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'Siberian Chiffchaff' Phylloscopus collybita tristis: discussion and photo gallery. |
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Updated, November 2011.
Parts of this article are based upon: Dean, A. R. & Svensson, L. 2005. 'Siberian Chiffchaff' revisited. British Birds 98: 396-410; and: Dean, A., Bradshaw, C., Martin, J., Stoddart, A. & Walbridge, G. 2010. The status in Britain of 'Siberian Chiffchaff'. British Birds 103: 320-338. These publications should be consulted for further details.
The Common Chiffchaff Phylloscopus collybita has a broad distribution across Europe and east to Siberia, with six subspecies currently recognised by most authorities. Broadly speaking, the nominate form collybita of western Europe is replaced by abietinus in eastern Europe and by tristis in Siberia. From further south in Europe, in Turkey and in Central Asia brevirostris, caucasicus and menzbieri have been described. The ‘chiffchaff complex’ is completed by three further closely-related species of southerly distribution: Iberian Chiffchaff P. ibericus, Canary Islands Chiffchaff P. canariensis and Mountain Chiffchaff P. sindianus. The taxonomy and identification of the ‘chiffchaff complex’ was discussed by Clement, Helbig and Small (1998).
The form tristis is frequently referred to as ‘Siberian Chiffchaff’ but, even following studies of mitochondrial DNA, its taxonomic status and whether it warrants recognition as a separate species remain unclear (Helbig et al. 1996). The taxonomy and diagnosis of ‘Siberian Chiffchaff’ have long been beset by confusion and divided opinion, and uncertainty still surrounds both its systematic and morphological limits, while the extent to which vocalisations are diagnostic is also contested. The taxonomic and plumage limits of tristis were considered in detail by Dean & Svensson (2005), who discussed at length the issue of 'fulvescens' from the West Siberian Plain.
East of the Yenisey, the plumage of tristis is broadly consistent, as described by Svensson (1992). It lacks yellow entirely away from the underwing coverts, the axillaries and the marginal coverts near the bend of the wing, and lacks olive on the crown and mantle. The upperparts are grey-brown to drab-brown while the underparts are off-white, with a rich buff suffusion of variable extent on the breast and flanks. Rich buff also infuses the supercilium and the ear-coverts, where it can assume a rusty-buff hue. The scapulars, lower back and rump show limited olive streaking, while the remiges and rectrices are edged with olive. The bare parts are somewhat less consistent in appearance but most individuals have a relatively slight bill which is predominantly black while the legs and upper surface of the feet are also quite intensely black. The plumage of east Siberian tristis recalls that of Mountain Chiffchaff P. sindianus lorenzii (sometimes called Caucasian Chiffchaff), though the latter has less obvious olive fringes to the flight feathers and a whiter and more striking supercilium, which frequently bridges the forehead. An analogy between the basic plumage hues of tristis and those of Booted Warbler Iduna calligata might also be drawn.
