The hispid cotton rat (Sigmodon hispidus) is a rat 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 distribution of S. hispidus ranges from Arizona in the west to Virginia to the east and from the Platte River in Nebraska in the north to, likely, the Rio Grande in the south, where it meets the northern edge of the distribution of S. toltecus (formerly S. h. toltecus).Carroll, D. S., L. L. Peppers, and R. D. Bradley. (2005). "Molecular systematics and phylogeography of the Sigmodon hispidus species group". pp. 85–98, in Contribuciones Mastozoologicas en Homenaje a Bernardo Villa (Sanchez-Cordero V. y R. A. Medellin Eds.) Instituto de Biologia e Instituto de Ecologia, UNAM; CONABIO, Mexico. Adult size is total length ; tail , frequently broken or stubbed; hind foot ; ear ; mass . They have been used as laboratory animals.
Taxonomy The currently accepted scientific name for the hispid cotton rat is Sigmodon hispidus. It is a member of the family Cricetidae.Meikle, D. and Powers, K. (2011) Sigmodon hispidus hispid cotton rat. Animal Diversity Web, University of Michigan Museum of Zoology. 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.
Distribution 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.Hall, E. Raymond. (1981). The mammals of North America. 2nd ed. Vol. 2. New York: John Wiley and Sons 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.
Habitat 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).Fleharty, Eugene D. (1972). "Some aspects of small mammal ecology in a Kansas remnant prairie". In: Zimmerman, James H., ed. Proceedings, 2nd Midwest prairie conference; 1970 September 18–20; Madison, WI. Madison, WI: University of Wisconsin Arboretum. pp. 97–103 Hispid cotton rats prefer grassy clearings, croplands, overgrown fields, and overgrown roadsides and right-of-ways. In Kansas prairies hispid cotton 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.Kaufman, Donald W.; Finck, Elmer J.; Kaufman, Glennis A. (1990). "Small mammals and grassland fires". In: Collins, Scott L.; Wallace, Linda L., eds. Fire in North American tallgrass prairies. Norman, OK: University of Oklahoma Press. pp. 46–80 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.Fitch, Henry S.; Kettle, W. Dean. (1983). "Ecological succession in vegetation and small mammal populations on a natural area of northeastern Kansas". In: Kucera, Clair L., ed. Proceedings, 7th North American prairie conference; 1980 August 4–6; Springfield, MO. Columbia, MO: University of Missouri. pp. 117–121 They are occasionally found in habitats dominated by early successional grassland species (i.e., annual grasses and forbs).Dickson, James G.; Williamson, J. Howard. (1988). Small mammals in streamside management zones in pine plantations. In: Szaro, Robert C.; Severson, Kieth E.; Patton, David R., technical coordinators. Management of amphibians, reptiles, and small mammals in North America: Proceedings of the symposium; 1988 July 19–21; Flagstaff, AZ. Gen. Tech. Rep. RM-166. Fort Collins, CO: U.S. Department of Agriculture, Forest Service, Rocky Mountain Forest and Range Experiment Station. pp. 375–378
Hispid cotton rats occur in grassy areas or early-successional habitats within open woods. In the Southeast hispid cotton rat population density increases with the density of broomsedge (Andropogon virginicus) and other low growing plants, but declines with succession to brush and trees. In Texas pine-hardwood forests, hispid cotton rats were captured most often in narrow streamside management zones which have more light and thus more ground cover, and slightly less often in wider zones. In longleaf pine-slash pine stands of central Louisiana hispid cotton rats were captured in sawtimber, sapling, and regeneration stands but not in pole-sized timber; stands with surface cover were more likely to support hispid cotton rats. Pole-sized timber is dense, little light reaches the ground, and surface cover is minimal.Mullin, Keith; Williams, Kenneth L. (1987). "Mammals of longleaf-slash pine stands in central Louisiana". In: Pearson, Henry A.; Smeins, Fred E.; Thill, Ronald E., compilers. Proceedings of the southern evaluation project workshop; 1987 May 26–27; Long Beach, MS. Gen. Tech. Rep. SO-68. New Orleans, LA: U.S. Department of Agriculture, Forest Service, Southern Forest Experiment Station. pp. 121–124 In Louisiana and