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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.


Siberian Chiffchaffs, Uzbekistan, May 2006 & Portland, Nov 2007.

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 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). For many years, the origins of variation in the appearance of Chiffchaffs in the west of the range of tristis were contentious, attributed variously to hybridization between tristis and abietinus or to individual, clinal and even taxon-level variation. Initial genetic studies were confined to mtDNA, which is inherited solely via the female line, and also 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 is also constrained 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 region (Shipilina et al. 2017).  As a result, unequivocal data is emerging on genetic origins and plumage variation. Significant genetic mixing between tristis and abietinus has been confirmed. It has been identified as 'the driving force underlying trait variation' and has also been implicated in vocal anomalies. The following pages explore the issues and their implications for field identification of 'Siberian Chiffchaff'.


The complete text is inevitably lengthy and the genetic issues become increasingly complex year by year. For subsequent reference, a Summary is included, which attempts to provide an accessible résumé of morphological and vocal issues.  References to genetics are unavoidable but in this text they are from a non-specialist's perspective and are inevitably cursory and subject to correction.


Topics


Photos


Case studies



An introductory note on colour nomenclature

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. However, certain individual chiffchaffs which currently defy easy diagnosis also 'stand out from the crowd' largely because they exhibit an evidently anomalous balance of these key 'colours'. Hence, colour nuances are central to discussions of plumage traits in Chiffchaffs and inevitably figure prominently in the following text. 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 prominence of a 'stony grey' shade (nomenclature again!). It denotes 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 often 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).

 

As the applicability of the description 'grey' is interminably debated, it is worth noting here that HSB analysis of screen portrayals shows that the mantle colour of both the 'grey and white' Chiffchaff and the classic tristis in plate 2 have a much higher grey content than that of the 'olive and yellow' collybita. However, the collybita and the 'grey and white' combine (different) shades of olive with neutral grey, with olive dominant in the former but grey dominant in the latter. In contrast, the tristis lacks olive in its mantle hue and combines russet with neutral grey, which produces its distinctive 'tan brown' appearance.

 

As well as genuine plumage variation, the appearance of any Chiffchaff will vary with light conditions, while the definitive, fresh plumage can be temporarily but significantly distorted by moult and wear. In the field, it is essential to draw conclusions based upon a prolonged period of observation. Brief observations are liable to be affected by temporary aberrations induced by adverse light conditions. Longer observations will reveal that such anomalies are indeed temporary and not persistent. Also, colour artefacts can very easily affect photographs. Conclusions must be based upon images of individuals in fresh plumage and where the appearance in the photo is in close accordance with the enduring appearance as assessed from prolonged observation in the field. These and other issues are discussed further in 'A casestudy from Scilly'  and  Colour issues, 'moult & wear' and photographs, which includes details of the HSB colour analyses of key photographs.

 

Chiffchaff hues

 

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.

 


The defining features of 'classic' Siberian Chiffchaffs

 

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 (or four) further species of southerly distribution: Iberian Chiffchaff P. ibericus, Canary Islands Chiffchaff P. canariensis and Mountain Chiffchaff P. sindianus. The last is further divided into nominate sindianus (Tajikistan and N Pakistan to W China and NW India) and lorenzii (NE Turkey, Caucasus and N Iran) and the two are treated as separate species by some authorities. Shirihai & Svensson (2018) apply the name Kashmir Chiffchaff to sindianus while maintaining Mountain Chiffchaff for lorenzii. Others have applied the name Caucasian Chiffchaff to lorenzii but this name risks confusion with the subspecies caucasicus of Common Chiffchaff.

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.  The taxonomy and identification of the ‘chiffchaff complex’ was discussed by Clement, Helbig and Small (1998).

In 2005, Dean & Svensson discussed in detail the taxonomic and plumage limits of tristis, describing the appearance of 'classic' tristis and also discussing the issue of 'fulvescens' from the West Siberian Plain. East of the Yenisey, classic individuals of tristis are reasonably consistent in appearance. The type description of tristis (Blyth 1843) can be examined in Appendix 1 but the most frequently-cited reference to the plumage of such classic tristis is the description provided by Svensson (1992), frequently dubbed 'the Svensson criteria'. The 'Svensson criteria' were intended to define 'classic' individuals and hence offer high 'confidence limits' in any diagnosis. They were not intended to provide absolute limits to the plumage of all Siberian Chiffchaffs. The issue of chiffchaffs found across the West Siberian Plain, which include individuals with traces of 'additional' olive and yellow, comprised a core discussion by Dean & Svensson (2005).

