‘Siberian Chiffchaff’ revisited - Home - British Birds Birds98 • August 2005 • 396-410 397...

396 © British Birds 98 • August 2005 • 396-410

‘Siberian Chiffchaff ’revisited

Alan R. Dean and Lars Svensson

ABSTRACT The systematics and morphology of Common Chiffchaff Phylloscopuscollybita of the Siberian subspecies tristis are much debated. Many putative tristis

in Britain are distinctly pale and frequently attributed to ‘fulvescens’, a forminitially described by Severtzov in 1873 from a series collected in Central Asia.

Treatment of the taxonomy and appearance of ‘fulvescens’ is inconsistent.It is frequently presented as an ‘intergrade’ population resulting from

unrestricted gene-flow between tristis and the North Fenno-Scandian andRussian race abietinus but this may not be the most appropriate interpretation.

This article reviews the variable treatment of ‘fulvescens’ in the literature, itsdifferences from abietinus and east Siberian tristis and the conflicting results of research into its taxonomic status. Based on the information presented,

the provenance and appearance of the pale,‘grey-and-white’ tristis-likechiffchaffs reported in Britain are considered.

The Common Chiffchaff Phylloscopuscollybita has a broad distribution acrossEurope and east to Siberia, with six sub-

species currently recognised by most authori-ties. Broadly speaking, the nominate formcollybita of western Europe is replaced by abie-tinus in eastern Europe and by tristis in Siberia.From further south in Europe, in Turkey and inCentral Asia, brevirostris, caucasicus and menz-bieri have been described. The ‘chiffchaffcomplex’ is completed by three further closelyrelated species of southerly distribution: IberianChiffchaff Ph. ibericus, Canary Islands Chiff-chaff Ph. canariensis and Mountain ChiffchaffPh. sindianus. The taxonomy and identificationof the ‘chiffchaff complex’ was discussed byClement et al. (1998).

The form tristis is frequently referred to as‘Siberian Chiffchaff ’ but, even following mito-chondrial-DNA studies, its taxonomic statusand whether it warrants recognition as a sepa-rate species remain unclear (Helbig et al. 1996).The taxonomy and diagnosis of ‘Siberian Chiff-chaff ’ have long been beset by confusion anddivided opinion, and controversy still sur-

rounds both its systematic and its morpholog-ical limits. Few reports of tristis in Britain areincontrovertible and there is perennial discus-sion about whether particular plumage charac-ters or vocalisations are compatible with tristis.

The following notes provide a review of theissues, including the historical context, the con-flicting results of ongoing research, and the dis-tinguishing characters of ‘Siberian Chiffchaffs’.It must be emphasised from the start that muchmore research is required in the breeding areasbefore there can be any prospect of resolving allthe issues. The objectives of this review are toprovide a clearer perspective and to dispel somecommonly held misconceptions. A universalconsensus remains some way off.

Plumage variation in Common ChiffchaffThe races of Common Chiffchaff displayvarying degrees of olive and yellow in theirplumage but this variation is to a large extentclinal, while there is also considerable indi-vidual variation. Thus, the appearance of theforms overlaps to a significant extent and inpractice it can be very difficult, sometimes

397British Birds 98 • August 2005 • 396-410

‘Siberian Chiffchaff ’ revisited

impossible, to assign a given indi-vidual to a particular race on thebasis of plumage colour.

There is a cline of decreasingcolour saturation running fromnorthern Norway eastwards acrossnorth Eurasia. A reduction inlipochrome pigment from west toeast (which also affects thesouthern subspecies brevirostris,caucasicus and menzbieri to someextent) results in decreasing oliveand yellow in the plumage.Williamson (1962) described abie-tinus as:

Paler and greyer, less deep olive abovethan the typical race; buff and yellowon the breast is reduced so that theunderparts, including undertail-coverts, appear whiter.

(see Appendix 1 for a moredetailed diagnosis of abietinuscompared with collybita) whiletristis has:

Upperparts brownish to greyish-brownwithout olive except on the edges towing and tail feathers, wing-coverts,and usually the rump… no yellow inthe supercilium, eye-ring and cheeks,this being replaced by buff… sides ofbreast and flanks ‘macintosh’ buff, theonly yellow being at the bend of thewing and under the wing.

Note that the features listed for diagnosingtristis involve the distribution of olive, yellowand buff. The basic colour of the upperparts(degree of ‘greyness’ or ‘brownness’) and theoverall ‘paleness’ are not part of the diagnosis.

Distinctions between tristis and greyerexamples of abietinus are sometimes masked byuse of the terms ‘Northern Chiffchaff ’ or‘Eastern Chiffchaff ’ to embrace any individualwith significantly reduced olive and yellow inthe plumage and, frequently, the semblance of awing-bar produced by diffuse paler tips (andedges) to the greater-coverts (see Dean 1985).Variation in appearance among true tristis isdiscussed below, but the plumage of typicalindividuals is rather similar to that of MountainChiffchaff although, unlike that species, it hasolive fringes to the flight feathers and an olivetinge on the lower back and rump.

234. Common Chiffchaff Phylloscopus collybita abietinus, Eilat, Israel,March.A fresh spring abietinus with quite prominent olive in the

upperparts.Yellow is restricted on the underparts compared with most nominate collybita, but still quite discernible on the sides of

the breast, the rear of the flanks, and on the supercilium.

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n235. Common Chiffchaff Phylloscopus collybita tristis (‘Siberian

Chiffchaff ’),Astana, Kazakhstan, May.

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236. Mountain Chiffchaff Phylloscopus sindianussindianus (left; from Ladakh, northern India, in late

July) and Common Chiffchaff Ph. collybita tristis (fromthe Siberian Altai, in autumn). Note olive fringes tothe flight feathers of tristis which distinguish it fromthe otherwise rather similar Mountain Chiffchaff.

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398 British Birds 98 • August 2005 • 396-410


‘Siberian Chiffchaff ’At its northerly boundary, the range of tristisextends from the Pechora basin and the Uralseastwards beyond the Lena River and discontin-uously perhaps as far as the Anadyr River(Clement et al. 1998; fig. 1). ‘Siberian Chiff-chaffs’ are reported in Britain every autumn andwinter, sometimes in numbers which are sur-prising for a taxon originating east of thePechora and largely wintering in India. TheseBritish birds have appeared, in the field, to lackyellow except at the bend of the wing, while theonly obvious olive has been to the fringes of thewing feathers, the tail feathers and the rump.Thus, they have appeared to possess key charac-ters of tristis as described in the literature.

