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'Siberian Chiffchaff' Phylloscopus collybita tristis: discussion and photo gallery. |
Parts of this item are based upon:
Dean, A. R. & Svensson, L. 2005. 'Siberian Chiffchaff' revisited.
British Birds 98:
396-410
&
Dean, A., Bradshaw, C., Martin, J., Stoddart, A. & Walbridge, G.
2010. The status in Britain of
'Siberian Chiffchaff'.
British
Birds 103: 320-338.
References to genetics are unavoidable but, in this text, they are from a non-geneticist's perspective and subject to correction.
Plate
1.
Two 'classic' Siberian Chiffchaffs Phylloscopus (collybita) tristis
Classic tristis are relatively 'colourless' or 'monotone'
rather than truly pale (as is often inferred). They lack yellow away from the
bend of the wing and lack olive in the crown and mantle.
Additionally, they have
a characteristic tan-brown hue to the upperparts and a rich buff suffusion to supercilium, ear-coverts, sides of breast and flanks,
evident here in both a spring and an autumn individual.
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. Further south three additional forms have been described : brevirostris in western and northern Turkey, caucasicus in the Greater and Lesser Caucasus and menzbieri, historically considered confined to Turkmenistan and north-eastern Iran. The form tristis is colloquially known as 'Siberian Chiffchaff' and is treated by some authorities as a distinct species. Its breeding range extends from the Mizen Basin (west of the Urals) east across Siberia to the Kolyma River. The taxonomy and diagnosis of ‘Siberian Chiffchaff’ have long been beset by confusion and divided opinion, with considerable uncertainty surrounding both its systematic and morphological limits. Investigations based upon mitochondrial DNA (mtDNA) confirmed 'genetic distance' between the currently designated forms within the chiffchaff complex and helped to clarify species boundaries. However, whether tristis warranted recognition as a distinct species remained inconclusive (Helbig et al. 1996; Clement, Helbig and Small 1998). The origins of variation in the appearance of Chiffchaffs in the west of the range of tristis have also remained contentious, attributed variously to hybridization between tristis and abietinus or to individual, clinal and even taxon-level variation. On-going genetic studies which were confined to mtDNA, which is inherited solely via the female line, led to differing interpretations. Marova et al. (2009, 2013) concluded that hybridization was widespread in the region of sympatry, while studies of migrants in the Netherlands by de Knijff et al. (2012) led to counter suggestions that the plumage of tristis was naturally more-varied than had been implied hitherto. The extent to which vocalisations are diagnostic has also been obscured by the issues of call variation within all taxa, hybridization with abietinus and the very tristis-like calls given by forms of Chiffchaff found in the Middle East and the Caucasus. More recently, techniques for examining 'whole genome sequence data' have been developed and applied to Chiffchaffs in the zone of sympatry between tristis and abietinus in the Urals and Arkhangelsk region (Shipilina et al. 2017). Significant genetic mixing between tristis and abietinus has been confirmed, with Shipilina et al. concluding that this was 'the driving force underlying trait variation' and was also implicated in vocal anomalies. The following pages explore these issues and their implications for field identification of 'Siberian Chiffchaff'.
Topics
Appendix 1. The 'type descriptions' of tristis and 'fulvescens'
Appendix 4. Historical records of 'Northern' or 'Eastern' Chiffchaffs
Appendix 5. Colour-corrected images of tristis from Dean & Svensson (2005)
Photos
Case studies
Any text discussing the appearance of Chiffchaffs is immediately beset by the issue of colour nomenclature. Several colours and shades - olive, yellow, brown, buff, grey and white - are exhibited by most Chiffchaffs to one degree or another. All subspecies of Chiffchaff vary in appearance to a degree but it is the extent and intensity of these key hues and the degree to which they are admixed that lead to a characteristic appearance for each subspecies and define the appearance of what might be termed 'classic' individuals. Hence, colour nuances are central to discussions of plumage traits in Chiffchaffs. However, the absence of a universally recognised and accepted 'colour nomenclature' adds yet further complexity to discussions of plumage colours and differences. Indeed, different observers often apply contradictory colour names to the same individual Chiffchaff while, conversely, identical colour names are often applied to two or more Chiffchaffs of quite different appearance. When discussing Chiffchaffs, it is near-impossible to avoid using the terms 'grey' and 'buff' but both of these suffer from especially diverse interpretations between different observers and this can and does lead to ambiguity and confusion.
In my own texts, I employ shorthand terms for certain colour liveries, such as 'olive and yellow', 'brown and buff' and 'grey and white'. Clearly, there is nothing very 'nuanced' about these terms and they are no more than labels of convenience. They are relative, not absolute terms, designed to indicate the key colours and shades which distinguish the Chiffchaffs to which they are applied. In a wider context, 'grey' can span any shade between white and black, as in the 'Kodak Grey Scale' below. In the term 'grey and white' livery, the label 'grey' is intended to convey a shade resembling 'pale neutral grey' in Smithe's 'Naturalist's Color Guide' or shades in the range 2 to 4 on the Kodak Grey Scale. 'Buff' is here used to designate the hue which infuses the breast and flanks of a truly 'classic' Siberian Chiffchaff (see plate 1). In this usage it lacks yellow and has a slightly 'rusty' tinge (in more detailed discussions in the text, the term 'rusty-buff' is sometimes employed). Thus, it signifies a somewhat warmer shade than is sometimes inferred by the term 'buff'. It essential that all these shorthand terms are interpreted with reference to the definitive and carefully chosen photographs from which they derive their meaning (see Plate 2 below). See also: Colour issues, 'moult & wear' and photographs .
Plate 2. A typical 'olive and yellow' collybita on the left, a typical 'brown and buff' tristis on the right and a 'grey and white' Chiffchaff in the centre (taxon much debated - see Casestudy1). Classic 'brown-and-buff' tristis lack olive and yellow in the body plumage (apart from yellow on the underwing coverts) while classic 'grey-and-white' Chiffchaffs lack the distinctive tan-brown and rusty-buff hues characteristic of classic tristis (see main text for further discussion and nuances). Chiffchaff plumages as a whole encompass a somewhat 'sliding scale' but terms such as 'brown-and-buff' and 'grey-and-white' are convenient 'shorthand' and encapsulate the relative 'colour balance' differences of archetypal forms. The image above provides a reference for the application of these terms in the texts on this site. A 'pixel map' from the mantle of each of the three Chiffchaff images above can be seen in Colour issues and photographs.