Classic tristis (see Plate 1) lack yellow entirely away from the underwing coverts, the axillaries and the marginal coverts near the bend of the wing, and lack olive on the crown and mantle. The upperparts have a characteristic hue of grey-brown, with a 'tan' suffusion, 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. In fresh plumage, the remiges and rectrices may have subdued olive margins while the scapulars, lower back and rump may show limited olive streaking. However, in classic tristis such olive tinges are rudimentary at best and rarely visible in the field (see plate 2). The bare parts are somewhat less consistent in appearance but many individuals have a relatively slight bill which is predominantly black while the legs and upper surface of the feet are also quite intensely black. Siberian Chiffchaffs are frequently described as being 'pale' but such classic tristis are not especially pale, apart from rather white central underparts. They can, however, appear rather 'monotone' or 'colourless'  to observers for whom nominate collybita (with its prominent olive and yellow hues) is the norm.

The deficiency of yellow and olive has become regarded as the 'defining' characteristic of classic  tristis (but see the following discussion of 'fulvescens'). However, equally characteristic are: (a) the brown component in the hue of the upperparts, which generally has a small but influential russet component, at its most distinctive producing a 'tan' or 'khaki' tinge (see HSB analyses) and (b) the rich buff wash to the supercilium, cheeks and sides of the breast and flanks. Any Chiffchaff which lacks these 'tan-brown' and 'buff' hues entirely is unlikely to be tristis. The plumage of 'classic' tristis recalls that of sindianus and 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 following sections examine in detail some of the issues surrounding the topic of 'Siberian Chiffchaff', including a number of important provisos. However, even though genetic studies now indicate that even classic-looking individuals may yet harbour foreign alleles (see below), it should not be forgotten that, when in fresh plumage, a 'classic' tristis has a distinctive appearance, resulting from a combination of :

 

 

Non-classic Siberian Chiffchaffs from the allopatric West Siberian Plain: '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. It is worth emphasising at this point that the principal features cited at this time for 'fulvescens'  involved enhanced olive fringes to the flight feathers and rump and not additional yellow in the supercilium, eye-ring and underparts. It was on the basis of this enhanced olive that Russian authors had promoted subspecific status. 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' (see Dean 2018). 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, 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 Yensisey, and was based on a series of migrants collected in Turkestan. Thus, their natal origins were uncertain and were not at that time assigned to the West Siberian Plain. See Appendix 1 for a transcription of the type description (kindly provided and translated by Dr Vladimir Loskot, 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', suggesting the presence of 'additional' yellow compared with 'classic' tristis. However, 'rusty yellow' in translation may perhaps refer to the 'buff' hues found in all tristis-types and not to any presence of discrete 'additional' yellow elements. Despite these historical uncertainties, the term 'fulvescens' is now firmly equated with Chiffchaffs differing from 'classic' tristis in the presence of traces of 'additional' olive and yellow and their designated origin is the region between the Urals and the Yenisey. As specimens from the 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.

'Siberian Chiffchaff' with 'fulvescens' traits, Worcs, Feb 2015

© 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>.

 

 

Two 'Siberian Chiffchaffs', one with 'fulvescens' traits

 

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 evident pale base to the bill, though it is as yet unclear whether this is confined 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 'fulvescens' sensu stricto (i.e. found in allopatry in the West Siberian Plain) might be better accommodated within tristis.