Yet, many ‘Siberian Chiffchaffs’ reported inBritain are described as being ‘noticeably pale’,with limited brown and a strong grey compo-nent in the upperparts, and the underpartsbasically whitish with little evident buff. Theolive fringes to the flight feathers are frequentlyquite well defined, generating a clear contrastwith the otherwise rather ‘colourless’ appear-ance. Although possessing a much strongerface-pattern, their appearance draws compar-isons with either Western Ph. bonelli or EasternBonelli’s Warbler Ph. orientalis, rather than with

Mountain Chiffchaff. Rather few are noted asmore drab, brown and buff, and thus closer tothe common image of ‘classic’ tristis.

Much discussion and controversy surroundthe appearance and provenance of these ‘grey-and-white’ individuals. One school of thoughtis that they are ‘true’ tristis from the paler end ofthe range of variation. Others suggest that suchbirds are ‘intergrades’ between abietinus andtristis. The term ‘fulvescens’ is frequently appliedto both of these interpretations. A third opinionis that such ‘grey-and-white’ individuals aremerely pale examples of abietinus. Clearly, themorphology and provenance of ‘fulvescens’ iscentral to the discussion of plumage limits in‘Siberian Chiffchaff ’.

What is ‘fulvescens’?Although mentioned in several recent publica-tions (e.g. Baker 1997), discussion of ‘fulvescens’in the British literature is often rudimentary.Somewhat more extensive treatment was pro-vided by Vaurie (1959) in The Birds of thePalearctic Fauna, by Williamson (1962) in hisIdentification for Ringers: The Genus Phyllo-scopus, by LS in his Identification Guide to Euro-pean Passerines (4th edition, 1992), and in theparagraphs on ‘Geographical variation’ in BWP

237. Common Chiffchaff Phylloscopus collybita tristis (‘Siberian Chiffchaff ’), Irkutsk, Siberia, May.A ‘classic’ specimen of tristis in spring, from eastern part of the range. Note the quite saturated brown upperparts, the buff suffusion to underparts (especially the throat, breast and flanks) and the absence

of yellow (apart from at the bend of the wing).

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Vol. 6 (C. S. Roselaar, in Cramp 1992). Percep-tions of ‘fulvescens’ among British observers arebased largely on these sources.

Vaurie described ‘fulvescens’ as:

Much greyer above than abietinus, olive pigmentsreduced to a greenish-yellow tinge on the lower back,rump, and uppertail-coverts and wings, underpartslighter, whitish or buff.

Williamson quoted Vaurie but went on to saythat birds of this description could be found atthe type locality of tristis (Calcutta) and amongspring migrants through Iran and the PersianGulf, while the ‘Northern Chiffchaffs’ whichoccur regularly in autumn in Britain were alsosimilar. He noted a wide variation in the colourof the upperparts and that on some individualsthe underparts were ‘entirely devoid of yellowstreaking’. His conclusion was that:

There is no doubt that over the wide geographicalranges of ‘fulvescens’ the species [Common Chiff-chaff] is unstable as regards the tone of the upper-parts and the amount of buff suffusion and yellowstreaking beneath, and the name [‘fulvescens’] is bestsynonymized with tristis, as recommended by Tice-hurst (1938).

Thus, while Vaurie described ‘fulvescens’ as

relatively ‘grey and white’, Williamson acknowl-edged variation in the tone of the upperparts of‘fulvescens’ and noted that some individualsshowed yellow streaking below while on othersthis was absent. He interpreted this variation asarising from secondary intergradation betweentristis and abietinus. It is important to note thatboth Vaurie and Williamson included in ‘ful-vescens’ birds from the region from northeastIran to southwest Transcaspia. Chiffchaffsbreeding in this area are now recognised asbelonging to a separate race, menzbieri. Hence,the variation in upperparts colour and yellowstreaking below commented upon byWilliamson was at least partly influenced byindividuals now considered to be from outsidethe distribution of ‘fulvescens’.

A somewhat different perspective on ‘ful-vescens’ is apparent in the paragraphs on ‘Geo-graphical variation’ in BWP. Here, the plumagesof tristis are portrayed in two groups. A paler,‘fulvescens’ type is described as having (interalia):

Upperparts brown to greyish-brown, with distinctolive tinge on rump and uppertail-coverts and some-times slightly on mantle; underparts whitish, washedbuff; tail-feathers, flight-feathers and tertials brown,outer edges olive-green.



Fig. 1. Map showing the range of the forms abietinus, tristis and ‘fulvescens’, based mainly on Marova & Leonovich(1993).The approximate eastern limit of abietinus is indicated by the red dashed line, and the eastern and westernlimits of ‘fulvescens’ by the orange dashed lines; the blue-hatched area shows overlap between these two forms.

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A second type, regarded as the ‘classic’ or‘typical’ tristis, is described thus:

Rather darker brown with no or only very slight olivetinge on mantle, rump and uppertail-coverts; under-parts with more distinct buff suffusion, appearing lesswhite; edges to tail- and wing-feathers, tertials, andbastard wing more brownish, less greenish.

In this treatment, there is no mention of ‘extra-neous’ yellow (i.e. yellow away from the bend ofthe wing and the underwing). Rather, it suggestsa darker and browner ‘classic’ form of tristis,more intensely buff on the breast and flanks,and a rather paler and greyer ‘fulvescens’ form,with brighter olive fringes to feathers of the tailand wings and somewhat whiter on the under-parts. While acknowledging that considerabletaxonomic confusion exists (see below), bothWilliamson and BWP advocated that ‘fulvescens’be included within tristis.

The original designation of ‘fulvescens’The form ‘fulvescens’ was first described by Sev-ertzov in 1873, based on a ‘type series’ of over100 migrants taken ‘in Turkestan’. Thus, it wasnot described from birds on the breedinggrounds, which Severtzov supposed to bewestern Siberia (although, rather confusingly,he adds ‘possibly near Irkutsk’, a locality whichis hardly in western Siberia). We have not hadthe opportunity to examine the type series andit is a matter of assumption that the ‘type series’actually consists of a single subspecies (see latercomments on a ‘variant’ portrayed within the‘type description’). Birds breeding from theUrals to the Yenisey are now generally equatedwith ‘fulvescens’.