The following sections examine in detail some of the issues surrounding the topic of 'Siberian Chiffcaff', including a number of important provisos. However, it should not be forgotten that a core-range tristis remains identifiable with a good deal of confidence by a combination of :
no olive in crown or mantle
no yellow away from underwing and bend of wing
characteristic hues of grey-brown in crown & mantle and buff wash on supercilium, cheeks & sides of breast & flanks (often with a 'rusty' tinge)
densely black bare parts (though this somewhat variable)
unequivocal delivery of the classic evenly-pitched, monosyllabic and plaintive call ('eeep' or 'iiihp')
In the West Siberian Plain, between the Urals and the Yenisey, tristis has less consistent appearance. Some individuals match the ‘classic’ birds from east of the Yenisey but others have very slight traces of yellow on the underparts, the supercilium and the upper part of the eyering, and traces of olive in the crown and mantle (Svensson 1992). The fringes to the remiges tend to be a little brighter, olive-green, while the plumage overall is sometimes slightly paler and greyer and with less extensive buff on the underparts. Since Sushkin (1925), Chiffchaffs from this region have been given the name ‘fulvescens’, following from the type description of Severtzov (1873), though this was based upon a series of migrants collected in Central Asia. Severtzov’s description (kindly provided and translated by Dr Vladimir Loskot, Curator of the Ornithological Department, Zoological Institute, Russian Academy of Sciences, St. Petersburg) was as follows:
‘Ficedula (Phyllopneuste) fulvescens, nob. - (Ph. tristis? Gould). Upper parts, from forehead to upper tail coverts and small wing coverts rusty-grey with olive tint, olive-brown in autumn; supercilium and under parts rather pale rufous-yellowish, brighter in autumn; cheeks not pure rusty; wings and tail feathers blackish, with olive fringes which, on coverts, cover blackish middle of feathers; small underwing coverts sulphur yellow; first primary twice as long as its coverts; 3=4=5>6>7>2>8. Male and female do not differ from each other; in juvenile birds, differing in general only in looser texture of feathers, sometimes unclear longitudinal stripes of pale sulphur yellow colour are present on the breast; in others, the breast stripes are similar but greyish (var. naevia), and then all the plumage is more greyish than usually. Bill and legs black; bill is relatively small even for a Leaf Warbler, and claws are large, especially on the hind and mid toes.’
Colour nomenclature is always problematic, especially in translation. However, interpreting ‘rusty’ as reddish-brown and ‘rufous-yellowish’ as a rich or rusty-buff with a tinge of yellow, then this description does equate with that of tristis with additional traces of olive and yellow.
In normal circumstances, the song and call of tristis are distinct from those of collybita and abietinus.
The characteristic call of tristis (here recorded in Russia) is a near-monosyllabic ‘peet’ or ‘iiihp’, predominantly even in pitch but descending and fading slightly at the end, which produces a plaintive and slightly 'off-key' quality.
Figure 1.
In sonogram, note predominantly even pitch ('flat' and horizontal trace) with just a slight downturn at the end.
The cd 'Calls of Eastern Vagrants' (Jännes 2002) also includes a particularly good and monotone example, recorded in the wintering grounds in India. The sound recalls a less sibilant and less 'tinny' version of a Dunnock's call or a higher-pitched less piping variation of a Bullfinch's call. This call is very different from the normal, upward inflected ‘hüit’ of collybita and abietinus, and is an important component in any identification of a potential tristis.
The song of tristis (here recorded in Russia by Antero Lindholm) is a fluent warble of closely-spaced and near-disyllabic notes: ‘chivvi-tee, chooee, chivvi-tee, chooee-tee, chivvy’, rising and falling and much more varied and liquid than western chiffchaff song. Sonograms of the song show characteristic notes with ascending modulations, which are absent from the typical song of collybita and abietinus.
(a) Calls
Van den Berg et al (2009) went as far as to suggest that call is diagnostic of tristis. This was based upon Chiffchaffs observed on migration in Kazakhstan, which were reported to show wide plumage variation but to call and sing consistently like tristis. The authors contended that hybridisation between tristis and abietinus occurs rarely 'if at all', so that even individuals with apparently intermediate features were thoroughbred tristis if they uttered a tristis type call.
However, using a combination of morphological, vocal and mtDNA data, Marova et al (2009, and in prep) concluded that hybridisation in the zone of overlap between tristis and abietinus, west from the southern Urals, was 'proven'. The evidence as presented is strongly indicative but whether the case is yet strictly 'proven' is open to debate, since the genetic studies so far have involved mtDNA (which is inherited only from the 'mother'). Current analyses using AFLP analysis will provide a conclusive answer one way or the other. Meanwhile, there is clearly a difference of opinion here but, if hybridisation is established, then some hybrids will doubtless give a call indistinguishable from that of thoroughbred tristis.
Additionally, calls which resemble or even match the typical call of tristis are encountered from Chiffchaffs in the Middle East (Lars Svensson & José Luis Copete in litt, and see for example Dubois & Duquet 2008).
