Yellow Pygmy Rice Rat

The dorsal fur of Oligoryzomys flavescens consists of bright orangish-brown hairs mixed with blackish hairs, the hairs on the flanks are all orange and the underparts are yellowish-grey. The boundary between the upper parts and the underparts is indistinct, grading from one colour to the other. The head-and-body length averages 87 mm (3.43 in) and the tails averages 110 mm (4.33 in). Skull features that distinguish this species include the long incisive foramina (openings in the hard palate) that usually reach the first molar, and the short mesopterygoid fossa (a depression behind the end of the palate) which does not extend as far as the third molar.

O. flavescens is native to South America. It occurs in eastern Brazil, Uruguay, eastern Paraguay and northern and central Argentina. It is found in a variety of habitats, often near water, from sea level up to about 1,800 m (5,900 ft). These include pampas, scrubland, primary and secondary forests, marshes, agricultural land, and gallery forests in the cerrado.

O. flavescens is the principal reservoir host of certain hantaviruses, which are harmless to rodents but cause disease in humans.