The House Bunting complex houses two distinct species, but might have had a history of hybridization.
In taxonomy, you have lumpers and splitters. Lumpers like to keep everything together, while splitters don’t mind dividing a species into two. The Saharo-Arabian desert belt is a splitters dream. This region extends from the Sahara in North Africa over the Arabian Peninsula into Pakistan and India. Several bird species have distinct populations in the eastern and western part of this arid environment. Distinct populations? Geographically separated, you say? Let’s start splitting!
Indeed, in recent years, it has been proposed to elevate some populations to species status. For example, the Houbara Bustard (Chlamydotis undulata) and MacQueen’s Bustard (C. macqueenii), and the African Desert Warbler (Sylvia deserti) and the Asian Desert Warbler (S. nana). In a new study, Manual Schweizer and colleagues focus on another species complex in the Saharo-Arabian desert belt: the House Bunting (Emberiza striolata) complex.
Recent taxonomic studies have culminated in the proposal to recognize two species in this complex: the House Bunting (E. sahari) in the west and the Striolated Bunting (E. striolata) in the east. In addition, morphologically intermediate birds have been found in Sudan and Chad. Might these be hybrids?
The east-west divergence is supported by two mitochondrial markers, suggesting that the split is justified. The intermediate birds, however, reveal a striking pattern. Morphologically, these specimens resemble the eastern species (E. striolata), but genetically they are closer to the western species (E. sahari). Incongruence between mtDNA and morphology has been reported in other studies as well and can be explained by incomplete lineage sorting or hybridization. The researchers speculate that ‘introgressive hybridization in a secondary contact zone is the most likely explanation.’ But to test this hypothesis, more genetic data is needed.
Luckily for the splitters, these results do not impinge (a wonderful word the authors used in the abstract) on the decision to recognize two species.
Schweizer, M., H. Shirihai, H. Schmaljohann and G. M. Kirwan (2017). Phylogeography of the House Bunting complex: discordance between species limits and genetic markers. Journal of Ornithology: 1-15.
This paper has been added to the Emberizidae page.