Birds of a feather: Comprehensive plumage colour analysis for a revised subspecies classification of the Chestnut-winged Babbler (Cyanoderma erythropterum) species complex

Quantitative analysis of colouration is an essential tool for subspecies delimitation but has always posed a challenge in avian taxonomy. In this study on the Chestnut-winged Babbler (Cyanoderma erythropterum) species complex from tropical Southeast Asia, we made use of colour measurements taken with digital cameras and applied two methodologies—(1) the 75% subspecies rule on quantitative colourimetric variables, and (2) the CIEDE2000 colour distance method to generate phylograms, which has probably never been applied in taxonomy before. Given its large number of described subspecies, many of which have been synonymised in modern taxonomies, the species complex serves as an appropriate model to test subspecies validity. Our data indicate that one synonymised subspecies (C. e. apega), from the islands of Bangka and Belitung, requires re-instalment and recognition, whereas one widely recognised subspecies (C. e. fulviventre), from the Banyak Islands, should be synonymised. Our approach also allowed us to redraw geographic subspecies boundaries. Our work indicates that current subspecies taxonomies of many poorly known tropical species may remain error-ridden and highlights the importance and viability of large-scale taxonomic revisions targeting avian subspecies globally while incorporating quantitative colourimetric approaches.