Microtus richardsoni
water vole

Microtus richardsoni is distributed discontinuously throughout the western Cordillera of North America, south as far as Utah and north to parts of Alberta and British Columbia (Burns 1982).

M. richardsoni lives in semiaquatic habitats of subalpine meadows and alpine areas at elevations from 3000-10,000 feet. This species lives near water, generally along stream and creek banks or around flooded marshes. M. richardsoni is found more often in old-growth stands, compared to mature forest stands. Populations of this species are found in areas with a high percent of exposed soil and a low percentage of canopy cover. Maser Storm 1970, Jannett 1979, Doyle 1987

Dorsally, M. richardsoni varies from grayish brown to dark brown or dark reddish brown, often darkened with black-tipped hairs, with the ventral fur being grayish brown to whitish. The tail is bicolored, brownish above and whitish underneath. The woolly fur of this species is grayer in winter. The total length is198-263 mm. The skull of M. richardsoni is characterized as having a heavy zygomatic arch and incisors that extend well beyond the nasal bone. Like those of all members of the subfamily Arvicolinae, the molars grow continuously and are characterized by their complicated chewing surfaces and hard enamel structure. M. richardsoni also has a specialized cutaneous sebaceous gland in both sexes located ventrally, mid-way between the fore and hind limbs. Jannett and Jannett 1981, Maser and Storm 1970, Parker 1990

Jannett (1979) observed a captive group of M. richardsoni to have induced estrus. Jannett also observed a 22 day gestation period and postpartum estrus. According to Brown (1977), the water vole produces two litters of 2-8 young (with a mean of 5) from mid-June to late-August, a relatively short breeding season. The young mature rapidly and females born in June occasionally (26% of the time) reproduce before the end of that breeding season. Ludwig (1988) reports a 1:1 sex ratio and that the breeding season may begin as early as late-May and end as late as early-September. Post-weaning parental care of the young is minimal although the female may allow young to remain in her home area for a limited period of time (Ludwig 1988).

M. richardsoni is solitary, active throughout the year, and thought to be mainly nocturnal, but has been seen during the day (Maser and Storm 1970, Doyle 1987). The home range seems to be less than 1000 square meters (Nowak 1991). This fossorial species digs 3 inch wide burrows in stream banks, with many of the passageways opening directly into the water. The water provides a convenient escape route from predators (Maser and Storm 1970). The burrows are conspicuously characterized by the large mounds of dirt left by the excavating voles. The nests, loosely constructed of grass, are found slightly above water level in burrows, under logs, driftwood, or dense vegetation (Nowak 1991). Secretions from the scent gland are deposited by the hind feet or by rubbing against some object and seem to be used for territory marking. In a laboratory setting, the majority of scent marking was observed within 20 cm of an introduced conspecific (Jannett and Jannett 1981). The same researchers observed marking behavior in pairs during precopulatory sequences, during fighting, and upon introduction of filter paper saturated with urine from a conspecific.

M. richardsoni eats a wide variety of herbs and plants, including the avalanch lily, dogtooth violet, lovage, northern valerian, mountain meadow knotweed, sweet colt's foot, mountain red heather, fringe-leaf cinquefoil, bear-grass, grass, wild clover, conifer seeds, two kinds of blueberry, lupine, bracted pedicularis, and arnica. Nowak (1991) reports that this species will often consume its own weight in food within a 24 hour period and that food is commonly stored for winter consumption. Maser and Storm 1970, Burns 1982

Where populations are high, M. richardsoni may become a serious pest, eating commercial crops of grain, hay, potatoes, alfalfa, turnips, and even forest plantings (Nowak 1991).

Populations of M. richardsoni are often small due to the short breeding season and the patchy distribution of appropriate habitat (Ludwig 1988). However, this species is not endangered.

Three subspecies are listed for M. richardsoni, including M. richardsoni arvicoloides, M. richardsoni macropus, and M. richardsoni richardsoni (Maser and Storm 1970). This species of vole differs from most other Microtus species by its propensity for water (Parker 1990).