Description: Imagine a “coyote in mouse’s clothing,” and you have a grasshopper mouse. These diminutive hunters are rodents by heritage but carnivores by habit, and they are among our most fascinating nongame mammals. Adults are reddish tan above and white below. Juveniles and the elderly (perhaps over four years old) are gray. These are stocky mice, only about six inches long but often weighing over 1 1⁄2 ounces (that is, typical mouse length but twice mouse weight).
Grasshopper mice are highly territorial, and initial encounters between individuals are vocal and violent. Once dominance is established, the subordinate mouse assumes a submissive posture and prevents further aggression. Owls, coyotes, foxes, and badgers kill grasshopper mice, but no predator can afford to make them a staple. Grasshopper mice are a step higher in the food chain than usual rodents, and hence populations are smaller.
Range: Grasshopper mice live on grasslands of the eastern plains, in shrubby habitats in the San Luis Valley and in valleys on the Western Slope.
Habitat: They are common along fence rows, which tend to have better cover than open pastures, and like areas of heavy grazing, which have more insects to eat and sandy areas essential for dust bathing.
Diet: Grasshopper mice eat 75 to 100 percent arthropods, depending on the season. Beetles, grasshoppers, spiders, scorpions and “pillbugs” are eaten, as are rodents as large as prairie voles and cotton rats, some carrion and seeds. Their incisors are not the usual broad rodent chisels, but are narrow, piercing daggers.
Reproduction: As is typical in well-armed animals that can harm each other, courtship is complicated. Females produce three to six litters of one to six young throughout the warmer months, with a gestation period of four weeks. Unlike most rodents (but like many carnivores), the male provides the female with food and thus helps to provide for the nursing young.
By David M. Armstrong
Department of Ecology & Evolutionary Biology
Environmental Studies Program, University Museum of Natural History
University of Colorado-Boulder
mausmann@aol.com