Cinnamon-rumped Seedeater

The cinnamon-rumped seedeater is 9.5 to 11 cm (3.7 to 4.3 in) long and weighs 8.6 to 10 g (0.30 to 0.35 oz). It has a short thick bill with a rounded culmen. The species is sexually dimorphic. Adult males of the nominate subspecies S. t. torqueola have a mostly blackish brown head with a whitish throat whose color extends back in a band across the side of the neck to the nape. Their nape and upperparts are blackish brown and their rump cinnamon. Their wings are mostly blackish with white bases on the primaries that show as a patch on the closed wing. Their tail is also blackish. They have a black band below the throat and pale cinnamon underparts that are palest on the belly and undertail coverts. Adult females have a grayish olive head and upperparts. Their wings and tail are dark brown with two whitish bars on the wings. Their throat and breast are pale creamy buff and their belly and vent pale cinnamon. Males of subspecies S. t. atriceps has a grayish brown to olivaceous brown back and a smaller white wing patch than the nominate. Females do not differ. Both sexes of both subspecies have a blackish iris and blackish legs. Males have a blackish bill and females a dark horn bill.

Subspecies S. t. atriceps of the cinnamon-rumped seedeater is the more northerly of the two. It is found along the Pacific side of Mexico from central Sinaloa and western Durango south to Nayarit and northern Jalisco and also in the far south of Baja California. The nominate is found from Jalisco and Guanajuato south to Oaxaca and as far east as Morelos and Puebla. The species inhabits open landscapes including grassy and weedy fields and pastures, croplands, moist savanna, and scrubby beaches. It favors areas with Polygonum grass. In elevation it ranges from near sea level to at least 2,000 m (6,600 ft).

The cinnamon-rumped seedeater feeds mostly on grass seeds, especially those of Polygonum, and much smaller amounts of berries and insects. In the breeding season it usually forages in pairs; at other times it is often in flocks of several hundred individuals that may include other seed-eating species.