There appear to be few, if any, detailedaccounts in English of Severtzov’s originaldescription. Clearly, the original descriptionbased on the ‘type series’ is important in estab-lishing the correct use of the name ‘fulvescens’and its implications in terms of appearance.Severtzov’s description (kindly provided andtranslated by Dr Vladimir Loskot, Curator ofthe Ornithological Department, ZoologicalInstitute, Russian Academy of Sciences, StPetersburg) was as follows:

Ficedula (Phyllopneuste) fulvescens, nob. – (Ph. tristis?Gould). Upperparts, from forehead to uppertail-coverts and small wing-coverts rusty-grey with olivetint, olive-brown in autumn; supercilium and under-parts rather pale rufous-yellowish, brighter in

autumn; cheeks not pure rusty; wings and tailfeathers blackish, with olive fringes which, on coverts,cover blackish middle of feathers; small underwing-coverts sulphur yellow; first primary twice as long asits coverts; 3=4=5>6>7>2>8. Male and female do notdiffer from each other; in juvenile birds, differing ingeneral only in looser texture of feathers, sometimesunclear longitudinal stripes of pale sulphur-yellowcolour are present on the breast; in others, the breaststripes are similar but greyish (var. naevia), and thenall the plumage is more greyish than usual. Bill andlegs black; bill is relatively small even for a leafwarbler, and claws are large, especially on the hindand mid toes.

In comparing the basic description withmodern interpretations of tristis, ‘fulvescens’would appear to have more extensive olive inthe upperparts and wing feathers and the pres-ence of yellow in the supercilium and on theunderparts. These features would today beregarded by many as indicating ‘intergrade’characters. Overall, there is little in the basicdescription to indicate a match with the ‘pale-and-grey’ individuals reported in Britain. Avariant ‘naevia’ in Severtzov’s diagnosis isdescribed as lacking yellow streaking on thebreast, at least in juvenile plumage, and beinggreyer overall. This perhaps comes closer.However, the location of the type specimen of‘naevia’ is unknown (Vladimir Loskot in litt.),so its precise characters cannot be confirmed.

Variation and plumage limits in abietinusand tristisExamination of skins confirms that birds fromthe Urals and the Ob basin are often slightlydifferent from more easterly tristis, beingslightly yellow beneath, with thin yellow streakson the lower throat, and a faint yellow tinge onthe fore-supercilium and/or eye-ring. Suchyellow tinges are absent on other birds in thisarea, and on all birds breeding farther east inSiberia. Such individuals with limited yellowhave been equated with the form ‘fulvescens’,notwithstanding the inconsistent descriptionsin the literature (see above). Following this con-vention, the term ‘fulvescens’ is used hereafter tosignify the yellow-streaked birds breeding in theregion from the Urals to the Yenisey.

From specimens, no consistent difference isevident between birds breeding in western andin eastern Siberia in the general hue of theupperparts (‘greyness’), though there is a slightdegree of individual variation and also a sugges-



tion that birds in fresh plumageand in winter are on average a littlepaler and greyer than birds insummer. Among the specimensavailable at the Natural HistoryMuseum (NHM), Tring, it is notpossible to detect a grouping ofindividuals from one part of therange of tristis (sensu lato) that isconspicuously ‘greyer and whiter’than the remainder, and similarconclusions have been drawnwhen visiting other large museumcollections.

It is perhaps insufficientlyappreciated in Britain how signifi-cant may be the reduction in oliveand yellow in the least colourfulabietinus. At an intensive ringingsite in southern Sweden, all abiet-inus trapped have displayed at leastsome yellow streaking below,yellow on the upper eye-ring, anda tinge of olive in the upperparts(Bo Petersson in litt.). On mostindividuals these colours remainevident in the field but extremeexamples (probably restricted tothe east of the range of abietinus)reportedly lack these hues almostentirely, apart from olive fringes tothe wings, tail and rump. The col-lection of specimens at Ams-terdam includes examples of suchindividuals from the lower Volgaregion of European Russia (C. S.Roselaar in litt.).

Extreme examples of abietinusseemingly display no more yellow– indeed, conceivably less – thansome examples of ‘fulvescens’. Itfollows that differences betweentristis (including ‘fulvescens’) andsuch examples of abietinus can berather subtle. In a working memofor a planned fifth edition of hisIdentification Guide to EuropeanPasserines (Svensson in prep.), LSrefined the criteria for diagnosingtristis thus:

(1) whole supercilium (including eye-ring) buff-white or pale ochrous-buff, without any pure yellow;

(2) underparts, including vent and



238. Two specimens of Common Chiffchaff Phylloscopus collybita tristis(‘Siberian Chiffchaff ’), both from Krasnoyarsk, Siberia; upper: May,

lower: September. Apart from the effects of wear and bleaching, there is little seasonal variation in the plumage of ‘true’ tristis; some autumnand winter individuals are arguably a little brighter and paler but this

is marginal and largely masked by individual variation.

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239. Common Chiffchaff Phylloscopus collybita tristis (‘SiberianChiffchaff ’), India, January. Some specimens collected in the winter

quarters are slightly paler and greyer than tristis collected in thebreeding season in Siberia. Note, however, that the ‘provenance’

of wintering birds is not certain.A.

R.D

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240. Common Chiffchaff Phylloscopus collybita abietinus, Stockholm,Sweden, September. Note the much greyer and ‘colourless’ appearanceof this autumn individual compared with that of the fresh spring bird inplate 234. Olive and yellow streaking is still present but is very subdued.

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undertail-coverts, buffish-white without anyyellow, breast and lower throat being strongestbuff;

(3) crown and mantle – at least upper mantle –greyish-brown lacking any olive tinge;

(4) a slight olive tinge on back, rump and scapulars;(5) remiges, greater-coverts and rectrices narrowly

edged olive-green (if not heavily worn);(6) black or blackish tarsi;(7) small, dark bill;(8) wing-bend and axillaries bright lemon-yellow;(9) feathered ‘knee’ (ankle) usually buff-white, or at

most faintly yellowish-white (not bright yellow);(10) P1 (outermost primary) comparatively short

and narrow, usually 4–8 mm > PC;(11) P2 usually =7/8 or =8, but sometimes a little

shorter (i.e. =8/9);(12) distance P1 < P2 rather long, 21–30.5 mm

(m 24.4, n 57).

[abbreviations: PC refers to primary coverts,m is mean, n is sample size]

An additional but variably evident feature of classictristis concerns the ear-coverts, which are frequentlybuff-brown or even rufous-tinged (sometimesdescribed as ‘rusty’), whereas the ear-coverts of abie-tinus are generally paler and mottled with buff andolive.

