Vocal variation and species limits in the Sclerurus mexicanus complex

Phylogeographic analyses have hypothesized that Sclerurus (Furnariidae) populations of the rufous-throated clade (S. rufigularis and S. mexicanus sensu lato) have a long history of evolutionary isolation, particularly within the S. mexicanus complex (Tawny-throated Leaftosser). Although it has long been recognized that S. mexicanus should be split into two or more species, choosing between alternative species-delimitation schemes is much less clear due to minimal understanding of phenotypic variation and distributional range limits. We explored the extent of vocal variation between all described subspecies of S. mexicanus by analyzing spectral and temporal traits of songs and calls. We found five distinct vocal groups within S. mexicanus that differ primarily in their songs' maximum frequency, pace, and note shape. Specifically, we found that mexicanus, pullus, andinus, and obscurior each are vocally distinct from one another and from a group composed of macconnelli, peruvianus, and bahiae. Song traits of S. rufigularis overlapped with those of sympatric macconnelli and peruvianus and allopatric obscurior. The vocal distinctiveness patterns paralleled phylogeographic patterns and support a taxonomic scheme of treating S. mexicanus as five different species: S. mexicanus, S. pullus, S. obscurior, S. andinus, and S. macconnelli (including peruvianus and bahiae).