Subalpine Warbler split into three species

The Subalpine Warbler complex (sensu lato) is a polytypic species, but the number of ‘subspecies’ considered as valid changed over time. Until the 1990s, only three subspecies were recognised: 1) the nominate S. c. cantillans in Iberia, southern France and Italy, plus the birds breeding in the Western Mediterranean islands were also considered to belong to cantillans; 2) S. c. albistriata in north-eastern Italy, the Balkans and Turkey, and 3) S. c. inornata in Northwest Africa.

Updates (2020):

The information below is now old but still useful as a background. A detailed study published in 2020 confirmed the three-way-split and more, see this for a summary: “Split of Western and Eastern Subalpine Warblers confirmed”.

Moltoni’s Warbler: from an invalid ‘subspecies’ to a full species

The Moltoni’s Warbler was described as Sylvia subalpina by C. J. Temminck in 1820 from birds collected in northern Italy. In 1937, C. Orlando described a new subspecies from Sardinia as Sylvia cantillans moltonii. Nowadays, these two names are considered as synonyms, with the priority given to the former (Baccetti et al. 2007). However, things weren’t always as simple as this during the second half of the 20th century. In fact, the Moltoni’s Warblers (either by the name subalpina or moltonii) were not considered to be different enough from the nominate cantillans to warrant the acceptance as a valid subspecies (see Baccetti et al. (2007) for details and references). In other words, the Moltoni’s Warbler was ignored for a long time until new data emerged.

Gabriel Gargallo (1994) found that the plumage, moult and vocalisations of the Balearic population (i.e. Moltoni’s Warbler) are different from those of the Iberian birds (Gargallo collected data from captured live birds as well as from museum specimens). He also found that Balearic birds are similar to the Sardinian birds (C. Orlando described moltonii from Sardinia as mentioned above). Gargallo was therefore the first author in recent time to propose that Moltoni’s Warbler should be considered as a valid subspecies (under the name Sylvia cantillans moltonii). Later, Shirihai et al. (2001) validated this proposition and even suggested that moltonii should be treated as an allospecies (At the time, these authors didn’t know that moltonii and subalpina are in fact the same taxon, and thus also breeds in mainland Italy).

Later research, mainly by Mattia Brambilla and his team, found that Moltoni’s Warbler breeds also in mainland Italy in syntopy with cantillans without interbreeding (e.g. Brambilla et al. 2006). The strong reproductive isolation between Moltoni’s Warbler and cantillans was confirmed by playback experiments (Brambilla et al. 2008a). Finally, a phylogenetic study showed that Moltoni’s Warbler is the most genetically divergent from all ‘the other’ Subalpine Warbler taxa (Brambilla et al. 2008b). The same study showed that there is no evidence of gene flow between the two groups (Moltoni’s on one hand and ‘the other taxa’ on the other). These studies confirmed that Moltoni’s Warbler is indeed a full species on its own right.

This short summary showed how the taxonomic status of the Moltoni’s Warbler have changed from being an ignored ‘subspecies’ to a full species within less than two decades.

What about the Western and Eastern Subalpine Warblers?

The genetic basis of the split of these two groups was provided by Brambilla et al. (2008b). These authors showed that the Subalpine Warbler complex in Europe (inornata not included in the study) is composed with three well defined clades. The first clade is the Moltoni’s Warbler as mentioned above; the second is the western cantillans ( Iberian peninsula and southern France); and the third clade is formed by southern cantillans (C and S Italy and Sicily) plus albistriata.

Even at this early stage, the authors already hinted to a future Western/Eastern split: “…we are aware that future splits in Sylvia cantillans cannot be excluded when more data are provided; in fact, a further subdivision into two branches, i.e. southern cantillans and albistriata on the one side and western cantillans on the other, representing two different (allo)species, could be expected”.

The ‘formal’ three-way split and description of a new subspecies

In 2013, Lars Svensson summarised the latest research on the taxonomy of the Subalpine Warbler complex and recommended the split of the complex into three different species (Svensson 2013). Moreover, he formally described a new subspecies for the ‘western cantillans’ clade identified genetically by Brambilla et al. (2008b). Here is a summary of the suggested species:

Western Subalpine Warbler (Sylvia inornata), with two subspecies:

• Sylvia inornata inornata: breeding in Northwest Africa. (Before this taxonomic revision, Sylvia cantillans inornata was the name of the North African birds).

