Sigmodon leucotis Bailey 1902

324.

White-eared Cotton Rat

Sigmodon leucotis

French: Sigmodon a oreilles blanches / German: WeiRohr-Baumwollratte / Spanish: Rata de algodén de orejas blancas

Taxonomy. Sigmodon leucotis Bailey, 1902, “Valparaiso Mts., Zacatecas, Mexico, 8700 feet [= 2652 m] altitude.”

Two subspecies are recognized.

Subspecies and Distribution.

S. l. leucotis Bailey, 1902 — Y-shaped distributional pattern in Mexico from approximately 27° N latitude in the Sierra Madre Occidental and 25° N in the Sierra Madre Oriental SE into the C part of the Transvolcanic Beltas far S as the state of Mexico.

S. I alticola Bailey, 1902 — montane areas from N Puebla S to NW Oaxaca.

Descriptive notes. Head-body 132-157 mm, tail 84-105 mm, ear 16-23 mm, hindfoot 26-31 mm; maximum weight 131 g for males and 140 g for non-pregnant females. The White-eared Cotton Rat is medium-sized; dorsum is brownish gray; venter is whitish gray, with dark gray hair bases; and forefeet and hindfeet are grayish brown. Tail is shorter than head-body length, practically hairless so annular scales are visible, and slightly bicolored. It is distinguished from other cotton rats in the fulvivenier species group (fulviventer, alleni, leucotis, and ochrognathus) by conspicuous whitish ears on brownish gray head and body and its small-to-medium size; skull with prominent premaxillary depressions on each side of rostrum; and absent to exceedingly reduced lingual roots on first lower molars. Important distinguishing cranial characteristics include short interparietal (length at midline less than 2 mm); parallelsided anterior portion of mesopterygoid fossa; and slightly hooked, as opposed to rounded, angular process of mandible. Itis distinguished from membersof hispidus species group (hispidus, arizonae, and mascotensis) by scales of tail less than 0-5 mm wide, shallow palatal fossa, and slightly developed median keel on palate. Chromosomal complementis 2n = 52, FNa = 52.

Habitat. Mesic montane grasslands within and around pine-oak forests and pine forests, including edges of farmland, rocky areas, and meadows with abundantfallen logs at elevations of 1800-3600 m. The White-eared Cotton Rat is most common in mixed grass and shrub cover on shallow rocky soils.

Food and Feeding. The White-eared Cotton Rat eats various plant parts (e.g. stems, leaves, and seeds), insects, lizards, and bird eggs. Diet varies seasonally, with stomachs of winter-caught individuals containing 70% starchy material, 20% green material, and 10% insects; spring diets, 70-95% stems and leaves, 5-10% seeds, and 20% insect parts; summer diets, 33% green material, 25% seeds, 11% fungi, and 31% insects; and fall diets, 89% green plant materials, 9% seeds, and 2% insects.

Breeding. Reproduction can occur year-round, peaking in summer. Gestation is ¢.35 days, andlitters have 5-12 young.

Activity patterns. The White-eared Cotton Rat is primarily diurnal, with aboveground activity concentrated in morning and late afternoon.

Movements, Home range and Social organization. Burrows of White-eared Cotton Rats are shallow and nearly horizontal, constructed at the base of dense vegetation, crevices, tree stumps, and fallen logs. Average density is 1-1 ind/ha.

Status and Conservation. Classified as Least Concern on The IUCN Red List. The Whiteeared Cotton Rat has a wide distribution, presumably large overall population, and no documented conservation threats.

Bibliography. Alvarez-Castaneda, Castro-Arellano, Lacher & Vazquez (2016a), Baker (1969), Baker & Shump (1978a), Ceballos (2014a), Jiménez (1971, 1972), Matson & Baker (1986), Ramirez et al. (2014), Shump & Baker (1978b), Swier et al. (2009), Webb & Baker (1962), Zimmerman (1970).