Subspeciation, hybridization and relationships in the Little Shrike-Thrush Colluricincla megarhyncha of Australia and New Guinea

Abstract

The shrike-thrushes C. megarhyncha and C. parvula are considered to be conspecific because they hybridize on the south-western edge of the Gulf of Carpentaria and the C. m. obscura subspecies group of northern New Guinea is a phenetic link. Geographical variation in C. megarhyncha is complex and has resulted from an interplay of ecotypy, past and present allopatric subspeciation and introgressive hybridization. In eastern Australia variation is clinal with a distinct step at the Burdekin Gap indicative of past isolation. Three or four subspecies grow may be recognized in New Guinea but far too many subspecific names are in use. The evolutionary history of C. megarhyncha is constructed from its pattern of geographical variation and the climatic regime of the late Quaternary and Holocene. Colluricincla comprises two groups of species and C. boweri is considered to be closest to the megarhyncha rather than the harmonica plus woodwardi group.