North American Beaver: Castor Canadensis

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Photo of north american beaver in a stream

Description Of The North American Beaver

North American beavers, with adults averaging 40 pounds in weight and measuring more than 3 feet in length, including the tail, are the largest living rodents in North America. The semi-aquatic mammal is equipped with large incisor teeth, webbed feet, and a wide tail. A large beaver’s tail is 15 inches long and 6 inches broad. It is covered with sparse, coarse hair and leathery scales.

Both in the water and on land, the beaver’s tail has essential uses. The animal uses its flexible tail in the water as a four-way rudder. A beaver slaps the water loudly with his tail when diving after being scared; the splashing noise notifies other beavers of danger and might even scare away potential predators.

On land, when a beaver is sitting or standing upright, the tail acts as a prop. The tail also is used for balance when the beaver walks with building materials inside the animal’s mouth.

The tail stores fat and release body heat because it is almost hairless, helping the beaver regulate its body temperature. ¹

Learn More: Nuisance Beaver Species

North American Beaver Size

Average measurements for both male and female Castor canadensis:

Weight: 24 to 71 lbs
Body Length: 29–35 in
Tail Length: 20–35 in

Behavior Of North American Beavers

Picture of north american beaver eating

Beavers generally live in family groups called colonies of up to 8 related individuals. For up to 2 years, the younger siblings remain with their parents, helping with infant care, food collection, and dam building. Families of beavers are territorial and defend themselves against other families.

Territory marking is done by creating mud piles around a territory’s edges and then depositing anal castoral secretions on these piles. By slapping their tails against the water, creating a powerful noise, beavers will also warn others of danger. However, this is not always effective as older beavers will often ignore the warning slaps of younger colony members.

Mainly, beavers are nocturnal. During the day, they are only occasionally seen, usually around dusk. To find food, beavers travel a good distance from their homes. They build canals to the food source to float the food back to their lodges if they find a good source. For winter feeding, logs and twigs are often stored underwater.

Beavers build dams to slow the flow of water and then build stable lodges for shelter. The dams are engineered according to the water speed; the dam is built straight in slow water, but the dam is built with a curve in fast water. This offers stability so that it will not wash away the dam. ²

North American Beaver Communication Methods

Beavers communicate through the deposition of scents around the edges of their territory outside of their family unit. The beaver is unique in that it constructs scent mounds made of muds, sticks, and grass. They will use their anal glands to deposit scents.

Near the anus, beavers have significant Castor and oil glands. For scent marking, Castor, a very intense, thick liquid, is created and leaves a long-lasting odor. The oil glands generate the oil used to waterproof the fur of a beaver. Between the sexes, the oil is slightly different and is used in reproductive communication.

Beavers employ different vocalizations within the lodge (although their voice box is rudimentary) and postures to communicate with family members. Beavers have occasionally been heard hissing if they are dissatisfied. ³

Reproduction Of North American Beavers

Photo of north american beaver resting on a shore

Beavers are monogamous, breeding throughout their range from January to February. Beavers mate underwater, and two days later, the female produces a vaginal plug which prevents further copulation. The gestation takes between 100 and 110 days, and in the main lodge or den chamber, females give birth. Beavers produce one litter (averaging three or four kits) per year, depending on latitude and elevation, with the kits being born from late April to June.

The kits are semi-precocial, with open eyes and erupted teeth, born fully furred. They can swim and explore their surroundings within minutes of birth, but they require a long parental care period before they are self-sufficient. At about 2 weeks of age, or as late as 6 to 8 weeks in Montana, kits start leaving the lodge or den. At about 6 to 8 weeks, they are weaned. Kits depend on the family group to feed, groom, and maintain dams and the winter food cache until they disperse at about 2 years of age. ⁴

North American Beaver Habitat

The habitat of North American Beavers can be identified as:

Lodges may be surrounded by water or partially located on land and water, consisting of several branches of trees and mud forming a hard barrier that protects them from predators attempting to penetrate the lodge
Always found near or in the water in riparian ecosystems, including streams, rivers, and lakes
Nearby areas used for dam and lodge-building materials and a vital food source with access to aspen, birch, poplar, and willow
Lodges are home to two adults and their offspring and have underwater entrances ⁵

Range Of The North American Beaver Species

Picture of North American beaver swimming in pond

All over the continental United States, except in the desert areas of the Southwest, beavers live in ponds, lakes, rivers, and streams. Beavers are well recognized for their ability to construct dams. This species can alter ecosystems by blocking streams/rivers using trees and mud. This often results in the creation of ponds and floodplains.

Beavers also construct homes out of branches and mud called lodges, which can often be accessed only from underwater entrances in the ponds. ⁶

North American Beaver Diet

The North American beaver is strictly a herbivore species. A variety of woody and herbaceous species are eaten by beavers. Important foods include willows, mountain alder, and aspen.

During summer, they will also consume herbaceous vegetation. For food, much of the woody vegetation beavers cut is not used. Caches of woody vegetation near shores of water are used for winter food. ⁷

Predators Of North American Beaver

Coyotes
Great-Horned Owls
Otters
Foxes
Bobcats ⁸

North American Beaver Conservation

Beaver populations have historically declined due to aggressive hunting of their soft silky fur and castor glands used for trade and converted into medicine and perfumes. Because the harvesting of beavers and flooding of waterways affects urban and agricultural land uses, habitat destruction and degradation are the primary threat to beavers. Human development has resulted in severe watershed impairments on which beavers depend.

Sources:

Saunders. “Beaver | Washington Department of Fish & Wildlife.” SUNY College of Environmental Science and Forestry, State University of New York, 1988, wdfw.wa.gov/species-habitats/species/castor-canadensis#desc-range.
Anderson, R. 2002. “Castor canadensis” (On-line), Animal Diversity Web. Accessed January 27, 2021 at https://animaldiversity.org/accounts/Castor_canadensis/
Smithsonian’s National Zoo and Conservation Biology Institute. “Beaver.” Smithsonian’s National Zoo, Smithsonian’s National Zoo & Conservation Biology Institute, 27 Oct. 2020, nationalzoo.si.edu/animals/beaver.
Boyle, Steve, and Stephanie Owens. “North American Beaver (Castor Canadensis): A Technical Conservation Assessment.” U.S. FOREST SERVICE, USDA, 6 Feb. 2007, www.fs.usda.gov/Internet/FSE_DOCUMENTS/stelprdb5181919.pdf.
NPS. “Acadia’s North American Beaver: The Ultimate Keystone Species (U.S. National Park Service).” National Park Service, National Park Service Department Of The Interior, 1 Oct. 2020, www.nps.gov/articles/north-american-beaver-acadia.htm.
“American Beaver.” National Wildlife Federation, National Wildlife Federation, www.nwf.org/Educational-Resources/Wildlife-Guide/Mammals/American-Beaver. Accessed 27 Jan. 2021.
Beaver — Castor canadensis. Montana Field Guide. Montana Natural Heritage Program and Montana Fish, Wildlife and Parks. Retrieved on January 27, 2021, from http://FieldGuide.mt.gov/speciesDetail.aspx?elcode=AMAFE01010
“Beavers In The Food Chain.” New York State Department Of Environmental Conservation, New York State, www.dec.ny.gov/docs/administration_pdf/2005jrnat4.pdf. Accessed 27 Jan. 2021.