About Beavers

Beaver on felled tree at PV © Ed Anzures
© Ed Anzures

Easily recognizable by its long, broad tail, and its noticeably big and sharp front incisor teeth, beavers are most active at night.

The most obvious signs of beavers are the distinctive "pencil points" of gnawed tree trunks and the lodges and dams they build.


The largest North American member of the rodent family, the beaver (Castor canadensis) measures 32 to 48 inches and weighs anywhere from 27 to 67 pounds.

Beavers are well adapted for their aquatic environment, with broad, flat tails (at a length of 12 to 20 inches) that they use to scull or steer, and large, webbed hind feet. They use their small and un-webbed front feet for carrying and digging. Beavers sport brown, thick fur, with a waterproof underfur. 

People often mistake the much-smaller muskrat for a beaver because of its aquatic habits and similar shape. But the muskrat only weighs two or three pounds and has a narrow, laterally flattened tail.

Life Cycle

Beavers in North Pond at Pleasant Valley Wildlife Sanctuary (Photo: Bill Bernbeck)

A family unit—called a colony—consists of two adults, the young of the year, and the young of the previous year. Beavers become sexually mature at two years old, at which time they are driven off by the adults to seek mates and find territories of their own.

Beavers are typically monogamous and, unlike many mammals, the male stays with the female year-round. They mate between January and March, and the kits are born four months later. The litter can contain between one and nine kits, but a typical litter is four.

The kits are born fully furred with their eyes open, and become skillful swimmers by the time they reach one-week old. They're able to eat vegetation at two to three weeks, and are weaned by the time they reach three months.

Beaver Dams

Beaver chewing stick in water © Amy Vaughn 1000
© Amy Vaughn

Beavers are unique among mammals in that they alter their habitat to meet their needs by damming streams to form ponds. This behavior actually benefits other species (including people) as well.

By building dams and flooding woodland swamps, beavers play an important part in the restoration of lost wetlands—over 50% of our wetlands have disappeared since European settlement in North America—providing habitat and food for a wide variety of plants and animals. Learn More >

Beavers build their dams in order to create deep ponds that won’t freeze at the bottom in winter. Within these ponds, they build "lodges" to provide protection for the young in summer and for the entire colony in winter. Lodges are large structures, from 15 to 40 feet across and three to six feet above the water. They line the living space (located above the waterline) with dry plant material. Entrances are located underwater.


Beavers are vegetarians, feeding on any number of plants and trees in the summer. In the winter they feed on the inner bark of trees, particularly aspen, willow, birch, and alder. In the fall they collect edible branches and anchor them in the mud at the bottom of the pond near the entrance to their lodge. In the winter, the colony stays inside the lodge, leaving only to gather the cached food from the bottom of the pond.

Beavers in Massachusetts

Before colonization by European settlers, the beaver thrived in Massachusetts, but unregulated hunting and trapping combined with extensive deforestation resulted in its extirpation by the end of the 18th century.

With the decline of agriculture at the beginning of the 20th century, the forests that beavers needed for habitat began to regrow. In 1928, beavers were discovered in West Stockbridge, the first recorded occurrence in the state since 1750. To help restore beaver populations, three additional beavers were brought from New York and released at Mass Audubon’s Pleasant Valley Wildlife Sanctuary in Lenox. Today they live throughout the state, with the exception of Cape Cod.

Situations & Solutions

Both humans and beavers change their surrounding to suit their needs, and from time to time, these needs may come into conflict. Property owners, in particular, may experience unwanted flooding. Since beavers are largely beneficial, it’s in our interest to find the least draconian solutions to beaver problems. Learn More about the options.