Chiffchaff plumages vary individually and a diminution of olive and yellow from west to east is frequently cited, though to what extent this is truly clinal warrants further investigation. A complete lack of yellow away from the underwing has been a defining characteristic of tristis since the type description by Blyth in 1843 (which can be examined in Appendix 1). Witherby et al. (1938), in 'The Handbook of British Birds', and Ticehurst (1938), in 'A Systematic Review of the Genus Phylloscopus', also emphasised the restricted yellow in the plumage while also noting the browner upperparts compared with abietinus. More recently, the most-frequently-cited reference to the definitive features of tristis has been the description provided in Lars Svensson's 'Identification Guide to European Passerines' (1992, 2023), often dubbed the 'Svensson criteria', which may be summarised as:
supercilium, eyelids and cheeks buffish (no yellow)
no yellow on underparts apart from axillaries and bend of wing
cheeks, sides of throat and breast tinged rufous-buff
upperparts brown or brownish-grey with no green on mantle, nape or crown
rump, edges of wing-coverts, remiges and rectrices tinged olive-green
black or blackish tarsi
small dark bill
To these morphological criteria might be added:
unequivocal delivery of the classic evenly-pitched, monosyllabic and plaintive call ('eeep' or 'iiihp')
While the deficiency of yellow and olive is fundamental, the brown component in the upperparts is also distinctive, often with a small but influential russet component, at its most distinctive producing a 'tan' or 'khaki' tinge (see HSB analyses). Equally, the buff hue to the supercilium, eye-lids and cheeks generally extends to the sides of the breast and flanks, with only the central belly and undertail coverts being rather whiter (see plate 1). Thus, the plumage as a whole has characteristic 'brown and buff ' hues. In the field, evaluation of precise hues requires that observations are extensive, are conducted at close range and in suitably neutral light conditions. In brief views or adversely bright conditions, the true hues can be diluted and lead to a misleading impression. When examined in appropriate conditions, which reveal the colours accurately, any individual which lacks these brown and buff hues entirely is unlikely to be tristis. The plumage of 'classic' tristis recalls that of Mountain Chiffchaff P. lorenzii, though the latter has even more subdued olive fringes to the flight feathers, a darker crown and a whiter and more striking supercilium, which frequently bridges the forehead.
The 'Svensson criteria' were intended to define 'classic' individuals and hence offer high 'confidence limits' in any diagnosis. However, only east of the Yenisey do all individuals conform with these morphological criteria. West of the Yenisey, while some individuals match the criteria for 'classic' individuals, others have very slight traces of 'misplaced' yellow and olive. Such individuals have become known as 'fulvescens'.
West of the Yenisey, the appearance of Chiffchaffs is less consistent. As noted by Ticehurst (1938), Russian authors including Sushkin (1925) designated Chiffchaffs from the region west of the Yenisey as fulvescens, primarily on the basis of brighter olive on the rump and the fringes to the remiges compared with classic tristis. Ticehurst suggested that individuals with such olive enhancements were to be found throughout the range (not just the west) and consequently questioned the validity of 'fulvescens'. From examination of specimens, Svensson (1992) noted that some individuals in the region west of the Yenisey match the ‘classic’ birds from farther east (as embraced by the traditional 'Svensson criteria') but others have traces of yellow on the underparts, the supercilium and often on the upper part of the eye-ring, and traces of olive in the crown and mantle. In recent literature, as well as brighter olive hues to the wing-edges and rump, the features associated with the term 'fulvescens' have come to include 'additional' or 'misplaced' olive and yellow in comparison with classic tristis, with yellow in the supercilium and upper eyering perhaps the most frequent manifestation of 'fulvescens' traits in this scenario. Candidate Siberian Chiffchaffs reaching western Europe not infrequently display such 'fulvescens' traits (see plates 3 & 4).
The name 'fulvescens' derives from the type description of Severtzov (1873), thus well before Sushkin's discussion of Chiffchaffs from the region west of the Yenisey, and was based on a series of migrants collected in Turkestan. Thus, they were not obtained from the West Siberian Plain and, although Severtzov sugested their breeding gounds might be in western Siberia, their natal origins were uncertain. See Appendix 1 for a transcription of the type description (kindly provided and translated by the late Dr Vladimir Loskot, past Curator of the Ornithological Department, Zoological Institute, Russian Academy of Sciences, St. Petersburg). There are potential ambiguities arising from linguistics and colour nomenclature e.g. the English translation of the type description results in the phrase 'rusty-yellow' for the supercilium and underparts, suggesting the presence of 'additional' yellow compared with 'classic' tristis. However, as this term is applied to the ground-colour (not an additional tinge or streaking), 'rusty yellow' in translation may well refer to the 'buff' hues found on the supercilium and underparts in all tristis-types. This likelihood is enhanced by the use of 'sulphur yellow' to describe 'unclear streaking' on the underparts of some juveniles (and also as the colour of the underwing coverts). This streaking on the underparts is described as 'greyish' in other juveniles, to which the name 'naevia' was applied. Despite these historical uncertainties, the term 'fulvescens' has now become firmly equated with Chiffchaffs differing from 'classic' tristis in the presence of traces of 'additional' olive and yellow, while their designated origin is the region between the Urals and the Yenisey. As specimens from the now-designated breeding range of 'fulvescens' (primarily the West Siberian Plain) are limited (Shirihai & Svensson 2018), a more-comprehensive determination of the features (morphological and genetic) and the variability of chiffchaffs from the region between the Urals and the Yenisey is still required, including just how far east traces of 'additional' yellow are encountered. See also Appendix 2 for a discussion of the geographical distribution of 'fulvescens' as treated in some earlier texts and the confusion with chiffchaffs now designated as menzbieri.
© A. Warr
Plate 3. Siberian Chiffchaff with 'fulvescens' traits, Powick, Worcs, February 2015
The 'Siberian Chiffchaff' in Plate 3 shows the 'tan-brown' upperparts, buff suffusion on underparts and warmer buff ear-coverts matching a 'classic' tristis but the yellow tinge
to the upper eye-ring, prominent yellowish-olive fringes to remiges and perhaps the extent of the pale base to the bill are all 'fulvescens' traits as the term is now interpreted.
Compare this individual carefully with those in Plate 1.
Full details of the Powick indivdual, and a more 'classic' individual also present at the site, can be found on Andrew Warr's blog <here>.
Plate 4. Two Siberian Chiffchaffs, left-hand individual displaying 'fulvescens' traits
Both individuals in Plate 4 show the characteristic
'brown and buff ' hues of Siberian Chiffchaff but, in the Powick individual, note the presence of
distinct yellow tinge in upper eye-ring and evident
yellowish-olive fringes in the visible 'shoulder' area.
Also the pale base to the bill, though is not exclusive to 'fulvescens'.
