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).