The Meadow Mouse is one of the more common and widely distributed of our small mammals. There are many species and subspecies and some form is to be found practically anywhere in North America.
These little mice prefer the open meadow country where there is plenty of grass the entire year. They may be found in the moist to semi-arid sections and anywhere from sea level to above timberline elevations.
Their presence can be readily detected by the characteristic runways through the grass. The mouse makes the runway both by cutting some of the grass and pushing the balance to the side, and the floor of the runway is kept free from all obstructions. A colony of mice will have a regular labyrinth of these paths with frequent openings into underground burrows and nests. The young are usually born in the underground nests. However, many of the species also build surface nests of thick balls of grass which are used during the winter time. In these nests, when snow blankets the landscape they are warm and secure, and able to run about their passage-ways, beneath the snow in their daily quest for food, for they do not hibernate.
Meadow Mouse
The food of the meadow mouse is chiefly vegetation: grass, foliage, seeds, twigs, roots and bark and at times they may become very destructive to field crops and orchards.
This little animal is very prolific and usually has several litters each year, with each litter consisting of from four to eight young. Were it not for their many enemies they would soon overrun the grass lands and do untold damage. As it is, their enemies, which are practically every predatory animal and bird, can barely keep them in check. Meadow mice serve as a valuable source of food for the smaller predatory animals such as coyotes, foxes and for the various hawks and owls.
There are four species of these mice that have been found in Yellowstone Park:
Sawatch Meadow Mouse: Microtus pennsylvanicus modestus. A medium-sized mouse with upperparts dull ochraceous, sprinkled with black. Underparts soiled whitish to ashy or cinnamon. In winter many black hairs along upperparts and underparts with wash of creamy white. Total length 7 inches, tail 1.8 inches. Has been found at Mammoth Hot Springs, Upper and Lower Geyser Basins and Shoshone Lake.
Dwarf Meadow Mouse: Microtus montanus nanus. A small-sized, rather short-tailed mouse with upperparts everywhere mixed gray, sepia and blackish, feet grayish; tail bicolor, dusky gray and whitish; underparts whitish. Total length 6 inches; tail 1.6 inches. Found in the grass of meadows and upland slopes over most of the park and appear to be the most abundant and generally distributed of the meadow mice in the park.
Cantankerous Meadow Mouse: Microtus longicaudus mordax. Resembles Sawatch meadow mouse in size but the tail is longer, ears larger, and color grayer. Upperparts grayish bister; sides grayer, underparts whitish. Lighter colored in the winter. Total length 7.4 inches; tail 2.8 inches. These mice have been found at Mammoth and Tower Fall and are probably common in most of the meadows of the park, equally at home on dry ground or in mountain streams.
Big-footed Meadow Mouse: Microtus richardsoni macropus. Largest of the meadow mice. Total length 8.8 inches; tail 2.8 inches. Upperparts dark sepia mixed with black, sides paler, feet gray; tail bicolor sooty whitish; underparts washed with silvery-white. In winter grayer above, more white below. Usually found close to water where they swim much in the manner of muskrats. This mouse had been taken at Heart Lake and its runways seen in marshy meadows of most of the western part of the park.