Further vocal evidence for treating the Bahama Nuthatch Sitta (pusilla) insularis as a species

Abstract

The case for recognising Bahama Nuthatch Sitta insularis as a species separate from Brown-headed Nuthatch S. pusilla has been made several times since 2004, based on plumage, morphometrics, voice and genetic distance, but only one of four world lists currently accepts it as such. We assembled three new sets of recordings and recently published evidence on playback responses. We found that S. insularis has at least five vocalisations that are homologous to but always much higher pitched (by 2–3 kHz) than those of S. pusilla, such that the main calls of the latter are strikingly different from those of the former, and playback studies all suggest a consistently weak response in one species to the calls of the other. Moreover, genetic divergence of insularis from mainland pusilla is greater than that of another Bahamian taxon, Bahama Warbler Setophaga flavescens, recently accepted by all world lists as a species, from mainland Yellow-throated Warbler S. dominica. Taken together with the notably larger bill of Sitta insularis, these factors reinforce the case for treating Bahama Nuthatch as a (regrettably now almost certainly extinct) species.