More problematically in a UK and west European context, confusion can arise between the classic tristis call and so-called 'alternative calls' given regularly by abietinus and collybita. Such 'alternative' calls are very different from the standard, rising ‘hüit’ or 'hweet' call and can easily lead to confusion. Among documented 'alternative' calls, perhaps the most frequent reference is to a strongly inflected 'sweeoo', which rises then falls rather sharply in pitch, creating a disyllabic sound, while the sonogram has the shape of a circumflex or an inverted 'v'. This type of call has been associated with 'eastern abietinus' (see for example Jännes 2002) but such a call is also to be heard from collybita and western abietinus, at any time of the year but especially during the late summer and autumn. It can recall one call of Thrush Nightingale Luscinia luscinia.
Despite the disyllabic quality, the fact that the 'sweeoo' type of call is rather abrupt, and has start and end frequencies which are closer than in the rising 'hweet' call, means that it can have a 'flatter' sound than the familiar 'hweet'.
Here is a composite recording which compares the 'sweeoo' call of a collybita (UK) with the classic 'eeep' call of tristis (Russia). A sonogram of the two calls is below (Fig. 2):
Figure 2.
In such a direct comparison, the 'alternative' call of collybita is more abruptly and strongly inflected and has a 'brighter' timbre, while the call of tristis is straighter and is more plaintive and slightly 'off-key'. However, it is easy to understand how the two might be confused when heard in isolation, at distance, or by someone not thoroughly familiar with the call of tristis.
Conversely, not all calls given by tristis match the ideal or classic 'straight' structure described above. Calls attributed to tristis may also have a slight rise and fall in pitch on occasions, and could be transcribed as a shallow 'sweeoo' rather than a truly evenly-pitched and monosyllabic 'eeep' or 'iiihp'. Here is a composite recording which compares two calls attributed to tristis: a classic, straight 'iiihp' call from Russia and a shallow 'sweeoo' call from India. A sonogram of the two calls is below (Fig. 3).
Figure 3.
Generally, compared with the 'sweeoo' calls of collybita and abietinus, the shallow 'sweeoo' call of tristis has a much more gentle transition from rising to falling pitch and a distinctly 'shallower' frequency range and lower peak frequency. The sonogram has the shape of a shallow inverted 'u' rather than an inverted 'v'. See Antero Lindholm & Anneka Forsten's website for a variety of such calls. Thus, a call which has the sound of a shallow 'sweeoo' does not necessarily exclude tristis. A recording and sonogram might provide structural clues but, clearly, attributing such calls to a given taxon by ear alone will be especially problematic.
Here is a composite recording which compares a 'sweeoo' call given by a nominate collybita in Warwickshire in July 2011 (my own recording) with a 'sweeoo' call given by a tristis in India in December 2007, recorded by Antero Lindholm. A sonogram of the two calls is below (Fig. 4).
Figure 4.
In such a direct comparison and from the sonograms, the former has quite an abrupt transition while in the latter it is much smoother, while there is a difference in peak frequency and frequency range, which creates a different timbre. Yet, both are clearly ‘sweeoo’ calls to the ear and could well be confused if heard in isolation or in the imperfect acoustic conditions which will generally attend field encounters.
As with all subspecies, the vocabulary of tristis is liable to be varied. Listen here to the series of recordings from October 27th 2009 by Maarten Wielstra, involving a Chiffchaff which looked and sang like tristis. Some of the calls in the series are decidedly different from the classic, evenly-pitched 'iiihp' or 'eeep' call of tristis.
While the question of hybrid origin is ever-present, and confirmatory recordings from the core-range of tristis in central Siberia would be helpful, the indications are that a 'sweeoo' type call can be given by all forms of Chiffchaff. Further, alternative calls vary, with some 'sweeoo' type calls given by collybita and abietinus being truncated and less-emphatically inflected, thus sounding more like a monosyllabic 'swee'. See 'The Sound Approach to Birding' (Constantine & The Sound Approach, 2006), page 91, and listen to the call at 0:16 - 0:18 in their recording of Common Chiffchaff on CD1 track 86. Some individuals give such calls persistently. There is then a particular risk of confusion.
