Hybridization between the White-Vented and Black-Vented forms of the Black-faced Woodswallow

Abstract

Australian populations of the Black-faced Woodswallow Artamus cinereus are divisible into two subspecies on the basis of whether the vent and undertail-coverts are white (albiventris) or black (melanops). These are in secondary contact in Queensland. Hybridization was quantitatively analysed using a hybrid index. Though genetic exchange between these subspecies is fairly extensive, there is a step in the morphological gradient of intergradation coincident with the Great Dividing Range and the head of the Gulf of Carpentaria. Their evolution is discussed and it is concluded that they diverged when conditions were extremely arid and the Carpentarian and Eyrean Barriers were simultaneously operative.