|The Mammals of Texas -
Rodentia : Family Muridae : Microtus
Description. A small mouse with short
tail, brown color, and only four mammary glands; tail
usually less than 35 mm in length, less than twice as
long as hind foot; pelage long and fluffy; upperparts
dull umber brown, underparts buffy gray, feet and tail
brownish gray. External measurements average: total
length, 141 mm; tail, 32 mm; hind foot, 21 mm. Weight,
Distribution in Texas.
Restricted in Texas to the higher parts of the Guadalupe
Mountains in Culberson County.
Habits. In the Guadalupe
Mountains of western Texas these mice live in colonies in
the grassy openings of the yellow pine forest, especially
in the vicinity of old logs that are partly decayed and
well-bedded in the soil. Their numerous, well-defined
runways meander through the tall grass, radiating chiefly
from the logs under which the mice live and rear their
families. They also occur on open ridges where their
runways wind about among stones, under shinnery oaks, and
even into the edge of dry woods.
Their globular nests of dried grasses
and herbs are placed in dense clumps of vegetation above
ground, in hollowed-out places under logs, or in special
underground chambers off their burrows. One located under
a log was cup-shaped, rather than globular, about 10 cm
in diameter, and contained four small mice.
Trapping records indicate that these
mice are more active in the daytime than are most small
mammals, especially in places where adequate ground cover
offers concealment. More than 90% of a series trapped in
the Guadalupe Mountains were caught in the daytime
although the traps were kept set day and night.
Their food is almost entirely
vegetation the green parts of grasses and herbs in
summer and the basal portions, roots, bulbs, and bark in
winter. There is no evidence that they store food other
than the small piles of cut vegetation seen along their
trails and at their feeding stations.
Breeding probably continues through
most of the year with an interval of about 30-40 days
between litters. Gravid females have been trapped in
every month from May to October, inclusive. The size of
litters, based on embryo counts, ranges from two to five,
averaging three. At birth the young are nearly naked,
blind, and helpless. They develop rapidly as indicated by
the records of young females in the "black"
juvenile pelage, weighing slightly more than 20 g, that
were sexually mature and gravid. Such mice were probably
not more than 6 weeks old.
In Texas, these mice are restricted to
the high parts of the Guadalupe Mountains and are of no
economic importance except as for food for fur-bearers
and other flesh-eaters. Their remains have been
identified in droppings of gray fox, bobcat, badger,
coyote, and skunk.
Photo credit: John L. Tveten.