 


Recent European genetic studies

In a paper published in Dutch Birding,  de Knijff et al. (2012) reported the results of a pilot study involving 41chiffchaffs trapped in the Netherlands during late-autumn and winter between 2009 and 2011. The ringers were asked to offer a diagnosis of subspecies based upon field appearance while genetic analyses were conducted subsequently on feather samples. Chiffchaffs in the study were selected primarily upon an appearance deemed to be non-collybita-like. The authors found the mtDNA haplotype of tristis not just in individuals identified in the field as tristis but in any individual which did not suggest nominate collybita. In particular, they found that Chiffchaffs diagnosed by their ringers as abietinus  invariably carried a tristis haplotype (i.e. they found no abietinus haplotypes at all). Consequently, it was proposed that plumage limits in tristis were much wider than traditionally supposed and that thoroughbred tristis could exhibit quite evident levels of yellow. However, there are a number of issues which temper these conclusions:  (a) perhaps influenced by an earlier paper in Dutch Birding (van den Berg 2009), which had suggested that hybridisation was rare 'if it occurs at all', the ringers did not consider the issues of  'fulvescens' and intergrades, so that any individual not matching a 'classic' tristis  (sensu the traditional 'Svensson criteria')  was assigned to abietinus;  (b) some individuals which, at least in the published photos, appear compliant with the 'Svensson criteria' for mainstream tristis (such as plates 530 and 531 in de Knijff et al. 2012) were still assigned to abietinus, suggesting that some ringers were inadequately conversant with the criteria to be applied.

While questions might be raised about some of its conclusions, this paper rightly initiated debate over the identification of abietinus and its status as a migrant through western Europe, as no abietinus haplotypes at all were found among the 41 samples. A more comprehensive study was conducted subsequently (van der Spek & de Knijff, 2021), involving 474 chiffchaffs trapped in the Netherlands between 2012 and 2018, supplemented by the earlier 41 samples. Understanding of the field criteria for tristis had improved and the majority of Chiffchaffs found to have tristis mtDNA  were in this second study designated as tristis in the field. Unlike the earlier study, however, this exercise 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.

In the second Netherlands study, van der Spek & de Knijff (2021) now addressed the topic of introgression as a source of intermediate traits. Discussing the individuals assigned to abietinus in the earlier study but proving to have tristis mtDNA, the authors reported that further genetic studies would employ whole genome techniques to investigate whether introgression was responsible for the presence of  'additional' olive and yellow. Based upon Russian studies (see below), 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'.  However, there is a danger here of creating further ambiguity. 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.

 


Hybrid origins of Chiffchaffs in the Urals region

 

In the Urals region, the ranges of tristis and abietinus are sympatric i.e. the two taxa both breed in this zone. In a 1500km long corridor extending from the southern Urals to the Archangelsk region, plumages are regularly encountered which display evident yellow compared with 'classic' tristis. Frequently, they are more intermediate between classic tristis and abietinus than in the original application of  '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. Such 'riphaeus' individuals were originally regarded as a valid taxon but they were subsequently deemed to be hybrids (Snigirewski 1931 and later also by Ticehurst 1938).

 

The question of hybridization in the zone of sympatry between tristis and abietinus, extending north and west from the southern Urals, was investigated extensively by Marova et al. (1993 et seq.). Using a combination of morphological, vocal and mtDNA data, they concluded that hybridization between the two taxa was extensive, in a region from the southern Urals north to the Kanin Peninsula. They reported an imbalance in gene flow, however, with 88.5% of the individuals they deemed to be hybrids carrying the mtDNA haplotype of tristis. (Unfortunately, they too applied the name 'fulvescens' to these hybrids in the sympatric region around the Urals, rather than the preferable 'riphaeus'.)

 

Since mtDNA cannot  identify hybrids directly (being inherited only from the maternal side), firmer resolution of hybrid origins 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'. Mismatches between phenotype ('appearance') and haplotype (mtDNA) were found only in the sympatric region and 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. More disconcertingly, it was reported that individuals with 'pure morphotoype' (e.g. matching tristis appearance) and with the corresponding mtDNA (e.g. also with tristis mtDNA) could still contain a significant proportion of 'foreign' alleles (e.g. tristis morphotype and tristis mtDNA but with a proportion of abietinus alleles). 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.

 


Implications for field identification

After much claim and counter-claim, Shipilina et al. have provided genetically-based evidence for the origins of morphological variation observed among tristis candidates. 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 (to quote informal comments on the web).  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 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 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. 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.


