Guide to subspecies

1.Z. p. cinereus 7.Z. p. oregonus
2.Z. p. curtatus 8.Z. p. pacificus
3.Z. p. idahoensis 9.Z. p. princeps
4.Z. p. kootenayensis 10.Z. p. saltator
5.Z. p. luteus 11.Z. p. utahensis
6.Z. p. minor

Geographic Variation

There are 11 subspecies recognized, most of which are in the mountains of the western United States and southwestern Canada. There is geographic variation in color, relative proportions of external parts (tail, hind feet, head, and body), and shape and size of the skull.

Three basic types of coloration occur in Z. princeps, as pointed out by Hall (1931:9). Yellow-sided dark-backed jumping mice exemplified by kootenayensis, idahoensis, and utahensis are found to the eastward in the Rocky Mountains. Reddishbrown-sided, brown-backed jumping mice typified by luteus and pacificus are found to the westward in the Sierra Nevada and in New Mexico and Arizona; mice with yellowish-buff or pinkish-buff-sides and light backs are the subspecies, cinereus, curtatus, and oregonus, that occur in the intervening Great Basin.

External dimension as a whole decreases from north to south, although not uniformly. For example, the smallest individuals are of the southernmost geographic subspecies (Z. p. luteus), but the largest are of the subspecies (Z. p. utahensis) that is near the geographic center of the range for the species. In the skull there is geographic variation in the length and shape of the zygomata, size and shape of the incisive foramina, alignment of maxillary tooth-rows, size and shape of auditory bullae, position of the postpalatal notch in relation to M3, and the presence or absence and size of the medial projection on the inferior ramus of the zygomatic process of the maxillary.

NATURAL HISTORY

Habitat.—Zapus princeps occurs most commonly adjacent to streams where grasses and herbs are in lush growth. It frequents mountain meadows neighboring small streams and is often taken from alder, aspen, or stands of willow, where the moist ground supports a heavy undergrowth of herbs. Davis (1939:330) found these mice in heavy herbage along a small stream bordered by quaking aspen near Victor, Teton County, Idaho. They were found along streams bordered by willow, rose, alder, huckleberry, sedges, and herbs of various kinds at Alturas Lake, Mill Creek, and at the head of the Pahsimeroi River. Linsdale (1938:195) found jumping mice in the Toyabe Mountains, Nevada, near the streamsides or in seepy areas close to the streams where associated vegetation included rose, willow, wild peach, sage, grasses, and herbs. In the Uinta Mountains, Utah, R. D. Svihla (1931:264) obtained them from willows along streams in mountain parks. Borell and Ellis (1934:37) in the Ruby Mountains, Nevada, found jumping mice to be common in heavy vegetation along streams. Louise Kellogg (1916:369) obtained jumping mice in northern California; all were near water, in grassy meadows, or under alders where vegetation was dense.

Zapus princeps is locally abundant, but its numbers seem to vary considerably from year to year as well as seasonally. Early autumn, when young of the year are abroad, seems to be the period of greatest abundance. Moore (1928:154) remarks that runways were plainly marked and well strewn with four-inch pieces of brome-grass. Davis (1939:334) notes that Z. princeps has runways, and found that sections, four inches long, of cut grass piled in runways was good evidence of the presence of the mouse.