Beavers face threats from predators, disease, human activity, and even other beavers, but the balance of these threats shifts dramatically depending on the animal’s age. Adult beavers are large enough to deter most predators, so their biggest historical killer has been humans. Kits, on the other hand, are vulnerable to a long list of wildlife. Only about 28% of beaver kits survive to be counted in the population the following year, based on demographic research in unexploited beaver colonies in southern Illinois.
Natural Predators
Wolves are the most significant wild predator of adult beavers. An adult beaver can weigh 40 to 60 pounds, which discourages many would-be attackers, but wolves hunt in packs and frequently encounter beavers near water. Black bears, brown bears, wolverines, and lynx also kill beavers when the opportunity arises, though these encounters are less common.
Young beavers face a much wider range of predators. Coyotes, fishers, river otters, minks, hawks, owls, and even alligators in the southeastern United States all prey on kits. Because kits are small and less experienced at escaping into water or the safety of a lodge, their first year of life is by far the most dangerous. Juvenile males in one long-term study had an annual survival rate of just 55%, compared to 87% for adult males.
Humans: The Biggest Killer by Far
Since European colonization of North America, the beaver population has been reduced by 80 to 90% from its historic level. Fur trapping drove that collapse. Beavers were hunted relentlessly for their dense, waterproof pelts, which were used in the hat trade for centuries. By the early 1900s, beavers had been eliminated from most of their range.
Today, trapping continues as a wildlife management tool. Across the U.S., state agencies issue permits for lethal removal of beavers when their dams flood roads, farmland, or timber stands. In Montana, for example, the state department of Fish, Wildlife and Parks authorizes killing beavers outside the normal trapping season through damage permits. For much of recent history, the default response to beaver-related flooding has simply been to trap and kill the animals. Conservation groups and federal agencies like the U.S. Fish and Wildlife Service are now promoting non-lethal alternatives, such as flow devices that regulate water levels through beaver dams without removing the animals.
Disease and Tularemia
The most well-known disease that kills beavers is tularemia, a bacterial infection sometimes called “beaver fever” (though that nickname is also used for giardiasis, a different illness). The bacterium thrives in rodents and rabbit-like mammals, and beavers are highly susceptible. During outbreaks, large numbers of animals can die in a short period. Tularemia can also spread to humans who handle infected carcasses or drink contaminated water, which is one reason wildlife agencies monitor beaver die-offs closely.
Parasites, including intestinal worms and the protozoan Giardia, are common in beaver populations. While giardiasis rarely kills beavers outright, heavy parasite loads weaken animals and make them more vulnerable to predation or harsh winters.
Other Beavers
Beavers are fiercely territorial, and fights between neighboring families or intruding dispersers are not rare. A large study examining more than 1,000 beavers across long-term research sites in Norway and the United States found that aggressive encounters leave visible scars on beavers’ tails, and those scars accumulate as the animals age. Territorial conflicts appear to be the primary driver of these fights, with dispersing young beavers attempting to claim new territory and established residents defending theirs.
Most beavers survive these encounters with injuries rather than dying from them. But fatal outcomes do happen. Researchers have documented cases where beavers killed other beavers during territorial disputes. In areas with high population density, aggressive encounters become more frequent, raising the stakes for dispersing juveniles looking for a place to settle.
Starvation and Winter Conditions
Beavers are herbivores that depend on bark, aquatic plants, and woody shrubs. In northern climates, they spend months locked under ice, relying on underwater food caches they stockpiled in the fall. If a food cache runs short, or if an early freeze catches a colony unprepared, starvation becomes a real risk. Research on unexploited beaver populations found that all recorded mortalities occurred during fall and winter, suggesting that cold-season food stress and exposure are major killers even in the absence of trapping.
Dispersal compounds this danger. Juvenile beavers leave their family colony at one to two years of age, and dispersal rates range from 38% to 59% depending on sex and age. A dispersing beaver traveling overland to find new territory is exposed to predators, lacks the protection of a lodge, and may struggle to find adequate food before winter sets in.
Environmental Pollutants
Because beavers spend their lives in and around water, they are exposed to whatever contaminants flow through their habitat. Research on Eurasian beavers in northeastern Poland measured cadmium, lead, copper, and zinc levels in the animals’ livers and kidneys. Lead levels were consistently low, well below thresholds considered dangerous. Cadmium told a different story: it builds up in beaver tissue over time, and every adult beaver in the study exceeded the safety threshold for cadmium in kidney tissue. Whether these levels directly cause beaver deaths in the wild remains unclear, but the pattern of bioaccumulation means older beavers in polluted watersheds carry an increasing toxic burden that could contribute to organ damage and shortened lifespans.
Beavers in areas with industrial runoff, agricultural chemicals, or mining waste face higher exposure. Because they eat bark and aquatic vegetation that absorbs contaminants from sediment and water, they function as indicators of watershed health. When beavers in a region show elevated pollutant levels, it signals broader environmental problems.
How Long Beavers Live
In the wild, beavers that survive their first year typically live 10 to 15 years, with some individuals reaching their early twenties in protected populations. Adult survival rates are relatively high once a beaver is established in a territory: around 87% annually for males and 76% for females in one untrapped population. The combination of a sturdy lodge, a family group, and large body size gives established adults strong defenses against most natural threats. The vulnerable periods are kithood, dispersal, and old age, when worn-down teeth can make it impossible to feed effectively.