Closely related to C. melanurus and C. mindanensis; molecular data indicate that they form a well-supported clade with C. lepidus, C. cyanopectus and C. argentatus (and taxa previously included within those species)#R. Much uncertainty exists over taxonomic status of distinctive rufous-backed form rufidorsa, which has sometimes been treated as a separate species, and sometimes as merely a morph; recent molecular study reveals some genetic difference between rufous-backed and black-backed forms, suggesting at least that they are not morphs#R; same study suggests that the extensive plumage polymorphism that is evident in broad zone of intergradation (S Malay Peninsula, Sumatra, Borneo) may be the result of introgressive hybridization that occurred in the distant past, when the two forms were diverging from one another (samples of polymorphic birds from intergradation zone were all genetically closer to rufous-backed type, with no evidence of present-day hybridization); in rufidorsa lack of blue-black on wings and dorsal area with associated dark frons and ear-coverts (4), slightly larger average size, with deeper bill, longer wing and longer tarsus#R (ns), non-migratory vs migratory habits (1), and broad zone of intergradation (1) suggest treatment as species is tenable, but zone of intergradation is so broad that this option appears impractical; for present, provisional recognition of rufidorsa as a subspecies#R#R seems marginally more appropriate and satisfactory. Population of Simeulue and Batu sometimes separated as race jungei and that of Nias as race captus, but both now seem better included within rufidorsa; birds of Mindoro (Philippines) have at times been separated as race vargasi. Original specific name erithaca is a noun, and therefore remains unchanged, irrespective of gender of genus in which placed#R; same is also applicable to name rufidorsa#R. Four subspecies currently recognized.
Food and feeding
Status and conservation
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