American beaver

Castor canadensis

Beavers are the largest rodent in North America. They're found in streams, rivers, marshes and small lakes. Their range extends across Canada and the United States except in the Arctic tundra, the Florida panhandle and Southwest deserts. They are herbivores and engineers who change their environment by cutting down and moving trees and branches to build dams and lodges.

Did you know?

  • A beaver can fell an 8-foot tree in five minutes.
  • In the 1700 and 1800s, trappers ranged across the continent, catching beavers for their valuable pelts. Pelts were used as currency in colonial America.
  • Beaverton, Oregon was once an area of marshes and small lakes created by beavers. The only dry places for the first settlers to live were atop beaver dams.
  • The beaver is the Oregon state animal.

Beaver lingo

Castor or castoreum: Beavers have been called castor cats. Castoreum is an oily substance the beaver excretes along with urine to mark territory. Castoreum is used to make perfume and as a food additive.

Beaver behavior and facts

  • Beavers prefer to eat herbaceous matter (green plants), both those growing in water and on land. They will eat woody vegetation if green plants aren't available, especially from late fall to early spring.
  • To create deepwater protection, they fell trees to build dams made of wood, grass and mud. They also use wood to build lodges to live in. The main lodge of a beaver dam is 6 to 10 feet in diameter.
  • Beavers have adaptations to keep warm and dry: an undercoat that traps air to insulate their skin; valves in their nostrils and ears that prevent water from entering; non-webbed front feet with digging claws and webbed hind feet for swimming; a flap of skin behind the front teeth that allows them to gnaw bark underwater without getting a mouthful of water or wood chips.
  • Beavers' most identifiable characteristics are their large front teeth and broad tail. Their teeth never stop growing and must be worn down by use. Beavers broad, scaly tails are used as rudders and can be slapped against the water to warn others of danger.
  • Beavers are diurnal (active during the day) but nocturnal near human activities. They don't hibernate. They live in colonies of four to eight. Each fall, they collect and anchor a supply of green branches underwater for winter food.

From birth to death

  • Gestation: 3 months
  • Babies are born in litters of two to four, usually in spring.
  • The young can swim within one day of birth.
  • Beavers leave their parents at age two.
  • Lifespan: 13 to 20 years

Vital statistics

  • Size: 28-inch bodies, with 12-inch-long, 4-inch-wide tails
  • Weight: 35 to 60 pounds


The population of beavers is stable to increasing in what remains of suitable habitat. Threats include civilization, habitat destruction, water pollution and hydroelectric dams. They are regulated by the Oregon Department of Fish and Wildlife.

Beavers, the Oregon Zoo and you

The zoo's beavers live in the Cascade Stream and Pond exhibit. They're fed rodent and monkey chow, carrots, apples, yams and browse. To replicate their activities in the wild, beavers are given branches anchored to the beach or clamped upright that they can fell by gnawing.

Beaver ponds conserve spring runoff: ensuring more constant stream flow, diminishing floods, conserving soil, and helping maintain the water table. Beaver ponds are also areas of high bio-diversity. They support large populations of insects which support birds, amphibians, reptiles and fish. These, in turn, supply food for mammals.


Aspen is a male American beaver, and the father of Filbert. Aspen's tail does not have markings on it...