Split of Western and Eastern Subalpine Warblers confirmed

A new study confirmed that the ‘Subalpine Warbler’ complex is indeed three species. In addition to Moltoni’s Warbler, the study recommended that Western and Eastern Subalpine Warblers should be recognised as different species as well. The ‘IOC World Bird List’ accepted the split as proposed by the study.

(Research about the “taxonomy of the Subalpine Warbler species complex” between 1990s and 2013 is well summarised in this old blog-post. If you are unfamiliar with the subject or want to refresh the memory, it’s recommended to start with that before reading about the news study).

Western Subalpine Warbler (Sylvia iberiae) photographed in Morocco by Phil Gower.
Western Subalpine Warbler (Sylvia iberiae) photographed in Morocco by Phil Gower.

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 analyzed in this study matched their correct taxon and population except one: inornata. This subspecies was described in 1909 based on birds (= types) 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).

Phylogenetic tree

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.

Conclusion

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.
  • Sylvia cantillans albistriata. Extreme north-east Italy, Balkans, Greece, and western Turkey.

Reference:

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 IOC split

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.

Phylogenetic tree of the ‘Subalpine Warbler’ species complex
Clade distribution and proposed taxonomy are on the right. Note how inornata type, shown in pink, is embedded within clade 2 (Moltoni’s Warbler). Samples obtained from breeding specimens are highlighted with coloured dots.

2 thoughts on “Split of Western and Eastern Subalpine Warblers confirmed”

  1. David Britton

    The Isabelline Shrike split to Turkestan (phoenicuroides) and Daurian/Isabelline (isabellinus) was not followed by an attempt by BBRC to assign previously accepted records to a specific new species. I wonder whether anything will be done about Subalpine Warblers where UK records are numerically far greater than Isabelline Shrikes.

    1. For the Subalpine Warblers, it will depend on whether the observers recorded (and submitted) enough data or not at the time of their observations.

      I guess, the observations made before 2008 (that’s before the study of Brambilla et al. 2008 that suggested the split) will probably be difficult because the observers may have not noted all the subtle details (unless there were photos of course).

      For the observations made after that date, and especially after 2013 (since Svensson’s papers), I guess those will be easy because the observers were more aware of the potential future splits and the subtle differences between the different taxa (and again, photos will make this even easier).

      In Morocco, we won’t have this problem. The only records of Eastern Subalpine Warblers we have so far were captured and ringed last year at the Merzouga Ringing Station.

      p.s. I corrected ‘Turkestan’ error, so also deleted the second comment where you mentioned it.

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