The origins and implications of 'fulvescens' traits have been the subject of debate for many years. A long-standing opinion is that traces of 'additional' or 'misplaced' olive and yellow arise from introgression from abietinus, as the ranges of the two forms are contiguous and, indeed, overlap in an area west and north from the Urals. However, discussions of introgression, hybridization and character variation across the range have been hampered by a widespread tendency to apply the name 'fulvescens' indiscriminately to all tristis-like Chiffchaffs differing from the 'classic' profile, whether from the region of sympatry around the Urals or from the allopatric West Siberian Plain. The potential for widespread hybridization, with a significant number of F1 hybrids and early backcrosses, lies only in the sympatric region. A low level of introgression may extend east across the allopatric West Siberian Plain but the levels of genetic mixing in the two regions are not comparable and the appropriate taxonomic treatments may also differ. Thus, to facilitate discussion, the name 'fulvescens' should be used explicitly to refer to those individuals from the allopatric region between the Urals and the Yenisey, which match classic tristis closely apart from slight 'additional' olive and / or yellow, often detectable only in the hand or in the highest-fidelity digital images. F1 hybrids and early backcrosses from the sympatric region around the Urals, frequently (but not inevitably) displaying more evidently intermediate morphology, are better referred to as 'riphaeus'. Ticehurst (1938) appreciated the distinction and used the two names in this sense colloquially, while noting that he did not advocate formal names for individuals which he regarded as variants of tristis ('fulvescens') and hybrids between tristis and abietinus ('riphaeus'), respectively. Clearly, F1 hybrids and early backcrosses ('riphaeus') cannot be designated as 'Siberian Chiffchaffs'. However, in Dean & Svensson (2005), Lars Svensson suggested that, pragmatically, 'fulvescens' sensu stricto (i.e. found in allopatry in the West Siberian Plain) might be better accommodated within tristis.
Past descriptions of candidate Siberian Chiffchaffs frequently described them as being 'very pale and grey'. While tristis can appear rather 'monotone' or 'colourless' to observers for whom nominate collybita (with its prominent olive and yellow hues) is the norm, they are not especially pale when viewed in normal light conditions (see Plate 1), except for the whiter central belly and under tail coverts. However, when viewed in adversely bright light, they can be prone to 'colour dilution', though this illusion is not restricted to tristis of course. Dean and Svensson (2005) discussed in detail the appearance of classic tristis and 'fulvescens', noting that tristis approached in appearance Mountain Chiffchaff P. (sindianus) lorenzii and emphasising that 'fulvescens' differed from classic tristis principally in exhibiting slight 'additional' olive and yellow. Thus, descriptions of tristis-candidates which emphasised a 'distinctly pale and grey' appearance, with little mention of the characteristic tan-brown and buff hues, were at variance with the established appearance of both classic tristis and 'fulvescens'. Increased attention to the features of Siberian Chiffchaff followed this publication and revealed that most tristis-candidates were, in fact, typical 'brown and buff ' individuals, though 'fulvescens' traits were not uncommon. The high incidence of very pale tristis-candidates inferred hitherto had been exaggerated (Dean et al. 2010). Their professed 'pallor' may have resulted at times from a 'prior image' (expectation). More often it resulted from a fleeting impression (so-called 'morphing'), resulting from visual and photographic artefacts, generated by overly bright light and inappropriate camera settings. Suitably extensive observations, conducted in more-neutral light conditions, confirmed that this overly pallid impression was transitory and that the more-enduring appearance in neutral light was quite in keeping with either classic tristis or 'fulvescens'. Unfortunately, some third-parties then jumped to the conclusion that 'grey and white' Chiffchaffs were invariably an optical illusion. This was a non-sequitor and an ill-considered reaction, which has hampered discussions of plumage limits in both tristis and abietinus. Very careful and prolonged observations have confirmed that, while infrequent, a small number of Chiffchaffs occurring in late autumn are reasonably described as 'grey and white'. See centre bird in plate 2 and 'A case study from Scilly' for an example. However, such genuinely grey-and-white Chiffchaffs are not necessarily tristis. Dean & Svensson (2005) had already suggested that 'grey and white' Chiffchaffs may have more than one origin, viz.
paler extremes of tristis / 'fulvescens'
paler examples of abietinus from the eastern part of its range
intergrades between tristis and abietinus
variants among all subspecies of Chiffchaff
it was possible that a form from an infrequently visited part of Chiffchaff's overall range exhibits relatively 'grey and white' appearance (and also utters a tristis-like call).
Such 'grey and white' individuals exhibit reduced olive and yellow in their body plumage compared with abietinus and collybita, while there are often relatively bright and contrasting yellowish-olive fringes to the remiges and rectrices. At their most distinctive, they resemble one of the Bonelli's Warblers (Western P. bonelli or Eastern P. orientalis) whereas true tristis resembles Mountain Chiffchaff P. lorenzii.
Three examples of such 'grey and white' Chiffchaffs are shown in Plate 5 : one was trapped and photographed in the hand by Gary Crittenden in Highland in November 2008; the second I photographed on St Agnes, Scilly, in October 2011; the third was photographed by Martyn Pitt at Belvide Reservoir in Staffs, in December 2012. While there are subtle differences between them, all three exhibit fundamentally the same livery. On October 28th 2011, the St Agnes individual gave a typical abietinus/collybita call (pers obs), while the Staffs individual gave a 'quiet collybita style call throughout its stay' from December 1st - 3rd 2012 (per Steve Nuttall).
Plate 5. 'Grey and white' Chiffchaffs P. collybita.
As noted above, apart from rump, face-pattern, broken eyering and bare parts, they are reminiscent of Western P. bonelli or Eastern Bonelli’s Warbler P. orientalis. In Plate 6, the 'grey and white' Chiffchaff on St Agnes, Scilly, in October 2011 is compared with an Eastern Bonelli's Warbler in Turkey, photographed in the hand by José Luis Copete.
Plate 6. 'Grey and white' Chiffchaff P. collybita compared with Eastern Bonelli's Warbler P. orientalis
In plates 7 & 8, three different images of the St Agnes Chiffchaff are shown above images of Chiffchaffs photographed within the range of abietinus: Sweden (© Lars Svensson) and Finland (© Petteri Lehikoinen), respectively. The image from Sweden is reproduced from plate 240 in 'Siberian Chiffchaff revisited' (Dean & Svensson, 2005). The image from Finland is reproduced, with permission, from plate 4 in Copete. J. L. & López, F. 2013. 'Identificatiön de subespecies en el Mosquitero Comün (Phylloscopus collybita collybita, P. c. abietinus, P. c. tristis, P. c. brevirostris, P. c. caucasicus y P. c. menzbieri)'. The Scandinavian individuals were equated with abietinus by very experienced ringers for whom abietinus is the norm, with Petteri Lehikoinen commenting re the Finnish bird that this was supported by biometrics and call as well as location.
Plate 7. Three images of 'grey and white' Chiffchaff P. collybita, Scilly, Oct 2011. Compare with examples of 'grey' Scandinavian Chiffchaffs P. c. abietinus in Plate 8.
Plate 8. Two examples of relatively 'grey' Scandinavian Chiffchaffs P. c. abietinus. Compare with 'grey and white' Chiffchaff, Scilly, Oct 2011, in Plate 7.
