Primary predators of the beaver include wolves, coyotes, mountain lions and black bears. Other animals that occasionally prey on beavers include foxes, wolverines, lynx, bobcats and alligators. Golden eagles and bald eagles sometimes attack beaver young.
Beavers build dams and lodges to protect themselves from predators. Working at night, beavers cut down trees and carry stones and mud to build dams to block streams or rivers. In the midst of the resulting pond, they construct lodges out of sticks and mud. The mud on the outside turns nearly as hard as stone. The entrances are underwater, making it virtually impossible for other animals to find them. Once complete, the lodges are impenetrable to predators, with the exception of black bears, who smash them open with their paws. When beavers sense danger, they slap the water with their broad tails to warn other beavers and then dive underwater, where they can remain for 15 minutes without surfacing.
Beavers are an integral part of a forest's ecosystem. The dams they build to protect themselves raise water levels, creating increased habitat for bird species. Beaver ponds also help populations of salmon and trout to grow. Though in the past it was thought that the cutting of trees by beavers led to the depletion of a forest; in fact the thinning of trees by beavers contributes to long-term growth in wooded areas.