Beavers have a relatively long life span, with some individuals recorded to have lived 21 years. Most do not live past 10 years. Their predators include coyotes, bobcats, river otters, and mink, which prey on young kits. Bears, mountain lions, wolves, and wolverines also prey on beavers.
Beavers become sexually mature in 1½ years and form life-long pair bonds. Beavers mate from November through March. They produce 1 litter per year and 3 or 4 young are born about 105 days after mating. Young beavers typically are weaned in 2 weeks.
Dens and Lodges
Beavers are skilled at building dams on streams. They build lodges in ponds and dens in stream banks, depending on what habitat is available (Figure 5). The lodge or den is used for raising young, sleeping, protection from predators, and food storage.
Figure 5. Cross-section of a beaver lodge.
Image by PCWD.
Beavers are very territorial. A colony generally consists of 4 to 8 related individuals that resist the addition of outsiders to the colony. Young beavers commonly are displaced from the colony shortly after they become sexually mature at about 2 years old. They often move to another pond to begin a new colony, though some become solitary and inhabit abandoned ponds.
Dam-building and tree-cutting tend to increase as beavers prepare for the freezing winter weather. In northern areas, beavers stockpile or cache tree limbs, grass, cattail, and cornstalks below the surface of the water to ensure access to food below the ice. A fresh food cache is a sign of an active lodge.
Beavers may be abundant wherever aquatic habitats and trees are available.
The size and species of trees cut by beavers can vary from softwoods that are 1-inch diameter-at-breast-height (DBH) to 6-foot DBH hardwoods. Some beavers girdle pines and sweetgums for the sap that seeps from the wound. Poplar and aspen are preferred food trees. Many species of trees are used for building dams.