These guidelines are sometimes misunder-stood in terms of the presence or absence ofyellow. The guidelines are intended to includeonly incontrovertible tristis and to avoid theinclusion of abietinus with particularly restrictedyellow. They are not designed to define the fullplumage limits of tristis. Traces of yellow maybe, in fact, a feature of a minority of genuinetristis and such individuals will be excluded bythe guidelines. However, until the discrimina-tion between such birds and abietinus with leastyellow is better understood, this approach isconsidered preferable. It should be noted thatthe German handbook (Glutz von Blotzheim &Bauer 1991) misunderstood the similar guide-lines in the third edition of Identification Guideto European Passerines (Svensson 1984a), andinterpreted them to mean that the presence oftraces of yellow below ruled out tristis entirely,but this was never intended. It is only east of theYenisey that apparently all Chiffchaffs lack anyyellow below, away from the underwing. Theexact subspecies composition of the birds foundbetween the Pechora and the Yenisey (wheretraces of yellow are commonly found on theunderparts), the true status of ‘fulvescens’, andthe plumage limits of tristis are still the subjectsof much research (and conjecture).

The ‘yellow-tinged’ chiffchaffs from the Uralsand the Ob basinThe presence of extraneous yellow in chiffchaffsfrom the Urals and Ob basin is popularly inter-preted as ‘intergradation’, resulting from unre-stricted gene-flow between abietinus and tristis(a so-called ‘hybrid swarm’). However, thisinterpretation is not universally accepted. Alter-native explanations for traces of yellow includethe hypothesis that they are a feature of a west-erly population of tristis (‘fulvescens’), in whichgene-flow with abietinus is evident but alreadyrestricted by a degree of assortive mating (seebelow). Various studies have been made oftristis and ‘fulvescens’, while others are still inprogress, primarily using vocalisations as anindicator of ‘subspecies integrity’ and reproduc-tive isolation.

Vocalisations as taxonomic indicatorsVocalisations are a key means of separating taxaand are important in establishing reproductivebarriers. The songs of collybita and abietinus aresimilar, the familiar and eponymous ‘chiff-chaffchiff-chaff chaff-chaff chiff-chaff ’; rather dry,rhythmic and repetitive in character and some-times preceded by a low, slightly churred ‘tret’,especially on the breeding territory. The song oftristis is quite different, being much more variedand rising and falling in pitch. There is a sug-gestion of the timbre of collybita in some notesbut each is enhanced with a terminal flourishand each series of notes has much greater flu-idity. The notes tend to cascade into oneanother and the delivery (though not the timbreof the notes) can recall the ‘cadence’ of the songof Willow Warbler Ph. trochilus. There is also –rather surprisingly – a similarity to the slightlyjerky lilt of the song of Greenish Warbler Ph.trochiloides, though the song of that species willbe less familiar to many British observers. Lis-tening to recordings of the song (e.g. Svensson1984b, Mild 1987) is far better than any tran-scription but, to British ears, the transcriptionproffered by Heard (1989) is as good as any:‘chivy-chooee chivy-chooee djiff ’. Generally,however, there are several more ‘chivy-chooee’components in each series.

Conflicting research findingsA number of bio-acoustical studies have investi-gated the songs of abietinus, tristis and ‘ful-vescens’. On the basis of detailed experiments,Martens & Meincke (1989) concluded that,



across the whole range occupied by tristis and‘fulvescens’, song was consistent and lacked com-ponents characteristic of abietinus. Theyrecorded songs from Jekaterinburg to Irkutskand used these in ‘playback’ experiments. Thisdemonstrated limited reaction by each form tothe other’s song, supporting the view thatassortive mating might be underway and thattristis (including similarly singing ‘fulvescens’)might already be best treated as a separatespecies in relation to neighbouring abietinus.They concluded that there was no evidence fora zone of extensive hybridisation nor for main-taining the distinction of ‘fulvescens’ from tristis.

Following research in the area of overlapbetween abietinus and tristis, Russian ornitholo-gists have resurrected the idea that ‘fulvescens’results from extensive intergradation (‘hybridis-ation’) between these two races (Marova &Leonovich 1993). Their research reported awide area of overlap in the breeding areas ofabietinus and tristis, from the Kanin Peninsulato the southern Urals and Bashkiria. ‘Mixed’songs were recorded in various parts of thiszone of sympatry. Together with the existence ofspecimens deemed to show ‘hybrid’ characters,the conclusion of Marova & Leonovich was thatextensive ‘hybridisation’ occurs across the wholearea of sympatry.

The different conclusions of Martens &Meincke were considered invalid by Marova &Leonovich, as the former based their experi-ments on the whole range of tristis rather thanon the zone of sympatry. Thus, ‘the recordingsused for analysis were taken considerably to theeast of the distribution of fulvescens’ (IrinaMarova-Kleinbub in litt.). In fact, Martens &Meincke used the Yenisey as a dividing linebetween ‘fulvescens’ and tristis, and comparedrecordings from both sides of the divide, so thisobjection is probably unfounded.

More recently, Antero Lindholm has made apreliminary study of the vocalisations of birdsfrom the region of Syktyvkar, Komi (c. 62°N51°E; Fig. 1). This is research ‘in progress’ butappears to indicate that so-called intermediatesong occurs in a region on the western fringesof the known range of ‘fulvescens’, and side byside with abietinus song. The appearance andsong of most ‘intermediate singers’ are tristis-like but a variable amount of abietinus-like ele-ments are present in the song (AnteroLindholm in litt.). At this stage, the results aredeemed to support the idea that ‘fulvescens’ is a

‘hybrid’ population, as advocated by Marova &Leonovich. However, Lindholm does not as yetdraw any firm conclusions, as these findingsneed to be confirmed on a larger sample, and adetailed comparison with eastern tristis is yet tobe carried out. Furthermore, a certain amountof ‘mixed’ singing can result from one speciesadopting part of the song of another specieswhich is present at high density in its natal area,and is not necessarily proof of hybridisation(Clement et al. 1998).

An alternative scenarioLS has suggested that the situation with tristisand abietinus may be similar to that with colly-bita and ibericus. It is now known that collybitaand ibericus still hybridise in the contact zone insouthwest France and northern Spain and thatmixed singers are produced (see above for anoutline of vocalisation studies). However,hybrids are less frequent than would beexpected if the two interbred freely and unhin-dered, and they are not as successful as pure off-spring (Salomon et al. 1997). A similar situationmight exist in the contact zone between tristisand abietinus.