Mississippi, hispid cotton rats were more numerous in cut than in uncut bottomland hardwoods. They were also more numerous in cottonwood (Populus spp.) plantations than in uncut cottonwood stands. In northern Georgia intensive site preparation following clearcutting of pine-hardwood mixtures increases forage production and increased numbers of small mammals (presumably including hispid cotton rats).Evans, Timothy L.; Waldrop, Thomas A.; Guynn, David C., Jr. (1991). "Fell-and-burn regeneration in the North Georgia piedmont: effects on wildlife habitat and small mammals". Proceedings, Annual Conference of Southeastern Association of Fish and Wildlife Agencies. 45: 104–114
In Colorado, hispid cotton rats occupy semimoist areas with abundant grasses and weeds and appear to be restricted to relatively warm areas.Lechleitner, R. R. (1969). Wild mammals of Colorado. Boulder, CO: Pruett Publishing Company In New Mexico, hispid cotton rats do not occur regularly in areas with a mean annual temperature lower than 55 degrees Fahrenheit (13 °C) and a growing season shorter than 180 days. In Trans-Pecos, Texas, hispid cotton rats occur at the warmer, low elevations in areas of moderate to dense grassy cover.Schmidly, David J. (1977). The mammals of Trans-Pecos Texas: including Big Bend National Park and Guadalupe Mountains National Park. College Station, TX: Texas A&M University
When water and wastewater are added to baldcypress (Taxodium distichum var. distichum) domes, small mammals including hispid cotton rat move to peripheral areas that are drier. The rising water tables favor marsh rice rats (Oryzomys palustris) over hispid cotton rats.
Cameron and McClure compiled reports of hispid cotton rat population densities. The mean hispid cotton rat population density range for all studies was 5.3 to 31.1 rats per hectare. Population density ranges in Texas include 1 to 14 rats per hectare in coastal prairie, 17 to 84 rats per hectare in unmowed right-of-ways, 9 to 29 rats per hectare in old fields, 6 to 54 rats per hectare in abandoned fields, and 0.7 to 5 rats per hectare in grass-prickly-pear (Opuntia spp.). In Florida population density ranges include 0 to 24 rats per hectare in sand pine scrub, 2 to 47 rats per hectare in pine flatwoods, and 27 to 94 rats per hectare in tropical hammock. In Kansas, the hispid cotton rat density ranged from 0.2 to 21 rats per hectare in grassland;Cameron, Guy N.; McClure, Polley A. (1988). "Geographic variation in life history traits of the Hispid cotton rat (Sigmodon hispidus)". In: Boyce, Mark S., ed. Evolution of life histories of mammals: theory and pattern. New Haven, CT: Yale University Press: 33–64 the highest estimated density was 65.4 hispid cotton rats per hectare in favored habitat.
In a study of the effects of habitat patchiness on movement, hispid cotton rats preferred only the largest patches which were by 330 feet (50×100 m). Patches were established by mowing strips between blocks of grasses. Hispid cotton rats were present in intermediate numbers on medium-sized patches which were , but were so scarce on the smallest patches that their movement pattern could not be analyzed.
In Kansas remnant prairie, the average annual home range of adult male hispid cotton rat was estimated as and that of adult females as . The greatest distance traveled by an adult male was and by an adult female was . In Texas male hispid cotton rats also had larger home ranges than females. Home ranges were larger in summer and winter than in spring and fall. Home range size was positively correlated with body mass and negatively correlated with population density. There was a relatively high degree of exclusivity (41%), indicating intolerance of conspecifics, particularly of the same sex. In Texas hispid cotton rats found their original home ranges (homed) from displacements of up to . Returns were relatively high from displacements of up to , suggesting that hispid cotton rats are familiar with the area within that distance. Hispid cotton rats released in areas with no cover homed better than hispid cotton rats released in typical hispid cotton rat habitat. Spencer and others used site fidelity as a measure of an individual's actual home range and concluded that hispid cotton rats have both single-day and multiday site fidelity and therefore establish true home ranges.
Cover requirements