Fairly common locally in the Andes, often near bogs or other areas with water. Often in flocks, feeding on the ground or in low bushes. Plumage is distinctive, with blackish head and breast, dark back, and bright yellow underparts. Namesake yellow rump usually concealed at rest. Sexes similar, but male averages blacker above. Juvenile looks very different, with greenish head and upperparts, and an orangish bill. No similar species in range, but sometimes associates with Thick-billed and Black Siskins.