Song variation in the Caatinga suboscine Silvery-cheeked Antshrike (Sakesphorus cristatus) suggests latitude and São Francisco River as drivers of geographic variation

Historical processes may result in patterns of differentiation among extant populations, which may lead to diversification and speciation. This is often expressed, and measured, as genetic and behavioral variation among populations. Suboscine birds acquire songs by innate mechanisms and are typically poorly studied relative to oscine birds, which may learn songs and thus develop unique dialects among populations. Behavioral features, including song, are extensively used to describe the structure and geographical variation in bird populations. In turn, this knowledge may shed light onto patterns of species diversification across ecoregions, which is particularly relevant in endemic species. Here we investigate for the first time song structure and variation in the Silvery-cheeked Antshrike, an endemic bird of a poorly studied South American dry forest, the Caatinga. We evaluate hypotheses for song diversification, correlating vocal acoustic parameters with geographic patterns and environmental variables. We measured temporal and spectral variables in the song of Sakesphorus cristatus across 14 localities spanning almost the entire range of the species’ distribution. The song presents a clear geographic pattern, and vocal variation was congruent with a barrier by the Sao Francisco River superimposed to a latitudinal clinal variation that was uncorrelated to climate variables. We argue that these regional differences may have a genetic basis since S. cristatus is a suboscine antbird that should not show song learning (social adaptation) and, apparently, does not have the song correlated to habitat features (acoustic adaptation). More detailed studies are required to test further hypotheses about the drivers of this potential genetic variation underlying the geographical variation in this suboscine bird song.