The appearance of the St Agnes individual (and the others in Plate 5) converges far more closely with greyer individuals within the range of abietinus (e.g. plate 8) than with photos of definitive examples of tristis (e.g. plate 1). Yet it has been claimed by some third parties to be an example of 'plumage morphing' of a Siberian Chiffchaff. As explained above, this is simply untenable. Further photos of the Scilly 'grey and white' Chiffchaff, together with images of a very 'brown and buff' tristis present at the same time, can be found in the case-study here, where the issue of so-called 'plumage morphing' is further addressed.
Two images from Estonia below, by Uku Paal, are somewhat darker and not 'Bonelli's-like' but illustrate further the deficiency of olive and yellow exhibited by some abietinus.
Ringing studies in Britain (Collinson et al. 2018) and the Netherlands (van der Spek & de Knijff 2021) found that the genetically confirmed abietinus and collybita in their samples were indistinguishable, including via biometrics, leading to the comment that, were it not for genetic differences, the validity of abietinus as a subspecies would be questionable. This issue is explored further within the following examination of genetic studies, which in many respects have assumed a central role in discussions of the chiffchaff complex.
In a 1500km long corridor extending from the southern Urals to the Archangelsk region, plumages are regularly encountered which include traces of 'misplaced' yellow in comparison with 'classic' tristis. They may be more
intermediate between classic tristis and abietinus than in the original application of the name 'fulvescens' sensu Sushkin (1925). Indeed, such intermediate-looking individuals were designated as riphaeus (not 'fulvescens') by the Russian ornithologists who first studied them and some Russian authors (e.g. Buturlin & Dementiev 1937) described 'riphaeus' from the Urals region as a product of hybridization between fulvescens and abietinus. Marova et al. (1993, 2009, 2013) employed a combination of morphological, vocal and mtDNA data to study Chiffchaffs in the region of sympatry between tristis and abietinus from Arkhangelsk to the southern Urals mountains. The authors concluded that hybridization was widespread in the region of sympatry. However, they reported an imbalance in gene flow, with 88.5% of the individuals they deemed to be hybrids carrying the mtDNA haplotype of tristis. Unfortunately, they applied the name 'fulvescens' to these hybrids in the sympatric region around the Urals, rather than the preferable 'riphaeus'.In 2012, de Knijff et al. (2012) published an mtDNA-based study of Chiffchaffs trapped in the Netherlands. Ringers had been asked to assign to either abietinus or tristis trapped individuals deemed to differ in appearance from nominate collybita, based upon their appearance in the field. Subsequent analysis of mtDNA found that all individuals assigned by their ringers to abietinus returned tristis mtDNA. No individuals at all were found with abietinus mtDNA (though, as samples for genetic analysis had been selected on the basis of an appearance not suggestive of nominate collybita, some abietinus - which can be very like collybita - may have been missed). Thus, this study concluded that some Chiffchaffs with tristis mtDNA exhibited a greater distribution of yellow and olive than was compatible with the traditional diagnosis of tristis. Perhaps influenced by a paper on Siberian Chiffchaffs published by van den Berg (2009), which argued that hybridization between tristis and abietinus was rare 'if it occurred at all', the Netherlands study did not consider hybrids and led to suggestions that the plumage of tristis was naturally more varied than had been implied hitherto.
Since mtDNA cannot identify hybrids directly (being inherited only from the maternal side), firmer resolution of the question of hybridization depended upon the development of techniques for examining the nuclear DNA of the forms. This proved elusive for several years but, in 2017, Shipilina et al. published a much-needed study, extending the earlier studies of Marova et al. to include 'whole genome sequence data'. This study confirmed that chiffchaffs within the sympatric region have 'a mix of genetic ancestry indicating extensive ongoing and past gene flow'. Additionally, mismatches were found between phenotype ('appearance') and haplotype (mtDNA) in the sympatric region but not among individuals from allopatric regions around the Yenisey. Contrary to suggestions following the earlier Dutch study, Shipilina et al. concluded that natural plumage variation among thoroughbred tristis is limited, that ‘genetic admixture is the driving force underlying trait variation in the sympatric region’ and that intermediate-looking individuals are hybrids. In a comment included in Dean (2018), Daria Shipilina wrote: 'So far we have captured birds in three different (allopatric) locations in Siberia: Middle Yenisey, Lower Yenisey and Yakutia and didn't find any variation in phenotypic characteristics; they had no [misplaced] yellow or olive hues'. It was inferred that even traces of misplaced yellow found in some individuals in the West Siberian Plain, east of the sympatric region, are a result of ‘fractional’ introgression of abietinus alleles. Marova et al. (2017) concluded : 'We assume that all specimens with mismatching phenotype and mtDNA – including those caught in the Netherlands – are of hybrid origin'.
More disconcertingly, Shipilina et al. (2017) reported that, based on whole genome sequence data, individuals with 'pure morphotoype' and with the corresponding mtDNA could still contain a significant proportion of 'foreign' alleles (e.g. an individual with tristis morphotype and tristis mtDNA could still possess a proportion of abietinus alleles in the genome).
In a second Netherlands study, van der Spek & de Knijff (2021) found that ringers' success in allocating Chiffchaffs to tristis in the field had significantly improved since the earlier study. They also reported that further 'whole genome' studies would be conducted, to determine whether introgression was responsible for the presence of 'additional' olive and yellow in individuals assigned to abietinus in the earlier study but proving to have tristis mtDNA. However, a proviso is required here. There were very different levels of 'success' between the first and subsequent studies, in diagnosing tristis in the field. This confirms that the ringers in the earlier study were inadequately informed on the appropriate criteria to apply, in deciding which Chiffchaffs were, and were not, attributable to tristis. For further genetic studies, it is essential that the individuals in the earlier Dutch study attributed by their ringers to abietinus were indeed distinct in appearance from tristis and did exhibit 'mismatching phenotype and mtDNA' . On the basis of the published images, this is questionable in several instances from the earlier study. Genetic studies based upon the second batch of Chiffchaffs should be more revealing.
The second exercise did not pre-select individuals for analysis on the basis of appearance and also confirmed the occurrence of abietinus as a scarce migrant through the Netherlands, thus tallying with a study by Collinson et al. (2018), which had confirmed the occurrence of abietinus in the UK. The Netherlands data suggested that tristis types occurred at a frequency of between 1% and 2% and abietinus at a frequency of c. 5% of all autumn chiffchaffs. Thus, both taxa were scarce but abietinus now appeared to be slightly more numerous than tristis.
