Comoro Black Bulbul (Hypsipetes parvirostris) - HBW 10, p. 244

Taxonomy: Hypsipetes parvirostris Milne-Edwards and Oustalet, 1885, Grand Comoro, Comoro Islands.
Sometimes considered to form a superspecies with all other members of genus, and in the past all have been treated as conspecific. Presence of two species of this genus in Comoros has long been contentious; significance of the olivaceous phenotypes restricted to Grand Comoro and Mohéli obscured by presence on all four main islands of H. madagascariensis. Shortly after its initial description, nominate race became treated as a hybrid between H. madagascariensis and H. crassirostris; subsequently, all Comoros forms considered sufficiently distinct in combination from Madagascar populations to merit subspecific rank, for which name parvirostris was used (despite the fact that the type was the supposedly “aberrant” olivaceous form); the larger olivaceous moheliensis was originally described as a race of H. crassirostris. It is now recognized that the olivaceous phenotype constitutes a separate species, which behaves as a parapatric vicariant of H. madagascariensis (replacing latter in montane forest habitats). Furthermore, recent molecular analysis suggests that moheliensis is not the sister-taxon of nominate and that it should be accorded rank of full species, a treatment supported by differences in size and vocalizations; retained as race of present species, pending fuller study of the two taxa. Two subspecies provisionally recognized.