Bears typically occupy the position of an apex predator in many ecosystems. This designation means that a healthy adult bear generally sits at the top of its food web, with no other animal regularly hunting it for sustenance. While their size and strength offer considerable protection, their status is not absolute, particularly when considering the extreme vulnerability of their young. The true threats to a bear’s survival are highly dependent on its age and, increasingly, its proximity to human activity.
Natural Threats to Bear Cubs and Juveniles
The most significant natural threats to a bear population are concentrated almost entirely on cubs and juveniles, a period when they are small enough to be viewed as potential prey. In North America, species such as gray wolves, cougars, and coyotes are known to predate on young bears, especially when cubs are separated from their mother. This predation is particularly common during the spring and early summer when the young bears emerge from the den.
Cougars often rely on ambush tactics and stealth, while wolf packs use coordinated hunting strategies to isolate the young bears. Even larger birds of prey, such as golden eagles, have been recorded snatching very small cubs. A cub’s survival rate to its first year is estimated to be around 60% in some populations, demonstrating the severity of this early-life threat.
Intraspecies Mortality: Predation by Other Bears
A major cause of death for young bears comes from within their own species through a behavior known as sexually selected infanticide. This reproductive strategy is primarily carried out by adult male bears, or boars, against cubs they have not sired. The act serves to eliminate the mother’s dependent offspring and induce her into an immediate estrus cycle.
Female bears will not become receptive to mating while nursing their young, a period known as lactational anestrus. By killing the cubs, the male terminates lactation, causing a hormonal shift that brings her into heat sooner. This action shortens the female’s reproductive interval, allowing the male to mate. In some brown bear populations, this intraspecies predation is responsible for up to 80% of all cub mortality, leading females to fiercely defend their young.
The Definitive Apex Predator: Human Interaction and Management
The single greatest cause of mortality for adult bears across nearly all species is human activity. In many populations of grizzly and brown bears, human causes account for 77% to 90% of all adult deaths. This mortality is not limited to a single factor but encompasses a range of direct and indirect interactions. Regulated hunting, where it is permitted, is a significant contributor, with legal harvest accounting for 39% to 44% of mortalities in some jurisdictions.
Beyond legal activities, a considerable number of bears are killed through human-wildlife conflict, often categorized as Defense of Life and Property (DLP) kills or management removals. Deaths are attributed to vehicle strikes, poaching, and management actions for public safety. Poaching, or illegal killing, is also a serious threat, with some research suggesting that up to 88% of non-hunting human-caused mortalities in remote areas go unreported to authorities.
Indirect factors rooted in human expansion, such as habitat loss and fragmentation, greatly increase a bear’s exposure to lethal threats. When human development, roads, and rail lines cut through traditional bear habitat, it forces bears into closer contact with people, leading to higher rates of vehicle collisions and conflict deaths. This proximity also attracts bears to human food sources, which often results in the bear being killed by wildlife officials as a “problem animal.”