209.

Southern Pygmy Mouse

Baiomys musculus

French: Baiomys austral / German: Stdliche Amerikanische Zwergmaus / Spanish: Ratén pigmeo meridional

Taxonomy. Sitomys musculus Merriam, 1892, Colima, Colima, Mexico.

Genetic subdivision of B. musculus was reported corresponding to coastal regions of Michoacan, and two species could be represented, suggesting additional studies are necessary. Eight subspecies are recognized.

Subspecies and Distribution.

B.m.musculusMerriam,1892—SNayarit,W&CJalisco,Colima,andMichoacan states(WCMexico).

B. m. brunneus J. A. Allen & F. M. Chapman, 1897 — SE Puebla and C Veracruz states (EC Mexico).

B.m.grisescensGoldman,1932—fromSCGuatemalaSEtoSWHonduras.

B.m.handleyiPackard,1958—knownonlyfromthetypelocalityinWGuatemala.

B.m.infernatisHooper,1952—SCPueblaandNOaxacastates(CMexico).

B.m.nigrescensOsgood,1904—ChiapasState(SMexico),SGuatemala,andElSalvador.

B.m.pallidusRussell,1952—Guerrero,Morelos,SWPuebla,andOaxacastates(SWMexico).

B. m. pullus Packard, 1958 — NW edge of Nicaragua.

Descriptive notes. Head-body 65-79 mm, tail 35-56 mm, ear 9-12 mm, hindfoot 14-17 mm; weight 6-10 g. The Southern Pygmy Mouse is one of the smallest mice in North America. It can be distinguished from the Northern Pygmy Mouse ( B. taylor) by size of hindfoot (16 mm or more) and size of baculum (3-3-9 mm), which is larger in the Northern Pygmy Mouse. Dorsum is brown-red to dark brown, and venteris pale or white.

Habitat. Tropical deciduous forests, thorn forests, xeric scrublands, coastal dunes, pastures, and croplands from sea level to elevations of 2000 m. Southern Pygmy Mice inhabit tropical and semi-tropical areas where grasses and shrubs provide sufficient cover; they are also found in abandoned fields and along edges of sugar cane plantations and coconut palms. Where they coexist, the Southern Pygmy Mouse prefers tropical lowlands, and the Northern Pygmy Mouse is most common in temperate highlands.

Food and Feeding. Southern Pygmy Mice feed mainly on herbs and fresh grasses but also seeds and small insects.

Breeding. Southern Pygmy Mice reproduce throughout the year, with less activity in winter and spring. Gestation lasts 20-25 days, lactation averages 20 days, and litters have 1-5 young (average three).

Activity patterns. Southern Pygmy Mice are diurnal and crepuscular.

Movements, Home range and Social organization. Home ranges can be 30 m in diameter, and densities are 15-20 ind/ha. Southern Pygmy Mice construct their nests with grass remnants in underground burrows between rocks or at bases of bunch grasses.

Status and Conservation. Classified as Least Concern on The IUCN Red List. Southern Pygmy Mice are abundant in croplands and pastures and face no known conservation threats.

Bibliography. Allen & Chapman (1897a), Ceballos & Miranda (1986, 2000), Chavez & Espinosa (2014b), Eshelman & Cameron (1987), Goldman (1932b), Hooper (1952b), Merriam (1892b), Osgood (1904), Packard (1960), Packard & Montgomery (1978), Russell (1952a).