Sigmodon hispidus

A chunky rat with long, coarse fur (mixed black and buff), a sparsely haired tail shorter than the head and body, ears nearly buried in the fur, and a whitish belly; adult total length 210-365 mm, tail 81-166 mm, hind foot 27-41 mm, ear 16-24 mm (Hall 1981, Hoffmeister 1986).

The following distinctions are based on specimens from Arizona. Differs from S. FULVIVENTER by having the underparts silvery or grayish rather than buffy or fulvous, a bicolored tail, dorsum darker than venter, tops of hind feet silvery or grayish rather than buffy, hind feet and ears averaging longer (hind foot of male HISPIDUS usually 30-32 mm, 26-31 mm in FULVIVENTER), preoptic foramen usually absent, and nasals usually truncate or notched rather than tapered posteriorly (Hoffmeister 1986). Differs from S. OCHROGNATHUS by lacking an orangish or ochraceous nose ring and eye ring (color in these areas is nearly the same as that of the sides and back), having a longer hind foot (usually 29 mm or more, but smaller in some females; usually 30 mm or less in OCHROGNATHUS), longer ears and tail (tail 88-132 mm, ear 17-21 mm, in HISPIDUS; tail 80-114 mm, ear 14-19 mm, in OCHROGNATHUS), a larger skull, and the posterior border of the interparietal lacking a median notch formed by the supraoccipital (Hoffmeister 1986). Differs from S. ARIZONAE in being smaller (total length 210-319 mm in HISPIDUS, 212-349 mm in ARIZONAE), usually having a shorter hind foot (usually 32 mm or less, though sometims to 33 mm; 28-40 mm [mean 34 mm or more in males] in ARIZONAE), presphenoid narrow rather than broad, distance between parietal and squamosal crests less than 3.2 mm rather than more, occipital "shield" angled rather than curved, anterior spine on the infraorbital plate broad and blunt rather than narrow and long, length of squamosal crest generally less than 7.0 mm rather than more, palatine slits rounded posteriorly rather than tapered posteriorly, antero-ventral border of the foramen magnum rounded rather than usually angular (Hoffmeister 1986, which see for further discussion of the often subtle differences between S. HISPIDUS and S. ARIZONAE).

Favors dense, grassy fields and roadside edges; also in brushy or weedy areas or among reeds and cattails along streams or ponds, in irrigated fields, and in desertscrub with little grass. Nests typically are built under logs, rocks, underground.

Populations fluctuate widely, perhaps cyclically; high densities every 2-5 years. Average density 10-12 per acre (Schwartz and Schwartz 1981); maximum density twice this. On a site in Oklahoma, density estimates ranged from 0.0/ha in July 1999 to 112.5/ha in October 2000 to 0.0/ha in January 2001 (Clark et al. 2003). Cold severe winters and hot dry summer often are associated with low populations and declines in abundance (e.g., Clark et al. 2003). Common prey item for various carnivores and raptors.

Breeds throughout the year, with peak activity in spring/fall; severe cold may curtail reproduction in winter. Gestation lasts 27 days. Litter size averages about 5-7; several litters per year. Sexually mature in 2-3 months. Short-lived; in Oklahoma, hardly any lived 6 months (see Caire et al. 1989).