The Morelet's Seedeater is the northernmost species in the genus Sporophila. Ranging from western Panama to the Rio Grande Valley of Texas, it inhabits savanna, pastures, and brushy fields, frequently near water. Historically in the United States, this species was considered common and ranged widely throughout the Rio Grande Valley of Texas, but since the 1960s it has been found mainly in Zapata, Webb, and Starr Counties, principally during summer and in small flocks. Habitat destruction and the use of agrochemicals are thought to be the main causes of this decline.
Males in their conspicuous black-and-white plumage are frequently observed singing from March to October. Females are more secretive and are usually observed only when feeding or traveling to roosts. Although considered a seed specialist, this species feeds many insects to nestlings; however, fledglings are fed exclusively grass seeds. This species has been little studied, and its ecological requirements and population trends remain poorly known.
In Central America, several members of the genus Sporophila occur sympatrically. In definitive plumage, male Morelet's Seedeater is easily distinguished, but juveniles and females are very similar in appearance to other seedeater species, making identification difficult in the field.