In a preliminary text for the forthcomingGeographical Variation and Distribution ofPalearctic Birds (Roselaar & Shirihai in prep.),Kees Roselaar has independently suggested asimilar hypothesis:

In the west of the range, from the Severnaya Dvinaand the Pechora basins east to the Urals, [tristis] over-laps with Ph. collybita abietinus. In this overlap zone,the situation is apparently comparable with that ofPh. ibericus and Ph. c. collybita in N Spain and SWFrance: locally, both taxa overlap without apparentinterbreeding (e.g. in the southern Urals, where bothare common), but elsewhere birds with mixed song ormixed plumage characters occur (Marova &Leonovich 1993). These latter birds are found mainlyat the extreme western end of the range of tristis,where mixing apparently occurs because favouredpartners are scarce or unavailable (mixed song mayalso be due to the fact that pure tristis adopts part ofthe song of the more common abietinus). Thus,mating in the overlap area is likely to be assortive, asin the ibericus/collybita case, preventing extensivegene-flow between both, a reason to consider tristis tobe a separate species, an action supported by the fairdifference in mitochondrial DNA between both (seeHelbig et al. 1996).

If vocalisations are already establishing bar-riers to interbreeding between abietinus and



westerly tristis, then tristis might be bettertreated as a separate species. In the eventualitythat tristis were accorded species status, then itmight also be preferable to formally recognisethe extreme end of its morphological variation,represented by ‘fulvescens’. It is interesting tonote at this point that some Russian authorswho have recognised ‘fulvescens’ as a valid racehave further considered that chiffchaffs occu-pying the Southern Urals result from ‘hybridisa-tion’ between ‘fulvescens’ and abietinus(Buturlin & Dementiev 1937, per Irina Marova-Kleinbub). Confirmation of the true taxonomicrelationships throughout this region must awaitmore extensive studies, using trapping, DNAand bioacoustic ‘play-back’ techniques. Muchclarification would surely result from a pro-gramme to trap singing or calling birds and,from known vocalisation, build up a knowledgeof morphology and DNA.

CallsThe typical call of collybita and western abie-tinus is a plaintive, soft, modulated andascending ‘hooeet’ or ‘hüit’. It has a discerniblydisyllabic structure, though less distinctly sothan the comparable call of Willow Warbler. Ingeneral, the emphasis lies on the second syllablein Common Chiffchaff, but more evenly onboth in Willow Warbler.

The principal call associated with tristis is anearly monosyllabic note, often rendered as‘peet’ or similar in English texts but perhapsmore accurately transcribed as ‘iiihp’ (Jännes2002). It is clearly higher-pitched than thetypical call of collybita, is rather shrill(‘squeaky’) and just perceptibly descendingtowards the end. It is often likened to the dis-tress call of a young chicken, or to the call ofCoal Tit Parus ater. The call of ‘fulvescens’-typebirds is reported to be very similar to, if notidentical with, the typical call of tristis.

From late summer in Britain, a rathershriller and clipped ‘sweeu’ is uttered by colly-bita (particularly, if not exclusively, by first-autumn birds). A variant call reported fromautumn migrants in western Europe is similarlydescribed, as ‘a slightly higher-pitched, faster,and more compressed version of the normalcall (‘chreep’, ‘treeu’)’, but has been attributed toeastern populations of abietinus (Jännes 2002).There is some evidence that migrant and win-tering populations, assumed to be from dif-ferent parts of the breeding range, utter slightly

different calls (Copete & Armada 2004). Allthese variants still lack the shrilly monosyllabicquality of the classic tristis call but can be con-fused when heard in isolation or by those notfully familiar with the ‘classic’ call.

The characteristic note is a good indicator oftristis and some observers believe that tristisnever utters calls significantly different fromthis. Variant calls are sometimes ascribed totristis, as in BWP (‘Voice’, section 4a) and inClement et al. (1998), for example. However, agreat deal of ambiguity is evident in thedescriptions of ‘alternative’ calls, which nodoubt arises as much from difficulties of tran-scription as from true variation in the calls.Furthermore, it is likely that some variant callswere reported from individuals whose racialidentification was questionable.

Until an unequivocal exposition of variantcalls is forthcoming, the identity of any tristis-like individual which is not heard to utter the‘classic’ call should be regarded as suspect.

What are the ‘grey-and-white’ tristis-likechiffchaffs reported in Britain?It is clear from the preceding account that muchresearch remains to be done before a clearpicture emerges of morphological, vocal andtaxonomic limits in chiffchaffs east of thePechora basin. On current information, it is notpossible to equate a distinctively pale, ‘grey-and-white’ plumage with ‘fulvescens’. Both thetype description and the specimens from thedesignated breeding area indicate that this formis distinguished from ‘classic’ tristis primarily bythe presence of limited yellow streaking on theunderparts, the eye-ring and the supercilium.Although some features of ‘grey-and-white’chiffchaffs appear intermediate between thoseof abietinus and tristis, and may result fromintergradation between these two subspecies,the appearance of these birds is not typical of‘fulvescens’.

With regard to reports of ‘tristis-like’ chiff-chaffs in Britain, the following three factors areall likely to be involved in the high incidence ofdistinctively ‘grey-and-white’ individuals:

(1)‘Paler and greyer’ individuals include ‘inter-grades’ between abietinus and tristis.

(2)Some ‘paler and greyer’ individuals are paleextremes of abietinus.

(3)There is a range of variation in the colour ofupperparts and underparts in all races of





chiffchaff, and some perceived ‘paler andgreyer’ individuals fall within this range ofvariation and do not represent a ‘disconti-nuity’ in appearance (i.e. there is a certainamount of ‘wishful grouping’).

Additionally, it is conceivable that:(4)A paler and greyer type comes from a little-

studied part of the tristis range, and is poorlydocumented in the literature and under-rep-resented in collections. It is perhaps worthrecalling here that Severtzov’s designation of‘fulvescens’ included a variant ‘naevia’ whichpurportedly lacked yellow and was greyeroverall.

The approach to identification must addressthe full suite of plumage and vocal characteris-tics, aided at a minimum by high-quality pho-tographs and preferably by trapping (the latteralso providing subsidiary if not conclusive bio-metric data). The criteria as prescribed in theforthcoming edition of Identification Guide toEuropean Passerines (Svensson in prep.), andtranscribed above, remain the most reliableguide to segregating certain tristis, though somegenuine tristis may be excluded in the process.Unless and until clarification of variant calls isforthcoming, any tristis-like individual thatdoes not utter the classic, shrill, almost mono-syllabic ‘iiihp’ should be regarded as question-able. The identity of some individuals willremain speculative; knowledge of the mor-phology (and taxonomy) of chiffchaffs fromEuropean Russia east to the Yenisey is far fromcomplete.

