Species limits in antbirds (Passeriformes : Thamnophilidae) : The Myrmotherula surinamensis complex

Current species-level taxonomy of Neotropical birds is in need of reassessment but lacks objective methodology and criteria for the ranking of allopatric populations. Previously (Isler et al. 1998), through empirical analysis of pairs of syntopic species, we developed methods and standards for employing vocalizations in determining species limits in the family Thamnophilidae. Building on this study, we now propose procedures for integrating vocal characters with morphology and geographic distribution in making species determinations in thamnophilids. We applied this methodology to populations of antwrens in the Myrmotherula surinamensis complex (including three subspecies of M. surinamensis and M. cherriei). Four diagnostically differentiated populations were identified, all of which corresponded to named taxa. Each population (some of which are narrowly sympatric) was distinguished unambiguously by morphology and vocalizations. Under these objective and conservative standards, we recommend that Myrmotherula surinamensis, M. multostriata, M. pacifica, and M. cherriei be recognized as distinct species. The level of differentiation found between M. surinamensis and M. multostriata illustrates the minimum threshold recommended for species status of allopatric populations of thamnophilid antbirds and should provide a useful reference point for future considerations of species limits.