• Sylvia inornata iberiae subsp. nov.: a new subspecies described by Svensson (2013) for the birds breeding in the Iberian Peninsula, southern France and extreme northwest Italy. See the map. (This is the same clade named ‘western cantillans’ by Brambilla et al. (2008b).

Eastern Subalpine Warbler (Sylvia cantillans), with two subspecies:

• Sylvia cantillans cantillans: breeding in central and southern Italy and in Sicily. The taxon cantillans, historically associated with the birds breeding in the Iberian Peninsula, is now the nominate subspecies of the Eastern Subalpine Warbler. This is because the type of cantillans was described from two specimens collected in Italy (Baccetti et al. 2007) and found out to belong to the Eastern Subalpine Warbler. Thus the need to find a new name for the Iberian birds, which Svensson did by describing iberiae.

• Sylvia cantillans albistriata: breeding in western Turkey, the Balkans and north-east Italy (provinces of Trieste and Gorizia).

Moltoni’s Warbler (Sylvia subalpina): monotypic. It breeds in the Balearic Islands (Mallorca and Cabrera), Sardinia, Corsica and northern Italy. The correct scientific name for this species is Sylvia subalpina rather than Sylvia moltonii following the recommendation by Baccetti et al. (2007) with which Svensson (2013) agreed.

References:

Baccetti, N., Massa, B. & Violani, C. 2007. Proposed synonymy of Sylvia cantillans moltonii Orlando, 1937, with Sylvia cantillans subalpina Temminck, 1820. Bull. Br. Orn. Cl. 127: 107-110.

Brambilla, M., Janni, O., Guidali, F. & Sorace, A. 2008a. Song perception among incipient species as a mechanism for reproductive isolation. Journal of Evolutionary Biology 21: 651–657.

Brambilla, M., Tellini Florenzano, G., Sorace, A. & Guidali, F. 2006. Geographical distribution of Subalpine Warbler Sylvia cantillans subspecies in mainland Italy. Ibis 148: 568–571.

Brambilla, M., Vitulano, S., Spina, F., Baccetti, N., Gargallo, G., Fabbri, E., Guidali, F. & Randi, E. 2008b. A molecular phylogeny of the Sylvia cantillans complex: cryptic species within the Mediterranean basin. Molecular Phylogenetics and Evolution 48: 461-472.

Gargallo, G. 1994. On the taxonomy of the western Mediterranean islands populations of Subalpine Warbler Sylvia cantillans. Bull. Br. Orn. Cl. 114: 31–36.

Shirihai, H., Gargallo, G., & Helbig, A. J. 2001. Sylvia warblers: identification, taxonomy and phylogeny of the genus Sylvia. Christopher Helm, London.

Svensson, L. 2013. A taxonomic revision of the Subalpine Warbler Sylvia cantillans. Bull. Br. Orn. Cl. 133: 240-248.

‘Subalpine Warblers’ identification

As a follow up of the taxonomic paper cited above, Lars Svensson published a new paper in British Birds about the identification of the different species in the ‘Subalpine Warbler complex’. Here is the summary:

In this paper, Lars Svensson summarises the current knowledge of variation within the Subalpine Warbler complex. A new morphological character, regarding differences in the tail pattern, is described here, which will help in the diagnosis of taxa away from the breeding grounds. This new character is central to the proposal of a three-way split of the complex: Western Subalpine Warbler, Moltoni’s Warbler and Eastern Subalpine Warbler. Based on current knowledge of morphological characters and confirmed by genetic sampling, it is established that the first British record of Moltoni’s Warbler was a male on St Kilda on 13th June 1894.

Also on the identification, see the interesting article (which includes a nice plate) by Brian J. Small linked below.

Small, B.J. 2013. Identification of male ‘Subalpine Warblers’. Surfbirds.

Svensson, L. 2013. Subalpine Warbler variation and taxonomy. British Birds 106: 651-668.

Update:

The Collins Bird Guide was updated in May 2015 with the additions of a number of new species (splits), and amended texts, captions and new plates for other species. Of interest to birds of Northwest Africa, the updates included the split of the African Crimson-winged Finch (Rhodopechys sanguineus), the split of the Saharan Scrub Warbler or Maghreb Scrub Warbler (Scotocerca saharae), and the split of the Subalpine Warbler complex into three species (plate in photo 3). See the website of Rare Bird Alert UK for the full list of the updates.

Update 2 (Dec 2017): the PDF of the taxonomic paper is online (added the link above). The same for the paper about a new North African subspecies of Common Chaffinch described by the same author.