Hybridization Between the White-Vented and Black-Vented Forms of the Black-Faced Woodswallow

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Abstract
Australian populations of the black-faced woodswallow Artamus cinereus are divisible into 2 ssp. on the basis of whether the vent and undertail-coverts are white (A. c. albiventris) or black (A. c. melanops). These are in secondary contact in Queensland [Australia]. Hybridization was quantitatively analyzed 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 they probably diverged when conditions were extremely arid and the Carpentarian and Eyrean Barriers were simultaneously operative.