<p>The White-shouldered Antshrike (<i>Thamnophilus aethiops</i>) is a widespread Amazonian suboscine bird with ten plumage-based subspecies showing deep mitochondrial genetic divergence. Variation in vocalizations is considered a key phenotypic proxy for species boundaries in the family Thamnophilidae, but remains uncharacterized in the White-shouldered Antshrike. Using a geographically comprehensive set of sound recordings, we analyzed vocal variation among subspecies to test for differences potentially relevant to reproductive isolation. Our data revealed range-wide clinal variation in multiple song traits, possibly mirroring patterns of nuclear gene flow documented in earlier studies. Although some geographically distant taxa exhibited diagnostic differences in certain traits, no taxon showed discrete vocal characters when intermediate populations were considered. These results suggest weak or nonexistent behavioral reproductive barriers among subspecies of the White-shouldered Antshrike.</p>