Species Profile

Mountain Beaver

Scientific Name: Aplodontia rufa
Taxonomy Group: Mammals
Range: British Columbia
Last COSEWIC Assessment: May 2012
Last COSEWIC Designation: Special Concern
SARA Status: Schedule 1, Special Concern

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Quick Links: | Photo | Description | Distribution and Population | Habitat | Biology | Threats | Protection | National Recovery Program | Documents

Image of Mountain Beaver

Mountain Beaver Photo 1



The Mountain Beaver is the most primitive living rodent. It resembles a medium-sized muskrat, except the tail is well furred and exceedingly short. The body is thick, heavy, and covered with coarse, dull, uniformly dark brown fur. The average adult weighs 806 g and is 300-470 mm long (of which the tail is 20-40 mm).


Distribution and Population

The Mountain Beaver occurs within and to the west of the Cascade and Sierra Nevada mountain ranges of western North America. In Canada, it is found only in extreme southwestern British Columbia. The subspecies Aplodontai rufa rufa is found south of the Fraser River from Hope to Langley; the subspecies A. rufa raineri is found east of Hope, north along the Cascade Mountains, to the Lytton-Merritt area, and west to about Princeton. There appears to be some overlap of the two subspecies in the area of the Skagit River south of Hope. A very crude estimate of the number of Mountain Beavers in Canada is about 1600 adults. Anecdotal evidence suggests that population declines have occured in the valley bottom of the Fraser River and in the foothills of the lower Fraser Valley.



Mountain Beavers occur in forested areas from near sea level to timberline, often preferring early to mid-seral stages. Specific requirements include soils that allow tunnel, burrow and runway construction; a cool and moist microclimate within tunnels and burrows; and suitable forage within 50 m. Deep soils with subsurface drainage that keeps the majority of the tunnels and burrows wet, even to the point of having water trickling through them, appear ideal for these rodents. The underground nest sites must remain dry and above the water table, however. Slopes around nests tend to have a grade of < 31%.



Female Mountain Beavers attain sexual maturity at two years of age. They produce one litter per year, between 6 February and 3 May, following a month of gestation. Litter size ranges from 2-6 (usually 2-3) young. The young are weaned at two months of age and emerge from the burrow within two more weeks. Adults occupy very small home ranges (0.03-0.2 ha), but subadults move away from the natal site soon after emerging, and establish their own nests. Dispersal of the rodents appears to be limited by the geography of the Fraser River valley. The maximum lifespan of Mountain Beavers is at least six years. Their diet consists of a wide variety of herbaceous and woody plants. Predators include bobcats, coyotes, cougars and golden eagles.



Within their present range in the Cascade Mountains in British Columbia, clear-cutting and associated silvicultural practices that severely disturb the soil layer are probably the major limiting factors preventing Mountain Beavers from using otherwise suitable habitat. These soil disturbances appear to be extremely damaging to Mountain Beaver populations through direct mortality and by limiting the recolonization opportunities after clearcutting. In the lower elevations of the Fraser River valley, habitat loss through urbanization and agriculture are probably the major limiting factors.



Federal Protection

More information about SARA, including how it protects individual species, is available in the Species at Risk Act: A Guide.

The Mountain Beaver is protected by the British Columbia Wildlife Act. Under this Act, it is prohibited to kill or poison any native terrestrial mammal without a permit. About one-quarter of the core Canadian range of the Mountain Beaver is within seven protected areas in British Columbia.

Provincial and Territorial Protection

To know if this species is protected by provincial or territorial laws, consult the provinces' and territories' websites.



PLEASE NOTE: Not all COSEWIC reports are currently available on the SARA Public Registry. Most of the reports not yet available are status reports for species assessed by COSEWIC prior to May 2002. Other COSEWIC reports not yet available may include those species assessed as Extinct, Data Deficient or Not at Risk. In the meantime, they are available on request from the COSEWIC Secretariat.

6 record(s) found.

COSEWIC Status Reports

  • COSEWIC assessment and status report on the Mountain Beaver Aplodontia rufa in Canada (2013)

    The Mountain Beaver, Aplodontia rufa, is a muskrat-sized fossorial rodent endemic to western North America. It is the only living species of the family Aplodontiidae and is considered a ‘living fossil’ because of its primitive physiology and skull features. Recent genetic analysis suggests one subspecies occurs in Canada, rather than two as previously believed.

Response Statements

  • Response Statement - Mountain Beaver (2013)

    The range of this species in Canada has contracted by 29% in the last 50 years and expansion into new habitat is constrained by large rivers. Within its range, habitat loss from urban development continues, and soil compaction caused by heavy machinery limits the use of otherwise suitable habitat. Climate change may further affect this species because it requires humid microclimates and low ambient temperatures. Rescue effect potential is limited by the short dispersal rates of the species and areas of unsuitable habitat along the border with the United States.

Management Plans

COSEWIC Annual Reports

  • COSEWIC Annual Report - 2011-2012 (2012)

    Under Canada’s Species at Risk Act (SARA), the foremost function of COSEWIC is to “assess the status of each wildlife species considered by COSEWIC to be at risk and, as part of the assessment, identify existing and potential threats to the species”. COSEWIC held two Wildlife Species Assessment Meetings in this reporting year (September 1, 2011 to September 30, 2012) from November 21 to 25, 2011 and from April 29 to May 4, 2012. On February 3, 2012, an Emergency Assessment Subcommittee of COSEWIC also assessed the status of the Tri-colored Bat (Perimyotis subflavus), the Little Brown Myotis (Myotis lucifugus), and the Northern Myotis (Myotis septentrionalis). During the current reporting period COSEWIC assessed the status or reviewed the classification of 67 wildlife species. For species already found on Schedule 1 of SARA, the classification of 32 species was reviewed by COSEWIC and the status of the wildlife species was confirmed to be in the same category (extirpated - no longer found in the wild in Canada but occurring elsewhere, endangered, threatened or of special concern). The wildlife species assessment results for the 2011-2012 reporting period include the following: Extinct: 1 Extirpated: 4 Endangered: 29 Threatened: 10 Special Concern: 15 Data Deficient: 2 Not at Risk: 6 Total: 67 Of the 67 wildlife species examined, COSEWIC reviewed the classification of 49 species that had been previously assessed. The review of classification for 26 of those species resulted in a confirmation of the same status as the previous assessment (see Table 1a).

Consultation Documents

  • Consultation on Amending the List of Species under the Species at Risk Act: Terrestrial Species – December 2012 (2013)

    As part of its strategy for protecting wildlife species at risk, the Government of Canada proclaimed the Species at Risk Act (SARA) on June 5, 2003. Attached to the Act is Schedule 1, the list of the species that receive protection under SARA, also called the List of Wildlife Species at Risk. Please submit your comments by March 4, 2013, for terrestrial species undergoing normal consultations and by October 4, 2013, for terrestrial species undergoing extended consultations. Consultation paths.

Recovery Document Posting Plans

  • Environment and Climate Change Canada's Three-Year Recovery Document Posting Plan (2016)

    Environment and Climate Change Canada’s Three-Year Recovery Document Posting Plan identifies the species for which recovery documents will be posted each fiscal year starting in 2014-2015. Posting this three year plan on the Species at Risk Public Registry is intended to provide transparency to partners, stakeholders, and the public about Environment and Climate Change Canada’s plan to develop and post these proposed recovery strategies and management plans. However, both the number of documents and the particular species that are posted in a given year may change slightly due to a variety of circumstances. Last update March 31, 2017