In the following we briefly analyze and compare voice of the different races of Subalpine Warbler (Sylvia cantillans). We also try to quantify the extent of any vocal differences using the criteria proposed by Tobias et al. (2010), as a support for taxonomic review. We have made use of sound recordings available on-line from Xeno Canto (XC).
We compare the voice of the three groups which have been proposed as possible distinct species (illustrated by some typical examples in the following sonograms of song and call in the pdf version of this note): Western Subalpine Warbler (inornatus/cantillans), Eastern Subalpine Warbler (albistriata) and Moltoni's Warbler (moltonii).
Vocal differences have been described by Shirihai et al. (2001):
moltoni is said to differ in a more rapid song, although not always. Contact call is more diagnostic, a rattled 'trrr'. We can confirm that indeed some song phrases are given at a higher pace, but equally so there are examples of much slower phrases. There is thus a considerable amount of overlap. The call note on the other hand is indeed quite constant in being a short rattle of c. 0.2-0.3s (distinct notes given at a very high pace), unlike the single or double call notes of the other two groups.
albostriata is said to differ from cantillans/inornata mainly in its contact call, doubled instead of single 'tek' calls, sounding like 'trek'. There aren't much recordings available of albostriata calls. As a matter of fact, the only one from the breeding grounds on XC is of single notes (!) if identified correctly (XC176535, it is sounding a bit agitated, thus possibly rather alarm than contact call?). A recording from Sweden attributed to this taxon (by ringing) contains both doubled and single notes. It would thus seem that both single and doubled notes are given. On the other hand, in the many available examples of cantillans calls we only found single notes.
All in all, the vocal difference of moltoni is quite clear: a sometimes faster-paced song (score 1) and a clearly different main contact call (quantified e.g. by length, # of notes or pace, score 4). Total vocal score about 5 if call differences are included.
The vocal difference between eastern and western races is less pronounced, with albostriata often (?) giving a doubled note as main contact call, in those cases distinguishable from cantillans/inornata. Vocal score about 2 at most (!). Furthermore, if we follow Svensson (2013) by adding S Italian birds to the Eastern group, then we get even more examples of 'single-noted' contact calls. In this case, the vocal difference of western vs eastern groups becomes almost insignificant.
This note was finalized on 11th March 2016, using sound recordings available on-line at that moment. We would like to thank in particular the many sound recordists who placed their recordings for this species on XC.
Shirihai, H., Gargallo, G. & Helbig, A.J. (2001). Sylvia Warblers. Identification, Taxonomy and Phylogeny of the Genus Sylvia. Princeton University Press, New Jersey.
Svensson, L. (2013). A taxonomic revision of the Subalpine Warbler Sylvia cantillans. Bull. Brit. Orn. Club 133(3): 240–248.
Tobias, J.A., Seddon, N., Spottiswoode, C.N., Pilgrim, J.D., Fishpool, L.D.C. & Collar, N.J. (2010). Quantitative criteria for species delimitation. Ibis 152(4): 724–746.
More Information: on261_subalpine_warbler.pdf