Fig. 123. Big jumping mouse (Zapus princeps trinotatus) in hibernation. Puyallup, Washington, January 30, 1939. (Fish and Wildlife Service photo by Victor B. [Scheffer], No. 576.)
Description.—The big jumping mouse is a medium-sized mouse, slightly larger than the house mouse, with an exceptionally long, tapering tail. Head and body measure about 4 inches and the tail about 5 inches. The body is slender with a small head, small eyes and small, naked ears. The forefeet are small and handlike but the hind feet are large with long, powerful legs. The long, naked tail is smoothly tapering to a narrow point. The fur is short, posteriorly directed, stiff and bristlelike. The dorsal area is dusky, the sides are orange or yellow, and the underparts are creamy white. Each upper incisor tooth has a groove on its anterior face.
Jumping mice are boreal mammals occurring in wooded regions ranging from the Arctic region southward to North Carolina, New Mexico and California. Jumping mice are of rather general distribution in Washington, being only locally common. They are partial to damp, boggy areas but avoid true swamps. They occur in clearings in the forests in the Puget Sound area and in meadows in river bottoms and in jungles in ravines. They reach their greatest abundance in the boggy meadows and glacial cirques of the mountains and spread out from such areas to seemingly less favored habitat on dryer slopes and heather meadows. Unlike many species, they do not seem to inhabit talus slides. They are entirely absent from the eastern Washington desert.
Sometimes the jumping mouse walks on all four feet but the ordinary means of progression is by short hops on the hind feet alone. When startled they travel in great bounds, covering six feet or more at a jump. When jumping they make considerable noise, swishing or rustling through the grass and landing with an audible thud. The long tail serves as a balancing organ. A specimen whose tail had been lost was reported by [Svihla] and [Svihla] (1933: 133) to turn somersaults in the air and invariably to land on its back rather than its feet.
Jumping mice become very fat and hibernate in middle summer or early fall. In the lowlands they disappear by late July but in the mountains they remain active until the middle of September. They spend the winter in nests of grass several feet beneath the surface. A hibernating individual figured by [Flahaut] (1939: 17) was curled in a ball, head down with the tail wrapped completely around the greatest circumference of the ball.
Near Seattle the principal food of the jumping mouse was the velvet grass (Holchus lanatus), and the seeds of grasses and the broad-leaved dock. The fruit of the blackberry (Rubus macropetalus) is eaten and occasional individuals are seen with the chin stained a deep purple from the juice.
The new-born young of the jumping mouse were reported by [Svihla] and [Svihla] (1933: 132) to average 0.8 grams in weight. They are pink, hairless, lacking even the facial vibrissae, with eyes closed and ears folded.