Identifying ‘Siberian’ Chiffchaff Phylloscopus collybita tristis

in Northumberland

by

Colin Bradshaw

2008 saw the British Birds Rarities Committee (BBRC) undertake an exercise in which they tested assessment criteria for the identification of ‘Siberian’ Chiffchaff P. c. tristis and attempted to ascertain whether the form was a scarce migrant or a genuine rarity. The final paper is soon to be published but, with the tristis season upon us and claims of ‘Siberian’ Chiffchaff from Northumberland already on the internet, perhaps it is time to review the identification criteria. The two photos below taken by Colin Pears, who initially thought them to be the same bird, on  Holy Island in October 2009 show the problem. The first (left hand) looks really good for tristis whilst the other virtually excludes it. However, it was discovered that a nominate Chiffchaff P.c. collybita would occasionally appear exactly where the ‘Siberian’ was performing causing some head-scratching all round!

‘Siberian’ Chiffchaff P.c. tristis    (above)

Holy Island, Northumberland  October 2009

Nominate Chiffchaff P.c. collybita     (right)

Holy Island, Northumberland  October 2009

(photos  C. Pears)

The key criteria are set out below. The important thing to realise is if the bird doesn’t call then you need to get ALL of the 6 visual criteria for acceptance. This requires excellent, prolonged views, preferably in different light conditions and ideally supported by photos.

Chiffchaffs of the tristis form are distinctive birds but they are NOT striking – they are rather subtle birds. On two occasions I have seen amazing-looking birds in Tynemouth. Both have been grey above, silver below and had an obvious green wing panel. They also showed a cracking silvery supercilium. But for the head pattern, these birds looked more like Bonelli’s Warblers sp. Phylloscopus bonelli sp. and both had a piping call. However, on current criteria, neither of these were P. c. tristis although no-one seems to be sure exactly what these grey and silver birds are.

Call is important in the identification of tristis and needs to be clearly described or sound recorded to prevent confusion with ‘Scandinavian’ Chiffchaffs P. c. abietinus. Some spring birds may sing and it is a distinctive song. However, once again it would need to be well-described  or preferably sound recorded.

The Criteria:

1. Absence of olive in the crown and mantle

2. Presence of a grey-brown or pale brown hue in the upperparts

3. Absence of yellow away from the underwing

4. Presence of warm buff in the supercilium and ear-coverts

5. Presence of buff at the breast-sides/flanks

6. Very black-looking bill and legs

7. A thin, piping monosyllabic Bullfinch-like or Dunnock-like call

8. A song markedly different from western Chiffchaff’s 

9. A different moult strategy

Absence of olive in the crown and mantle

Presence of a grey-brown or pale brown hue in the upperparts

This assessment is difficult to develop unless you are aware of the problems of the term olive. In the context of tristis it means grey-green. These are not green birds, they are brown or grey-brown birds. If you are seeing any green or grey-green tones on the upperparts you are not looking at a tristis. If you aren’t able to judge this, you didn’t see it well enough to claim a tristis.

Absence of yellow away from the underwing

Presence of buff at the breast-sides/flanks

Any yellow in the underparts away from the bend of the wing excludes tristis. Once again care is required as these almost always show a sullied pale brown or buff on the flanks and even cream on the throat but any frankly yellow tones means you are not looking at a tristis. Birds with completely clean flanks are not likely to be tristis either. If you aren’t able to judge either flank colour or underpart tones, you didn’t see it well enough to claim a tristis.

Presence of warm buff in the supercilium and ear-coverts

For me this is probably the clincher when I’m assessing photographs. Consistently, photos of tristis show a warmth over the supercilium and especially on the ear coverts. This can be very subtle on the supercilium but, on the cheeks, can even show as a pale rusty patch. I find supercilium tone difficult to assess in the field so this is a feature that photos are especially useful for.

Very black-looking bill and legs

Chiffchaff has black looking legs anyway but on tristis the bill is all black, or with a very small patch of pale at the base of the lower mandible, and the legs tend to look jet black and very spindly.

A thin, piping monosyllabic Bullfinch-like or Dunnock-like call

This is difficult. There are many late autumn Chiffchaffs that have an unusual call. Chris Knox, Mike Hodgson and I had a couple of birds at Tynemouth in the last week of October 2009 and their call was very different from the standard di-syllabic “hu-itt” of nominate Chiffchaff P. c. collybita. It was a high-pitched, slightly down-slurred peep which is likely to be the call classed as the most frequent ‘alternative’ call of abietinus which is a downward-inflected ‘sweeoo. It wasn’t the near-monosyllabic ‘eeep’ or ‘iiihp’ on an even pitch, slightly ‘off-key’ and with a plaintive quality, characteristic of tristis. Because of the potential both for ‘wishful-hearing’ and our often slightly sloppy way of recording (i.e. writing down) bird calls, there is huge potential for inaccuracies in both the transcribing and assessment of call

A sound recording of P.c. tristis call, made by Ian Mills of a bird at Lynemouth in January 2002, is available at this link

For comparison a sound recording of nominate P.c. collybita call, made by Mike Hodgson of a bird at Holywell Pond in early November 2009, is available at this link

A song markedly different from western Chiffchaff’s 

The song is much more varied and melodic than that of abietinus and nominate collybita. It includes characteristic notes with ascending modulations, which are absent from the typical Chiffchaff. There is a disyllabic structure and a typical song-phrase which Alan Dean has annotated as: ‘chivvi-tee, chooee, chivvi-tee, chooee-tee, chivvy’.

A different moult strategy

One other feature may be useful although the jury is still out on this; tristis  appears to moult a lot later than nominate and many are in heavy moult in March-April. Thus a Chiffchaff with a musical and unusual song which, in spring, is still in heavy moult, is highly likely to be ‘Siberian’ Chiffchaff.

The following photos of ‘Siberian’ Chiffchaff P.c. tristis were taken in India in November and March. An additional photograph of a bird at present Lynemouth, Northumberland in January 2002 is also included for comparison.

‘Siberian’ Chiffchaff P.c. tristis   Pangot, India   March (C. Bradshaw)

‘Siberian’ Chiffchaff P.c. tristis   Bund Buretha, India    November (C. Bradshaw)

‘Siberian’ Chiffchaff P.c. tristis   Lynemouth, Northumberland   January 2002   (videograb J. Steele)

However, these criteria can be difficult to use even in ideal conditions. Here is a photograph of a bird trapped in Norway showing a warm supercilium and rusty cheek patches and a lack of yellow but which seems to show quite marked green tones in the upperparts. Is this an intergrade, a P.c. abietinus, or just an odd P.c. collybita?

Chiffchaff  Phylloscopus collybita   Molen, Norway   September 2008             (M.S. Hodgson)

Finally, here is photograph of a nominate race Chiffchaff P.c. collybita taken in spring in Northumberland.

Nominate Chiffchaff  Phylloscopus collybita collybita   Bamburgh   April 2007   (M.S. Hodgson)

Because of all the potential difficulties associated with correctly identifying ‘Siberian’ Chiffchaffs in Britain, the standard of evidence required to accept records at a county level should be similar to that provided for this record of a bird found at Newbiggin  in November 2008.

Acknowledgements

Thanks are due to Alan Dean and Jimmy Steele for their useful input and comments and to Colin Pears, John Malloy, Ian Mills and Mike Hodgson for additional audio and photographic material.

November 2009