The intriguing 'Basalt' form of Mourning Wheatear is more than just a morph, says new research.
Many will have looked through their Western Palearctic field guides and noticed the black morph of Mourning Wheatear Oenanthe lugens known as 'Basalt Wheatear', endemic to the dark volcanic rock deserts of northern Jordan and southern Syria. It has been generally believed to be an ecotype, or a form specifically adapted to a discrete habitat, but otherwise indistinguishable from others of its species.
However, a new analysis of the form's status, biometrics and genetics suggest that the so-called morph is best treated as a subspecies of Mourning Wheatear, now described as O l warriae.
The species itself is usually divided into eight subspecies, now increasingly treated as up to five separate species: Mourning itself, Maghreb Wheatear O halophila, South Arabian Wheatear O lugentoides, Abyssinian Black Wheatear O lugubris and Schalow's Wheatear O schalowi. Basalt Wheatear lacks the rufous undertail coverts of the complex, and also differs in its rump pattern and measurements.
It is entirely separate in breeding range from all other Mourning Wheatear forms, which show no tendency to show this morph away from the basalt deserts, and mixed pairings have never been reliably reported. It shares its white wing panel with O l lugens, but closely resembles Variable Wheatear O picata opistholeuca in its black plumage.
Considering these morphological and distributional differences, the authors conclude that the form should be treated as a distinct subspecies, as it is indistinguishable from O l lugens genetically.
Shirihai, H, Kirwan, G M and Helbig, A J. 2011. A new taxon in the Mourning Wheatear Oenanthe lugens complex. Bulletin of the British Ornithologists' Club 131: 270-291.