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Reithrodontomys megalotis

(Baird, 1858)

Western Harvest Mouse

G5Secure Found in 4 roadless areas NatureServe Explorer →
G5SecureGlobal Rank
Least concernIUCN
Identity
Unique IDELEMENT_GLOBAL.2.105306
Element CodeAMAFF02030
Record TypeSPECIES
ClassificationSpecies
Classification StatusStandard
Name CategoryVertebrate Animal
IUCNLeast concern
Endemicoccurs (regularly, as a native taxon) in multiple nations
KingdomAnimalia
PhylumCraniata
ClassMammalia
OrderRodentia
FamilyCricetidae
GenusReithrodontomys
COSEWICPS:E
Other Common Names
Souris des moissons (FR) western harvest mouse (EN)
Concept Reference
Wilson, D. E., and D. M. Reeder (editors). 1993. Mammal species of the world: a taxonomic and geographic reference. Second edition. Smithsonian Institution Press, Washington, DC. xviii + 1206 pp. Available online at: http://www.nmnh.si.edu/msw/.
Taxonomic Comments
Substantial chromosomal variation in R. megalotis suggests that other species may be lumped in this taxon (Musser and Carleton, in Wilson and Reeder 1993, 2005). Several of the 16-17 nominal subspecies listed by Webster and Jones (1982) and Hall (1981) have not been subjected to a modern taxonomic analysis; the validity of these subspecies is open to question. In a mitochondrial DNA analysis, Bell et al. (2001) confirmed that Reithrodontomys zacatecae is distinct from R. megalotis, but those two species along with R. sumichrasti formed a monophyletic clade.
Conservation Status
Rank MethodExpertise without calculation
Review Date2016-04-04
Change Date1996-11-08
Edition Date2003-10-14
Range Extent Comments
Southern British Columbia (Okanagan Valley), southeastern Alberta Similkameen Valley), North Dakota, and southern and western Wisconsin south to northern and central Baja California (Alvarez-Casteneda and Rios 2003), Oaxaca, Veracruz, western Texas, western Oklahoma, Kansas, and northeastern Arkansas; east to Indiana (recently invaded); from below sea level in Death Valley to above 3960 m in southern Mexico (Webster and Jones 1982). See Nagorsen (1994 COSEWIC report) for details on distribution in Canada. See Mercado-Morales (1990) for recent records from Mexico.
Threat Impact Comments
In Canada, limiting factors include habitat disturbances from livestock grazing, hay mowing, fire, cultivation, and especially habitat loss and fragmentation from urban development (Nagorsen, 1994 COSEWIC report).
Ecology & Habitat

Diagnostic Characteristics

See Hoofer et al. (1999) for information on discrimination between R. MEGALOTIS and R. MONTANUS using cranial characters.

Habitat

Old fields, meadows, weedy roadsides, agricultural areas, grassy situations within pine-oak forest, and riparian borders. Prefers dense vegetative cover. Also may be found in shrubby arid regions. In Canada, ideal habitat includes dry gullies with dense shrub cover bordering grassland and shrub-steppe rangeland (Nagorsen, 1994 COSEWIC report). Climbs in vegetation. Uses runways made by voles. Spherical nests usually are constructed on the ground under heavy vegetation or in shrubs.

Ecology

May forms mixed-sex social units dominated by a male.

Home range usually is about 0.5-1.5 acres.

Density commonly may be about 5-10 per acre, up to 60/acre in optimum habitat (Gray 1943, Whitford 1976). In Canada, Nagorsen (1994 COSEWIC report) reported 1-7/ha. In Arizona, density was highly variable over 12 years, ranging from local extirpation to about 13 per ha; density averaged about 5-6 per ha in winter, about 1 per ha in late summer-early fall (Skupski 1995). In Wisconsin, autumn densities varied from about 0.75/ha in sandy fields to 45/ha in an abandoned field with a dense cover of low vegetation (Jackson 1961, Svendsen 1970). (Skupski 1995). Populations may decline during peaks in vole abundance. In Kansas, populations declined following grassland fire (Kaufman et al. 1988); moved to unburned area (Clark and Kaufman 1990).

Long-distance movements (up to 3200 m) were recorded in Kansas; vast majority moved less than 300 m (Clark et al. 1988). Movements of up to at least several hundred meters occurred in Arizona, but distance moved from one month to the next usually was less than 90 m (Skupski 1995).

Reproduction

Breeds year-round but mostly early spring to late autumn. In southeastern Arizona, breeding occurred year-round, with a peak in August when food resources likely were high (Skupski 1995). Gestation lasts 23-24 days. Litter size is 1-6 (mean 4). Young are weaned in slightly less than 3 weeks. Sexually mature in 2-4 months. May produce multiple litters annually.
Terrestrial Habitats
Woodland - HardwoodWoodland - MixedShrubland/chaparralGrassland/herbaceousOld fieldDesertCropland/hedgerow
Palustrine Habitats
Riparian
Other Nations (2)
CanadaN3
ProvinceRankNative
AlbertaS1Yes
British ColumbiaS3Yes
United StatesN5
ProvinceRankNative
IndianaS3Yes
MontanaS5Yes
MissouriS4Yes
TexasS5Yes
MinnesotaS3Yes
North DakotaSNRYes
OklahomaS3Yes
ArkansasS3Yes
Navajo NationS5Yes
KansasS5Yes
New MexicoS5Yes
IllinoisS4Yes
WyomingS5Yes
OregonS4Yes
NevadaS4Yes
IdahoS4Yes
IowaS4Yes
ArizonaS5Yes
UtahS5Yes
WisconsinS3Yes
CaliforniaSNRYes
NebraskaS5Yes
ColoradoS5Yes
WashingtonS4Yes
South DakotaS5Yes
Roadless Areas (4)
California (3)
AreaForestAcres
MatilijaLos Padres National Forest5,218
San DimasAngeles National Forest7,160
Sawmill - BadlandsLos Padres National Forest51,362
New Mexico (1)
AreaForestAcres
Peloncillo (NM)Coronado National Forest43,339
References (43)
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  2. American Society of Mammalogists (ASM). 2025. Mammal Diversity Database (Version 1.13) [Data set]. Zenodo. https://doi.org/10.5281/zenodo.10595931. Online. Available: https://www.mammaldiversity.org/
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