Although the UK and Netherlands genetic studies both confirmed the occurrence of abietinus, albeit as a scarce migrant, both also found that - among the Chiffchaffs trapped during their studies - chiffchaffs carrying abietinus mtDNA were impossible to distinguish from nominate collybita in the field, including via biometrics such as wing-length. Thus, beyond genetic analyses, the diagnosis of abietinus posed a more perplexing task than the diagnosis of tristis. Indeed, both Collinson et al. (2018) and van der Spek & de Knijff (2021) suggested that, were it not for genetic differences, the validity of abietinus as a subspecies would be questionable. The proviso here, however, is that the origins of the abietinus detected in the Netherlands and UK studies are unknown and it is perhaps unlikely that they included individuals from across the full range of abietinus. Examination of museum specimens has long confirmed that most abietinus are very similar to nominate collybita. Both Ticehurst (A Systematic Review of the Genus Phylloscopus, 1938) and Svensson (Identification Guide to European Passerines, 1992), emphasised their similarity. By implication, many individuals will be impossible to separate from collybita in the field. However, both Ticehurst and Svensson also noted variability in abietinus, with Ticehurst describing the extremes of collybita and abietinus as 'very distinct'. Svensson noted that the upperparts of abietinus average a little less olive and slightly greyer, while the underparts are a little less yellow. More critically, individuals in the east of the range he described as displaying more grey and buff and individuals in the NE as sometimes paler overall and with whiter underparts. Various comments have been made relating to: (a) the likelihood of hybrids between tristis and abietinus reaching Britain and (b) the variability of abietinus. These comments infer that, in the case of tristis, the likelihood of individuals reaching Britain is constant across the range, from the Urals to the Kolyma River. In the case of abietinus, they infer that individuals reaching Britain (which are relatively small) are representative of the full range from Norway to the Urals and south to the Black Sea.
The geographical origins and genetic profiles of tristis reaching Britain (and western Europe) are far from adequately established. Likewise plumage variation among abietinus and the extent to which it is geographically related. Considerably more research into these issues is required.
Although many questions remain relating to tristis-candidates reaching Britain and western Europe, Shipilina et al. (2017) have provided genetically-based evidence for the origins of morphological variation observed among tristis studied in western Siberia while also confirming that, in contrast, the appearance of individulas in the Yenisey region and Yakutia is consistent. They concluded that the taxa tristis and abietinus hybridize extensively in the sympatric region and genetic admixture is the principal origin of Chiffchaffs which deviate in appearance from 'classic' individuals. What are the implications of these genetic results for field identification of Siberian Chiffchaff?
It seems that both appearance and vocalisations are controlled by a limited area of the genome, so that even an individual with the appearance and song of tristis may yet harbour ‘foreign alleles’. The paper notes that: ‘analysis of genomic composition of birds within the sympatric zone showed that several individuals express diagnostic plumage characters and perform diagnostic song despite harbouring the foreign mtDNA type and/or a considerable proportion of foreign nuclear alleles’. Full trait data were available for only a limited sample but indicated that abietinus morphotypes carrying tristis mtDNA were significantly more numerous than tristis morphotypes carrying abietinus mtDNA (among mixed populations studied by Marova et al. (2017), 56.7% of abietinus phenotypes cf. 4% of tristis phenotypes harboured a contrary mtDNA haplotype). Despite this imbalance, Marova et al. (2009, 2013) reported an individual with tristis morphotype and tristis song yet carrying abietinus mtDNA.
These statistics on mtDNA mismatches have been interpreted as implying that a Chiffchaff which ‘looks like’ tristis and 'sounds like' tristis has a reasonably high probability of actually being a thoroughbred tristis. However, this overlooks the finding by Shipilina et al. that even individuals with matching morphotype (appearance) and mtDNA may yet harbour 'a significant number of foreign alleles' i.e. the nuclear genes are mixed. What the findings of Shipilina et al. indicate is that a Chiffchaff which ‘looks like’ tristis has a reasonably high probability of having tristis mtDNA - but it may still harbour a proportion of abietinus genes elsewhere in the genome.
Also, in practice, in the field, matching morphotype and mtDNA begs the question of what is meant by ‘looks like tristis’? In the context of the paper by Shipilina et al., ‘looks like tristis’ means an absolute absence of misplaced yellow (as per the original ‘Svensson criteria’). Unfortunately, a complete absence of such yellow can only be guaranteed by examination in the hand. For this reason, the Swedish RC, for example, at one time would accept only trapped individuals. In the field it is impossible to confirm an absolute absence of misplaced yellow (or olive).
Similarly, what is meant by 'sounds like tristis'? While careful examination of sonograms will reveal 'mixed' singers, in the field 'mixed' song can be very difficult to distinguish from standard tristis song (Marova et al. 2013; & pers obs), with the more varied tristis-style notes determining the overall character of the song and readily masking interspersed abietinus notes.
Compounding the practical difficulties, in the studies by Marova et al. and Shipilina et al., pure tristis song was relatively frequent among individuals with 'intermediate' appearance (i.e. with some yellow streaking), which may be assessed as 'looks like tristis' in the field, while individuals with 'pure' tristis morphotype (determined in the hand) were frequently 'mixed singers'. These studies did not involve call but van den Berg et al. (2009) reported that tristis-style Chiffchaffs encountered on migration in Kazakhstan exhibited 'wide plumage variation' yet called and sang exclusively like tristis (though sonograms were not provided). This was interpreted as indicating extensive plumage variation among thoroughbred tristis but the findings of Shipilina et al. proffer a rather different interpretation : that 'wide plumage variation' was a sign of genetic admixture and that hybrids may call (as well as sing) like tristis.
Shipilina et al. (2017) suggested that their results brought into question the feasibility of identifying abietinus and tristis on the basis of appearance. So, do we return to an approach which disbars field identification completely or even demand 'whole genome' sequencing of candidate tristis? I am no geneticist but I would argue not. While the level of genetic mixing in the sympatric zone around the Urals (colloquially dubbed here as the ‘riphaeus’ zone) is relatively high, the level of introgression among individuals with very limited traces of yellow found in the allopatric West Siberian Plain (here the ‘fulvescens’ zone sensu stricto) is likely to be low (‘fractional’ to use the word employed subsequently in the Shipilina et al. paper). In this region, the two forms are basically allopatric. Individuals with such 'fractional' introgression from the allopatric West Siberian Plain surely remain designated reasonably as Siberian Chiffchaffs? (See Appendix 3 for tentative comments on the genetic issues.)
The criteria adopted by the BBRC’s ‘tristis panel’ in 2008 were described in detail by Stoddart (British Birds, 2008, 101: 165-166) and Dean et al. (British Birds, 2010, 103: 320-338) and reflect this interpretation. The identification criteria they recommended were formulated in 2008 (nine years prior to the 'whole genome' findings of Shipilina et al.) but the panel concluded that individuals which matched the ‘Svensson criteria’ under close and careful scrutiny in the field were acceptable, thus accommodating the likelihood that, if examined in the hand (or in high resolution digital photos), some would reveal marginal 'fulvescens' traits. However, individuals with field-evident levels of yellow were excluded by the panel’s criteria, as their origins were uncertain and could well include F1 hybrids and early backcrosses from the sympatric ('riphaeus') region around the Urals. It was recognised that some hybrids from the sympatric zone would overlap in appearance with those from the allopatric zone exhibiting just trace levels of yellow but a ‘pragmatic’ approach to field identification was advocated.
