Small seed-eating bird of humid tropical lowlands; fairly common. Found in grassy and weedy areas and forest edges, often in same places as slightly larger Thick-billed Seed-Finch. In pairs or small flocks, mixing readily with Morelet's Seedeaters and other seed-eating birds. Note stubby bill (unlike Thick-billed Seed-Finch) and plain brownish olive plumage of female (not rich brown like seed-finch). Males in Mexico and most of Central America are black. In southern Central America and South America males have variable amounts of white on the underparts and rump, hence the name.