Birds in Lincolnshire - “Grey areas” – the problem with Chiffchaffs

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Birds in Lincolnshire

“Grey areas” – the problem with Chiffchaffs

“Grey areas” – the problem with Chiffchaffs by Alexander Lees

A Chiffchaff showing characteristics of the Eastern form Phyloscopus [colybita] tristis was present at Marston Sewage Treatment Works, Lincolnshire on the afternoon of the 24th December 2003 and was still present the next day, occupying a linear winter territory along the bridleway that transects the site. As can be seen from the accompanying, admittedly poor images (400 asa in low light), the bird is uniformly grey-buff lacking any yellow tones to the body and has a hint of greenish to the remiges bearing a resemblance to a Bonelli’s Warbler sp. The bird’s dusky cheeks, greyish nape and black bill and legs are also all typical of tristis. The bird appeared to lack any distinctive wingbar but this a feature perhaps more likely to be associated with autumn 1st winters and this bird may be the returning individual from the 2001/02 winter. I located the bird by its call a distinctive mournful “veet” or “peet” and immediately recognised it as being this taxon before I caught sight of the bird, having found four previous birds in the UK. Considering the photos and the rendition of the call one would think that the identification of this individual would be fairly straightforward…

However on the 31st December I spoke to three observers (none of whom who had previous experience of this taxon) who described a Chiffchaff they had seen in the same area, which although answering to the description of Siberian Chiffchaff was apparently giving a “Western Chiffchaff” (P. colybita & abietinis) type call. I was fairly certain that I had also heard the bird giving a classic “huiit” type call on the 25th but was unable to confirm that the utterance hadn’t come from one of the colybita birds also present on site. If the other observers were correct (see however http://www.wepsite.net/warbler/chiffchaff.htm for a review of chiffchaff vocalisations and potential observer aural pitfalls) then it is unlikely that the bird’s status as a pure Siberian Chiffchaff can be upheld, as one would assume that such a bird is genetically compromised with DNA from western populations. However chiffchaff song and call-type plasticity has been well documented with birds able to switch vocalisations perhaps as a result of mimicry rather than any genetic level differences, most famously in the case of the Portland Iberian Chiffchaff (P. brehmii) which to quote the late Chris Mead "transmogrified" into a Common Chiffchaff. The presence of mixed singers in the populations of this “species”, which has now been further subdivided into two sub-species further muddies the waters. If the call type is flexible then any Siberian Chiffchaff in Western Europe is liable to revert to a western type call in the absence of conspecifics.

Parallels may be drawn with many groups, most notably the flava wagtails, of which eastern birds give a Citrine call but which are perhaps more readily separable in the field than the Chiffchaff complex but are not widely mooted as potential splits, although recent work with molecular markers may change this situation. Having just returned from a week on Tenerife I can testify to the extreme range of variation in both plumage, song and call types of Chiffchaffs present there in winter. Canary Islands Chiffchaff (P. canariensis) is abundant but numbers of P. c. colybita were also present along with birds that may have been P. brehmii. The calls of the Tenerife population of the Canary Island (sub)species are close to that of colybita and differ from those of birds on other islands in the same group (see British Birds 91:9) with birds on the outer islands being more divergent - perhaps because of limited contact with colybita?

Chiffchaff showing characteristics of the Eastern form Phyloscopus [colybita] tristis © Alexander Lees 2004

Bearing this in mind it would seem rather oversimplistic to throw away a tristis type bird if it should vary its vocabulary. Likewise, it would appear most logical that tristis birds from the western most part of their range are most likely to occur in Europe and the increasing occurrence frequency may suggest that new “pseudovagrant” wintering populations in Western Europe are being established. Furthermore if there is such overlap in plumage and vocal characteristics between these various new species can there specific status really be allowed to stand? They are by virtue of their allopatric breeding ranges and some unique characteristics perhaps good phylogenetic species, but with the current trend climatic towards climatic amelioration the differences may either be reinforced by assortative mating or eliminated by introgression over evolutionary time. Ultimately the group is a somewhat dynamic assemblage and nit picking over anthropogenic species concepts may never lead to a clear resolution of the problem. However, documenting the identification and thus our ability to ascertain the status of such birds is fundamental to our knowledge of both migratory flexibility and speciation/introgression events.

Alexander Lees
Also see Chiffchaff - Barton Pits 28th November 2001

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