The split of the Subalpine Warbler complex (sensu lato) into three different species (i.e. Moltoni’s, Western and Eastern Subalpine Warblers) was proposed a few years ago. However, currently the Moltoni’s Warbler (Sylvia subalpina), which is the most divergent of the three taxa, is the only widely adopted split by different taxonomic authorities.
Although the full three-way split of the species complex as proposed by Lars Svensson is not yet accepted by major World checklists, the proposed reassignment of the different populations to the correct taxon/subspecies is adopted by at least the IOC Checklist and HBW Alive (e.g. cantillans is now restricted to the birds breeding in C and S Italy and Sicily, while the birds breeding in extreme NW Italy, S France and Iberia are now assigned to the new subspecies iberiae). It should be noted that some regional taxonomic committees (e.g. Dutch Birding/CSNA, Swedish Taxonomic Committee) have already adopted the three-way split.
[Note: I am aware of a genetic study that confirmed the split between the Western and Eastern Subalpine Warblers. The study has not been formally published yet.]. Update: the study published in 2020, see this blog-post for a summary: Taxonomy of ‘Subalpine Warbler’ complex revisited, confirming the three-way split.
“Subalpine Warblers” in Morocco
Of the five taxa of the Subalpine Warbler complex (sensu Svensson 2013), only three taxa were cited in the Birds of Morocco (Thévenot et al. 2003): the breeding inornata, the common migrant S. c. cantillans [now iberiae] and the accidental winter visitor S. c. moltonii. The latter, now a full species, is not only a wintering visitor to Morocco but probably mainly a passage migrant wintering further south in West Africa (see Piot & Blanc 2017).
There have been no known records of the two subspecies of the Eastern Subalpine Warbler (the redefined cantillans breeding in C. and S. Italy and Sicily and albistriata breeding further east) in Morocco.
First Eastern Subalpine Warblers (albistriata) in Morocco
During a bird ringing session at Merzouga, south-east Morocco, three presumed Eastern Subalpine Warblers of the albistriata subspecies were caught and ringed on 12 March 2019. A fourth individual was caught and ringed later. The ringing operation is organized by the Catalan Ornithological Institute and other partners and headed by Marc Illa. These would be the first know records of this taxon in Morocco.
Note to birders: among the three “subalpine warblers”, only the Moltoni’s Warbler is officially added to the species considered by the Moroccan Rare Birds Committee (see the full list). However, it would be good to record any Eastern Subalpine Warbler because it’s likely to be added to the list in the future once its split is widely accepted.
While the Eastern Subalpine Warbler in Morocco must be rarer during migration, the total absence of historical and recent records is surely attributed to the similarities between the different taxa and the difficulties in their identification in the field. When caught for ringing, things become much easier.
Piot, B. & Blanc, J.F. 2017. Moltoni’s Warbler Sylvia subalpina in Senegal and West Africa. Malimbus 39: 37-43.
Svensson, L. 2013. A taxonomic revision of the Subalpine Warbler Sylvia cantillans. Bull. Br. Orn. Cl. 133: 240-248.
Thévenot, M., Vernon, R. & Bergier, P. 2003. The Birds of Morocco. BOU Checklist No. 20, Tring.
Added the fourth individual and a ‘note for birders’ to the text. Marc Illa said in an email that “…all four birds were ringed, measured, photographed and sound recorded”. Despite this, he wanted to be ‘scientifically correct’ and asked to keep the word “presumed” in front of the species name.