Case studiesExamples of ‘grey-and-white’ tristis-like chiffchaffs were recorded in England at Upton-on-Severn, Worcestershire, and at Coleshill,Warwickshire, during winter 2004/05. Both frequented the vicinity of sewage works, anincreasingly common habitat for reports of‘Siberian Chiffchaffs’. The Worcestershire birdwas trapped and examined in the hand. Goodphotographs were obtained of both, and theseprovide useful illustration of some of the pointsmade above. Although both were rather ‘greyand white’ the two individuals were somewhatdifferent in appearance in important characters.

The Upton-on-Severn birdThis individual was trapped in December 2004and found to possess a good suite of characters

for tristis. Although quite ‘grey and white’, it wasless pale than the Warwickshire bird and alsodisplayed evident, if limited, buff on the breastand flanks (plates 241 & 242).

In plate 241, note the obvious deep buff onthe ear-coverts, upper eye-ring and on thesupercilium. There is no yellow away from thebend of the wing, while olive is absent or verylimited on the crown and mantle. These are allgood indicators of tristis. There is olivestreaking in the scapulars, while the fringes tothe flight feathers are prominent and ratheryellowish-olive, more so than is typical in‘classic’ tristis. In plate 242, note the buff washto the sides of the throat and on the flanks; thisis fairly restricted, however, and the centre ofthe throat is much whiter. It is unlikely,however, that abietinus would ever show noyellow at all away from the underwing in com-bination with a distinct buff suffusion to thesupercilium and underparts.

The general hue of the upperparts is quitegrey, enhancing the contrast of the olive fringesin the plumage. In these respects it differs quitesignificantly from classic tristis, which has muchmore saturated brown or grey-brown upper-parts, more prominent buff on the cheeks andthroat, and less bright olive fringes, producing amuch more subdued appearance overall. Thebill of the Upton-on-Severn individual alsoappears rather more robust than is typical of‘classic’ tristis, which has a relatively small, darkbill. Compare this individual with the tristis inplates 235 & 237 and the abietinus in plate 240.The Upton-on-Severn individual may well haveoriginated from the region of sympatry and‘intergrading’ of tristis and abietinus. However,

241. Purported ‘Siberian Chiffchaff ’ Phylloscopuscollybita tristis,Worcestershire, December 2004.

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it is greyer than is typical of ‘fulvescens’ andlacks the yellow streaking which characterisesthat form. It is tempting to speculate that itscharacters recall those which Severtzov ascribedto the variant ‘naevia’ but, unfortunately,precise data on the characters and provenanceof ‘naevia’ are lacking. The call was described as‘like that of tristis’. Supplied descriptions andtranscriptions included ‘monosyllabic “seee”,not dissimilar to call of Bullfinch Pyrrhulapyrrhula, but higher-pitched and weaker intone’ but also ‘almost disyllabic’ and ‘pseeoo’.The last at least suggests one of the supposed‘variant’ calls of tristis or the call ascribed toeastern abietinus rather than the virtuallymonosyllabic and shrill ‘peet’ or ‘iiihp’ of classictristis (see above). A rather similar-looking indi-vidual, judging from a published photograph,was observed in Lincolnshire during 11th–15th

March 1989 (Catley 2000). That bird was heardsinging and calling, and the description of itsvocalisations shows clear affinities with tristis.

The Coleshill birdThe Coleshill bird was especially pale, withmarkedly grey-looking upperparts and ‘clean’whitish underparts (plate 243). Severalobservers commented that its general huesrecalled a Bonelli’s warbler while, at a distancewhen flycatching, the whiteness of the under-parts even prompted comparisons with SpottedFlycatcher Muscicapa striata. This individualwas a prime example of the divergence inopinion over tristis characteristics, with viewsstrongly divided between those who regarded itas a ‘good tristis’ and those who deemed it to bean ‘intergrade’ or a pale abietinus.

Several early and more distant photographssuggested a tinge of yellow on the fore-super-cilium and this encouraged speculation that thebird was an ‘intergrade’. It was clear, however,that many such photographs were not ‘colourneutral’. In some, although admirably sharp, thebird looked too brown above and the olivefringes to the flight feathers, quite clear in thefield, were suppressed.

Thanks to the persistence of one or two pho-tographers, photographs of high fidelity wereeventually obtained. The colour balance ofthese pictures (reproduced here) is clearly accu-rate, matching impressions in the field and alsospanning the full range of hues through white,buff, yellow and olive. These photographsdemonstrate that the supercilium was in factlight buff above the lores (and not yellow). It is

clear from this experience that‘buff ’ may be translated into a‘tinge of yellow’ in digital pho-tographs, particularly if the imagesize is rather small.

At face value, there are severalcharacters visible in the photo-graph of the Coleshill bird whichsuggest tristis. Olive is confined tothe scapulars, back, rump andedges to the flight feathers. Thereis no olive on the crown or upperpart of the mantle. The only yellowis at the bend of the wing and alimited amount on the underwingcoverts (plate 244). All these fea-tures are good tristis characters.Although buff is present in the



242. Purported ‘Siberian Chiffchaff ’ Phylloscopuscollybita tristis,Worcestershire, December 2004.

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243. Purported ‘Siberian Chiffchaff ’ Phylloscopus collybita tristis,Warwickshire, February 2005.

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supercilium, it is confined to the front of theeye. To the rear of the eye the supercilium iswhite and, together with the ear-coverts, is lessextensively buff than in ‘classic’ tristis. Thefringes of the flight feathers are again a littlemore yellowish-olive than is typical in tristis.The bare parts are also an area of concern. Thecutting edges to the bill are arguably ratherextensively pale for tristis. More importantly,the legs and especially the upper surface of thefeet are less intensely black than on the majorityof ‘classic’ tristis.’

The most pronounced features of this indi-vidual were its paleness and generally grey-and-white appearance. Above all else, its palenessand white underparts led many observers toconclude that ‘it must be something different’.This was certainly an extremely pale chiffchaffbut such a degree of paleness is not character-istic of tristis, certainly not ‘classic’ individualsfrom east of the Yenisey. There is none of thesaturated colour of the upperparts which char-acterises ‘classic’ tristis, nor the buff wash on thebreast and flanks. Various descriptions of its callwere forthcoming but, again, these did notinclude the almost monosyllabic ‘peet’ or ‘iiihp’of classic tristis and at least some observersreported a clearly disyllabic call which theyregarded as ‘not that different from collybita’.

