Chestnut Seedeater

The chestnut seedeater is about 10 cm (3.9 in) long and weighs an average of about 8.6 g (0.30 oz). It is one of the smallest of its genus. It has a smallish bill with a rounded culmen. The species is sexually dimorphic. Adult males have a medium gray crown to just below the eye; the rest of their head is chestnut. Their body is almost entirely chestnut with medium gray uppertail coverts. Their tail is mostly dark brown with cinnamon-brown feather edges. Their wings' greater and median coverts are dark grayish brown with light gray edges. Their flight feathers are dark grayish brown with cinnamon-brown edges and the primaries have white bases that show as a patch on the folded wing. Females have a mostly warm sandy brown head with a buff face. Their upperparts are also warm sandy brown and their tail is darker brown. Their wings are darker brown with sandy edges on the coverts. Their underparts are mostly warm buff with a whitish belly. Both sexes have a dark brown iris and black legs. Males have a black bill; females have a dark horn-colored one. Juveniles resemble adult females.

The chestnut seedeater is found from most of Uruguay and northeastern Argentina's Entre Rios Province north through eastern Paraguay and Brazil to Tocantins. At its widest its range spans from northeastern Paraguay across Brazil from western Mato Grosso do Sul to Rio de Janeiro state. It inhabits grasslands with some shrubs, especially but not exclusively seasonally flooded lowlands and marshes.

The chestnut seedeater feeds on grass seeds, especially those of native grasses, and also includes some small arthropods in its diet. It typically feeds while clinging to stems, sometimes upside down as the stem bends. In the breeding season it forages in pairs or family groups and outside it in larger groups that include other seed-eating species.