Plumage limits of tristis and abietinus

 

Despite the provisos described above, typical Siberian Chiffchaffs, with a combination of the characteristic hues of 'brown and buff' and sufficiently limited levels of olive and yellow, are reasonably distinctive phenotypically (Plate 1 & Gallery). 'Classic'  tristis (as found in the heart of Siberia) and individuals which differ from them only marginally (with very restricted 'additional' olive and yellow) do not invite confusion with typical abietinus. Some individuals which closely resemble 'classic' tristis may yet harbour 'abietinus alleles' and non-invasive (field) criteria cannot be failsafe. However, pragmatic identification criteria (as outlined above) will correctly identify an overwhelming majority of chiffchaffs originating in eastern Siberia and the West Siberian Plain

 

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. It seems likely that most if not all would have an origin in the west of the subspecies' range  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. Such paler and greyer individuals will create convergence with the appearance of tristis and with intergrades.

 

It is a frequently quoted feature of the Common Chiffchaff population that there is a diminution of yellow and olive from west to east. A re-examination of the issue of diminution of olive and yellow from west to east seems necessary, involving principally a wide sample of abietinus right across its range. Is abietinus in fact effectively identical to collybita right across its range? Is the diminution of olive and yellow from west to east genuine?  If so, is it clinal, taking place gradually across the range, or is it confined to the extreme east, and more likely a product of gene-flow with tristis (i.e. riphaeus-types)? Also, how far east across the West Siberian Plain are individuals with traces of 'misplaced' yellow encountered?

 

What is the identity of Chiffchaffs which not only exhibit rather limited levels of yellow and olive but also lack the characteristic 'tan-brown and buff' hues of tristis? Such individuals are relatively scarce but are recorded on occasions in the UK. At their most distinctive, their grey and white livery with contrasting olive fringes to the remiges resembles one of the Bonelli's Warblers (Western P. bonelli or Eastern P. orientalis) whereas true tristis resemble Mountain (Caucasian) Chiffchaff P. lorenzii. Such 'grey and white' Chiffchaffs have created even more discussion and controversy than Chiffchaffs with 'fulvescens' traits. Are such individuals eastern variants of abietinus as described by Svenson (1992), are they hybrids or do they have some other origin? Some claim that 'grey and white' Chiffchaffs do not exist but involve temporary 'plumage morphing' and are some kind of mirage, involving an artificial 'dilution' of tristis hues in bright light. This, however, is unsustainable. While the appearance of all taxa - including tristis -  will vary with light conditions, careful and prolonged examination in varying light conditions (sometimes over more than one day) confirms that the grey-and-white Bonelli's-like Chiffchaffs which are recorded occasionally in the UK lack entirely the characteristic 'brown and buff' hues, with their distinctive tan or rusty tinges, which characterise tristis. Additionally, they tend to have a tinge of yellow infusing the white (not buff) ground-colour of the upper eyering, with the ground colour paler than the adjoining supercilium. Hence the upper eyering is distinct and contrasting, unlike 'classic' tristis in which the upper eyering tends to be of similar hue to - and to merge with - the adjoining supercilium (though it is often more apparent in 'fulvescens' types). While they exhibit reduced olive and yellow in their body plumage compared with most abietinus and all collybita, there are often relatively bright and contrasting yellowish-olive fringes to the remiges and rectrices.

 

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).

 

Three examples of 'grey-and-white ('Bonelli's-like')' Chiffchaffs

Plate 5.  'Grey and white' Chiffchaffs P. collybita.

 


 

In their basic appearance, such 'grey and white' Chiffchaffs do not at all recall Mountain (aka Caucasian) Chiffchaff P. lorenzii, as do core-range tristis. In fact, as noted above, apart from rump, face-pattern and bare parts, they are more 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.

 

'Grey and white' Chiffchaff c.f. E Bonelli's Warbler

 

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 three examples of  'grey' Scandinavian Chiffchaffs P. c. abietinus in Plate 8.

 

 

'Scandinavian Chiffchaffs' from Sweden and Finland

 

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 certain photos taken within the range of abietinus than with photos of definitive examples of tristis (e.g. plate 1). 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.

 

This is not to deflect from the fact that many / most abietinus are very similar to collybita. However, to infer that abietinus is invariably identical to collybita runs contrary to the evidence from a range of published photos. Many images of abietinus, including several 'grey and white' individuals, can be found on the Finnish 'BirdLife' website. 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. As noted above, the variation of abietinus across its full range is far from adequately established and warrants more research.

