A case study from Scilly, October 2011


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A 'case study' from Scilly, involving a distinctly brown tristis and a 'grey and white' (Bonelli's-like) Chiffchaff

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. In view of some of the exaggerated claims in internet discussions about 'plumage morphing' (see below), it is worth noting at once that, during very prolonged observations over a period of days, the appearance of each remained consistent and profoundly distinct.

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 calls typical of abietinus (and collybita). It (or a near-identical individual) later relocated to ivy clothing a wall near the Parsonage, where very detailed observations and close-up photographs were enabled.

Thus, with the concurrent presence of a 'brown-and-buff' tristis giving the classic Siberian Chiffchaff call, and a 'grey-and-white' Chiffchaff - originally claimed as tristis but lacking the characteristic hues and giving a call matching abietinus/collybita -  many of the elements of the 'tristis issue' were encapsulated on this small island during mid-October 2011.


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 proved to be an individual with exceptionally well-developed 'brown and buff' hues. It remained until the 19th and photographs were taken by various observers. As the tristis fed frequently on the ground, the neutral grey of the soil gave full emphasis to the brown and buff hues, which can easily become diluted when a bird is viewed against the sky or in overly severe light. 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. 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, 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 Siberian Chiffchaffs with distinctly 'brown' upperparts trapped at Ottenby Bird Observatory, in Sweden, in early November 2011 and at Languard in Suffolk, in November 2011. The latter was confirmed to have tristis mtDNA (not a guarantee of thoroughbred tristis but useful supplementary data).


The 'grey-and-white' Chiffchaff

On October 16th 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, a similar (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 slight yellow tinge to the upper part of the eye-ring (Plate 2e). There were the inevitable slight variations in hues depending upon posture, light conditions (from semi-shade to bright sunlight) and the bird's surroundings (perched in bright green vegetation to right out in the open and even on the ground on a concrete surface). 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 very easily be confused 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 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 lit.). 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. In my own experience, genuinely 'greyer' Bonelli's-like Chiffchaffs, including the Scilly individual, also give an abietinus (& collybita) call, though others are claimed to have given a tristis-style call. (That such 'grey' individuals can give collybita / abietinus style calls has been questioned but see Casestudy 3, which demonstrates unequivocally that even Chiffchaffs with well-defined tristis/'fulvescens'-like plumage features (e.g. tan-brown and rusty-buff hues) can employ abietinus/collybita calls persistently and exclusively. Clearly, call provides a guide but not an infallible diagnosis.)

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, showing yellow tinge in upper part of eyering.

A. R. Dean


'Plumage morphing': a distraction and not an explanation

Despite close, careful and prolonged attention, fully confirming the 'grey and white' livery of such Chiffchaffs, and despite that at least some individuals call as abietinus/collybita, there are those who have continued to maintain that such Chiffchaffs are 'brown and buff' tristis in which the colours have been affected by adverse light conditions and have 'morphed' into a 'grey and white' livery. Thus, a few words on this issue are warranted.

The appearance of Chiffchaffs (and all species) certainly varies with light conditions, as I have long emphasised (see discussion in the Gallery). 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. However, such instances rarely if ever discuss the duration of the 'morphed' appearance in comparison with the typical appearance (the truth is that strongly 'morphed' appearances are generally fleeting). It is a complete non-sequitur to suggest that, because tristis may look paler in brighter light, genuinely grey Chiffchaffs do not really exist! Photos which suffer from colour loss (photographic 'burn out') are generally self-evidently over-exposed, too strongly lit from a particular angle, or suffering from other colour artefacts. Photos taken at long range are particularly subject to colour loss or distortion and will rarely capture important colour nuances. Images capturing a fleetingly misleading appearance cannot be compared with long series of photos taken at close range, showing consistent and well-balanced colours, lighting and feather-detail, and which illustrate an appearance which has been established by prolonged observations in the field. The images above show the St Agnes individual in a variety of postures, surroundings and light conditions. There are slight variations correspondingly - a little colder here, a little more olive there - yet its fundamental appearance remains the same. Note also the natural look of the surrounding vegetation (this is nearly always not the case in photographically 'morphed' images). Additionally, different cameras can often produce rather different colour impressions. Below are two sets of images of the St Agnes Chiffchaff : one my own, taken with a 'bridge' camera; the other higher resolution DSLR images by Chris Turner (to whom many thanks). They show the bird in comparable postures. Again, there are subtle differences (slightly warmer, slightly colder, respectively) but both sets of images show a consistent 'grey and white' livery with no resemblance to the 'tan brown and buff' livery of a core-range tristis.

Chiffchaff, grey individual, Scilly, October 2011

A. R. Dean

Chiffchaff, grey individual, Scilly, October 2011. Chris Turner.

Chris Turner

Plates 3a & 3b. Same 'grey and white' Chiffchaff photographed by two different photographers (and using different camera models). Scilly, October 2011.

On St Agnes in October 2011, a 'brown and buff' tristis and a 'grey and white Bonelli's-like' Chiffchaff' were present at the same time. Although not together, each maintained its distinctive appearance during several hours of observation in comparable light conditions. At no time was there other than minor variation in the appearance of each individual and at no time did their appearances converge. See Plate 5 below, Plate 5 in the main text and Plates 7 & 8 in the main text The basic appearance of 'grey and white Bonelli's-like' Chiffchaffs is fully established and documented, has clearer plumage affinities with greyer abietinus diagnosed in Scandinavia than with mainstream tristis and cannot be 'explained away' by raising the spectre of 'colour morphing'.


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

Plate 4. Siberian Chiffchaff compared with 'grey and white' Chiffchaff, Scilly, October 2011


'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


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