|The Mammals of Texas -
Northern Rock Mouse
Rodentia : Family Muridae : Peromyscus
nasutus (J.A. Allen)
Description. A rather large,
long-tailed, grayish buff mouse; tail sharply bicolor,
brownish to blackish above and white below, slightly
tufted, more than 100 mm in length and longer than the
combined length of head and body; tops of front and hind
feet (including ankles) white; ears about as long as hind
feet. External measurements average: total length, 193
mm; tail, 104 mm; hind feet, 22.5 mm. Resembles both P. boylii and P. pectoralis,
but differs from the former in having white ankles like pectoralis.
Differs from pectoralis in having a noticeably
longer tail and heavier molars (length of maxillary
toothrow 4.5 mm as opposed to less than 4.0 mm). Differs
truei in grayish buff
rather than ochraceous buff upperparts and with smaller
ears; differs from P. attwateri in
shorter hind feet (less than 24 mm) and in white rather
than dusky ankles.
Distribution in Texas. Known in Texas
only from the Trans-Pecos, where it has been recorded
from mountainous regions of Brewster, Culberson, El Paso,
Jeff Davis, and Presidio counties.
Habits. This species is found
among boulders on rocky mountain slopes and in rockpiles
in Texas madrone and oak associations where the crevices
and cracks are covered with a thick layer of leaves. In
the Franklin Mountains (El Paso County), the rock mouse
is common in rocky areas and talus slopes. P. boylii
is absent from rocky areas where nasutus is
abundant, but boylii is abundant in adjacent areas
with fewer rocks and more vegetation. It appears that nasutus
prefers rugged, rocky habitat with sparse vegetation.
In captivity the rock mouse is docile
and easily handled. It is highly gregarious, and a dozen
or more individuals of young and adults of both sexes
often crowd into one nest without apparent conflict.
Little information is available on its
breeding habits. Pregnant females have been taken in
June, July, and August. Vernon Bailey reported capture in
New Mexico of a female containing four large fetuses in
late July and another in late August with six fetuses.
Individuals captured alive in the Franklin Mountains
readily bred in captivity and produced several litters of
two to six young. The gestation period is about 30 days.