706.

Small Vesper Mouse

Calomys laucha

French: Calomys nain / German: Eigentliche Vespermaus / Spanish: Raton laucha pequeno

Other common names: Little Laucha

Taxonomy. Mus laucha G. Fischer, 1814, type locality not given. Restricted by P. Hershkovitz in 1962 to “ Asuncion, [Central Dept.,] Paraguay.” Fixed by neotype designation by P. Teta and others in 2017 as “Estacion Experimental Agropecuaria Pergamino, Pergamino, Buenos Aires, Argentina.”

There is some evidence that at least two geographically distinct forms of C. laucha exist. Monotypic.

Distribution. SE Bolivia, W Paraguay, N & C Argentina, Uruguay, and extreme S Brazil.

Descriptive notes. Head-body 55-67 mm, tail 45-54 mm, ear 8-1 1-7 mm, hindfoot 13-4-15 mm; weight 11-19 g. The Small Vesper Mouse is the smallest species of Calomys . Dorsum is gray, mixed with brown or even golden brown; dark dorsal band extends from forehead to rump;sides are always paler but often with some mix of gray and brown hair; buffy line separates dorsum from venter, which is always washed with white; and in some populations, chin and throat have fully white hairs. Buffy hair tufts occur anterior to ears in populations from drier habitats, but all specimens throughout the distribution have white post-auricular patches. Tail is bicolored, brown above and white below, and no more than 43% of head-body length. Adult females have 8-10 mammae.

Habitat. Grasslands, forest fringes, arid and semiarid shrubby fields, and margins of agricultural areas.

Food and Feeding. The Small Vesper Mouse is a generalist with an herbivorous-granivorous diet.

Breeding. Average length of estrous cycle of the Small Vesper Mouse, as determined from vaginal smears, was 7-4 days (range 6-8). Average gestation was 21-5 days (range 21-23). Lltters offirst pregnancies averaged 3-7 young (range of 1-6). There was a negative correlation between number of embryos and number of embryos per pregnancy. A study on pampas of Argentina showed that more than 40% of females were pregnant in October—May, and pregnant females were present year-round.

Activity patterns. The Small Vesper Mouseis terrestrial, nocturnal, and crepuscular.

Movements, Home range and Social organization. Sex ratio of 1-2 male:1 female was reported for the Small Vesper Mouse. Extensive gene flow was detected among populations in central Argentina . Studies in laboratory conditions suggest monogamy.

Status and Conservation. Classified as Least Concern on The IUCN Red Lust.

Bibliography. Bilenca & Kravetz (1999), Bilenca et al. (1992), Busch & Kravetz (1992, 1993), Busch et al. (2001), Courtalon et al. (2003), Crespo (1966), Ellis, Mills, Childs et al. (1997), Ellis, Mills, Glass et al. (1998), Ellis, Mills, Kennedy et al. (1994), Fraschina et al. (2012), Garcia et al. (1991), Hershkovitz (1962), Hodara & Busch (2010), Hodara, Busch et al. (2001), Hodara, Suarez & Kravetz (1997), Jayat, Ortiz & Miotti (2008), Laconi & Castro-Vazquez (1999), Laconi et al. (2000), Mills, Ellis, McKee, Maiztegui & Childs (1991, 1992), Peters et al. (2013), Polop & Sabattini (1993), Salazar-Bravo (2015c), Teta, Gonzélez-Ittig et al. (2017), Vallejo & Gudynas (1981), de Villafane, Merler et al. (1992), de Villafafe, Quintana et al. (1994a, 1994b), Yahnke (2006), Yahnke et al. (2001), Yunes et al. (1991).