It has sometimes been claimed that such 'alternative' calls do not provide a source of confusion with the classic call of tristis as they are restricted to young birds in the late summer and early autumn, and are not encountered after late September. However, it is now clear that 'alternative' calls may be used at any time of the year. They have been heard during the winter in the UK (pers obs) and also in Spain, from birds with the appearance of western forms (Copete & Armada 2004). Additionally, in some years they have been heard commonly in spring from individuals in the UK and elsewhere in Europe (see separate article on this topic).
The classic evenly-pitched,
monosyllabic and somewhat mournful call of tristis ('eeep' or 'iiihp',
with a flat shape in a sonogram, thus:
) is a strong indicator but it is essential that the call is heard
clearly and that the observer is thoroughly familiar with the call of tristis.
Ideally, the call should be confirmed by sound recording and sonogram.
If hybridization is indeed quite widespread in the region of overlap between abietinus and tristis (see Marova et al 2009), then it seems likely that some hybrids will use a tristis-like call.
Although their occurrence in NW Europe is not established, it should be borne in mind that the call of some more southerly forms such as brevirostris can be indistinguishable by ear from that of tristis (Lars Svensson & José Luis Copete in litt).
The normal call of collybita and abietinus is a 'bright' and rising 'hweet', quite different from the call of tristis. However, so-called 'alternative' calls are also given regularly by collybita and abietinus and have a rising and falling frequency with an abrupt transition and a rather disyllabic sound, usually transcribed as 'sweeoo'. Despite their disyllabic quality, such calls are rather abrupt and the fact that their start and end frequencies are closer means that they can have a 'flatter' sound than the familiar, rising 'hweet'. Correspondingly, such calls can be confused with the classic, straight tristis call.
If all individuals have been
correctly diagnosed, then emerging evidence suggests that the call of
tristis does not invariably match the idealised, evenly-pitched and
monosyllabic 'eeep' or 'iiihp' but may rise and fall in frequency slightly,
thus sounding like a shallow 'sweeoo'. The transition from rising to
falling pitch is more gradual (less abrupt) than in collybita/abietinus,
the peak frequency is lower and the frequency range narrower (more
compressed). Thus, in a sonogram, the shapes of the calls recall a
shallow inverted 'u'
for tristis and an inverted 'v' for collybita/abietinus,
thus:
. However, there is some convergence in structure
and 'sound' between such 'sweeoo' calls, with a 'two-way' potential for confusion.
(b) Songs and hybridization
In the region of overlap between tristis and abietinus west from the southern Urals, ‘mixed singers’ are encountered and have been studied in depth by Marova & Leonovich (1993), Marova & Alexseev (2008), Marova et al (2009 and in prep) and Lindholm (2008). These authors also considered that some Chiffchaffs in these areas of overlap displayed plumage features intermediate between tristis and abietinus. In 'mixed singers', each song phrase comprises an intimate mixture of notes from the songs of tristis and abietinus (this should not be confused with 'song switching' or 'song imitation', where one taxon interchanges between complete song phrases of its own taxon and those of another taxon). The precise extent of the zone of overlap and ‘mixed singing’ is currently undetermined. Marova & Leonovich (1993) mapped an outline embracing a region some 1500km long by 400 km wide but, within this large area, the co-occurrence of the two forms is fragmented (Marova & Alekseev 2008 and Marova et al 2009 and in prep). Marova & colleagues and Lindholm all concluded that a combination of 'mixed singing' and intermediate plumage indicated a significant level of hybridisation, a conclusion re-affirmed by Marova et al (2009 and in prep) following DNA studies.
