The magnitude of differentiation in vocal signals examined in a phylogenetic context has helped uncover cryptic diversity in subsocine passerines such as the antbirds (Thamnophilidae). On the basis of variation in 14 acoustic traits of loudsongs and a phylogenetic hypothesis inferred from a mitochondrial gene tree, we investigated species limits in a group of trans-Andean Myrmeciza antbirds with a convoluted taxonomic history (M. l. laemosticta, M. l. palliata, M. nigricauda, and M. berlepschi). Diagnostic differences in three vocal traits suggest that the two subspecies of the Dull-mantled Antbird (M. l. laemosticta and M. l. palliata) should be treated as distinct species. We present evidence that only two diagnosable vocal characters may be sufficient for two populations to be considered distinct species in this group. The vocal results are consistent with the molecular phylogenetic analysis, which revealed a long independent history of isolation of M. l. laemosticta from M. l. palliata, roughly congruent with the divergence observed between species currently recognized in this assemblage. We propose elevating the Magdalena Antbird (M. palliata) to species rank and thus that four species be recognized in the M. laemosticta complex.