American beaver

(Castor canadensis)

Conservation Status

American beaver
IUCN Red List

LC - Least Concern

 
NatureServe

N5 - Secure

SNR - Unranked

 
Minnesota

not listed

 
     

Description

American beaver is the largest rodent in North America. The head and body length is 25 to 30. A mature adult usually weighs 44 to 59 pounds, though they can be much larger.

The body is stout. The powerful hind legs are longer than the front legs so the rear end is higher than the front end when the beaver walks. The coat is reddish-brown or blackish-brown, glossy, and thick. The hind legs and have webbed feet. The claw on the second toe is doubled and functions as a comb.

The skull is disproportionately large. There are 20 teeth, including disproportionately large upper and lower incisors. The incisors are ¾ to 1 long and about ¼ wide, and have chestnut brown enamel. The ears and nostrils are closable.

The tail is broad and flat—paddle shaped. It is 9 to 10 long, naked, and scaly.

Size

Head and body: 25 to 30

Tail: 9 to 10

Sign

Dams – A beaver will build a dam in a stream or river to slow the flow of water. Where sufficient stable water is available it will not build a dam but rather burrow into the bank. The front (downstream) side of a dam consists of large branches with the but ends facing downstream. Mud and debris make up the center of the dam. The back (upstream) side is made up of small branches.

Lodges – A lodge is a large pile of branches covered with mud, debris, and aquatic vegetation. It can rise up to 10 feet above the pond floor. It is excavated from within. In the winter, vapor can often be seen rising from a thinly covered opening used for ventilation (smoke hole) at the top of the lodge. Lodges are usually built near or at the edges of lakes and ponds.

Canals – A canal may be up to two feet wide and deep. It provides a safe water passage and can be used to help transport felled trees to the pond.

Cut trees – After downing a tree or branch a beaver may completely strip the outer bark to get at the cambium. Tree stumps near pond edges may show ¼ wide incisor marks.

Scat – Beavers defecate in the water.

Similar Species

The stout build, brown fur, and flat, broad, scaly tail make identification unmistakable.

Habitat

Lodges built on islands, banks of ponds,and shores of lakes

Ecology

Behavior

 

Lifespan

10 to 12 years

Life Cycle

Beavers are mostly nocturnal, though they are occasionally seen during the day. They are usually found in colonies of 4 to 10 related individuals.

Females usually breed first in their second year, sometimes in their third year. Gestation is 100 to 128 days. Between April and June the give birth to usually four or more kits, averaging five in Minnesota. The young remain with the parents until their second year, when they are either driven out or choose to leave. They usually relocate within six miles. The average life span is 11 years.

Food

Bark, cambium, and small twigs of aspen, poplar, birch, maple, willow, beech, and alder. Aquatic vegetation.

Distribution

Distribution Map

 

Sources

7, 24, 29, 30.

Biodiversity occurrence data published by: Minnesota Biodiversity Atlas (accessed through the Minnesota Biodiversity Atlas Portal, bellatlas.umn.edu, 12/25/2025).

Timm, R. M. 1975. Distribution, natural history, and parasites of mammals of Cook County, Minnesota. Occasional Papers, Bell Museum of Natural History, University of Minnesota 14:1–56.

Hazard, Evan B. 1982. The Mammals of Minnesota. University of Minnesota Press, Minneapolis, Minnesota. 280 pp.

The counties in light green lack modern records but have historic county or township specimens or records.

12/25/2025  
   
   
   
   

Occurrence

Common

Taxonomy

Class

Mammalia (Mammals)

Subclass

Theria

Infraclass

Placentalia (Placental Mammals)

Magnorder

Boreoeutheria

Superorder

Euarchontoglires (Primates, Rodents, and Allies)

Order

Rodentia (Rodents)

Suborder

Supramyomorpha

Infraorder

Castorimorphi

Superfamily

Castoroidea

Family

Castoridae (Beavers)

Subfamily

Castorinae

Genus

Castor (Beavers)

 

Suborder

The classification of the American Beaver above the family level is currently subject to revision based on modern phylogenetic research. The traditional classification places the family Castoridae (Beavers) in the suborder Castorimorpha.

Molecular DNA studies have established three monophyletic rodent clades, recognized as the suborders Hystricomorpha, Sciuromorpha, and Supramyomorpha, a new suborder that includes the family Castoridae.

The suborder Castorimorpha is currently the designation found in many online resources, including the Catalogue of Life. The suborder Supramyomorpha is the designation used by the Mammal Diversity Database (MDD) of the American Society of Mammalogists (ASM).

MinnesotaSeasons.com follows the classification adopted by the Mammal Diversity Database (MDD), as it represents the most current, scientifically vetted taxonomy (see Burgin et al., 2025).

Subordinate Taxa

Historically, up to 25 subspecies of the American Beaver (Castor canadensis) were described, often based on minor differences in size, pelage color, and skull morphology across their wide North American range.

However, recent comprehensive genetic studies have generally not supported these traditional subspecies classifications. Consequently, major modern taxonomic authorities, including the Integrated Taxonomic Information System (ITIS) and the Mammal Diversity Database (MDD), currently do not recognize any subspecies for Castor canadensis, treating it as a single, widespread species across its native range.

