Hispid Cotton Rat

Sigmodon hispidus
(Say and Ord)

 

 

 Color photo by Barbara L. Clauson.
Copyright 1999.   All rights reserved.

Description:   The hispid cotton rat is a relatively large rodent with hispid pelage--that is, dorsal hairs are a mixture of black or dark brown and buffy or gray hairs. It can be distinguished from other members of its family by: 1) large size, 2) scaly, thinly haired tail shorter than head plus body, 3) coarse stiff black guard hairs that give a grizzled appearance, 4) grayish-white or buffy underparts, 5) moderately large, grayish or black ears, nearly hidden by hair. Sexes are similar in appearance and size.

Adult Size:   Total length 202-340 mm; tail 87-122 mm, frequently broken or stubbed; hind foot 29-35 mm; ear 16-20 mm; weight 50-250 grams.

Distribution:  
The species range extends from northern South America to the Platte River in Nebraska and from Arizona to Virginia. Cotton rats have been reported from most counties in Kansas with the exception of the extreme northwestern corner of the state.

Natural History:   Cotton rats live in grassy fields, weedy patches, roadside ditches, marshy areas, and heavy vegetation at the edges of forests. They do not hibernate and are active throughout the year. Large cotton rats accumulate fat stores that allow them to reduce activity in the coldest of winter weather. They do not dig extensive burrows, but may use burrows of other small mammals. Hispid cotton rats forage from dusk through dawn year-round and are active during daylight hours in winter. Populations undergo large numerical fluctuations annually. Peak numbers are seen in the fall with steady declines from November through May or June. Numbers, both in Kansas and throughout the species' range, also vary greatly from one year to the next. Population density may be near zero or as high as 100 per hectare (40 per acre) at the same place. Cotton rats wear runways into the soil. These runways frequently contain piles of clipped vegetation, but cotton rats are not known to store food. Nests are made of dried grass and other plant fibers, and frequently are above ground, especially under rocks, boards, or in brush piles. In winter, as many as 12 rats may occupy a single nest.

  In Kansas, hispid cotton rats breed from March through November. The gestation period is about 27 days, and females may breed within a few hours of giving birth. Litter size varies from 4 to 12 or more and is dependent on size of mother; large females generally have large litters. Neonates weigh around 6 grams when born, are furred, and become independent of the parents within 3 weeks. Females can breed at six weeks of age, when they weigh about 50 grams. Their high productivity is balanced by high mortality. Cotton rats are favored prey of hawks, owls, coyotes, foxes, bobcats, several species of snakes, and other small predators. They also are susceptible to death in cold, wet weather in the spring when their fat stores are low. Hispid cotton rats rarely live as much as one year in the wild, but can live several years in laboratory colonies.
  Cotton rats eat stems and leaves of grasses and other herbaceous vegetation. They also consume seeds, especially waste grain in agricultural fields, insects, and other animal material, such as young prairie voles or eggs of ground nesting birds. In Texas and further south, they can damage agricultural crops during population eruptions.

Right: A subadult hispid cotton rat.

Taxonomy:   Hispid cotton rats in Texas were named Arvicola texiana by Audubon and Bachman in the 1850's. They included this cotton rat with voles and lemmings based on general appearance, although it is more closely related to Peromyscus, Neotoma, and Reithrodontomys. The subspecies, which occurs in Kansas, has had its present Latin name since 1891.

Historical Biogeography:   Hispid cotton rats expanded their range northward in Kansas rapidly during the 1930's and 40's. The range expansion may be a result of gradually warming temperatures since the retreat of the last glaciers. It also may have been influenced by the flush of weedy growth after abandonment of farms and farmsteads during the 30's. Populations seem to be established throughout the state, but because of the large temporal and spatial fluctuations in numbers, they can be difficult to find. Populations in individual habitat patches may disappear only to be reestablished by immigrants from surrounding patches.

References:   Fleharty and Olson (1969); Fleharty et al. (1972); Fleharty and Choate (1973); McClenaghan and Gaines (1978); Sauer (1985); Campbell and Slade (1995)


Return to the Mammals of Kansas index page.