A case study from Scilly, October 2011


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A 'case study' involving a Siberian Chiffchaff and a 'grey and white' (Bonelli's-like) Chiffchaff present at same time on St Agnes, Scilly
(with a note on so-called 'plumage morphing)

During October 2011, Chiffchaffs reaching St Agnes, Isles of Scilly, presented an instructive case-study in the variation among Chiffchaffs of presumed eastern origin, in the appearance of a classic tristis, and the confusion which genuinely 'grey and white' Chiffchaffs continue to present. During the third and fourth weeks of the month, Chiffchaffs reaching the island displayed a very wide range of plumages, with very significant differences in the amount of olive and yellow in the plumage and in their overall 'paleness'.

On October 16th and 17th reports of 'pale Chiffchaffs' came from both the Troy Town and Lower Town areas, with suggestions in each case that the birds were 'Siberian Chiffchaffs'. However, the appearances of the two were radically different. Fortunately, both remained for several days, which enabled observers to make careful assessments of plumage and calls, though both called rather infrequently.

The individual at Troy Town proved to be a classic (even 'ultra-typical') Siberian Chiffchaff Phylloscopus collybita tristis, in terms of 'brown and buff' plumage and evenly-pitched, plaintive call. Very much in contrast, the Lower Town individual proved to be an archetypal 'grey-and-white' Chiffchaff, with plumage hues very reminiscent of a Bonelli's Warbler P. orientalis / P. bonelli and with at least some calls typical of abietinus (and collybita). It (or an identical individual) later relocated to ivy clothing a wall near the Parsonage, where very detailed observations and close-up photographs were enabled.


The Siberian Chiffchaff

The individual at Troy Town was first observed on October 16th by Derek Pratt, whose attention was drawn by the unfamiliar call, and he alerted Steve Addinall and Ken Shaw. From the information conveyed by Derek, Ken and Steve suspected that the bird might well be a Siberian Chiffchaff. Steve, who has a particularly good ear, quickly picked out the call and immediately equated it with recordings of tristis to which he had listened previously. He likened the call to that of a Dunnock rather than to the often-cited Bullfinch, which agrees with my own interpretation. Subsequently, the bird frequently fed out in the open on the ground in one particular field, which enabled prolonged and detailed observations by many birders. It remained until the 19th and photographs were taken by various observers. I am indebted to Robin Hemming for permitting me to include three of his excellent images, which were taken in soft, shaded, late-afternoon light on October 17th using a high-quality DSLR, this guaranteeing good colour balance. A fourth image, one of my own, was taken the following day using a 'bridge' camera. It is of lesser quality but is included to illustrate that, despite two very different cameras used on different days, the variation in hues is only rudimentary and the over-riding appearance is consistent.

The Siberian Chiffchaff displayed no olive in the crown and mantle and no yellow away from the bend of the wing. In addition to these 'starting point' features for tristis, it also displayed a distinctive grey-brown hue to the crown and mantle and a warm buff wash to the supercilium, upper eye-ring, cheeks, and the sides of the breast and flanks (Plates 1a to 1d). This suffusion was richest on the fore-supercilium and cheeks and, in sunny conditions, it could take on a rusty or even pinkish hue.  The characteristic grey-brown and buff hues in the plumage recalled Mountain or Caucasian Chiffchaff P. lorenzii, though the supercilium was strongly buff-suffused rather than whitish. The legs and bill were 'densely' black and the latter rather delicate. It required considerable patience to hear the bird call but, when it did so, the call was again classic tristis: a monosyllabic, evenly pitched 'eeep' or 'iiihp', fading at the end and with a characteristic plaintive quality.

Siberian Chiffchaff, St Agnes, Scilly, October 2011

Plate 1a

© Robin Hemming

Siberian Chiffchaff, St Agnes, Scilly, October 2011

Plate 1b

© Robin Hemming

Siberian Chiffchaff, St Agnes, Scilly, October 2011

Plate 1c

© Robin Hemming

Siberian Chiffchaff, St Agnes, Scilly, October 2011

Plate 1d

© A. R. Dean

Compare the images above with photographs in the Gallery, which include unequivocal Siberian Chiffchaffs in Siberia and Kazakhstan. See also photographs of a Siberian Chiffchaff with distinctly 'brown' upperparts trapped at Languard in Suffolk, in November 2011. This was the first in Britain confirmed to have tristis mtDNA (not a guarantee of thoroughbred tristis but useful supplementary data).


The 'grey-and-white' Chiffchaff

On October 16th, the same day as the Troy Town tristis was discovered, a 'very pale' Chiffchaff was reported near Lower Town, with suggestions that it was a Siberian Chiffchaff. When other observers caught up with this bird it was immediately evident that it did not have the necessary feature-set of a diagnosable Siberian Chiffchaff. Rather, it was a good example of a 'grey-and-white' Chiffchaff, the identity of which are still much debated. During prolonged observations on October 16th and 17th, this individual called several times, uttering both a rising 'hweet', typical of abietinus/collybita, and also a rising and falling, sharply inflected 'sweeoo'. At no time did it use a tristis-like call. On October 27th and 28th, an identical (probably the same) individual was seen at very close range (down to 3 or 4 metres) near the Parsonage and also behind the old observatory buildings. For observers for whom nominate collybita is the norm, it was indeed an arresting individual, with a dominant pale grey component to crown and mantle, markedly white underparts, bright green fringes to remiges and rectrices, and paler fringes to tertials. At such close range it was determined that there were, in fact, fine olive streaks in the crown and mantle and a yellow tinge to the white ground-colour of the well-contrasting upper section of the eye-ring (Plate 2f). It was viewed in various light conditions light conditions (from semi-shade to bright sunlight) and in various surroundings (perched in bright green vegetation to right out in the open and even on the ground on a concrete surface). There were the inevitable slight variations in hues accordingly, yet the strikingly grey-and-white body plumage and bright olive-green (even yellow-green) fringes to the remiges were consistent in its appearance, in all these circumstances, and during observations totalling well over two hours - see Plates 2a to 2e. The face pattern (with well-defined eye-stripe and broken eye-ring), short primary projection and slight, all-dark bill were clearly those of a Chiffchaff.  However, the plumage hues of Chiffchaffs which are so strikingly grey-and-white (in a UK context), and often with bright olive fringes to the remiges, could be confused very easily with those of one of the Bonelli's Warblers  P.bonelli / P. orientalis (see additional comments and images in the main text). On October 28th it was heard to call, using the familiar, rising 'hweet' typical of collybita/abietinus.

