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Costa Rican Pygmy Rice Rat

Oligoryzomys costaricensis

French: Colilargo du Costa Rica / German: Costa-Rica-Zwergreisratte / Spanish: Rata arrocera pigmea de Costa Rica

Taxonomy. Oryzomys costaricensis J. A. Allen, 1893, El General, 2150 ft (= 665 m), Puntarenas, Costa Rica.

Oligoryzomys costaricensis was formerly considered subspecies of O. fulvescens, but phylogenetic analysis of gene sequences and analysis of chromosomal complements support its recognition as a distinct species. Its relationship to forms from northern South America require additional study. Monotypic.

Distribution. W Nicaragua, Costa Rica, and W & C Panama.

Descriptive notes. Head—body 60-96 mm, tail 80-117 mm, ear 10-18 mm, hindfoot 19-26 mm; weight 10-24 g. The Costa Rican Pygmy Rice Rat is very small; tail is c.150% head-body length, naked, unicolored, and pale brown. Pelage is full, long (7 mm on mid-back), soft, but rather coarse. Dorsum is yellowish brown to yellowish chestnut, heavily mix with black hair; sides are paler, ocherous buff with little or no black, passing gradually into clear, rather strong buff of ventral surface, which is separated from color of upperparts by quite a distinct but narrow fulvous lateral line. Ears are small, oval, well-haired on both surfaces, dusky brown externally, darkest on anterior one-third, and more yellowish on inner surfaces. Upper surfaces of forefeet and hindfeet are buffy white, scantily haired, especially hindfeet where short light-colored hair scarcely conceals scaly annulations; palms and soles are naked and flesh-colored.

Habitat. Savannas, marshes, forests clearings, and cultivated lands near human dwellings, occasionally invading them, from sea level to elevations of ¢.1200 m.

Food and Feeding. Diest of the Costa Rican Pygmy Rice Rat contains fruits and other plant materials, supplemented with insects and sometimes other invertebrates.

Breeding. Costa Rican Pygmy Rice Rats build nests with dry grass cut into pieces, arranged in blind tunnels under tufts of grass; center is a simple chamber not much enlarged (c.10 cm). Each nest is occupied by one individual. Pregnant females were found in July.

Activity patterns. The Costa Rican Pygmy Rice Rat is nocturnal.

Movements, Home range and Social organization. Costa Rican Pygmy Rice Rats are usually seen moving around with small, quick jumps between clumps of vegetation. Some indications of social activity are reported; more than one, once up to three individuals, were found together. Even in potentially preferred habitat, local populations demonstrate seasonal and yearly heterogeneity in abundance and spatial distribution. Populations also show rapid demographic responses, apparently to precipitation.

Status and Conservation. Not assessed on The IUCN Red List. Although apparently not very common, broad distribution and potentially high and rapid population turnover of the Costa Rican Pygmy Rice Rat suggestlittle conservation concern. Nonetheless, long-term studies on islands associated with the Panama Canal show that it can become locally extirpated. It is present in several conservation units in Panama and Costa Rica.

Bibliography. Armién, A.G. et al. (2009), Armién, B. et al. (2016), Carleton & Musser (1995), Enders (1930), Fleming (1970b), Genoways & Timm (2005), Glanz (1982, 1990), Goldman (1920), Handley (1966), Méndez (1993), Reid (1997), Ruedas et al. (2004), Salazar-Bravo et al. (2004), Suzan, Armién et al. (2008), Suzan, Giermakowski et al. (2006), Suzan, Marcé et al. (2008), Villalobos-Chaves et al. (2016).