Westward expansion of the tawny-bellied cotton rat (Sigmodon fulviventer) in west-central New Mexico

In New Mexico, the tawny-bellied cotton rat (Sigmodon fulviventer) previously was known only from central and southwestern parts of the state. In central New Mexico, most records were from areas of tall grass and marshes associated with the middle Rio Grande valley. In 2003, we discovered S. fulviventer in grassy and marshy habitats >100 km west of the Rio Grande in west-central New Mexico. Because past surveys in this region did not report captures of Sigmodon, we suspect our distributional records represent recent westward expansion of S. fulviventer in the state.