Microtus richardsoni

Water Voles can swim and dive, and are always found near water, often near fast-running glacial or spring-fed streams. Captive young Voles swam voluntarily when they were only 17 days old, before they were even weaned. Water Voles live in alpine and sub-alpine meadows, usually at elevations between about 900 and 3,200 m. They are not known to cross valleys or expanses of forest to move from one habitat to another. They use underground nests year-round, but nests are also found on the surface after snowmelt. These may have been used during the winter, or may have been built when melting snow flooded tunnels. Water Voles do not store food, but consume dry portions of herbaceous vegetation, root buds, rhizomes, and corms (starchy underground stems) in winter, and eat seeds and bulbs in summer.

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This species range is in two distinct segments. The smaller portion extends from the Coast Mountains of western British Columbia in Canada to the Blue and Cascade mountains of Washington and Oregon in the United States. The larger portion extends from the Rocky Mountains of southeastern British Columbia and southwestern Alberta, Canada, southward to western Montana, western Wyoming, Idaho, and central Utah in the United States.

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).

Biogeographic Regions: nearctic (Native )

occurs (regularly, as a native taxon) in multiple nations

Canada

Origin: Native

Regularity: Regularly occurring

Currently: Present

Confidence: Confident

Type of Residency: Year-round

United States

Origin: Native

Regularity: Regularly occurring

Currently: Present

Confidence: Confident

Type of Residency: Year-round

Global Range: Northwestern North America. Two disjunct ranges: southwestern British Columbia south through Washington and Oregon; southeastern British Columbia and southwestern Alberta through eastern Oregon, eastern Washington, western Montana, western Wyoming, Idaho, to central Utah (Hall 1981).

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

Average mass: 51 g.

Average basal metabolic rate: 0.701 W.

Length: 26 cm

Sexual Dimorphism: Males are larger than females.

Length:
Average: 252 mm
Range: 234-274 mm

Weight:
Range: 72-150 g males; 68-140 g females

Habitat and Ecology

Systems

• Terrestrial
• Freshwater

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

Terrestrial Biomes: taiga ; forest

Aquatic Biomes: lakes and ponds; rivers and streams

Comments: Subalpine and alpine meadows close to water, especially swift, clear, spring-fed or glacial streams with gravel bottoms. Marshes, pond edges. Uses underground nests throughout the year. Burrows into streambanks. Makes runways in wet meadows.

Non-Migrant: Yes. At least some populations of this species do not make significant seasonal migrations. Juvenile dispersal is not considered a migration.

Locally Migrant: No. No populations of this species make local extended movements (generally less than 200 km) at particular times of the year (e.g., to breeding or wintering grounds, to hibernation sites).

Locally Migrant: No. No populations of this species make annual migrations of over 200 km.

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

Comments: Leaves and occasionally stems of forbs are the major foods. Also eats grasses, sedges and willows. May eat some seeds and insects. Feeds on subterranean parts of plants throughout the year.

Populations may fluctuate dramatically yearly or seasonally. In Alberta, monthly density estimates (June-September) in several streamside sites ranged from 0.2-12.2 per ha; seasonal recruitment increased population size 0.8-6.2 times, highest numbers in August or September (Ludwig 1988).

Comments: Active throughout the year.

Observations: In the wild, these animals are estimated to live up to 1.5 years (Bernhard Grzimek 1990). Without further studies, however, their maximum longevity is unknown.

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).

Average birth mass: 5.05 g.

Average gestation period: 22 days.

Average number of offspring: 5.8.

In Alberta, mating activity was recorded late May or early June through August or September; young first entered trappable population in early July; maximum of 2 litters per year; average litter size about 5-6 (range 2-9); about 26% of young bred before their first winter (Ludwig 1988). In laboratory animals gestation lasted a minimum of 22 days.

Barcode of Life Data Systems (BOLDS) Stats
Public Records: 0
Specimens with Barcodes: 1
Species With Barcodes: 1

Year Assessed

Assessor/s

Reviewer/s

Justification

History

• 1996
  Lower Risk/least concern

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.

IUCN Red List of Threatened Species: least concern

Canada

Rounded National Status Rank: N4 - Apparently Secure

United States

Rounded National Status Rank: N5 - Secure

Rounded Global Status Rank: G5 - Secure

Population

Population Trend

Major Threats

Conservation Actions

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).