Beavers (Castor canadensis) are the largest native rodents in North America (figure 2). They are found throughout North America, except for the Arctic tundra, and desert Southwest. Beavers can live almost anywhere with year-round water and winter forage. Trapping during the late 1800s significantly reduced beaver numbers. Although an estimated 60 million beavers lived in the United States before European settlement, they had been nearly exterminated by 1900. During the 20th century, beaver populations rebounded, primarily because of restrictions on trapping and translocation programs conducted by wildlife agencies. Most adult beavers weigh between 35 and 50 pounds and are about 3 feet long from head to tail. Some beavers weigh more than 100 pounds.

Figure 2—The beaver is a stocky animal well adapted for life
in the water. They have large front teeth (incisors), webbed
rear feet, and a broad flat tail.

Given a water source and a supply of food (trees and brush), beavers can create suitable habitats for themselves. Beavers frequently build dams to modify their environment. In addition, they mound sticks and mud to build lodges (figure 3) and burrow into banks to construct underground dens. In colder climates, beavers collect and store plants, forming food caches for the winter. This behavior is less common in warmer climates.

Beaver dams and the ponds behind them reduce erosion while increasing vegetation diversity and edge habitat, where water meets the land. Other wildlife species generally benefit, but beavers can be destructive. Reduced waterflow can harm some wildlife. High beaver populations also can harm native plant communities. Extensive foraging by beavers can destroy plant restoration projects. Beavers have severely hampered efforts to establish vegetation for improved salmon habitat in the Pacific Northwest.

Beavers generally are active for about 12 hours each night, but may be active during the day. Beavers are regarded as monogamous, forming family groups that include an adult male and female, along with their offspring. Emerging evidence suggests that beavers living where winter food is not limited, in the South for instance, may have larger colonies with several reproductively active females. Females give birth to two to four kits each spring. The kits remain with the family for a couple of years before dispersing to establish a new territory.

Figure 3—This beaver lodge was made from sticks and mud.
A runway (trench) leads to the entrance. —Drawing by
Dr. Jeanne Jones