A small seed-eating species of forest edges, open woodlands, and nearby weedy areas; usually found in groups of two to five birds. Both sexes have bright yellow-green shoulders and a buff vent, which are diagnostic but can be difficult to see. Otherwise, the Black-faced Grassquit is rather similar, but can be distinguished by its slimmer bill and duller back. Furthermore, male Yellow-shouldered Grassquits have an entirely black head, whereas black is limited to the face on the Black-faced Grassquit. The song is a series of four or five high-pitched buzzy notes that either rising or dropping in pitch, followed by one to three notes at another different pitch.