Skip to main content
King County logo

Here are some interesting and pertinent facts. Beavers are:

  • rodents. They are the largest member of the rodent family in North America.
  • semi-aquatic. They spend much of their lives in ponds, rivers, streams, and adjacent woodlands.
  • nocturnal. They do most of their work at night. They are also active year-round, even when their pond surfaces freeze in winter.
  • monogamous. Adults usually mate once a year, in February, and produce two to four kits in May.
  • territorial. Colony densities rarely exceed one colony for every half-mile of stream.

Beaver family groups, or "colonies," are made up of one to eight individuals (five on average) with all members working together to build lodges and dams and gather food. Colonies typically consist of two adults and the young of the current and previous years. When the new kits are about to be born in the spring, the 2-year-old beavers usually leave their family group to establish a colony of their own. This pattern is why most beavers are out establishing new homes in the spring and summer.

Beavers form dams out of branches, logs, rock, and mud to create ponds. These ponds help keep beavers safe from predators, and the diverse wetland systems that result also support a wide variety of fish, amphibians, birds, and mammals (see Environmental Benefits). Beaver lodges are built from branches and logs plastered together by mud, though beavers will also make dens in the banks of ponds and rivers. Beavers feed close to water where they are safer from predators, and they eat the bark, leaves, and twigs of many tree species as well as herbaceous aquatic plants such as lily pads, skunk cabbage, grasses, and sedges.

The King County Beaver Working Group is in the process of writing a literature review on beaver life history to provide information that is helpful to understand when trying to co-exist with beavers. That paper should be out in early 2019.

Beavers caught on wildlife cam

The following links provide more information about beaver biology and ecology.