The panel’s criteria were pragmatic but exacting and explicitly excluded individuals with field-evident levels of misplaced yellow and olive, which places them on the wrong side of the 'riphaeus' line. Also excluded were the still-contentious ‘grey and white Bonelli’s-like’ Chiffchaffs, which not only have traces of yellow but also lack the characteristic ‘tan-brown and buff’ hues of classic tristis.
The evident proviso for the 'pragmatic' approach advocated by the panel is that a majority of tristis candidates reaching the UK and western Europe originates from across the West Siberian Plain or beyond (i.e. outside the region of sympatry in the Urals region) and that a relatively small proportion originates from the zone of hybridisation. As referenced above, several commentators have noted that the hybrid zone comprises only a small fraction of the total range of tristis (sensu lato) and that, correspondingly, the proportion of candidates originating from the hybrid zone will be small. This remains to be confirmed and I have argued elsewhere (Dean 2013) that, as the sympatric zone is the nearest potential source of tristis-types to western Europe, it conceivably provides a higher proportion of individuals than regions farther east. It cannot be assumed that the likelihood of origin is equal right across the range of tristis as far as the Kolyma. Whole genome sequencing of tristis candidates reaching western Europe is a prime requirement. In the interim, the phrase 'showing the characters of Siberian Chiffchaff ' may be appropriate for records of individuals identified solely on the basis of field observations.
'Relaxed criteria', embracing putative 'Siberian Chiffchaffs' with field-evident levels of misplaced yellow and olive (for which some have argued in recent years, e.g. van den Berg 2009) or with conflicting vocalisations, must remain excluded. Needless-to-say, such anomalous Chiffchaffs 'still have a story to tell' and should be documented and not ignored. What is not desirable, certainly, is to abandon any attempt to classify and document Chiffchaffs reaching western Europe from the Urals and Siberia.
It tends to be overlooked that Dean & Svensson (2005) suggested several possible sources of 'greyer' Chiffchaffs. They noted that, as well as greyer examples of both abietinus and tristis, options to be considered included hybridization between these two forms ('riphaeus' types), individual variation among all the races and the possibility of Chiffchaffs in some part of the range consistently combining greyer livery with a tristis-like call. In respect of the last of these options, recent studies confirm that such Chiffchaffs do exist, in the SE of the species' range : notably menzbieri and perhaps caucasicus (further studies are needed but some publications suggest that brevirostris is less distinct in appearance from European forms although one call is tristis-like). For a long time it was considered that SE forms were unlikely to reach NW Europe but, during 2015, Chiffchaffs with brevirostris/caucasicus mtDNA (the two are indistinguishable by mtDNA) were trapped in the Netherlands (two) and Germany (one) : van der Spek & de Knijff (2021).
The genetic studies of
Raković
et al. (2019)
implied a much-enlarged breeding range for menzbieri, extending from the
traditionally recognised range in Turkmenistan and NE Iran, continuously through
the Elborz mountains of Iran and into southern Armenia. In the UAE, Chiffchaffs
with menzbieri DNA were trapped in March 2019 (one) and December 2020
(two) : Motteau et al.( 2022). As these comprised three of four
Chiffchaffs genetically analyzed (the other being abietinus), the
implication is that menzbieri is a regular component of the Chiffchaffs
wintering in the UAE (and probably elsewhere in the Middle East - see
Dean,
updated 2021). The much-wider breeding and wintering ranges implied by these
studies raise the likelihood that menzbieri, too, could reach Europe. Thus, a
comprehensive approach to the diagnosis of tristis must give regard to the appearance and calls of
the more-southerly
races.
See <here> for discussion of the appearance and vocalisations of Chiffchaffs breeding in the Elborz Mountains of Iran and in Armenia.
Call will certainly provide invaluable guidance when identifying Chiffchaff taxa, at least when an individual calls frequently and with a consistent call. However, many candidate tristis call infrequently (even not at all) while call will not exclude the possibility of hybrid origin. Also, 'alternative' and 'plastic' calls of collybita / abietinus may simulate or suggest the standard call of tristis and vice versa and it is now clear that such calls are not confined to juveniles in the immediate post-breeding period, as has been claimed in the past. Some individuals combine 'variant' calls with plumage anomalies and thereby raise further questions about their genetic origins. Adding to these complexities, there have been several instances of Chiffchaffs with plumage features associated with tristis yet calling persistently like collybita/abietinus. During the winter 2013/2014, several such individuals were photographed and/or video'd and also sound-recorded, placing their combination of plumage and call beyond question (see 'Case Study 3'). Earlier assertions that calls are a failsafe guide to distinguishing Chiffchaff taxa, and render detailed plumage evaluation unnecessary, are now shown to be misguided. Diagnosis must always be founded on a careful evaluation of both plumage and vocalisations. The topic of vocalisations is examined in more detail below.
The characteristic call of tristis ► (here recorded in Russia) is a near-monosyllabic ‘eeep’ (or ‘iiihp’ in Scandinavian renditions), 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, distinctly rising ‘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. Sonograms of the song show characteristic notes with ascending modulations, which are absent from the typical song of collybita and abietinus. These ascending and disyllabic-sounding notes generate a characteristic rising and falling character, much more varied and liquid than western chiffchaff song. A typical sequence might be transcribed as: ‘chivvi-tee, chooee, chivvi-tee, chooee-tee, chivvy’. While tristis song does contain occasional notes with a descending pitch overall (and which can recall abietinus/collybita notes in structure), such notes are in a minority and are absent entirely from some tristis songs (and perhaps from the repertoire of some individuals). Also, they often start with a short rising element and have a distinctly narrower bandwidth than true abietinus/collybita notes. See discussion in Lindholm (2008) for details of note structure in the songs of abietinus and tristis and also a comprehensive examination of 'mixed singers' (see also 'Mixed Singers' below).
Ivanistkii et al. (2020) have reported that the short, dry 'tret' calls, which Chiffchaffs interpose between the strophes in their songs, also differ between the various taxa of the chiffchaff complex (including here the 'Mountain Chiffchaffs' lorenzii and sindianus). The exception was that the 'tret' calls of collybita and abietinus were indistinguishable and there was a proviso over brevirostris, which (at least during their study) used such calls relatively infrequently. Intriguingly, their findings included that the 'tret' calls of tristis differed between central Siberia and NE Yakutia.
Although adults of all races have 'standard' contact calls, which they employ consistently under most circumstances, there are also so-called 'plastic' and 'alternative' calls. Such variant calls are employed regularly by juveniles in autumn while, in the cases of collybita and abietinus at least, alternative calls are also employed by adults under certain circumstances and in certain years (for reasons which are not yet understood). So-called 'plastic' calls are associated with juveniles which are deemed to be learning their calls. At this early stage, collybita may give a call which is very reminiscent of tristis, being both even in pitch and monosyllabic. Here ► is a composite recording which includes, first, a juvenile collybita (Warks, July 2013) and then a tristis (Warks, January 2013). In such direct comparison, the call of the juvenile collybita is marginally less even and rather more 'fuzzy', less 'pure', than the tristis call but they are in general rather similar. Below is a sonogram comparing the pitch and structure of the two calls (Fig. 2.).
