Geographic variation in size and coloration in the Turdus poliocephalus complex: A first review of species limits

Abstract

Among the most dramatically variable of bird species under the traditional polytypic ‘biological' species concept is Turdus poliocephalus Latham 1801, which is distributed across parts of Southeast Asia and Oceania. This variation, nonetheless, has never seen comprehensive review, and particularly not in view of modern species concepts. In this study, I examined plumage coloration patterns and morphometric variables in series of specimens representing 49 of 52 described subspecies and 64 of 72 allopatric populations, and document patterns of geographic variation in plumage coloration and sexual dimorphism. Overall patterns of variation indicate 12 distinct plumage types, with 31 geographically contiguous populations that present one of the 12 plumage types. Finally, taking into account differences between populations within these contiguous sets of populations, 38 diagnosable units can be discerned. Recognition of these subunits as species is warranted: the biological species concept might recognize the 31 geographically contiguous plumage-type units, whereas the evolutionary and phylogenetic species concepts might best recognize all 38 of the distinct population units.