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Western Harvest Mouse
Conservation status
Least Concern
Scientific classification
Kingdom: Animalia Phylum: Chordata Class: Mammalia Order: Rodentia Family: Cricetidae Subfamily: Neotominae Genus: Reithrodontomys Species: R. megalotis
Binomial name
Reithrodontomys megalotis (Baird, 1857)

The Western Harvest Mouse (Reithrodontomys megalotis) is a small neotomine mouse native to southwest British Columbia, most of the western United States extending continuously to west Texas, northeast Arkansas, northwest Indiana, southwest Wisconsin, the interior of Mexico to Oaxaca. Many authorities consider the endangered Salt Marsh Harvest Mouse to be a subspecies, but the two are now usually treated separately.

Western Harvest Mice have brownish fur with buff sides, a white belly, and an indistinct white stripe on the fur along the spine. Adults grow up to eleven to seventeen centimeters in length with a tail length of five to ten centimeters. Their height (from the ground to the highest point of their back) is between 1.5 and 2.0 centimeters. A mature mouse weighs anywhere from nine to twenty-two grams.

The Western Harvest Mouse is nocturnal, with particularly intense activity on very dark nights. This mouse is particularly resourceful, making use of the ground runways of other rodents. It is also a very agile climber. Its primary food source is seeds, but springtime dining is augmented with new plant growth. In June, July and August the mouse is known to consume certain insects, especially grasshoppers and caterpillars. Again resourceful, the Western harvest mouse stores seeds and other foodstuffs in underground vaults. Its many predators include the fox, weasel, coyote, hawk, snake and owl species.

Similar species are the Plains Harvest Mouse, which has a more distinct but narrower stripe on its spine, and the Fulvous Harvest Mouse, which has a longer tail. Also similar is the Salt Marsh Harvest Mouse, which has an underbelly fur that is more pinkish cinnamon to tawny. Finally, the House Mouse has incisors without grooves, unlike those of the Western harvest mouse.

Breeding nests are spherical constructions woven from grass or other plant material. A nest is approximately 13 centimeters in diameter and lined with a more downy material of fibrous plants. A nest may have one or more entrances near its base. Most commonly, the nest is built on the ground in a protected area such as within a shrub or beside a fallen tree; however, the mouse will occasionally place the nest aboveground within a shrub.

The Western Harvest Mouse breeds from early spring to late autumn, with reduced activity at midsummer. The gestation period is 23 to 24 days. Repeated fertilization often occurs immediately after giving birth. It is not uncommon for a female to have ten to fourteen litters per annum, with a typical litter size of two to six individuals; however, litters of up to nine offspring can occur. Thus an annual production of forty to sixty young per female is normal. The newborn mice weigh approximately 1.0 to 1.5 grams.

• Pearson (1996). Reithrodontomys megalotis. 2006 IUCN Red List of Threatened Species. IUCN 2006. Retrieved on 12 May 2006.
• Reithrodontomys megalotis (TSN 180343). Integrated Taxonomic Information System. Accessed on 18 March 2006.
• Musser, G. G. and M. D. Carleton. 2005. Superfamily Muroidea. In Mammal Species of the World a Taxonomic and Geographic Reference D. E. Wilson and D. M. Reeder eds. Johns Hopkins University Press, Baltimore.
• National Audubon Society Field Guide to North American Mammals, ed. by John O. Whitaker Jr., Chanticleer Press (1997) ISBN 0-679-44631-1