Figure 2.
See also '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.
It is sometimes claimed that such 'plastic' calls are unlikely to be heard after early September, well before the arrival time in western Europe of tristis. However, it is now known that 'plastic' calls can persist into November, at least. Although rarely as similar to tristis as the 'plastic' call illustrated above, confusion can also arise between the classic call of tristis and 'alternative' calls given at times by abietinus and collybita at any time of the year. 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 call usually transcribed as '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'. It can recall one call of Thrush Nightingale Luscinia luscinia. 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. They have been heard even 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 adults, in the UK and elsewhere in Europe (see separate article on this topic).
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 evidently rising 'hweet' call, means that even well-inflected 'sweeoo' calls can have a 'flatter' sound than the familiar 'hweet' call.
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. 3):
Figure 3.
In such a direct comparison, the 'alternative' call of collybita is quite 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 and/or 'fulvescens' match the ideal or classic 'straight' structure described above. Calls attributed to tristis may also have a clear 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 'eeep' call from Russia and a shallow 'sweeoo' call from India. A sonogram of the two calls is below (Fig. 4).
Figure 4.
Generally, compared with the 'sweeoo' calls of collybita and abietinus, the shallow 'sweeoo' call of tristis / 'fulvescens' 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.
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 / 'fulvescens' in India in December 2007, recorded by Antero Lindholm. A sonogram of the two calls is below (Fig. 5).
Figure 5.
This direct comparison and the sonograms illustrate the relatively abrupt transition of the collybita call and the smoother transition of the tristis / 'fulvescens' call, together with the differences in peak frequency and frequency range, which create 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. For example, listen to the recording and examine the sonogram of an abietinus/collybita style 'sweeoo' call given by a 'mixed singer' Chiffchaff in Warks in March 2014). The vocabulary of other forms of Chiffchaff is varied and tristis is unlikely to provide an exception. Listen here ► and here ► to series of recordings from October 2009 by Maarten Wielstra, involving a Chiffchaff in the Netherlands 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.
Alternative calls themselves vary, with some 'sweeoo' type calls given by collybita and abietinus being truncated and less-emphatically inflected, thus resembling the 'plastic' calls of younger juveniles and converging with the shallow 'sweeoo' call given by some tristis (both readily sounding more like a monosyllabic 'swee'). Some individuals give such calls persistently. The indications are that 'sweeoo' type calls can be given by all forms of Chiffchaff and provide the most evident case of call convergence.
As well as the regularly encountered 'standard' and 'alternative' calls, Chiffchaffs of all taxa occasionally utter 'wayward' or 'eccentric' calls, which differ from the established calls which are employed more systematically. As these too may sometimes suggest the standard calls of another Chiffchaff taxon, they must also be considered when encountering an anomalous call. Generally, such 'eccentric' calls will not be used persistently and will also lack consistency in their structure and 'sound', while 'standard' calls will also be interspersed in 'eccentric' call-sequences.
The calls of Chiffchaff races in the Middle East and the Caucasus
The calls of Chiffchaffs encountered in Turkey (brevirostris), the Caucasus (caucasicus) and in northern Iran and Kopet Dagh in Turkmenistan (menzbieri) are relatively flat and may resemble or even match the typical call of tristis (e.g. Copete & López 2013; Lars Svensson in litt., Dubois & Duquet 2008). Indeed, texts asserting that the call of tristis is diagnostic, irrespective of appearance, have led to some visitors to the Middle East from western Europe misidentifying southern forms of Chiffchaff as tristis. The taxonomy of these forms is still debated. Currently, they are accorded subspecific rank but, historically, they have also been subsumed within abietinus (and menzbieri sometimes with tristis / 'fulvescens' - see Appendix 2). More recently, Shirihai & Svenssson (2018) have advocated that brevirostris be subsumed into collybita and caucasicus into abietinus (with reservations expressed too over recognition of menzbieri). Under this proposal, complications would be resurrected (1) over the vocabulary of 'abietinus' across the resulting much-expanded range. However, while brevirostris may bridge the appearance of collybita and abietinus, the forms found further east in this region are evidently greyer above and whiter below compared with typical abietinus and have relatively little yellow on the underparts i.e. in the regions embracing the ranges of caucasicus and menzbieri as now perceived. See 'Other sources of 'greyer' Chiffchaffs' above. Also, although brevirostris and caucasicus are effectively indistinguishable genetically, as a pair they differ from abietinus while all other forms also show meaningful genetic differences (Raković et al. 2019). As the southern forms have calls which are relatively 'flat' and resemble the call of tristis rather than abietinus / collybita, taxomic recognition of all three southern forms seems warranted, a conclusion further supported recently by the genetic and acoustic studies of Marova et al. (2021).
See <here> for discussion of the appearance and vocalisations of Chiffchaffs breeding in the Elborz Mountains of Iran and in Armenia. That text includes sonagrams of Chiffchaffs attributed to menzbieri and comparative sonagrams from Helbig et al. (1996) and Clement et al. (1998) depicting, inter alia, calls attributed to caucasicus and brevirostris - similarities and potential subtle differences are explored. For discussion of the calls of enigmatic Chiffchaffs wintering in Kuwait see <here>.
[Footnote (1) : Across its European range the standard call of abietinus is identical to that of collybita, contrary to some earlier assertions that the call of 'eastern abietinus' - meaning in a European context - involved or included a tristis-like call. This error probably arose when European birdwatchers first began to visit the Middle East and heard tristis-like calls which they assumed were being given by migrant abietinus. This is further confirmation that call alone is not a sufficient basis for assigning Chiffchaffs to subspecies. Within the range of abietinus as defined by its current taxonomy, the standard call of abietinus is consistent. ]
Conflicts between morphology and call type
The paragraphs above relate primarily to calls used by Common Chiffchaff which can cause confusion with the typical call of tristis. An even more perplexing issue involves Chiffchaffs with plumage features associated with tristis/'fulvescens' yet persistently employing fully-crystallized collybita/abietinus calls. These have not been isolated, hesitant calls with the character of 'plastic' calls but prolonged series of fully-developed collybita/abietinus calls. Several of these individuals occurred in Britain during the winter of 2013/2014 and were observed over several weeks. They used such collybita/abietinus calls persistently and not as a fleeting departure from the typical tristis call. Are such anomalous callers the result of cultural call 'copying' among perceived competitors (and if so what does it imply about their geographical origins) or do they have a genetic origin? Do call anomalies have a cultural origin or are they too a sign of genetic introgression? This intriguing issue is explored further, with examples, in 'Case Study 3'.
