Where harvest mice live in dense vegetation they make small runways and food piles similar to those of Microtus but in more open areas they leave no perceptible signs. Near Yakima the nest of a harvest mouse was found among the roots of an overturned apple tree. This nest was an irregular ball composed of fine grasses and shredded bark closed above, with a side entrance and a central cavity three inches in diameter. Near Moses Lake three nests of harvest mice were discovered on the ground under cover of a dense growth of tumbleweed, and six live harvest mice were captured in the same area. These nests were cuplike, open above, and were composed of dry grasses, bits of weeds, and newspaper. The smoothly rounded inner cups measured about three inches in diameter.
Embryos were found in harvest mice in Washington from March to April and numbered 3 to 6.
Peromyscus maniculatus (Wagner)
Deer mouse
Description.—The deer mouse is slightly larger than the house mouse, the head and body measuring from 3-1/2 to 4 inches. The length of the tail varies considerably in the several races, ranging from approximately 2-1/2 inches in gambelii to 4 inches or more in some individuals of oreas. The eyes are large and protrude slightly. The ears are large, erect and naked. The tail is sparsely furred with short, posteriorly directed hairs. The color of the upper parts varies from yellowish buff in gambelii to reddish brown in oreas and dusky in austerus. Young deer mice are gray or bluish gray above. Underparts and feet are white. The tail is bicolored, being dusky above and white below.
Fig. 106. Deer mouse (Peromyscus maniculatus austerus), in captivity, Seattle, Washington, September 18, 1939. (Fish and Wildlife Service photo by Victor B. [Scheffer], No. 723.)
In Washington Peromyscus may be separated from other naked-eared mice by ungrooved teeth and slightly tapering, bicolor tail. Nearly every part of North America is inhabited by one or more kinds of Peromyscus. The single species, maniculatus, which occurs in Washington, ranges from the Atlantic to the Pacific and from the Arctic to tropical Mexico. [Osgood] (1909: 17) remarks: "... it is probable that a line, or several lines, could be drawn from Labrador to Alaska and thence to southern Mexico throughout which not a single square mile is not inhabited by some form of this species."