Arizona cotton rat

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Arizona Cotton Rat
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Order: Rodentia
Family: Cricetidae
Genus: Sigmodon
Subgenus: Sigmodon
Species group: S. hispidus
Species: S. arizonae
Binomial name
Sigmodon arizonae
Mearns, 1890

The Arizona cotton rat or Colorado River cotton rat (Sigmodon arizonae) is a species of rodent in the family Cricetidae. It is found in Mexico and the United States.


The Arizona cotton rat has a typical rat-like appearance, and is sufficiently similar to the hispid cotton rat that it was considered to be part of the same species until 1970, when genetic analysis confirmed its distinct nature. It has bristly brownish fur over most of its body, with whitish underparts and grey feet. The scaly tail is dark in color, with very sparse fur. Adults range from 25 to 36 centimetres (9.8 to 14.2 in) in total length, including the 10 to 15 centimetres (3.9 to 5.9 in) long tail, and weigh anything from 83 to 300 grams (2.9 to 10.6 oz). Males are slightly larger than females, but the two sexes are otherwise similar in appearance.[2]

Females have ten or twelve teats, suggesting a maximum litter size of around this number. Reproduction is thought to occur year-round.[2]

Distribution and habitat[edit]

The Arizona cotton rat is found in southern and central Arizona, the extreme southwestern corner of New Mexico,[3] and in western Mexico from Sonora to Nayarit.[1] They live close to rivers, streams, and other sources of fresh water in semidesert, open grassland, or swampy habitats throughout the region. They rely particularly on areas of dense grassy vegetation.[4] Two of the five recognized subspecies are believed to have gone extinct during the twentieth century,[2] including the nominate subspecies, Sigmodon arizonae arizonae. Three subspecies therefore remain:

  • Sigmodon arizonae cienegae - Arizona, northern Sonora
  • Sigmodon arizonae major - southern Sonora, Sinaloa, Nayarit
  • Sigmodon arizonae plenus - western La Paz County, Arizona


  1. ^ a b Linzey, A.V.; Timm, R.; Álvarez-Castañeda, S.T.; Castro-Arellano, I. & Lacher, T. (2008). "Sigmodon arizonae". IUCN Red List of Threatened Species. Version 2009.2. International Union for Conservation of Nature. Retrieved 6 February 2010. 
  2. ^ a b c Gwinn, R.N.; et al. (2011). "Sigmodon arizonae (Rodentia: Cricetidae)". Mammalian Species. 43 (1): 149–154. doi:10.1644/883.1. 
  3. ^ Frey, J.K.; et al. (2002). "First record of the Arizona cotton rat (Sigmodon arizonae) in New Mexico". Southwestern Naturalist. 47 (3): 491–493. JSTOR 3672513. 
  4. ^ Anderson, D.C. & Nelson, S.N. (1999). "Rodent use of anthropogenic and 'natural' desert riparian habitat, lower Colorado River, Arizona". Regulated Rivers: Research & Management. 15 (5): 377–393. doi:10.1002/(SICI)1099-1646(199909/10)15:5<377::AID-RRR549>3.0.CO;2-Q. 
  • Musser, G. G. and M. D. Carleton. 2005. Superfamily Muroidea. pp. 894–1531 in Mammal Species of the World a Taxonomic and Geographic Reference. D. E. Wilson and D. M. Reeder eds. Johns Hopkins University Press, Baltimore.