strife. Therefore, the direct answer is that grizzly bears do engage in cannibalistic behavior, often linked to reproductive strategies or simple opportunism.
Infanticide: The Primary Mechanism of Bear-on-Bear Predation
The most common and well-documented form of bear-on-bear predation leading to consumption is sexually selected infanticide. This reproductive strategy is primarily carried out by adult male bears (boars) who target the young cubs of a female (sow). By killing the cubs, the male eliminates a rival’s offspring and drastically shortens the time until the female becomes receptive to mating again. This maximizes the infanticidal male’s own reproductive success.
The killing of young is often followed by the consumption of the cub’s body, which provides the male with a high-protein meal. This is recorded as the most frequent type of cannibalism in bears. Female grizzlies respond to this threat by actively avoiding habitats frequented by dominant adult males. Mother bears are intensely protective and will fiercely defend their offspring, occasionally engaging in dangerous conflicts with the attacking boar. Studies show that males commit about 80% of reported infanticidal attacks in brown bears.
Scavenging and Adult Bear Conflict
Beyond the reproductive motivation of infanticide, grizzly bear cannibalism also occurs through opportunistic scavenging and, rarely, through outright adult conflict.
Opportunistic Scavenging
Opportunistic scavenging involves a bear consuming the carcass of a conspecific that died from another cause, such as illness or a vehicle collision. This consumption reflects the grizzly’s nature as a highly effective scavenger. The bear views the remains simply as a convenient source of calories. This type of cannibalism is considered casual, as it is not directly connected to the primary cause of death.
Conspecific Strife
The second, non-infanticidal scenario involves active conflict between two adult bears, often resulting in “conspecific strife” cannibalism. These events are extremely rare, typically precipitated by intense competition over a valuable resource, such as a large carcass or a territorial boundary. If two large males fight, the loser may be killed and partially consumed by the victor, especially during resource scarcity. The motivation in these adult conflicts is dominance and survival, with consumption being an opportunistic outcome of a violent dispute.