|The Mammals of Texas -
Yellow-nosed Cotton Rat
Rodentia : Family Muridae : Sigmodon
Description. Similar to S. hispidus but paler, and with the snout distinctly orange
or rusty; tail hairier and distinctly bicolor, nearly
black above, grayish buff below; underparts grayish
white. External measurements average: total length, 259
mm; tail, 114 mm; hind foot, 28 mm. Weight, 50-80 g,
occasionally as much as 112 g.
Distribution in Texas. Isolated
at higher elevations in the Chisos Mountains, Big Bend
National Park region, Brewster County; Davis Mountains,
Jeff Davis County; and the Sierra Vieja, Presidio County.
Habits. Yellow-nosed cotton rats
live primarily on rocky slopes with scattered bunches of
grass. In the Chisos Mountains their runways have been
located in lodged needle grass in Laguna Meadow at the
foot of Emory Peak. There, the rats occupied an area of
about 40 ha. Their runways radiated from underground
dens, some of which were under clumps of agaves; others
were among the roots of large junipers. A surface nest
under a pile of dead blades of agaves was composed of dry
grasses and long fibers from the agave plants. It was
about 12 cm in outside diameter. Other nests have been
found beneath the dead lower leaves of sotol.
These rats seem to be active mainly in
the daytime, as confirmed by trapping records from 1944.
In spite of the fact that the vegetation appeared to be
too sparse to offer concealment by day, no individuals
were captured in night trapping.
The breeding season appears to extend
from March to October. Young about 3 weeks old have been
captured in early May, late June, and early November
which suggests that several litters may be reared each
season. The gestation period is approximately 35 days.
At birth, young cotton rats weigh
4.5-6.6 g and are haired. They gain about 2 g in weight
each day and reach sexual maturity by 45 days. Captive
females have produced offspring at 71 days of age.
Photo credit: John L. Tveten.