Bears occupy a high position in nearly every ecosystem they inhabit. Their immense size, formidable strength, and generalist diets typically place them beyond the reach of most other carnivores. Despite this standing, bears are not entirely immune to threats from other animals, though successful predation is rare and often depends on the bear’s age, health, or specific circumstances. Threats include predators specializing in hunting young bears, rivals capable of challenging a mature adult, and the significant threat that bears pose to one another.
The Vulnerability of Cubs
The highest rate of predation occurs among bear cubs, which lack the size and experience necessary to defend themselves against determined hunters. A mother bear (sow) is fiercely protective, but her offspring are often targeted when they are separated or when the mother is distracted while foraging. In North America, threats to young black and brown bears include coordinated pack hunters like gray wolves and solitary ambush hunters such as cougars.
Wolf packs use coordinated strategies to separate the young from the mother bear, significantly impacting cub survival rates. Cougars (mountain lions) are silent stalkers that use superior agility and ambush skills to prey on isolated cubs, particularly in mountainous terrain. Golden eagles, with their massive wingspans and powerful talons, have also been documented preying on very small cubs from above. Coyotes and bobcats may opportunistically take advantage of very young or vulnerable cubs that wander too far from the sow.
Apex Predators That Target Adult Bears
Successful predation on a healthy, mature adult bear is an extremely rare event, typically requiring specialized strength, massive size, or group coordination. The most well-documented natural predator is the Siberian tiger (Amur tiger), which shares territory with Ussuri brown bears and Asiatic black bears in the Russian Far East. Tigers possess the size and power to take down even large brown bears, often employing an ambush strategy. While these encounters are not common, bears constitute a small but consistent percentage of the tiger’s annual diet, often focusing on smaller adults, sub-adults, or those emerging from hibernation.
In other regions, large, coordinated packs of gray wolves pose an occasional threat, primarily to sub-adult or older, weaker brown bears. They often engage in prolonged attacks to wear down the large animal. While wolves and bears primarily compete over carcasses, there are documented instances of multiple wolves surrounding and attacking a bear. In the marine environment, the only theoretical threat to the polar bear is the orca (killer whale), but there is no documented evidence of them actively hunting the bears, as their habitats and primary prey sources rarely overlap.
Intraspecies Mortality
Intraspecies conflict is the most significant non-human threat to a bear and a leading cause of mortality across several species. This internal conflict is driven largely by territorial disputes, competition for mates, and infanticide. Adult male bears (boars) are the primary perpetrators of infanticide, systematically killing cubs that are not their own offspring.
This brutal behavior serves an evolutionary purpose, as the death of the cubs causes the female to return to estrus sooner, allowing the male to mate and pass on his genes. Infanticide can account for a substantial percentage of cub deaths, sometimes as high as 45% in some brown bear populations. Cannibalism often occurs following the killing of a conspecific, though this is usually the opportunistic consumption of a carcass rather than direct predation. This behavior is particularly prevalent in polar bears, where larger males frequently kill and consume smaller individuals.