Marova and colleagues applied the name ‘fulvescens’ to the ‘mixed singers’ with ‘transitive’ features which they identified west of the Urals. This use of the name ‘fulvescens’, for a potentially hybrid population in a region of overlap, is different from the name ‘fulvescens’ as applied to birds from the West Siberian Plain, which is beyond the normal breeding range of abietinus. Martens & Meincke (1989) reported that the song of ‘fulvescens’ was consistent with that of tristis across it entire range but their studies did not extend west of the Urals. Thus, when Marova & Leonovich (1993) reported ‘mixed singing’ among birds which they termed ‘fulvescens’, their results seemed in conflict with those of Martens & Meincke (1989). However, the two study areas were on opposite sides of the Urals and hence geographically distinct. Clearly, confusion can arise when the name ‘fulvescens’ is applied in these two rather different contexts and, in their discussion of the conclusions of Marova & Leonovich versus those of Martens & Meincke, this ambiguity was not fully clarified by Dean & Svensson (2005) .
A region of overlap between tristis and abietinus was first documented from the southern Urals by Snigirewski. To individuals with intermediate appearance from this region he had earlier applied the name ‘riphaeus’ (Snigirewski 1931). Their appearance and taxonomy were discussed by Ticehurst (1938), though he did not believe that a formal name should be adopted for birds that he deemed to be ‘intergrades’. However, if abietinus and tristis do indeed hybridise in the southern Urals and west of the Urals, then the name ‘riphaeus’ is a useful and unequivocal name.
The normal range of abietinus does not extend east of the Urals. A significant ‘zone of overlap’ between abietinus and tristis, potentially producing first-generation hybrids and early back-crosses on a regular basis, lies only west and northwest from the southern Urals. East from the Urals, the traces of additional yellow and olive which differentiate west Siberian Chiffchaffs from ‘classic’ tristis may arise from introgression of abietinus genes into the tristis population. However, if this is the explanation, then the level of gene-flow, from beyond the current range of abietinus, must be relatively low. The region east of the Urals is not currently a true region of overlap. The relatively low level of gene flow in a ‘zone of introgression’ is distinct from that in a ‘zone of overlap and hybridisation’, as purported west from the southern Urals, where the potential for hybrids and gene-flow is significantly higher.
Hence, it seems preferable to apply the name ‘riphaeus’ to the birds with more evidently intermediate appearance and ‘mixed singing’ from the region of overlap between tristis and abietinus, west from the southern Urals. The name ‘fulvescens’ is better restricted to the population from the West Siberian Plain, beyond the current region of overlap between tristis and abietinus. Morphologically, ‘riphaeus’ as a whole is likely to include a higher proportion of individuals with evident abietinus plumage traits, while most ‘fulvescens’ are close in appearance to classic tristis. It seems likely that most 'fulvescens' are genetically close to 'classic' tristis and are perhaps best treated as a form of 'Siberian Chiffchaff'. In contrast, 'riphaeus' may well include a significant number of individuals which are genetically intermediate, as well as morphologically intermediate, and such hybrid individuals cannot be regarded as 'Siberian Chiffchaffs'. Nevertheless, the difference in appearance will be one of degree. Individual variation in the extent of intermediate characters can be anticipated in both ‘groups’ and there will be no clear-cut dividing line between ‘riphaeus’ characters and ‘fulvescens’ characters. Individuals diagnosed as Siberian Chiffchaff should match 'classic' tristis or display only marginal 'fulvescens' traits. Confident identification will also include appropriate vocalisations.
As mtDNA is inherited only via the female ('mother'), it does not provide incontrovertible proof of hybridisation. However, when supported by morphological and vocal data, it presents a very strong case (Marova 2009). Further genetic studies involving Applied Fragment Length Polymorphism (AFLP) are in progress or in active planning, for Chiffchaffs in the tristis/abietinus overlap zone (Irina Marova, V.N. Alexseev and colleagues) and for Chiffchaffs wintering in England and on migration through Kazakhstan (Greg Conway and Staffan Bensch). AFLP provides data which demonstrates the presence or otherwise of a hybrid lineage. Thus, there are now genuine prospects that the genetic foundations of 'fulvescens' and 'riphaeus' will be resolved and their appropriate taxonomic treatment established.
