Moltoni's Subalpine Warbler, Skaw, Unst, Shetland, June 2009 (Dougie Preston)
There is just one acceptable British record of this form - that of a singing male at Skaw, Unst, Shetland, from 1-11 June 2009 (see an exhaustive selection of images at the Shetland Wildlife website, as well as definitive sound recordings made of the bird, at http://www.nature-shetland.co.uk/naturelatest/archives/birdarchive09jun.htm
MOLTONI'S SUBALPINE WARBLER (from hereafter recognised as Sylvia moltonii) differs from both Western and Eastern Subalpine Warbler in plumage, moult, timing of breeding, habitat and contact calls (Gargallo 1994, Shirihai et al. 2001, Brambilla et al. 2007). Recent studies have shown that the breeding ranges of Moltoni’s Warbler and Western Subalpine Warbler (Sylvia cantillans) overlap at several localities in mainland Italy without evidence for interbreeding (Brambilla et al. 2006). Playback tests conducted within and outside the area of overlap in Italy have demonstrated that the two groups do not respond to each other’s songs (Brambilla et al. 2008a). A molecular phylogenetic study indicated that Moltoni’s Warbler and Eastern Subalpine Warbler form separate clades and failed to find evidence for gene flow, even in areas where the two forms have overlapping breeding ranges (Brambilla et al. 2008b). The level of sequence divergence between Moltoni’s Warbler and both Subalpine Warblers is consistent with those typically observed in species taxa, including several pairs of Sylvia warblers (Brambilla et al. 2008b). Therefore, Moltoni’s Warbler and Subalpine Warbler are best treated as separate species (cf. Brambilla et al. 2008a,b,c).