On the basis of their pale and grey, non-collybita-like appearance, such individuals have often been claimed as tristis but, in fact, they are phenotypically rather distant from a core-range Siberian Chiffchaff. Morphologically, they recall  less-colourful examples of abietinus, particularly from the east of that form's range (Kees Roselaar and Lars Svensson in litt.). See Plate 5 below, Plates 7, 8 & 9 in the main text and some of the photographs of Chiffchaffs on the breeding grounds in Finland). On the Scilly individual, a rather long-looking tail also recalled abietinus. Such genuinely 'greyer' Bonelli's-like Chiffchaffs occurring in the UK, including the Scilly individual, may give an abietinus (& collybita) call, though others have been reported using a tristis-style call. It should be noted that some Chiffchaffs from the Middle East and Caucasus regions may combine such 'grey and white' livery with a tristis-like call (see comments in main text and also examples from Iran <here>). It has now been established that Chiffchaffs bearing brevirostris / caucasicus mtDNA have reached Germany and the Netherlands (van der Spek & de Knijff 2021). Thus, the Middle Eastern races of chiffchaff must certainly be considered when an enigmatic chiffchaff is encountered in western Europe.


A note on so-called plumage 'morphing'

Some 'third hand' commentators have attempted to imply that such 'grey and white' Chiffchaffs are invariably no more than typical tristis 'morphed' by bright light. This is illogical. The appearance of any bird is influenced by the prevailing light conditions and plumage hues can  be diluted considerably in overly bright light. On several occasions, photos showing the same Siberian Chiffchaff exhibiting, firstly, typical tristis hues and, secondly, paler and greyer appearance have been published, with the implication that this demonstrates that grey, Bonelli's-like Chiffchaffs are just an optical illusion and a result of so-called 'morphing' owing to adverse light. However, the use of the word ‘morphed’ (which is itself a misplaced use of the word ‘morph’) has been applied precisely because it relates to a transient appearance, which has temporarily distorted the appearance of a chiffchaff which at other (and more enduring) times has shown typically tristis-style livery. That is the reason why these observers have known that the birds involved in their purported 'morphing' episodes were not genuinely ‘grey and white’ – this was a temporary effect. Too often, after the event, looking at a single photo captured in a fraction of a second supplants careful observation of the enduring appearance in the field. Even worse, not infrequently the 'paler' images are evidently over-exposed or have 'white balance' errors and in these cases the paler appearance is a photographic artefact rather than a genuine observation by eye. Genuinely 'grey and white' Chiffchaffs are confirmed by prolonged observations in varying light conditions and supported by long series of photos, taken by more than one observer and portraying a consistent appearance over a long timeframe. It is worth noting at once that the classic tristis and the 'grey and white' Chiffchaff on St Agnes were present on the same small island at the same time and both were watched over several hours and on more than one day, from various angles and against various backgrounds. They were photographed by several different photographers using different models of camera. At all times and in all circumstances the appearance of each and the differences between them were consistent and sustained. Whatever the identity of these ‘grey and white’ individuals, it is clearly irrational to suggest that they are some kind of 'permanent' optical illusion. It is an obvious non-sequitur to suggest that, because typical tristis may under certain circumstances appear temporarily paler and greyer, therefore genuinely ’grey and white’ chiffchaffs do not exist. Anyone dismissing out-of-hand the reality and significance of relatively 'grey and white' Chiffchaffs, and failing to document them comprehensively, is missing an opportunity to advance understanding of the true diversity among the Chiffchaff complex.


 

Chiffchaff with 'grey-and-white' Bonelli's-like plumage

Plate 2a.

 Chiffchaff with 'grey-and-white' Bonelli's-like plumage

Plate 2b.

© A. R. Dean

Chiffchaff with 'grey-and-white' Bonelli's-like plumage

Plate 2c.

© A. R. Dean

Chiffchaff with 'grey-and-white' Bonelli's-like plumage

Plate 2d

© A. R. Dean

Chiffchaff with 'grey-and-white' Bonelli's-like plumage

Plate 2e.

© A. R. Dean

 'Grey-and-white' Chiffchaff with yellow tinge in eyering

Plate 2f. Enlarged detail. Note the well-contrasting upper eyering, with an evident yellow tinge.

© A. R. Dean


Chiffchaff, grey-and-white type, Scilly, Oct 2011

Plates 3a & 3b.

© A. R. Dean (upper photos) & Chris Turner (lower photos)


Comparative images of Siberian Chiffchaff and 'grey and white' Chiffchaff

Plate 4. Siberian Chiffchaff compared with 'grey and white' Chiffchaff, Scilly, October 2011. The plumages of these two are clearly divergent.


'Grey and wte' Chiffchaff, Scilly, c.f. grey example of abietinus, Finland

Plate 5. 'Grey and white' Chiffchaff, Scilly, October 2011 compared with abietinus, Finland, September 2008. The plumage hues of these two are clearly convergent.


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