And is the taxon zagrossiensis valid?
Just because you see a bird in a certain country doesn’t mean that it breeds there. It could be passing through. Or perhaps it is a lost migrant, blown off course by strong winds. In Iran, you can observe several species of the lesser whitethroat complex (Sylvia curruca). Ornithologists are quite certain that the nominal species (S. curruca) and Hume’s whitethroat (S. althaea) breed in this Middle-Eastern country. But the jury is still out on some other members of this widespread species complex. For example, some researchers argue that the desert whitethroat (S. minula) breeds in northeastern Iran, while others think it just visits the area in winter. A recent study in the Journal of Ornithology sampled more than 30 individuals across Iran to solve this mystery.
The latest molecular studies divide the lesser whitethroat complex into six geographical groups (based on mitochondrial DNA): althaea, blythi, halimodendri, margelanica, curruca and minula. Raziyeh Abdilzadeh and his colleagues compared the genetic make-up of the Iranian birds with these six groups. This analysis revealed that all samples could assigned to three groups: curruca, althaea and halimodendri. The samples of halimodendri – which is considered a subspecies of Hume’s whitethroat – were collected in February and represent wintering or migrating birds. Moreover, none of the samples were members of the minula group. There is thus no evidence that the desert whitethroat breeds in Iran.
This study also sheds some light on another mystery: the taxon zagrossiensis. In 1911, Sarudny considered the birds in the Zagros mountains to be a distinct taxon, classified as S. althaea zagrossiensis. Birds from this area are slightly darker compared to the nominal lesser white-throat. The current analyses do not support this classification. Indeed, the researchers note that “Our data suggest that birds inhabiting the mountains of western Iran and the central Zagros mountains, at least as far east as Shiraz, sometimes recognized as caucasica and zagrossiensis, respectively, belong to the curruca clade sensu Olsson et al. (2013), based on mitochondrial haplotypes.” The origin of the darker plumage of these birds remains to be investigated. Did they acquire it through hybridization with another member of this species complex?
Abdilzadeh, R., Aliabadian, M., & Olsson, U. (2020). Molecular assessment of the distribution and taxonomy of the Lesser Whitethroat Sylvia curruca complex in Iran, with particular emphasis on the identity of the contentious taxon, zagrossiensis Sarudny, 1911. Journal of Ornithology, 161:665–676.