Synonyms

Castor caecator

Castor canadensis ssp. acadicus

Castor canadensis ssp. phaeus

Castor canadensis ssp. idoneus

Castor canadensis ssp. rostralis

Castor canadensis ssp. sagittatus

Castor canadensis ssp. baileyi

Castor canadensis ssp. carolinensis

Castor canadensis ssp. concisor

Castor canadensis ssp. repentinus

Castor canadensis ssp. belugae

Castor canadensis ssp. duchesnei

Castor canadensis ssp. subauratus

Castor canadensis ssp. labradorensis

Castor canadensis ssp. missouriensis

Castor canadensis ssp. caecator

Castor canadensis ssp. canadensis

Castor canadensis ssp. leucodontus

Castor canadensis ssp. pallidus

Castor canadensis ssp. mexicanus

Castor canadensis ssp. shastensis

Castor canadensis ssp. frondator

Castor canadensis ssp. taylori

Castor canadensis ssp. texensis

Castor canadensis ssp. pacificus

Castor canadensis ssp. michiganensis

Castor subauratus ssp. shastensis

Castor subauratus ssp. subauratus

Common Names

American beaver

Canadian beaver

North American beaver

 

 

 

 

 

 

Glossary

Cambium

A layer of softer growing tissue, one to several cells thick, under the bark of trees.

 

Visitor Photos

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Ramona Abrego

Beaver working on his house collecting material and packing over the branches and even came up to the shore within 5 feet of me to get a good look at me and raised his body up out of the water.

American beaver   American beaver
     
American beaver   American beaver

Lynn Rubey

American beaver

American beaver near the opening of the den in the bank along the river in The Big Stone National Wildlife Refuge.

 

American beaver   American beaver

Beaver dam

 

Beaver-gnawed tree

MinnesotaSeasons.com Photos

American beaver   American beaver

Beaver

 

Dam

     
American beaver   American beaver

Dam

 

Dam

     
American beaver   American beaver

Lodge

 

Lodge

     
American beaver   American beaver

Sign

 

Sign

 

Camera

Slideshows

Beaver
DianesDigitals

About

Copyright DianesDigitals

Beaver
Craig A. Mullenbach

 

slideshow

Visitor Videos

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Dan W. Andree

"A Quick Look at a Beaver Feeding etc."
Published on Jul 12, 2016

About

This short video shows some interesting eating behavior of a beaver as well as a little tail slapping. Filmed early spring 2016.

Other Videos

North American Beaver - Tail Slap @ Iron Mtn.
JCVdude

About

Uploaded on Sep 23, 2010

The beaver (genus Castor) is a primarily nocturnal, large, semi-aquatic rodent. Castor includes two extant species, North American Beaver (Castor canadensis) (native to North America) and European Beaver (Castor fiber) (Eurasia). Beavers are known for building dams, canals, and lodges (homes). They are the second-largest rodent in the world (after the capybara). Their colonies create one or more dams to provide still, deep water to protect against predators, and to float food and building material. The North American beaver population was once more than 60 million, but as of 1988 was 6--12 million. This population decline is due to extensive hunting for fur, for glands used as medicine and perfume, and because their harvesting of trees and flooding of waterways may interfere with other land uses.

Beavers are known for their natural trait of building dams on rivers and streams, and building their homes (known as "lodges") in the resulting pond. Beavers also build canals to float build materials that are difficult to haul over land. They use powerful front teeth to cut trees and other plants that they use both for building and for food. In the absence of existing ponds, beavers must construct dams before building their lodges. First they place vertical poles, then fill between the poles with a crisscross of horizontally placed branches. They fill in the gaps between the branches with a combination of weeds and mud until the dam impounds sufficient water to surround the lodge.

A beaver skeleton

A beaver skeleton on display at The Museum of Osteology, Oklahoma City, Oklahoma.

They are known for their alarm signal: when startled or frightened, a swimming beaver will rapidly dive while forcefully slapping the water with its broad tail, audible over great distances above and below water. This serves as a warning to beavers in the area. Once a beaver has sounded the alarm, nearby beavers dive and may not reemerge for some time. Beavers are slow on land, but are good swimmers that can stay under water for as long as 15 minutes.

Beavers are herbivores, and prefer the wood of quaking aspen, cottonwood, willow, alder, birch, maple and cherry trees. They also eat sedges, pondweed, and water lilies.

North American Beaver.mov
RDWildlife

About

Uploaded on Oct 3, 2011

During our careers, we have spent a tremendous amount of time in and around beaver (Castor canadensis) habitat. While it has been very common to see beaver at a distance in the water, they generally reserve their land travels for night time. So yesterday, we were surprised and delighted to see this beaver just a few feet away browsing on willow. This stretch of the Rio Grande is currently dry, thereby causing this beaver to adapt to living alongside the highway in a small storm water drainage area. If you watch closely, you'll notice multiple bite marks and damage to the left eye. We believe he likely escaped one of our many native predators (no water, no protection). Our company provides non lethal beaver management solutions, call us today 505.818.7396 or visit www.rdwildlife.com to learn more.

 

Camcorder

Visitor Sightings

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Jake
5/17/2020

Location: Palmyra Township, Renville County

Many willow observed cut down around man-made pond over the early spring.  Sighted the young beaver early AM. Sighting location is over 10 miles from the Minnesota River and is not near any natural waterways.

Lynn Rubey
9/3/2019

American beaver

Location: Big Stone National Wildlife Refuge

American beaver near the opening of the den in the bank along the river in The Big Stone National Wildlife Refuge.

Ramona Abrego
5/17/2019

American beaver

Location: Becker County

Beaver working on his house collecting material and packing over the branches and even came up to the shore within 5 feet of me to get a good look at me and raised his body up out of the water.

Kirk Nelson
4/20/2014

American beaver

Location: Crosby Farm Regional Park

Beaver-gnawed tree

 

 

Binoculars