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 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 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
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