Western Harvest Mouse
Order Rodentia : Family Muridae : Reithrodontomys megalotis (Baird)

Description. A medium-sized harvest mouse; tail about as long as head and body; the dark dorsal and light ventral stripes about equal in width; ears pale flesh color (or buffy cinnamon); upperparts brownish buff, darkest in middle of back; underparts whitish. Differs from R. fulvescens in shorter tail, pale rather than blackish ears basally; from R. montanus in larger size, and lack of dark color at base of ears. External measurements average: total length, 140 mm; tail, 71 mm; hind foot, 18 mm. Weight, 10-16 g.

Distribution in Texas. Western Texas, from the Panhandle southward to Trans-Pecos.

Habits. These mice prefer grassy or weedy areas where adequate food and a certain degree of protective cover are available, especially in the vicinity of water. Meadows, marshes, and weed-covered banks of irrigation ditches seem to offer optimum habitat conditions. The species seldom is found in forested areas.

They utilize the runways and underground burrows of other rodents and frequently take over vacated burrows of pocket gophers. The nest usually is placed on the ground or slightly above it under some protective cover such as a board, a clump of lodged grass, or a tangle of weeds. It is a globular structure, about 7 cm in diameter, composed of plant fibers, and usually has only one opening. These mice are also known to use the nests of marsh wrens in cattail marshes. They appear to be strictly nocturnal and active throughout the year. They are almost entirely vegetarians and feed on the green parts and seeds of plants.

In Texas, the breeding season extends through most of the year. Several litters a season seem to be the rule. A captive female produced seven litters, totaling 17 young, in one year. Litter size in wild mice, based on 24 embryo counts, ranged from one to seven and averaged about four. The gestation period is about 23 days. At birth the young mice are blind, naked, and helpless and weigh from 1 to 1.5 g. By the end of the first week they are covered with pigmented hair dorsally; by the 11th or 12th day the eyes open, at which time the mice begin to eat solid food. They are weaned by the 19th day. Sexual maturity is reached in about 4 months.

These mice seldom are of economic importance. They are utilized as food by a number of flesh eaters, including weasels, foxes, owls, and snakes.