The grizzly bear, a subspecies of brown bear, is one of North America’s most imposing terrestrial animals. These formidable creatures are primarily found in the wilderness of Alaska, Canada, and the northwestern United States. A full-grown male can weigh between 135 and 390 kilograms, while females typically range from 95 to 205 kilograms. Given their immense size and power, the list of animals that successfully prey on a grizzly bear is exceptionally short.
Defining the Apex Predator Status
The grizzly bear’s ecological standing is at the very top of its food chain, secured by physical adaptations. Their immense body mass is supported by a distinctive, muscular hump over their shoulders, which provides tremendous strength for digging and delivering powerful forelimb strikes. Grizzlies can sprint at speeds up to 56 kilometers per hour. Their defense is also behavioral, characterized by intense aggression, especially when defending a food source or offspring. A mother grizzly is fiercely protective, a factor that deters most potential predators from approaching her cubs. This combination of size, strength, speed, and protective instinct ensures that a healthy, adult grizzly bear is rarely viewed as potential prey.
Species That Prey on Young Grizzlies
The most common instances of predation occur when the bears are at their most vulnerable stage of life: as cubs or young juveniles. Grizzly bear cubs are born weighing less than 500 grams, and they remain dependent on their mother for up to two years. During this time, a cub separated from its mother is a potential target for several large predators.
Coordinated packs of gray wolves pose a threat, often isolating a cub or juvenile bear through focused group efforts. Mountain lions are known to prey on bear cubs, utilizing their stealth and agility to ambush young bears that have become isolated from the mother. Smaller carnivores like coyotes may occasionally target very young, unprotected cubs. These external predators primarily succeed when the mother is distracted, separated, or if the young bear lacks the size and experience to defend itself.
Predation Through Intra-Species Conflict
A significant threat to a young grizzly bear often comes from within its own species, specifically from adult male grizzlies. This form of mortality is known as sexually selected infanticide, where a large male kills a cub that is not his own. The primary biological driver for this behavior is to bring the female back into estrus sooner than she would if her cubs survived.
Infanticide is a notable cause of cub mortality, with studies showing that up to 45% of cub deaths in some populations can be attributed to adult males. Cannibalism may follow these predatory events, or it can occur opportunistically when a bear finds the carcass of a conspecific. While intra-species conflict is most often directed at cubs, fights between adult bears over territory or feeding rights can occasionally result in death.
Natural Predators of Mature Grizzlies
For a healthy, mature grizzly bear, true natural predation is a rare event. Any successful predation on an adult grizzly requires specific circumstances. The most credible threat comes from large, determined packs of gray wolves.
These encounters rarely involve the wolf pack hunting a healthy adult grizzly for food but rather engaging in a conflict over a carcass or a shared resource. Predation, when it does occur, is limited to old, sick, or injured adult grizzlies that can no longer effectively defend themselves against a coordinated attack. The risk involved in attempting to take down a powerful animal means that even large predators will not challenge a healthy adult grizzly.