Sigmodon hispidus

The hispid cotton rat (Sigmodon hispidus) is a rodent species long thought to occur in parts of South America, Central America, and southern North America. However, recent taxonomic revisions, based on mitochondrial DNA sequence data, have split this widely distributed species into three separate species (S. hispidus, S. toltecus, and S. hirsutus). The southern edge of the S. hispidus distribution is likely near the Rio Grande, where it meets the northern distribution of S. toltecus (formerly S. h. toltecus). The northern extent of S. hispidus distribution is to the Platte River in Nebraska and from Arizona to Virginia. Adult size is total length 202–340 mm (7.9–13 in); tail 87–122 mm (3.4-4.8 in), frequently broken or stubbed; hind foot 29–35 mm (1-1.3 in); ear 16–20 mm (0.6-0.9 in); mass 50-250 g (1.7-9 oz). They have been used as laboratory animals. The currently accepted scientific name for the hispid cotton rat is Sigmodon hispidus Say and Ord. It is a member of the family Cricetidae. Although 25 subspecies are accepted, including the type subspecies, the most distinct genetic subdivision within S. hispidus separates the species into two genetic lineages, an eastern one and a western one, which hybridize along a contact zone. In the United States, the hispid cotton rat ranges from southern Virginia and North Carolina (especially the coastal plain) west through Tennessee, northern Missouri, Kansas, and extreme southern Nebraska to southeastern Colorado, New Mexico, and southeastern Arizona; south to the Gulf Coast; and south to northern Mexico. It does not occur on the coastal plain of North Carolina nor in the mountains of Virginia. Disjunct populations occur in southeastern Arizona and extreme southeastern California into Baja California Norte. In Kansas, it appeared within the last 50 years. Hispid cotton rats occupy a wide variety of habitats within their range, but are not randomly distributed among microhabitats. They are strongly associated with grassy patches with some shrub overstory and they have little or no affinity for dicot-dominated patches. Habitat use and preference by hispid cotton rats usually appear to depend on the density of monocots. However, some studies are equivocal on the importance of other vegetation. For example, hispid cotton rats may respond favorably to a high percentage of dicots in a stand if cover remains optimal. In Kansas, hispid cotton rats increased on root-plowed prairie that experienced an increase in the diversity and biomass of early successional forbs. Male hispid cotton rats exhibit a lower degree of habitat selectivity than females. In Texas, males were found on different habitat types (grassy, shrubby, and mixed) about in proportion to availability; females tended to choose mixed habitats more often than expected based on availability. Habitat use varies with season and breeding status. In Texas, grassy areas with some shrubs were preferred in spring and areas with more shrubby cover were preferred in fall. In Kansas, remnant prairie the preferred habitat of hispid cotton rats has dense undergrowth and an upper layer of protective vegetation such as big bluestem (Andropogon gerardii)/kochia (Kochia scoparia)/annual sunflower (Helianthus annuus). Hispid cotton rats prefer grassy clearings, croplands, overgrown fields, and overgrown roadsides and right-of-ways. In Kansas prairies hispidcotton rats occur at relatively high abundance in ungrazed uplands and sandy mixed-grass native prairie, but also prefer disturbed areas. The use of disturbed areas was probably important in the recent invasion of hispid cotton rats into north-central Kansas from the northern presettlement limit of their range in Oklahoma. On Texas rangelands, hispid cotton rats appeared to respond to increased biomass of standing crop and increases in the proportion of the standing crop in potential food plants such as bristlegrasses (Setaria spp.). Rat density was four times greater on areas planted to exotic grasses including King Range bluestem (Bothriochloa ischaemum) and buffel grass (Enchrus ciliaris) than on native range dominated by windmill grass (Chloris spp.) and Texas wintergrass (Stipa leucotricha). In northeastern Kansas, hispid cotton rats occurred at high population densities in tallgrass prairie (dominated by perennial grasses); population density declined to levels too low to accurately estimate over 28 years of succession to brush and trees. They are occasionally found in habitats dominated by early successional grassland species (i.e., annual grasses and forbs).