An isolated population of Western Orphean Warbler in Libya has been described as a new subspecies, and revised criteria for separating the orphean taxa have been published.
Several authorities have been seen by many birders as perhaps a bit 'tardy' in splitting the western and eastern forms of Orphean Warbler, in its traditional sense. Now, a new paper has set out more discrete differences between the two subtle taxa, perhaps bringing a more universal recognition of the two speciesof Western and Eastern Orphean Warbler closer. Birdwatch has already accepted the split in its Birds of Britain: the Complete Checklist 4th Edition, available from the Birdwatch Bookshop.
The two species differ in their mitochondrial DNA by up to 6.4 per cent, well over the percentage of many accepted species pairs, and have a clear range divide through central Europe from Switzerland to northern Libya. It is there, where a small population found in north-eastern Libya has caused taxonomic confusion with different workers assigning the birds to either species or treating them as intermediate between the two, a status only tenable if they are not actually separate species.
Svensson (2012) examined seven specimens taken in north-east Libya (three housed in the Natural History Museum, Tring, and four in the American Museum of Natural History, New York) and was able to assign all to Western Orphean on the basis of their diagnostic tail and near-diagnostic undertail coverts patterning. However, the Libyan birds also have a longer bill and paler grey upperparts, so there is a level of intermediateness between the two species trumped by the tail pattern diagnostic of Western. The song is very similar to Western and as yet no diagnostic differences have been officially noted. The new subspecies has been named Sylvia hortensis cyrenaicae, leaving the rest of Western birds as the nominate subspecies.
Svensson also delimits identification criteria for Western and Eastern Orphean Warbler, leaving the tail pattern as diagnostic: Eastern, not yet recorded in Britain, has notably more extensive white on the inner web of its outer tail feather and short broad tips to the two tail feathers next to this, whereas the outer tail feather has a pointed narrow white wedge on the outer web and a small wedge on the fifth feather next to it. The two species also have different songs and calls and almost always differently-patterned undertail coverts, as well as more subtle difference which are diagnostic in combination.
Reference
Svensson, L. 2012. A new subspecies of Western Orphean Warbler Sylvia hortensis and criteria for separating Western from Eastern Orphean Warbler S. crassirostris. Bulletin of the British Ornithologists' Club 132: 75-83.