 

'Scandinavian Chiffchaffs' from Estonia

 

 


 

It is intriguing (and potentially instructive) to examine reports at migration 'hot spots' involving significant falls of Chiffchaffs perceived as distinct in appearance from nominate collybita. Pennington et al. (2004) noted that 60 Chiffchaffs on Fair Isle on October 10th 1991 were comprised  'wholly of greyish northern / eastern races' while most of the 100 on 18th October 1990 'were also abietinus or tristis'. Flood et al. (2007), discussing Chiffchaff falls on Scilly, stated that 'abietinus made up at least 30% of 212 on 22nd October 1984'. The annual reports of the Flamborough Bird Observatory and Flamborough Ornithological Group include double-figure counts for abietinus in at least nine years between 1991 and 2010, with a peak of 41 on 13th October 2002 (Brett Richards in litt.). Thus, these reports imply that between 40 and 100 Chiffchaffs perceived as distinct from nominate collybita may reach a single locality on a single date (see Dean 2013). Such significant concentrations of Chiffchaffs perceived as differing from nominate collybita cannot be dismissed as a product of wholesale and persistent 'plumage morphing' of normal collybita morphotypes. So, is it now to be concluded that these Chiffchaffs were all tristis? The numbers of Siberian Chiffchaffs reaching the UK have been on an upward trend for some years and a record total was documented during 2019 in British Bird's 'Report on Scarce Migrant Birds' (White & Kehoe 2021). This record total - for the UK as a whole and an entire year- was 524. The annual mean for 2010 - 2019 was 276. Thus, up to 100 tristis at a single location on a single day seems rather implausible. Yet, such totals would also be decidedly unexpected for abietinus in normal circumstances. If the figures published by van der Spek & de Knijff (2021), based upon mtDNA analyses, are genuinely representative (see above), then, among all migrant Chiffchaffs tested, 1% to 2% were tristis and about 5% abietinus. As noted above, the origins of the abietinus detected in the Netherlands and UK studies are unknown but, season-wide, abietinus from western parts of the range seem likely to have predominated. There is a migratory divide between the Scandinavian populations of abietinus, which migrate south-westwards in autumn, and the Finnish and more-easterly birds, which migrate south-eastwards (BWP6 1992 and Wernham et al. 2002).  The BTO 'Migration Atlas' (Wernham et al. 2002) notes that: 'A proportion of Scandinavian birds probably use Britain as part of their normal migration routes in both spring and autumn, whereas birds from further east usually arrive only after being displaced by easterly winds'. Significant falls of Chiffchaffs during October are perhaps associated with exceptional meteorological conditions and easterly winds. Given this scenario, their source regions could well differ in profile from those at other times. Genetic analyses of Chiffchaffs arriving in numbers during such later-autumn 'fall conditions' would seem very worthy of investigation.

 


Other sources of 'greyer' Chiffchaffs

 

It tends to be overlooked that Dean & Svensson (2005) suggested that 'greyer' Chiffchaffs may not all have a single origin. 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 caucasicus and menzbieri (further studies are needed but some publications suggest that brevirostris is less distinct in appearance from European forms although its 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.

 


 

Vocalisations

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.

 

Sonogram of typical tristis call

 

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).


Chiffchaff 'tret' calls

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.

 


Potential problems with calls: (a) 'standard', 'alternative' and 'eccentric' calls; (b) the calls of other races; (c) conflicts between morphology and call-type

 

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.).

 

 

sonogram of collybita juv versus tristis calls

 

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):

Sonograms of collybita c.f. tristis calls

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).

 

Sonogram of two different tristis calls

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).

 

Sonogram of 'sweeoo' calls from collybita c.f. tristis

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 Turkmenia (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:

 

 


BBRC 'tristis panel' (2008)

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.

 



 

Siberian Chiffchaff types with vocal and plumage anomalies

© A. R. Dean

Plate 10. Apparent 'Siberian Chiffchaffs' with enigmatic vocal and plumage attributes


Case studies


Acknowledgements

For much useful discussion, information, clarification and / or provision of excellent photos, I am indebted to 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 2023).  '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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