While the absence of yellow (apart from onthe underwing) and the lack of olive in thecrown and upper mantle suggest tristis intro-gression, the appearance of this individual does



244. Purported ‘Siberian Chiffchaff ’ Phylloscopuscollybita tristis,Warwickshire, February 2005.

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245. Purported ‘Siberian Chiffchaff ’ Phylloscopuscollybita tristis,Warwickshire, February 2005.

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not correspond with ‘fulvescens’ as defined anddiscussed above. Even among the experts con-sulted there was no unanimity of opinion onthe identity of this individual. It remains a pos-sibility that individuals like this are abietinusfrom the easternmost part of the range. Thebird’s appearance cannot be matched by speci-mens in the collection at NHM, Tring (pers.obs.), but the specimen collection at Ams-terdam apparently includes examples of abiet-inus from European Russia (south Volga) whichare not dissimilar to the Warwickshire indi-vidual (C. S. Roselaar in litt.).

One final item of interest is that a number oftristis and tristis-like individuals in Britain havebeen reported as calling relatively infrequentlycompared with collybita and abietinus associ-ating with them. This infrequent calling wasnoted for both the Worcestershire bird and theWarwickshire individual.

Summary• Considerable confusion surrounds the sys-

tematic and morphological limits ofCommon Chiffchaff of the Siberian sub-species tristis.

• The plumage of typical tristis from east of theYenisey is predominantly brown or greyish-brown on the upperparts; the underparts aresuffused with buff, particularly across thebreast and lower throat; and yellow is lacking

in the plumage, apart from at the bend of thewing and on the underwing-coverts. It israther similar to Mountain Chiffchaffalthough, unlike that species, it has olivefringes to the flight feathers and an olive tingeon the lower back and rump.

• In contrast, many tristis-like individualsreported in Britain are decidedly pale andgrey, often with conspicuously white under-parts. Such individuals are frequently attrib-uted to the form ‘fulvescens’, which isgenerally regarded as a westerly componentof tristis, breeding between the Pechora basinand the Yenisey.

• The form ‘fulvescens’ was originally describedby Severtzov in 1873, from a series ofmigrants taken in Central Asia. Both the basicdescription from the ‘type series’ and themore recent examinations of specimens fromwestern Siberia indicate that ‘fulvescens’ is not,however, noticeably greyer or whiter thanmore easterly tristis. Rather, it differs pri-marily in the presence of limited yellowstreaking at the sides of the breast, in thesupercilium and on the upper part of the eye-ring. This additional yellow has been inter-preted by some researchers as indicative ofintergradation between tristis and abietinus.

• Research within the breeding range has pro-duced conflicting conclusions about thestatus of ‘fulvescens’. Opinion remains dividedas to whether ‘fulvescens’ results from wide-spread and unhindered interbreedingbetween tristis and abietinus in a zone ofsympatry (a ‘hybrid swarm’) or whether it issimply a westerly component of tristis.

• An alternative scenario is that limited inter-breeding occurs between tristis and abietinusbut that reproductive barriers are alreadydeveloping, based primarily on vocal differ-ences, and that breeding is to some extentassortive. Under this scenario, tristis may bebetter treated as a separate species and ‘ful-vescens’ perhaps should be regarded as a sub-species of tristis.

• From specimens, it is not possible to detect agrouping of individuals from one part of therange of tristis (including ‘fulvescens’) whichis conspicuously ‘greyer and whiter’ than theremainder.

• Although some ‘grey-and-white’ chiffchaffsmay involve intergrades, their appearancedoes not match typical ‘fulvescens’. A variant‘naevia’ included by Severtzov in the ‘type

description’ was noted as lacking yellow, atleast in juvenile plumage, and being greyeroverall. However, the location of the typespecimen of ‘naevia’ is currently unknown, soits precise characters are uncertain.

• Other reports of ‘grey-and-white’ chiffchaffsalmost certainly include pale extremes ofabietinus from European Russia, which maybe surprisingly deficient in both olive andyellow. It is also conceivable that a paler andgreyer type exists in a little-studied part ofthe tristis range, and is poorly documented inthe literature and little represented in collec-tions. Finally, the extent of individual varia-tion among the westerly races of chiffchaffmust not be underestimated.

• The full plumage limits of tristis and abie-tinus, and the extent of their overlap, remainto be determined. The most reliable criteriafor segregating certain tristis are presentedabove (and will be published in the forth-coming edition of Identification Guide toEuropean Passerines), although they mayexclude some genuine tristis. Plumage andbiometric criteria should be supported byprecise interpretation of vocalisations.

Acknowledgments

For clarification of research findings within the breedingrange of ‘fulvescens’ we are indebted to Dr Irina Marova-Kleinbub. Comments on ‘fulvescens’ and a translation ofSevertzov’s type description were kindly provided by DrVladimir Loskot. Further comments on the type descrip-tion were offered by Dr Pavel Tomkovich.Antero Lindholmsupplied details of his vocalisation studies from the regionof Komi, while Kees Roselaar provided information onboth tristis and abietinus, and kindly consented to the inclu-sion of an extract from his forthcoming book, written withHadoram Shirihai. For useful discussion of tristis and tristis-like chiffchaffs in general, or the Warwickshire and Worces-tershire individuals in particular, we are grateful to LeeEvans, Martin Garner, P. A. Lassey, Killian Mullarney, AndrewWarr and S. M. Whitehouse. Bo Petersson kindly com-mented upon the plumage variation of abietinus trapped insouthern Sweden. Excellent photographs of the Warwick-shire and Worcestershire chiffchaffs featured here wereprovided by John Harris, Brian McGeough, Jim Milne, SteveSeal and Andrew Warr. Although only a few of the imagescould be published, all the photographs provided invalu-able reference material. Mark Adams kindly arrangedaccess to the skin collection at NHM, Tring, and providedvaluable assistance on site. Help with contacts and refer-ences was provided by Per Alström, Martin Collinson andGeorge Sangster. Finally, for assistance in a variety of ways,we thank Steve Cawthray, Dave Clifton and John Galletly.

References

Baker, K. 1997. Warblers of Europe,Asia and North Africa.Christopher Helm, London.

Buturlin, S.A., & Dementiev, G. P. 1937. [Identification Guideto the Birds of the USSR.Vol. 4. Passeriformes.] Moscow-



Leningrad. (In Russian)Catley, G. P. 2000. Song and call of a ‘Siberian Chiffchaff ’.

