210.

Northern Pygmy Mouse

Baiomys taylori

French: Baiomys de Taylor / German: Nordliche Amerikanische Zwergmaus / Spanish: Raton pigmeo septentrional

Taxonomy. Hesperomys (Vesperimus) taylor Thomas, 1887, “San Diego, [Duval County], South Texas,” USA .

Eight subspecies are recognized.

Subspecies and Distribution.

B.t.taylorThomas,1887—fromNTexas(SUSA)SalongtheEcoastofMexicotoNVeracruzState.

B.t.allexOsgood,1904—SNayarit,W&CJalisco,Colima,andSWMichoacan(WMexico).

B.t.analogusOsgood,1909—fromEJaliscoEtoCEPuebla(SCMexico).

B.t.aterBlossom&Burt,1942—SEArizonaandSWNewMexico(SWUSA),andNESonoraandNWChihuahuastates(NWMexico).

B.t.canutusPackard,1960—SSonora,Sinaloa,andNWNayaritstates(NWMexico).

B.t.fuliginatusPackard,1960—ESanLuisPotosiState(CMexico).

B.t.paulus|.A.Allen,1903—fromNCChihuahuaStoNGuanajuatostates(NW&WCMexico).

B. t. subater Bailey, 1905 — EC Texas (S USA).

Descriptive notes. Head-body 53-76 mm, tail 34-53 mm, ear 9-12 mm, hindfoot 12-15 mm; weight 6-9 g. The Northern Pygmy Mouse is one of the smallest species of mice in North America. Dorsum is reddish brown to dark gray or black; venter is gray, with white or cream highlights. Tail color differs among subspecies and can be gray or bicolored. The Northern Pygmy Mouse differs from the Southern Pygmy Mouse ( B. musculus) by size of hindfeet (less than 16 mm) and average length of baculum, which is significantly shorter and thinner in the Northern Pygmy Mouse.

Habitat. Grasslands, xeric scrublands, thorn forests, forests of oak ( Quercus, Fagaceae) and conifers, and croplands from sea level to elevations of ¢.2450 m. Northern Pygmy Mice are found mainly in dense grasslands or grassy areas.

Food and Feeding. Northern Pygmy Mice feed on a variety of grass seeds, leaves, and roots. In semiarid habitats, they eat fruits of prickly pear ( Opuntia lindheimeri, Cactaceae) and legume seeds (e.g. Prosopisjuliflora, Fabaceae).

Breeding. Northern Pygmy Mice reproduce throughout the year, with peak in late autumn and early spring. Captive individuals are polyestrous, with estrous periods of 7-5 days. Some evidence suggests that they use delayed implantation as a reproductive strategy. Gestation lasts 20-23 days. Litters have 1-5 young (average two). Both parents care for offspring. Lactation lasts 17-24 days. Males reach sexual maturity in 70-80 days after birth and females 60-90 days.

Activity patterns. The Northern Pygmy Mouse is nocturnal and crepuscular.

Movements, Home range and Social organization. In Texas, densities of Northern Pygmy Mice are 1-84 ind/ha, with lower densities in summer and highest densities in autumn and winter. In the Basin of Mexico, densities are 15-20 ind/ha. Home range are 45-729 m®. They build runways similar to those of species of Microtus, but they are smaller in size. They construct nests of vegetation under trunks, cacti, or herbs.

Status and Conservation. Classified as Least Concern on The IUCN Red List. The Northern Pygmy Mouse is a common, has a wide distribution, and faces no known conservation threats.

Bibliography. Allen (1903c), Bailey (1905), Blossom & Burt (1942), Ceballos & Galindo (1984), Chavez & Espinosa (2014a), Eshelman & Cameron (1987), Hall (1981), Osgood (1904), Packard (1960), Thomas (1887), Villa (1953).