Identification of Siberian Chiffchaff

Kjetil Aa. Solbakken

The Chiffchaff Phylloscopus collybita is one of the most numerous insectivorous birds throughout Europe, and breeds from the British Isles eastwards to Eastern Siberia.

In Norway the subspecies abietinus is a common breeder in most of the country apart from the northernmost areas, while the subspecies collybita is probably a regular breeder in small numbers in costal areas in the south and southwest. East of the Urals abietinus is replaced by the subspecies tristis, commonly referred to as Siberian Chiffchaff. To the west there is a broad overlap zone where birds showing intermediate characters between the two subspecies breed. These birds are commonly referred to as "sub-tristis" or "fulvescens". It seems to be a continuous variation from tristis to abietinus, and a "sub-tristis" could therefore look like anything in between. Siberian Chiffchaff is currently on the report list of the Norwegian RC (NSKF) as in most countries in western Europe, after a debate on one of the early AERC-meetings where arguments that "true tristis" might me more rare than the number of records suggested. To this date only three records have been accepted in Norway. A number of older records are currently under reconsideration, and a few more will probably be added to the total during this process.

Siberian Chiffchaff is underreported by observers, and combined with the fact that some otherwise plausible submitted records have been rejected due to inadequate documentation, this has doubtless added to the rarity of this subspecies in Norway. It is nevertheless a fact that most of the documented claims that have been rejected have been birds with "sub-tristis" characters. From October onwards it is time so watch out for these eastern Chiffchaffs along the coasts of western Europe, but the identification process should be carried out with great care. Less than one in ten of the grey Chiffchaffs are likely to be the real thing, and field identification without trapping the bird is not advisable. Last autumn, as usual, Norwegian birding websites and the pager system was flooded with observations of "tristis" or "tristis-type" Chiffchaffs. With a closer look many, if not most, of these will prove to be "sub-tristis" birds on the grey end of the colour scale. So the important question is: What is the difference between a real tristis and a "sub-tristis"? The author doesn't claim to possess the definitive answer to this question, but nevertheless I present a picture gallery with birds from recent autumns to illustrate some of the variation within the abietinus - tristis continuum. NSKF has not yet assessed any of these birds.

Svensson (1992) presents the following identification criteria for tristis in the hand: Supercilium, eye-lids and cheeks buffish and generally with no yellow. No yellow on underparts except for underwing coverts and axillaries. Less olive green, more brown or brownish grey on upperparts, but edges of wingcoverts, wingfeathers and tailfeathers tinged olive-green. Rump tinged olive-green too, and a slight green tinge on the back and scapulars in many, but no green hue on mantle, nape or crown in `classical` tristis. Legs and bill blackish. Size and wing-formula much as in abietinus, though P2 rarely as long as = 6/7. Trapping the bird is probably necessary to identify a suspected tristis with any certainty, since the plumage characters separating a real tristis from a grey "sub-tristis" is very subtle. Birds with even the finest yellowish hue on supercilium, eye-lids or underparts except underwing, or green cast on crown or mantle, should not be referred to as tristis, but rather as "sub-tristis".

If possible a hand-held eastern Chiffchaff should be documented from multiple angles. At least good profile pictures should be supplemented with pictures of the upperparts. See for example the bird from Titran 16. October 2003. I addition wing-length and wing-formula are important supporting characters.

References:
Svensson, L. 1992. Identification Guide to European Passerines. Stockholm. 368 pp.