Status, distribution, and biology of the Mountain Beaver, Aplodontia rufa, in Canada

Abstract

The distribution and status of the Mountain Beaver, Aplodontia rufa, in Canada is reviewed, based on museum specimens, published and unpublished sources, other collected observations, and on sign surveys conducted from 1996 to 1998 east of the Cascade Mountain divide. Biological information presented from the sign surveys includes densities of nest sites, habitat parameters, the diet based on plants found in haypiles outside nest sites, and the effects of clearcutting on Mountain Beaver. In Canada, Mountain Beavers are limited to extreme southwestern British Columbia because the Fraser River is an effective barrier to northward dispersal along the Coast Mountains, and because climates become too dry to support Mountain Beavers east and north of the Cascade Mountains. Typical habitat on the east side of the Cascade Mountains consists of sites with damp soils, often near streams, at elevations between 1200 and 1800 m. Principal summer food species found in haypiles within forests were Sitka Valerian (Valeriana sitchensis), Horsetail (Equisetum spp.), Twisted Stalk (Streptopus spp.), Thimbleberry (Rubus parviflorus), and Cow-parsnip (Heracleum lanatum). Narrow-leaved Fireweed (Epilobium angustifolium) was the most common food in haypiles in clearcuts. Densities of underground nest sites in small (<2.5 ha) areas of high quality habitat reached up to 5.8 nests/ha. Densities over large areas where high habitat quality was relatively widespread averaged 35.3 nests/km2. Where high quality habitat was not as widespread, densities averaged only 5.9 nests/km2. Very low densities of 2 nests/km2 were found where the heavy machinery associated with clearcutting and the site preparations for planting had severely disturbed the soil layer while 42 nests/km2 were found where logging had been conducted in similar areas but without soil disturbance. The status of the Mountain Beaver in Canada is considered vulnerable because the range appears to be contracting in the lower Fraser River valley due to habitat lost to urbanization and agriculture, and because of its susceptibility to intensive forestry operations elsewhere in its range in Canada.