Yellow-nosed Cotton Rat
Order Rodentia : Family Muridae : Sigmodon ochrognathus Bailey

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.