The hispid cotton rat is a mammal of the southern United States and Mexico, probably a fairly new arrival in Colorado. These are modest-sized rats, to 11 inches long and about 3 1/2 ounces. Their fur is blackish brown, the color of watermelon seeds, and harsh to the touch (hence the common name). Their tail is nearly naked, and the ears are largely obscured in fur. Cotton rats are smaller than woodrats and differ in habitat. They resemble voles
superficially, but are much larger and have longer tails.
Range: Climatic warming and irrigated agriculture have both encouraged its movement westward along the Arkansas Valley to the vicinity of Pueblo.
Habitat: Cotton rats nest in depressions or shallow burrows, favoring moist fields, vegetable and melon fields, and other grassy areas. Unlike the introduced Norway rat, they seldom live around buildings or dumps.
Diet: Cotton rats consume mostly plants, but will eat birds’ eggs, nestlings, and young voles. They feed on forbs and grasses and harvest far more plant material than they actually eat as they construct and mark runways through the vegetation. They are active at dawn and dusk and are nocturnal.
Reproduction: Cotton rats breed through the warmer months, producing several large litters (to 10 or more) of well-haired young after a gestation period of 27 days. Foxes, owls and snakes take their toll on these animals, and early litters often die in late spring freezes. Cotton rats seldom live more than one year.
By David M. Armstrong
Department of Ecology & Evolutionary Biology
Environmental Studies Program, University Museum of Natural History
University of Colorado-Bouldermausmann@aol.com