Sigmodon arizonae
Arizona cotton rat

Arizona cotton rats (Sigmodon arizonae) are found in the Southern U.S., through Mexico and Central America to the northern South America. They have been collected on coastal plains and the lower Pacific-facing slopes of the Sierra Nevada Occidental. They have also been found at moderate elevations in eastern Nayarit (Mesa del Nagar, 1300 m; Ocota Airstrip, 1900 m) but occur more often in the coastal plains of the western and central portion of their range. (Andersen, 1994; Cameron and Spencer, 1981; Carelton, et al., 1999)

Sigmodon arizonae is found in a wide variety of landscapes, but seem to prefer tall, dense grasslands, usually with ample water availability. They are generally found in areas supporting sedges, rushes, and cane grass-like plants. However, this species has been found within the arid upper tropical sub-zone where the dominant vegetation was savanna-woodland, pine and oak forest, deciduous tropical forest, palm forest, or mangrove swamp. These animals are often found near rivers and their floodplains, lakes and ponds, or drainage sloughs through agricultural fields and pastures. These animals can be found in different types of riparian vegetation, including stands of cattails and water hyacinths. (Andersen, 1994; Brylski, 1999)

These cotton rats greatly resemble their congeners, Sigmodon hispidus, and until recent studies of their chromosomes revealed that they were a distinct species, were lumped with S. hispidus. (Davis and Young, 1999)

Sigmodon arizonae is a large cotton rat, measuring 200 to 349 mm in length, of which 85 to 156 is contributed by the tail, and weighing between 125 and 211 g. This species can be distinguished from other cotton rats in the region, Sigmodon fulviventer and Sigmodon ochrognathus by its larger size and longer hind foot, which usually measures more than 34 mm. There are also differences in coloration of fur. (Davis and Young, 1999)

The pealge of these animals is not remarkable. They appear to be salt and pepper, brownish rats. Although they look like voles, they are much larger. (Cameron and Spencer, 1981; Davis and Young, 1999)

There is little information to be found on this subject for S. arizonae, or other members of the genus.

Little is known about the reproduction of this species as separate from S. hispidus because until recently they were considered the same species. However, it is likely that what is known about reproduction in S. hispidus, the sister species of S. arizonae will apply reasonably well to the latter species. (Davis and Young, 1999)

Sigmodon hispidus is known to undergo a postpartum estrus. These animals copulate 3 to 6 hours after giving birth, with ovulation following between 6.5 and 12 hours after partuation. (Cameron and Spencer, 1981)

Gestation in cotton rats lasts approximately 27 days. The litter size in S. hispidus ranges from 1 to 15. The neonates are well-developed for rodents, and are able to run at birth, although their eyes are not opened. Neonates weigh about 7.23 g. Growth is rapid, with the young gaining 1 or 2 g per day. Eyes typically open within 60 hours of birth. The young are weaned between 10 and 25 days. (Cameron and Spencer, 1981; Davis and Young, 1999)

In females of S. hispidus, conception took place at 40 days of age and estrus could occur from as early as 10 days of age. Sexual maturity in males, as determined by the presence of sperm in the epididymis, was always achieved by 3 months of age. (Cameron and Spencer, 1981)

Although no information is available for this species, it is likely that parental care is not extensive. The young are born well developed, and attain independence very early in life. Females probably provide the bulk of parental care, nursing the young for 10 to 25 days. It is likely that they also groom and protect the young. Male parental care has not been reported for this genus. (Cameron and Spencer, 1981; Davis and Young, 1999)

Longevity of S. arizonae has not been reported. However, S. hispidus individuals appear not to live much beyond a year, given the length of residence any individual has been known to have in an area. (Cameron and Spencer, 1981)

Cotton rats are active at all hours of the day. They are both diurnal and nocturnal. Activity patterns are influenced by biotic and abiotic factors. Although typically terrestrial, moving around on four feet, these animals are known to swim when necessary. When swimming, cotton rats use their hind feet for propulsion while holding their front feet near their body, and never swimming under water. (Cameron and Spencer, 1981)

Sigmodon hispidus builds nests on land. These appear to be mainly surface and burrow nests made of woven grasses. Nests range in shape from cup-shaped to a hollow ball-shaped. They typically have only one entrance. (Cameron and Spencer, 1981)

Sigmodon hispidus is considered a solitary species. There are dominance interactions, which appear to be based mainly on weight of animals, with heavier animals exerting dominance over lighter animals. Although there are no reports for the sociality of S. arizonae, it is likely that they resemble their sister species. (Cameron and Spencer, 1981; Davis and Young, 1999)

The home range size for this species has not been reported.

There is no information or data found on this subject for S. arizonae. However, it is safe to make some generalizations based on the fact that these animals are mammals. Most mammals are known to communicate with vocalizations. Tactile communication is important in the context of agonistic and reproductive behavior. Scent cues are often used, especially in marking territories, and identification of individuals. Often there are visual signals in communication, such as body posture.

Sigmodon arizonae feeds mainly on grasses, but will also feed on citrus, other crops, some insects, and carrion. (Brylski, 1999)

Although there is a paucity of information on this subject for S. arizonae, this species is likely preyed upon by a variety of raptors and carnivores. Given their apparent ability to reproduce quickly, they could be an important component of the diets of such animals, as are individuals from their sister species, S. hispidus. (Cameron and Spencer, 1981)

Arizona cotton rats are likely a source of food for a variety of raptors and carnivores.

Cotton rats are used for laboratory experiments for polimyetitis and diptheria they are also used for food by some people. (Cameron and Spencer, 1981)

They can eat crops, cause diseases, and alter landscapes. (Cameron and Spencer, 1981)

Sigmodon arizonae is not listed by IUCN or CITES. However, the species may have some conservation concerns. There are reported to be five distinct subspecies of S. arizonae. However, two of these are reported to be probably extinct, and the status of the others is not currently known. (Davis and Young, 1999)

There are five reported subspecies of S. arizonae. These include S. a. arizonae, and S. a. jacksoni, each of which were reported from only one locality in Central Arizona and which are probably extinct. There are also S. a. cienegae, which is found in central and sourth-eastern Arizona into Mexico, S. a. plenus, found along the Colorado River, and S. a. major, found through southern Sonoro and Sinaloa in Mexico. (Davis and Young, 1999)