A new study confirmed that the ‘Subalpine Warbler’ complex is indeed composed of three different species (Moltoni’s Warbler, Western and Eastern Subalpine Warblers). The ‘IOC World Bird List’ accepted the split as proposed by the study.
(Note: the main research about the “taxonomy of the Subalpine Warbler species complex” between mid-1990s and 2013 is well summarized in that old blog-post. I would recommend to start with that before reading about the new study, especially if you are unfamiliar with the subject).
The taxonomy and nomenclature of the Subalpine Warbler complex has been the subject of many research during the last two decades. However a number of issues were still pending, and that’s probably why the “three-way split” hasn’t been widely recognized. As an example, North African taxon inornata hasn’t been included in any recent genetic study.
Zuccon et al (2020) aimed to address these issues and present a robust revision of the ‘Subalpine Warbler’ complex. To do this, the authors used new genetic samples – including from the Maghreb – obtained in the breeding season, and also analysed the available type specimens. To clarify the identification of the lost types, the authors studied the original descriptions of the involved taxa and other archival documents. The study was published in the Zoological Journal of the Linnean Society earlier this year.
Position of the types in the phylogenetic tree
Type specimens are very important because the names of the taxa – species or subspecies – are based on them (That’s why they are deposited in museums when a new species or subspecies is described). If the type is wrong, then the associated name becomes invalid (generally becomes a synonym).
All type specimens genetically analysed in this study matched their correct taxon and population except one: inornata. This subspecies was described in 1909 based on birds (= type specimens) collected in Tunisia, so they were assumed to be from the local birds. This study, however, showed that one of the types (called “lectotype”) is not a local North African bird but a migrant Moltoni’s Warbler (In figure below the lectotype of inornata, highlighted in pink, is embedded within clade 2).
That means the name inornata is invalid (it became a synonym of subalpina). Remember that since the recommendations of Svensson (2013), inornata became associated with the whole Western Subalpine Warbler as Sylvia inornata (with the taxon he described, iberiae, as its subspecies).
The study identified five well-supported clades: clade 1, Central and Northern Italy; Clade 2, Corsica, Sardinia and Balearics; clade 3, North Africa, Spain, France and the westernmost end of Italy; clade 4, Southern Italy (including Sicily), and clade 5, the Balkans, Greece and Turkey.
Looking at these clades and the 5 taxa currently in use (cantillans, albistriata, inornata, iberiae and subalpina), we can see that only two clades matched exactly with their respective taxa. These are clade 4 (matched with the nominate subspecies of the Eastern Subalpine Warbler) and clade 5 (matched with the subspecies albistriata of the same species). We can also add clades 1 and 2, because together they are forming the Moltoni’s Warbler (Although these two clades are well structured into ‘islands group’ and ‘mainland group’, the difference between them is small).
Clade 3, however, included birds from whole area of the Western Subalpine Warbler (North Africa and Europe). Because inornata is now invalid as we have seen above, the only available name for this clade is iberiae. Note that although North African and European birds are in the same clade 3, they didn’t mix but formed two different clusters. However, the difference is too small and the authors consider that a new name for North African birds is not needed.
The authors recommended the recognition of three species in this complex:
- Moltoni’s Warbler (Sylvia subalpina). Monotypic. North-central Italy, Corsica, Sardinia, and Balearics.
- Western Subalpine Warbler (Sylvia iberiae). Monotypic. North Africa, from Tunisia to Morocco, Iberia, southern France, and extreme north-west Italy.
- Eastern Subalpine Warbler (Sylvia cantillans). Polytypic, with two subspecies: Sylvia cantillans cantillans (Southern Italy and Sicily) and Sylvia cantillans albistriata (Extreme north-east Italy, Balkans, Greece, and western Turkey).
Zuccon, D., Pons, J.-M., Boano, G., Chiozzi, G., Gamauf, A., Mengoni, C., Nespoli, D., Olioso, G., Pavia, M., Pellegrino, I., Raković, M., Randi, E., Rguibi Idrissi, H., Touihri, M., Unsöld, M., Vitulano, S., & Brambilla, M. 2020. Type specimens matter: New insights on the systematics, taxonomy and nomenclature of the subalpine warbler (Sylvia cantillans) complex. Zoological Journal of the Linnean Society. doi:10.1093/zoolinnean/zlz169
The split adopted by IOC
The ‘IOC World Bird List’ accepted the split as suggested in this study. They wrote in their website yesterday: “Split Western Subalpine Warbler from (Eastern) Subalpine Warbler with adjustment of scientific name following Zuccon et al. 2020”.
The split will likely be published in the next version of the checklist.