The skins of 44 molting prairie voles were pinned out flat. The flesh
sides clearly show the areas of molt. Various stages in the molt process
were observed also in animals caught in live traps. The molt begins when
the animal is three or four weeks old; at this time the juvenal pelage
is replaced by the subadult pelage. The second molt occurs when the
prairie vole is between eight and twelve weeks old, and is the means by
which the adult pelage replaces the subadult pelage. These same two
molts were found by Hatfield (1935) to occur in captive _Microtus
californicus_. Molting voles of the species ochrogaster were trapped in
each month of the year.
The molting processes of juveniles and subadults follow the same
pattern. The first area of molting is in the pectoral region. The molt
patch extends caudad toward the tail and cephalad toward the chin. New
pelage separates this area of active molt into two strips on the fourth
or fifth day. By this time each strip has spread laterad to the legs and
sides, and is 10 to 20 mm. wide. Ultimately each strip unites with its
opposite, usually at the center of the dorsum. This area of molt then
spreads cephalad and caudad. Fourteen to fifteen days after the
beginning of the molt, the entire dorsum is in process of being covered
with new pelage. Shortly before the completion of the molt, the dorsal
area of molt divides into two patches, one on the rump and one on the
nape. The areas last to be covered with new pelage are the crown and
that between the ears and the eyes. A slight variation in the above
process occurred in some specimens in which the lateral strips joined
immediately cephalad of the tail instead of at the center of the dorsum.
The entire process takes approximately three weeks.
Large voles (45 grams or more) grow hair in irregular patches that
measured 5 to 15 mm. In these large voles the molt is accomplished
slowly and does not cover large areas of the body at any one time. The
small areas of molt are visible for 7 to 10 days, and were found on
approximately three quarters of the large voles examined.