[There is a parallel case. In the overlap zone between Iberian Chiffchaff P. ibericus and Common Chiffchaff P. c. collybita in SW France and NE Spain, breeding is assortive (Salomon et al. 1997) but AFLP analysis has demonstrated that hybrids are more common than morphological and vocal features originally suggested and that most ‘mixed singers’ are genetical hybrids (Bensch et al. 2002). Thus, by analogy, it seems that a comparable situation may exist in the overlap zone between abietinus and tristis.]
Chiffchaffs with tristis-like features are encountered regularly in the UK, as late autumn migrants and as wintering individuals. Historically, relatively few have been trapped and examined in the hand but, in the field, many display a suite of plumage features which appears to match the criteria for tristis described by Svensson (1992). See Millington (2006) for a detailed description and well-considered comments on a tristis observed and identified in the field in Norfolk and then confirmed in the hand.
Greg Conway is undertaking a comprehensive study of Chiffchaffs wintering in England, which involves trapping a large number of individuals in southwest England. His studies are concerned with all three ‘traditional’ northerly subspecies (collybita, abietinus and tristis/'fulvescens') but he has shown that, when examined in the hand, many tristis-like individuals possessed very slight traces of 'additional' yellow or olive (Conway 2005). Thus, they matched ‘fulvescens’ rather than ‘classic’ tristis. Genetic studies are in progress to investigate the true subspecies composition of Chiffchaffs wintering in the UK.
As well as Chiffchaffs with plumage matching that of ‘classic’ tristis or that of ‘fulvescens’ from the West Siberian Plain, occasional individuals with more enigmatic features are encountered. These individuals have little or no ‘additional’ yellow or olive and in this respect they match tristis or ‘fulvescens’. However, these enigmatic individuals also lack the distinctive grey-brown or drab-brown hue to the upperparts of ‘classic’ tristis and have little or no warm buff/rusty buff in the underparts, supercilium and cheeks. They are not merely slightly paler individuals within the expected range of plumage variation anticipated within tristis and 'fulvescens'. Overall they have predominantly ‘grey and white’ body plumage, and often relatively bright and contrasting yellowish-olive fringes to the remiges. Additionally, they tend to have paler bare parts than is usual with tristis, with even a yellowish tinge to the upper surface of the feet.
The upsurge in digital photography has shown that Chiffchaffs with the evident 'brown and buff' hues characteristic of tristis are sometimes described inaccurately as 'grey and white', which can lead to confusion in discussions and also create an exaggerated impression of the frequency of truly 'grey and white' individuals. This is part of a more general problem with the variable 'colour nomenclature' employed by different observers. Phenotypically, the strikingly 'grey and white' Chiffchaffs described above are rather distant from a core-range Siberian Chiffchaff, and much closer in appearance to less-colourful examples of abietinus, particularly from the east of that form's range (Kees Roselaar and Lars Svensson in litt.). Their plumage ‘ground colours’ do not resemble Mountain Chiffchaff or Booted Warbler; indeed, in overall livery they are very reminiscent of Eastern Bonelli’s Warbler P. orientalis.
Figure 1. Composite image, showing a 'grey and white' Chiffchaff on the left in comparison with a typical 'brown and buff' tristis on the right. The 'grey and white' Chiffchaff can be related directly to the Kodak Grey Scale. The tristis has a pale grey suffusion, especially on the nape and scapulars, but its predominant ground colours are quite different, with evident and characteristic brown and buff hues. 'Grey and white' Chiffchaffs such as the left-hand individual have often been claimed as tristis but they are clearly very different phenotypically from a classic tristis such as the right-hand individual. Occasionally 'grey-and-white' Chiffchaffs have been recorded giving a tristis-like call but more often they give standard collybita/abietinus calls.
At least some enigmatically ‘grey and white’ Chiffchaffs have given a call which is like tristis. More often, however, ‘grey-and-white’ individuals utter rising 'hweet' and/or downward inflected 'sweeoo' calls, as associated with collybita and abietinus (see Vocalisations and article on variant calls). There are even occasional reports of ‘tristis-like’ Chiffchaffs switching between a ‘tristis-like’ call and a ‘collybita-like’ call but such reports are rare and there is often a question as to whether an ‘unseen’ collybita nearby might have been responsible.
