Reithrodontomys megalotis
(Western Harvest Mouse)

Order: Rodentia
Order Description:Rodents
Family: Cricetidae
Family Description:
Mice and Rats

The western harvest mouse is small; total length is 4 ½ to 6 ¾ inches (114-170 mm); the tail is 2 to 3 7/8 inches (50-96 mm), their weight is about 3/8 to ¾ of an ounce (9 – 22 g). They are brownish above, they have buff along their sides, and they are whitish to gray underneath. Their long tail is bicolored, but sparsely haired. An important characteristic is a deep groove running down the middle of the front of each incisor.

From southern British Columbia, southeastern Alberta, southwestern Saskatchewan, North Dakota, and southern and western Wisconsin, south to northern Baja California, portions of Mexico, Texas, western Oklahoma, Kansas and northeastern Arkansas, and east to Indiana.

Found, up to 3960 m, in old fields, meadows, weedy roadsides, agricultural areas, grassy situations within pine/oak forests, and riparian borders. May also be found in shrubby arid regions. Prefers dense vegetative cover. In Idaho, prefers grassy areas in shrub steppe (Idaho study reported highest density in crested wheatgrass).

Prefers seeds of weeds and grasses, but also eats some herbaceous material. In Idaho, eats beetles, seeds, and leaves of sagebrush, halogeton, and grass.

This mouse is primarily nocturnalClick word for definition, with most activity occurring on moonless, rainy nights. They use runways made by voles, and typically occur in areas where voles are present. In a California study, individuals began moving along vole runways about 0.5 hr after sunset, and runway activity ended about 0.5 hr before sunrise. This species climbs in vegetation. Their home range is usually about 0.5 to 1.5 acres (0.2-0.6 ha). Long-distance movements of up to 2 miles (3200 m) have been recorded in Kansas, but a vast majority moved less than 0.19 miles (300 m). Population densityClick word for definition has been recorded at 2 to 4 per acre (0.4 ha), but may reach 24 per acre (0.4 ha) in optimum habitat. Populations may decline during peaks in vole abundance. They form mixed-sex social units dominated by a male. They build spherical nests, typically on the ground, but some above ground in shrubs. Adults molt twice annually. Like most mice, they have a very high mortality rate; few reach 12 months of age.

They breed year-round, but mostly in early spring to late autumn. GestationClick word for definition lasts 23 to 24 days. Litter size varies from 1 to 6 young (average 4). may produce multiple litters annually. Young are weanedClick word for definition in slightly less than 3 weeks, and reach sexual maturity in 2 to 4 months and females may produce multiple litters annually. Obviously their reproductive capacity is very high.

Status: Unprotected nongame species

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Important State References:
Larrison, E.J. and D.R. Johnson. 1973. Density changes and habitat affinities of rodents of shadscale and sagebrush associations. Great Basin Natur. 33:255-264.

Information written by Donald Streubel,© 2000
Map image provided by
Stephen Burton,© 2000
Design by Ean Harker©1999, 2000.