These birds were common, often in flocks, in weedy areas and roadsides. This species is divided into two subspecies groups. The "cinnamon-rumped" group lacks wing-bars and is confined to the Pacific Coast of southern Mexico. The "white-collared" group consists of three subspecies ranging from southern Texas to Panama. Some authors split these groups into two species, Cinnamon-rumped Seedeater and Morellet's Seedeater respectively.
These "white-collared" birds have fairly conspicuous wing-bars as seen here. Immature males resemble females but usually have a white spot at the bases of the primaries which females lack. For this reason, I think this bird is probably an adult female, although its wing-bars are whiter, less buffy, than usual.
Digiscoped with Panasonic DMC-LZ5 | Nikon FieldScope III | 30XWA | hand-held (no adapter)