436.

Small-eared Pygmy Rice Rat

Oligoryzomys macrotis

French: Colilargo a petites oreilles / German: KleinohrZwergreisratte / Spanish: Rata arrocera pigmea de orejas pequenas

Other common names: Small-eared Colilargo

Taxonomy. Oryzomys (Oligoryzomys) microtis J. A. Allen, 1916, Manacapuru, north bank of lower Rio Solimoes, 70 km WSW Manaus, Brazil.

Taxonomy of O. macrotis, given its broad distribution, needs to be revised. Oryzomys chaparensis (type locality in Bolivia) 1s currently treated as a synonym. Monotypic.

Distribution. Amazon Basin of E Peru, Brazil, and N Bolivia.

Descriptive notes. Head-body 78-98 mm, tail 74-125 mm, ear 11-15 mm, hindfoot 21-26 mm; weight 14-19 g. The Small-eared Pygmy Rice Rat is a small species of Oligoryzomys, similar in size and general color to the Delicate Pygmy Rice Rat ( O. delicatus) but very much less rufous above, more white below, and with very much smaller ears. Upperparts are dull yellowish brown, finely lined with black-tipped hair; underparts are white (in holotype but faintly tinged with buff in some specimens); upper surfaces of feet are thinly covered with light buffy brown hair; soles are dark brown;tail is shorter than head-body length, brown, nearly naked, and finely annulated, with tip not distinctly tufted; and ears are small, brownish, and nearly naked. Chromosomal complement is 2n = 64, FN = 66.

Habitat. Edge habitats within the lowland rainforest of the Amazon Basin. Dense grass (“capim”) on upper edges of sand bars, seasonally available or disturbed habitats along river margins, and disturbed habitats close to the water’s edge, such as old or active garden plots, pastures, and adjacent to human dwellings.

Food and Feeding. No information.

Breeding. In Bolivia, pregnant Small-eared Pygmy Rice Rats were recorded in March, May, August, and September; lactating females were recorded in June-July and August; and numbers of embryos were 3-5. In Jurua River Basin, Brazil, reproductive individuals were recorded in dry season (August—-November). Litters based on embryo counts were 2-8 (mode four, n = 47). The Small-eared Pygmy Rice Rat has reproductive features of an “rselected species,” with fast growth, early reproductive maturity, and large litter sizes. These features are expected for a species that lives primarily in seasonally ephemeral habitats.

Activity patterns. Small-eared Pygmy Rice Rats are terrestrial and nocturnal. Individuals from western Amazonia were caught on the ground.

Movements, Home range and Social organization. No information.

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

Bibliography. Allen (1916), Anderson (1997), Carleton & Musser (1989), Gardner & Patton (1976), Hice & Velazco (2012), Olds & Anderson (1987), Patton, da Silva & Malcolm (2000), Patton, Weksler, Bonvicino & Percequillo (2016), Voss et al. (2001), Weksler & Bonvicino (2005, 2015b).