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
Image of Mountain Beaver
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 ProtectionMore 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
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 (1 record(s) found.)
- Response Statements (1 record(s) found.)
- Management Plans (1 record(s) found.)
- COSEWIC Annual Reports (1 record(s) found.)
- Consultation Documents (1 record(s) found.)
- Recovery Document Posting Plans (1 record(s) found.)
COSEWIC Status Reports
COSEWIC Annual Reports
Recovery Document Posting Plans
- Date modified: