Very small, finchlike bird of grassy and weedy areas in tropical lowlands, especially in marshy areas. Often in flocks, mixing readily with slightly larger White-collared Seedeater. Breeding male (only in spring–summer) is striking: slaty bluish above and rusty below with a rusty rump. Nonbreeding male, female, and immature are much plainer: buffy brown overall, paler below, with distinct paler wing edgings (unlike plain-winged White-collared Seedeaters in west Mexico), and distinct orangey tones to the bill (bill dusky on White-collared).