ause the progress of
spring molt is seemingly more regular than that of autumn molt. In
spring, molt proceeds posteriorly in a more or less regular line on both
dorsum and venter; in most specimens it is completed first on the
venter. In autumn, molt is irregular, or at best is coincident over
large parts of the body, and frequently is seen only by searching
through the pelage with a fine probe or dissecting needle. In both
spring and autumn, molt seemingly is delayed in females that are
pregnant or lactating.

In both winter pelage and summer pelage, the upper parts have blackish
or grayish guard hairs and shorter, more numerous cover hairs. All the
cover hairs are gray basally; some have a buffy band terminally and
others have a buffy subterminal band with a terminal black tip. The
generally darker over-all color of upper parts in summer pelage results
(as seen in Nebraskan specimens) from a narrower band of buff on the
cover hairs (only approximately one half the width of the band on hairs
in winter pelage), a darker buffy band (ochraceous buff rather than pale
ochraceous or straw color), and a relative sparseness of the pelage,
which allows the gray basal portion of some hairs to show on the
surface. The more grayish venter of summer-taken specimens results from
much more of the grayish basal portion of the white-tipped hairs showing
through than in the longer, denser pelage of winter.

Wear on the pelage seems in general to produce a paler over-all color of
upper parts, evidently due mostly to abrasion of the terminal black tip
of the cover hairs, but possibly actual fading of the pelage is involved
also. Worn winter pelage is especially notable for its paleness; the
buffy tones are accentuated and the upper parts, especially posteriorly,
may even appear fulvous. The difference in color of upper parts between
specimens in worn winter pelage and fresh summer pelage (or for that
matter specimens in fresh _versus_ worn winter pelage) from the same
locality is greater in our material than the difference between some
specimens in comparable pelages from localities more than 500 miles
apart.

We have seen no specimens taken in winter in which we could discern that
the autumn molt had been incomplete, but three old adult males in summer
pelage indicate that spring molt is not always completed. KU 50154,
obtained on August 14, 1952, 5 mi. N and 2 mi. W Parks, Dundy Co.,
Nebraska, has the entire posterior back and sides