Arizona Cotton Rats (Sigmodon arizonae) are quite common at the Sweetwater Wetlands here in Tucson. These rats are easily observed because they are active not only at night, but during the day as well.
Arizona Cotton Rats feed mainly on grasses and are usually found in wetland areas here in Tucson. Most of these rats race for cover at my approach, but this one ignored me and was instead intently focused on the obviously delicious sprig of green grass.
Besides Arizona Cotton Rats, there are three other species of cotton rat here in Arizona, the Yellow-nosed Cotton Rat (Sigmodon ochrognathus), the Tawny-bellied Cotton Rat (Sigmodon fulviventer), and the very similar Hispid Cotton Rat (Sigmodon hispidus). The Yellow-nosed Cotton Rat is the only other cotton rat found here in Pima County, and they are generally found in more mountainous grassy areas.
Cotton rats can be identified by their short (less than nose to rump length), mostly hairless, uniformly colored tails, multicolored fur (buff, brown, black etc.), and hair covering the ear-hole.
Arizona Cotton Rats have pale gray undersides that distinguish them from Tawny-bellied Cotton Rats, and they lack the rusty ochre nose of a Yellow-nosed Cotton Rat. Arizona Cotton Rats and Hispid Cotton Rats are very similar, but they have little territory overlap, so these two are best distinguished by location where they are observed.