The origins of 'mixed singers'
As well as individuals with a conflict between morphology and call, Chiffchaffs using songs incorporating notes of both Common Chiffchaff and Siberian Chiffchaff are sometimes encountered in the UK and western Europe. These can be genuine 'mixed singers' (with an intimate mixture of notes from the two taxa in a single song strophe) or 'song switchers' (giving full strophes of the two taxa alternately). Song anomalies have been associated with genetic admixture (see Shipilina et al. (2017) but, as song is deemed to be primarily learned in oscine passerines, some claim that such mixed song could be the result of 'copying' by thoroughbreds. No doubt both mechanisms could be involved in individual cases. However, in each case the implication is that the individuals involved originate from the 'overlap' zone in and around the Urals. This is clearly the case for 'hybrids' but also for 'mixed singers', as individuals raised farther east in Siberia will not be hearing abietinus song during the critical song-learning phase. Again, see 'Case Study 3'.
None of this should undermine the significance of the classic tristis call, which still provides an important element in identification. However, to regard call as an unfailing key is over-simplistic and diagnosis of tristis should always embrace both vocal and plumage features.
In summary:
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 of taxon 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.
The normal call of collybita and abietinus is a 'bright' and rising 'hweet', quite different from the standard call of tristis.
However, so-called 'alternative' calls are also given regularly and consistently by collybita and abietinus and have a rising and falling frequency 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 close 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.
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, tristis too may
use a 'sweeoo' variant call, though this is shallower than the 'sweeoo' call
of abietinus/collybita. The transition from rising to falling pitch is usually 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
(i.e.
).
Thus, there is some convergence in structure and 'sound' between such variant 'sweeoo' calls, with a 'two-way' potential for confusion. A recording and sonogram will provide structural clues but, clearly, attributing such calls to a given taxon by ear alone can be problematic.
Chiffchaffs of all taxa will occasionally employ 'eccentric' calls which may suggest the standard call of another Chiffchaff taxon. Generally, such calls are used intermittently, or the call-structure lacks consistency, so that prolonged listening and recording will reveal its 'eccentricity'.
More perplexing are occasional individuals with plumage traits which are associated with tristis (e.g. a deficiency of yellow and olive in the plumage) yet employ persistent series of perfectly formed abietinus/collybita calls. Some have proved additionally to be 'mixed singers' (see Case Study 3'). A cultural origin has been suggested for such vocal anomalies (leading to one taxon 'copying' from another) but studies of tristis and abietinus in their sympatric zone have revealed an origin in genetic admixture (see Shipilina et al. (2017).
It should be borne in mind also that the calls of the more southerly forms brevirostris, caucasicus and menzbieri can be similar or even indistinguishable by ear from that of tristis (Lars Svensson & José Luis Copete in litt.; pers obs). Chiffchaffs with the mtDNA of caucasicus/brevirostris have been trapped in the Netherlands (two) and Germany. Thus, a tristis-like call does not guarantee the identity of an enigmatic Chiffchaff. (See <here> for discussion and sonagrams of Chiffchaffs in Iran and Armenia, where the significance of calls with a 'terminal arch' is explored.)
Variant, anomalous and convergent calls illustrate the importance of assessing both vocalisations and morphology of any candidate 'Siberian Chiffchaff'.
In 2007 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 traditional 'Svensson criteria' for classic tristis, while taking into account the form's characteristic 'tan-brown and buff' hues. Also, allowance was made for individuals which were clearly very like 'classic tristis' but exhibited very limited 'fulvescens' characters (generally imperceptible in the field and often detected only in good, close-up photographs). To insist on an absolute absence of 'additional' yellow and olive would, in effect, exclude field identification of tristis completely, as the absolute absence of these 'misplaced' hues can only be confirmed in the hand. To exclude field identifications would, in turn, undermine the objective of establishing a measure of the true status of Siberian Chiffchaff in Britain. Further, as discussed above and in the Appendices, individuals with very slight 'additional' yellow and olive (i.e. with limited 'fulvescens' traits) are compatible with chiffchaffs from the West Siberian Plain and beyond the true zone of overlap with abietinus. Although there may be slight introgression across the West Siberian Plain, the panel concurred with the suggestion by Ticehurst (1938) and by Lars Svensson (in Dean & Svensson 2005) that individuals with such restricted 'fulvescens' traits are best incorporated with tristis (though with no formal taxonomic implications in the term 'fulvescens'). Conversely, 'riphaeus'-like individuals (with more evidently intermediate plumage), individuals with anomalous calls, and 'Bonelli's-like' grey-and-white individuals (sensu Dean & Svensson 2005), were excluded by the panel's criteria, as the origins of such individuals remained equivocal. While questions remain to be answered, a clearer picture of the status of tristis (here including 'fulvescens' sensu stricto) in the UK emerged. Full details were published in: Dean, A., Bradshaw, C., Martin, J., Stoddart, A. & Walbridge, G. 2010. The status in Britain of 'Siberian Chifchaff'. British Birds 103: 320-338. The panel's investigations demonstrated that the 'Siberian Chiffchaffs' meeting these criteria reach Britain in significant numbers. 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, a conclusion confirmed by analyses for subsequent years that have been published in the 'Report on Scarce Migrants' published periodically in British Birds. The tristis panel's report also examined in detail the issues of morphology, vocalisations, genetics and hybridization (as known at that time); 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 the panel's publication by anyone wishing to explore the topic further.
© A. R. Dean
Plate 10. Apparent 'Siberian Chiffchaffs' with enigmatic vocal and plumage attributes
A case-study from Worcestershire, by Andrew Warr, winter 2014/2015 (external link)
For much useful discussion, information, clarification and / or provision of excellent photos, I am indebted to Jem Babbington, Niclas Backström, Staffan Bensch, Colin Bradshaw, Martin Cade, Oscar Campbell, Richard Chandler, Martin Collinson, Greg Conway, José Luis Copete, Gary Crittenden, Philippe Dubois, Daniel Duff, Martin Garner, Dave Hutton, Gabriel Jamie, Hannu Jännes, Magnus Hellström, Robin Hemming, Peter Kennerley, Mike Langman, Paul Leader, Petteri Lehikoinen, Antero Lindholm, Vladimir Loskot, Irina Marova, John Martin, Richard Millington, Steve Nuttall, Martyn Pitt, Jelmer Poelstra, Brett Richards, Roger Riddington, Kees Roselaar, Steve Seal, Daria Shipilina, Brian Small, Andy Stoddart, Lars Svensson, Pavel Tomkovich, Chris Turner, Vincent van der Spek, Grahame Walbridge, Andy Warr and Maarten Wielstra. Mark Adams kindly arranged access to the skin collection at NHM, Tring.
Citation: Dean, A. R. 2009 (updates to 2024). 'Siberian Chiffchaff' Phylloscopus collybita tristis: discussion and photo gallery. http://deanar.org.uk/tristis/tristis.htm.
It is intended to keep the contents updated as new information emerges. Thus, any citation should include the date on which the text was consulted.
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