The western harvest mouse is one of Colorado’s smallest rodents, a grassland mouse barely heavier than a few coins, and. Open occurrence databases hold 1,604 records for it in Colorado, most of them from survey trapping rather than photographs, since it is tiny, nocturnal, and easily overlooked.
Where the harvest mouse lives
This is a mouse of weedy fields, tallgrass margins, ditch banks, and marshy edges, wherever dense low cover and grass seed come together. Its records concentrate on the eastern plains and the South Platte lowlands, in Weld, Yuma, Larimer, and Adams counties and out across the shortgrass and farmland, with scattered records into the western valleys. A soft brown mouse with a white belly and a tail about as long as its body, it is told from a young house mouse by the pair of lengthwise grooves running down its upper incisors.
A weaver of grass nests
Rather than burrow, the harvest mouse weaves a tidy ball of shredded grass, often lodged a little above the ground in standing vegetation, and threads runways through the cover to reach seed. Its records build from spring through fall, tracking both the growing season when food and cover are richest and the months when surveyors are afield, then drop away as winter flattens the grass.
Status in Colorado
The western harvest mouse is native to Colorado and secure here, ranked S5 by NatureServe. It stays widespread and common in grassland and old-field habitat across the state’s lower elevations.
Full species profile
