Black-and-rufous Warbling-Finch

The black-and-rufous warbling finch is 15 cm (5.9 in) long and weighs 16.0 to 19.5 g (0.56 to 0.69 oz). The species is slightly sexually dimorphic. Adult males have a slate-tinged brownish gray crown and nape, a white supercilium that becomes rufous behind the eye, and a white "moustache" on an otherwise blackish face. Their upperparts and wings are slate-tinged brownish gray and their tail dark with white tips on the feathers. Their throat, breast, and flanks are cinnamon to rufous, the center of their belly white, and their undertail coverts tawny. Adult females are described as having more olivaceous upperparts and paler orange-tinged underparts than males but these apparent differences have been questioned. Both sexes have a brown or dark brown iris, a small, pointed, bill with a black maxilla and a gray mandible, and dark gray, blackish, or brownish legs. Juveniles have brown or olive-brown upperparts, underparts with dark brown streaks on a light brown background, and little or no white on the tail.

The black-and-rufous warbling finch is found from southeastern Brazil's Paraná state and southeastern Paraguay south through Uruguay and through northeastern Argentina as far as southern Buenos Aires Province. It inhabits open landscapes of grass, shrubs, and marsh vegetation and also open woodlands. It is usually found near water. In elevation it ranges from sea level to about 100 m (300 ft) in most of its range but reaches 900 m (3,000 ft) in Brazil. Though one source includes Bolivia in the species' range others do not, and the South American Classification Committee has no records in the country.

The black-and-rufous warbling finch's diet has not been studied but is assumed to be mostly seeds with some insects. It forages in dense vegetation or on the ground or floating vegetation near cover. It usually forages singly or in pairs and sometimes in family groups.