The Buff-breasted Earthcreeper (Upucerthia validirostris) is endemic to western Argentina, and the Plain-breasted Earthcreeper (U. jelskii, including subspecies saturata in the north and pallida in the south), ranges from northern Peru to northwestern Argentina. They have been considered subspecies, as constituents of a superspecies, and as different species. From north to south, a morphocline, involving an increase of rustiness of the plumage and of ∼15% in bill length, 10% in wing length, and 20% in tail length, links jelskii to validirostris. The cline linking jelskii and pallida is gradual, over ∼1800 km; that between pallida and validirostris is steep, over ∼80 km. The northernmost record of validirostris is from the northern Calchaquies Valley, Salta, northwestern Argentina, a valley surrounded by mountains of up to ∼6300 m above sea level through which the lowest pass is at over 4900 m, forming a barrier between validirostris and the southernmost record of pallida to the north. The song, continuous song, duet, and call of validirostris are structurally indistinguishable from those of jelskiilpallida and from the single available recorded song of saturata. In all playback experiments, validirostris answered by approaching and vocalizing to voices of validirostris and jelskii /pallida and vice versa. Treatment of validirostris as a single species is warranted, and three subspecies can be tentatively recognized: southern validirostris (large, rufescent birds with buff bellies restricted to Argentina), central and northern jelskii (small, pale birds ranging from northwestern Argentina to central Peru), and northern saturata (small, dark, and brownish birds in northern central Peru).