All species of _Zapus_ agree closely in color pattern. A broad longitudinal dorsal band of some shade of yellow-brown flecked with black hairs is bordered by a lateral band of a lighter color usually containing fewer black hairs than on the dorsum. The underparts are usually white but are sometimes suffused with color resembling that on the sides. Between the white underparts and the darker color of the sides there is often a narrow, clear ochraceous stripe. Dorsal and lateral hairs are uniformly grayish-white at their bases; only the distal parts of the hairs are responsible for the external color of the animal.
The pelage of juveniles is usually finer and softer than the pelage of adults. The lateral and dorsal bands are not so conspicuously marked in young animals, and individual hairs are not so long or so wide as in adult animals.
FIGS. 35-37. Photomicrographs of underhairs (middle third) from each of the species of the genus _Zapus_. × 500.
FIG. 35. _Zapus t. orarius_, adult, female, No. 20293 MVZ, 3 mi. W Inverness, 300 ft., Marin County, California.
FIG. 36. _Zapus p. oregonus_, adult, male, No. 47856 KU, Harrison Pass R. S., Ruby Mt's, Elko County, Nevada.
FIG. 37. _Zapus h. pallidus_, adult, male, No. 22954 KU, 4 mi. N, 1-3/4 mi. E Lawrence, Douglas County, Kansas.]
Preble (1899:7) and Howell (1920:226) remark as to the noticeable difference between pelages of spring and early fall. The pelage in spring is described as bright and fresh whereas that in fall is dull and worn. Actually both bright and worn pelages can occur in any one population at any one time. Some newly molted individuals are in fresh unworn pelage; some individuals, which are molting, are in ragged, worn pelage; and other individuals perhaps could be found to represent intermediate stages.
Variations from the normal color of the pelage are rare. Among more than 3,000 specimens of _Zapus_ examined there were only 12 individuals (five _Z. princeps_, 6 _Z. hudsonius_, and 1 _Z. trinotatus_) that were abnormally colored. A single white spot was noted on each of 10 (5 _Z. princeps_, 4 _Z. hudsonius_, and 1 _Z. trinotatus_) of these individuals; the spots were on the dorsal, anterior half of the body. The skin beneath the patch of white hair was in each animal like that beneath the neighboring normally-pigmented hair. One specimen of _Z. hudsonius_ (NMC No. 6669) is everywhere black, excepting the dorsal surface of the toes of the forefeet. Most of the individual hairs from various areas of the body are black for their entire length; some, however, have non-pigmented silvery tips. One specimen of _Z. hudsonius_ (KU No. 645) lacks any black; dorsally the pelage is nearest to Ochraceous-Buff and it is white on the venter. Individual hairs of the dorsal area are white for the basal two-thirds of their length (as compared to gray and brown in the animals with normal pigmentation) and near Ochraceous-Buff on the distal third (as compared to hairs which are dark brown tipped with Ochraceous-Buff). The feet and tail are white.