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Facts on Beavers

There are two species of beaver that live today: Castor canadensis in North American, and Castor fiber in Eurasia. The following facts refer to the North American beaver.

How long do beavers live?
Lifespan: Up to 24 years.
Beavers live 5 to 10 years in the wild.

How big are they?
Size head to tail: 30" - 51".
Weight (adult): 40 - 60 lbs.
Beavers are the largest living rodents in North America.
The tail of a large beaver may be 16 inches long and 5-7 inches wide.

What is their mating and family behavior?

Beavers are generally monogamous and mate for life. They usually only take a new partner after losing one, but occasionally practice other mating strategies.
Beaver families range from a kit-less pair to 10 animals, averaging 6 members in any given family.
Juvenile beavers generally remain with parents until 2 years of age, at which point they disperse to start their own colony, though they may remain nearby if resources are abundant.

What do beavers eat?
Aspen, cottonwood, willow and dogwood are the primary tree species that beaver prefer, but they will take any tree that seems to fit the bill for dam and lodge construction. Beaver also eat plant tubers, roots, shoots, and many herbaceous plants during the growing season.
Beaver will chew on larger trees just to sharpen their teeth and fall the tree to get at the more tender branches.
When the surface of the water is frozen, beavers eat bark and stems from a food "cache" (a safe storage place) they have anchored to the bottom of the waterway for winter use.

And what's up with the big teeth?
Beavers have large, sharp, upper and lower incisors, which are used to cut trees and peel bark while eating.
The incisors grow their entire lives, but are worn down by grinding them together, tree cutting, and feeding.
The beaver's incisors (front teeth) are harder on the front surface than on the back, and so the back wears faster - this creates a sharp edge that enables a beaver to easily cut through wood.

Why do beavers have such a big flat tail?
The beaver's tail has important uses both in the water and on land - in the water, the animal uses its flexible tail as a four-way rudder; on land the tail acts as a prop when sitting or standing and acts as a counter balance when carrying building material.
When diving after being frightened, a beaver loudly slaps the water with its tail; the sound warns all beavers in the vicinity that danger is near.
The tail stores fat, and because it is nearly hairless, releases body heat, helping the beaver to regulate its body temperature.
Beavers do not use their tails to plaster mud on their dams.

Why do beavers build dams?
Beavers are second only to humans in their ability to manipulate and change their environment.
Beavers build dams to flood areas for protection from predators, for access to their food supply, and to provide underwater entrances to their den; flooded areas also wet the soil and promote the growth of favored foods.
The feel and sound of flowing water stimulate beavers to build dams; however, they routinely let a leak in a dam flow freely, especially during times of high waters.
In cold areas, dam maintenance is critical - dams must be able to hold enough water so the pond won't freeze to the bottom, which would eliminate access to the winter food supply.
Beavers living on rivers or streams with fast moving water and lakes that maintain a constant level do not build dams they are called bank beavers.

For more beaver facts click here.


  • Photos from top to bottom: (1) beaver building a dam - courtesy of Defenders of Wildlife (2) beaver dam at Liberty Creek Bridge (3) beaver after a relocation by The Lands Council


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