Six populations of Warbling Antbird (Hypocnemis cantator) currently considered subspecies are more appropriately recognized as species, given the multiplicity of vocal differences that distinguishes them. These vocal differences are as great or greater than vocal differences documented between syntopic species-pairs in the family Thamnophilidae (Isler et al. 1998). Evidence is also provided that two forms currently considered subspecies are syntopic and that two others are parapatric without apparent physical barriers. Vocally, the pair of syntopic taxa were distinguished dramatically, but solely, by common calls. The finding that common calls were as diversified as songs in this species-group suggests that calls may be as important as songs in reproductive isolation. Future field studies should therefore focus on clarifying the function of different types of thamnophilid vocalizations and elucidating their role in speciation. This is the first contribution to a multifaceted analysis of the vocalizations and genetic structure of typical antbirds (Thamnophilidae) in Amazonia. In future work, results of the vocal analysis will be compared with a parallel genetic study, after which the two analyses will be integrated to suggest a phylogeny. The present study and preliminary studies of genetic differentiation (e.g., Bates et al. 1999) make it clear that the H. cantator complex has had a long evolutionary history that produced greater species-level diversity than was recognized previously.
Límites de Especies en Thamnophilidae: El Complejo de Hypocnemis cantator