The origins of these enigmatic grey-and-white individuals are uncertain (Dean & Svensson 2005, Dean 2007). It may be, however, that they do not have a single origin. Greyer examples of abietinus from the east of that form's range are almost certainly involved but others may be intergrades between tristis and abietinus from the overlap zone ('riphaeus') or even morphologically anomalous examples of tristis.
Currently, it seems wise to refrain from assigning such distinctly 'grey and white' individuals to a definite taxon, certainly in an extralimital context. It is to be hoped that on-going field and genetic studies will provide the requisite answers in due course.
A reliable picture of the taxonomic and plumage limits of tristis will emerge only after genetic studies currently in progress are concluded. However, in the meantime, the BBRC co-opted a 'tristis panel' to examine all reports of 'Siberian Chiffchaff' in the UK during the 'sample' year of 2008. The panel examined all individuals using the currently accepted 'Svensson criteria' for classic tristis, while making allowance for individuals which are clearly very like 'classic tristis' but show marginal 'fulvescens' characters. Individuals with very slight 'additional' yellow and olive are fully compatible with 'fulvescens' from the West Siberian Plain and beyond the true zone of overlap with abietinus. Although there may be some slight introgression across the West Siberian Plain, the panel concluded that 'fulvescens' (unlike 'riphaeus') is best treated as a form of tristis (as suggested by Svensson in Dean & Svensson 2005). Conversely, individuals with more evidently intermediate plumage or anomalous calls, and 'grey and white' individuals (sensu Dean & Svensson 2005), were excluded by the panel's criteria, as the origins of such individuals remain equivocal. While many questions remain to be answered, a clearer picture of the status of tristis (including 'fulvescens') in the UK has emerged. Full details have been published in: Dean, A., Bradshaw, C., Martin, J., Stoddart, A. & Walbridge, G. The status in Britain of 'Siberian Chifchaff'. British Birds 103: 320-338. The panel's investigations demonstrated that the numbers of 'Siberian Chiffchaffs' currently reaching Britain are significant. For 2008, reports of 57 individuals were submitted to the panel, of which 49 (86%) were accredited. Applying this endorsement rate to all known reports in Britain during 2008 suggested that around 120 Siberian Chiffchaffs may well have occurred during the year. Thus, Siberian Chiffchaff was confirmed as a scarce rather than rare visitor.
The report also examines in detail the issues of
morphology, vocalisations, genetics and hybridisation; the seasonal and
geographical distributions of Siberian Chiffchaffs reaching Britain; comparative
data from other European countries; and the numbers of Siberian Chiffchaffs
reaching Britain in comparison with those of Yellow-browed and Pallas's Leaf
Warblers. Reference should be made to this publication by anyone wishing to
explore the topic further.
For much useful discussion, information and clarification I am indebted to Staffan Bensch, Colin Bradshaw, Martin Collinson, Greg Conway, José Luis Copete, Philippe Dubois, Martin Garner, Hannu Jännes, Magnus Hellström, Peter Kennerley, Mike Langman, Paul Leader, Antero Lindholm, Vladimir Loskot, Irina Marova, John Martin, Richard Millington, Jelmer Poelstra, Roger Riddington, Kees Roselaar, Brian Small, Andy Stoddart, Lars Svensson, Pavel Tomkovich, Grahame Walbridge and Maarten Wielstra. For provision of excellent photographs I thank Colin Bradshaw, Martin Cade, Richard Chandler, Robin Hemming, Gabriel Jamie, Paul Leader, Richard Millington and Steve Seal. Mark Adams kindly arranged access to the skin collection at BMNH, Tring.
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Dean, A.R. 2009, updated 2011. 'Siberian Chiffchaff' Phylloscopus collybita tristis: discussion and photo gallery. http://www.deanar.btinternet.co.uk/tristis/tristis.htm.
