Six subspecies currently recognized that segregate into 2 groups, russet-backed (ustulatus group) and olive-backed (swainsoni group), differing in plumage, breeding habitat, winter range, and in some vocalizations (M. A. Ramos in Phillips 1991, Am. Ornithol. Union 1998). Russet-backed group winters in Mexico and Central America, and olive-backed group in nw. and central South America (Bond 1963, Marshall 1988, Phillips 1991).