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, 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. (Updated 2017/06/12)


Distribution and Population

Mountain Beavers occur within, and west of, the Cascade and Sierra Nevada mountain ranges of western North America. In Canada, they are found in southwest British Columbia (B.C.) within the Cascade Mountains and south of the Fraser River. There are five populations. The main population comprises most of the Canadian distribution, and is relatively contiguous. Two small isolated populations to the west occur on Chilliwack and Sumas mountains in the lower Fraser Valley. Two other isolated populations to the east occur on Pike and Missezula mountains. (Updated 2017/06/12)



Mountain Beavers occupy underground den sites usually associated with deep friable soils near streams or seepages. Each adult occupies its own den site, with core use areas usually less than 1 ha, with the majority of activity within 25 m of the den. Forays of up to 200 m may occur. Their preferred habitat is open areas within forest and early-seral forest stages. These sites contain the highest abundance of preferred foods, including herbaceous plants, ferns, and young shrubs and trees. (Updated 2017/06/12)



Mountain Beavers live an estimated 5-6 years. Adult females (at least 2 years old) have an average of 2.5 young in spring, with young dispersing from their natal dens in late summer. Dispersal abilities appear to be limited because the Fraser River has prevented geographic expansion of the species northward into what is apparently suitable habitat in the Coast Mountains, and the dry interior plateaus and valleys have prevented expansion into apparently suitable habitat in the wet belt of the Columbia Mountains. Mountain Beavers are limited to cool, wet sites because they lack the ability to effectively conserve water and they begin to experience hyperthermia when temperatures exceed 28°C. (Updated 2017/06/12)



Climate change is considered a threat because Mountain Beavers require cool humid microclimates, and low ambient temperatures. Increasing summer temperature is expected to reduce distribution at the east side of their range in British Columbia. As well, the population on the western range likely would not be able to expand northward because the Fraser and Thompson rivers act as barrier to movement. The threat has not been quantified because the extent of mortality and range loss is not known. In the lower Fraser River valley, habitat loss to urbanization continues with 100 km² zoned for new suburban development in two subpopulations of Sumas and Chilliwack mountains of the Abbotsford and Chilliwack areas. Development is ongoing in this area, but full conversion is not expected within the present 20-year planning horizon. Declines due to habitat conversion within the next 12 years are estimated to be less than 1% of total population because these sites represent a small part of the Canadian range. Forestry has positive and negative impacts; food is created in clearcuts but machinery compacts soil used for denning. Silvicultural practices using heavy machinery can severely disturb the soil layer and are a major limiting factor preventing Mountain Beavers from using otherwise suitable habitat. Effective measures (i.e., harvesting only during deep snow periods) exist but their rate of application is unknown. In summary, clearcutting without soil compaction is beneficial for Mountain Beaver, but the extent of soil compaction is unknown. Therefore, as a very coarse estimate, the decline within the next 12 years is presented as a maximum, and is estimated as 3% if effective measures are not applied. (Updated 2017/06/12)



Federal Protection

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

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