By Jenny LaRoche
Geographic Range
Sigmodon fulviventer (tawny-bellied cotton rat) is a native mammal of the nearctic range. It is found from New Mexico and the southeastern corner of Arizona southward into central Mexico along the Sierra Madre Mountain Range. (National Geographic Society, 1979; Wilson and Ruff, 1999)
Habitat
Sigmodon fulviventer inhabits grassy areas dotted with shrubby growth. The shrubs afford cover and allow dense growth of grasses. Currently, only scattered habitat patches that have been protected from heavy grazing exist. (Baker and Shump Jr, 1978; Davis and Schmidly, 1994)
These animals are found in the following types of habitat:
temperate 
.
Terrestrial Biomes:
desert or dune ; savanna or grassland ; chaparral .
Physical Description
(7.04 to 7.74 oz)
(8.78 to 10.63 in)
Sigmodon fulviventer is the largest of the cotton rats and is distinguished from other cotton rats by its large size and coloration. It is also known as the tawny-bellied cotton rat, due to the buff-brown color of its underside. A salt and pepper pattern is found on the dorsal portion of the pelage. The tail is consistently black, with small tail scales and a heavy coating of hair. (Baker and Shump Jr, 1978; Davis and Schmidly, 1994; University of New Mexico, 2002; Wilson and Ruff, 1999)
These animals weigh between 200 and 220 g. They measure 223 to 270 mm in length, with a tail length between 94 and 109 mm. The skull is arched, short and broad, and contains 16 teeth. The upper incisors are well developed, and the large molars have high crowns.
Some key physical features:
endothermic ; bilateral symmetry .
Sexual dimorphism: sexes alike.
Reproduction
These animals can breed approximately monthly during the breeding season.
Breeding peaks in late summer or fall.
No information was found on mating systems for S. fulvivener. Little is known about the mating systems of the genus. (University of New Mexico, 2002; Wilson and Ruff, 1999)
Breeding is seasonal and peaks in late summer or fall. Gestation is between 27 and 33 days in length, and results in a litter size averaging between 7 and 9. Within 18 to 36 hours of birth, the babies of S. fulviventer are fully furred, able to walk, and have opened eyes. They are weaned in 10 to 15 days. The young leave the nest when they are about two weeks old and begin to breed at about six weeks of age. (University of New Mexico, 2002; Wilson and Ruff, 1999)
Key reproductive features:
iteroparous ; seasonal breeding ; gonochoric/gonochoristic/dioecious (sexes separate); sexual ; fertilization ; viviparous .
Sigmodon fulviventer constructs a nest woven out of grasses in which it resides and cares for their young. It is not clear whether the male helps to raise the offspring. The female nurses the precocious youngsters until they are between 10 and 15 days old. Shortly after, the young disperse. (Baker and Shump Jr, 1978; Wilson and Ruff, 1999)
Parental investment:
no parental involvement; precocial ; pre-fertilization (protecting: female); pre-hatching/birth (provisioning: female, protecting: female); pre-weaning/fledging (provisioning: female, protecting: female); pre-independence (protecting).
Lifespan/Longevity
Maximum lifespan/longevity for S. fulviventer is not known. However, in the wild, they are not expected to live beyond 2 months of age. (University of New Mexico, 2002)
Behavior
Sigmodon fulviventer prefers tall grassy areas where nests and runways can be hidden. It is reported to be quite excitable and pugnacious. Individuals of this species quarrel frequently. (Baker and Shump Jr, 1978; Cahalane, 1954; University of New Mexico, 2002)
Key behaviors:
terricolous; motile .
Communication and Perception
No information was found on communication for S. fulviventer. However, as mammals, it is likely that they have the ability to perceive visual information, accoustic information, and scent cues. It is also likely that they use these in intraspecific communication. Tactile communication is likely to occur during fighting as well as between mothers and their offspring.
Food Habits
The diet of S. fulviventer consists largely of grasses and sedges, as well as cultivated grains and vegetables. It will also feed on insects, grasshoppers, and quail eggs. (Cahalane, 1954)
Primary Diet:
omnivore .
Animal Foods:
birds; eggs; insects.
Plant Foods:
leaves; roots and tubers; seeds, grains, and nuts.
Predation
- coyotes (Canis latrans)
Sigmodon fulviventer serves as a principle food for many predators such as coyotes. (Cahalane, 1954)
Ecosystem Roles
Sigmodon fulviventer is part of the small mammal food base for a number of carnivores and raptors. (Cahalane, 1954)
Economic Importance for Humans: Negative
The reproductive capacity of S. fulviventer is impressive, and when coupled with a plentiful food supply the populations of these rodents can explode. When this happens, farmers may suffer financial losses due to crop damage. These rats will eat all kinds of cultivated grains and vegetables. (Cahalane, 1954)
Ways that these animals might be a problem for humans:
crop pest.
Economic Importance for Humans: Positive
Sigmodon fulviventer is the principal food of numerous predators, serving as a "buffer species" between predators and game birds. (Cahalane, 1954)
In captivity, cotton rats have been influential in developing therapeutic clinical intervention strategies for many viral infections of humans. Examples include influenza virus, respitory wyncytial, adenovirus, poliovirus, and parainfluenza virus. Current research studies are being conducted on cotton rats to see if they are succeptible to HIV and to try to relate them to human HIV research. (Langly, Prince, and Ginsberg, 1998)
Ways that people benefit from these animals:
research and education.
Conservation Status
IUCN Red List: [link]:
Lower Risk - Least Concern.
US Federal List: [link]:
No special status.
CITES: [link]:
No special status.
Sigmodon fulviventer is not listed by CITES or IUCN.
For More Information
Find Sigmodon fulviventer information at
Contributors
Jenny LaRoche (author), University of Wisconsin-Stevens Point. Chris Yahnke (editor, instructor), University of Wisconsin Stevens Point.
Nancy Shefferly (editor), Animal Diversity Web Staff.