Brit. Birds 93: 456.Clement, P., Helbig,A. J., & Small, B. 1998.Taxonomy and

identification of chiffchaffs in the Western Palearctic. Brit.Birds 91: 361–376.

Copete, J. L., & Armada, R. 2004. Unusual calls of ChiffchaffsPhylloscopus collybita in NE Spain in autumn-winter : analert to Spanish observers. Rare Birds in Spain (websitehttp://www.rarebirdspain.net/arbsi026.htm).

Cramp, S. (ed.). 1992. The Birds of the Western Palearctic.Vol. 6. OUP, Oxford.

Dean,A. R. 1985. Review of British status and identificationof Greenish Warbler. Brit. Birds 78: 437–451.

Glutz von Blotzheim, U. N., & Bauer, K. M. 1991. Handbuchder Vögel Mitteleuropas.Vol. 12.AULA-Verlag,Wiesbaden. (In German)

Heard, C. D. R. 1989. Racial identification of winteringchiffchaffs. Birding World 2: 60–65.

Helbig,A. J., Martens, J., Seibold, I., Henning, F., Schottler, B.,& Wink, M. 1996. Phylogeny and species limits in thePalearctic Chiffchaff Phylloscopus collybita complex:mitochondrial genetic differentiation and bioacousticevidence. Ibis 138: 650–666.

Jännes, H. 2002. Calls of Eastern Vagrants (CD and booklet).Hannu Jännes/EARLYBIRD Tours, Helsinki.

Marova, I. M., & Leonovich,V.V. 1993. [Hybridisation ofSiberian and European Chiffchaffs in the zone ofsympatry.] Proc. Zool. Mus. Moscow University 30:147–164. (In Russian)

Martens, J., & Meincke, C. 1989. [The Siberian ChiffchaffPhylloscopus collybita tristis: song and reaction of acentral European population in field tests.] J. Orn. 130:455–473. (In German)

Mild, K. 1987. Soviet Bird Songs (two cassettes and booklet).Privately published, Stockholm.

Roselaar, C. S., & Shirihai, H. In prep. Geographical Variationand Distribution of Palearctic Birds.

Salomon, M., Bried,A. J., Helbig,A. J., & Riofrio, J. 1997.Morphometric differentiation between male CommonChiffchaffs Phylloscopus [c.] collybitaVieillot, 1817, andIberian Chiffchaffs P. [c.] brehmii Homeyer, 1871, in asecondary contact zone (Aves: Syllviidae). Zool.Anzeiger236: 25–36.

Severtzov, N.A. 1873. [Vertical and Horizontal Distribution ofTurkestan Wildlife.] Turkestan. (In Russian)

Svensson, L. 1984a. Identification Guide to EuropeanPasserines. 3rd edn. Privately published, Stockholm.

— 1984b. Soviet Birds (cassette and leaflet). Privatelypublished, Stockholm.

— 1992. Identification Guide to European Passerines. 4thedn. Privately published, Stockholm.

— In prep. Identification Guide to European Passerines. 5th edn.Ticehurst, C. 1938. A Systematic Review of the Genus

Phylloscopus (Willow-warblers or Leaf-warblers). BMNH,London.

Vaurie, C. 1959. The Birds of the Palearctic Fauna – OrderPasseriformes.Witherby, London.

Williamson, K. 1967. Identification for Ringers, 2.The GenusPhylloscopus. 2nd edn. BTO,Tring.



Alan R. Dean, 2 Charingworth Road, Solihull, West Midlands B92 8HTLars Svensson, S:ta Toras väg 28, S-260 93 Torekov, Sweden

Appendix 1: Identification of Phylloscopus collybita abietinus (Nilsson 1819)

Taken from Svensson (in prep.). Ssp. collybita and abietinus are extremely similar. When long and com-parable series (same season, similar wear, etc.) are examined, the following characteristics emerge (allmeasurements in mm unless stated, primaries numbered ascendantly):

(1) Ssp. abietinus is slightly larger; wing-length on skins up to 68 mm, whereas collybita has amaximum of 63 mm. In more detail:abietinus �� 59.5–68, m 63.77, n 35; �� 57–64, m 60.08, n 12;collybita �� 55.5–63, m 60.08, n 77; �� 52.5–60, m 55.87, n 43.For live birds, an additional 1 mm to all measurements should be allowed.

(2) Ssp. abietinus has, on average, subtly paler upperparts, which are a little purer greyish-green;whereas collybita is a trifle darker and slightly tinged brown, primarily on mantle and crown. Withincreasing wear in late May, some collybita attain a darker, more brown-grey crown than the moregreenish mantle, producing a contrast which is rarely as pronounced on abietinus (usually no morethan a slight suggestion). The darker crown in (some) collybita is partly due to darker feather-basesbeing exposed (perhaps due to somewhat earlier and heavier wear), but also to a slightly darkerground colour.

(3) The tarsi in abietinus are, on average, slightly darker than in collybita, blackish-brown (sometimesdescribed as ‘dark flesh’) rather than medium to dark brown.

(4) The distance between first and second primaries (P1 < P2), is on average slightly shorter in collybita than in abietinus: in collybita 19–26, m 23.13, n 118, in abietinus 22.5–29.5, m 25.88, n 51.

(5) The distances between tip of wing (P4) and outermost secondary (S1), tenth primary (P10), andtip of primary-coverts (PC) differ as follows: P4 > S1 in abietinus 11.5–15, in collybita 9–12.5;P4 > P10 in abietinus 10–13, in collybita 8.5–11; P4 > PC in abietinus 35–41, in collybita 31–39.

'Siberian Chiffchaff revisited

(6) Ssp. collybita has marginally longer bill (to skull) but shorter wing. The ratios between these (Bs/W x 100) are as follows: abietinus 16.4-19.1 (n 45), although some females with wing shorter than 60 mm maybe up to 19.7 (n 3); collybita 17.9-22.4 (n 111).

(7) By using a more elaborate formula, more birds can be separated: (P4 > P10) + (P4 > SI) + (P2 > PI) - tarsus - (Bs/W x 100) = MCV

If MCV (Multiple Character Value) is greater than 10.0, the bird is most likely an abietinus, if less than 10.0 it is probably a collybita. The variation in the two taxa is 8.0-19.9 in abietinus, and 10.7 or less in collybita (including negative values). Only 12 out of 125 (9.6%) fell in the overlap zone 8.0-10.7. Furthermore, 85% of all abietinus (n 40) had a value greater than 10.0,93% of all collybita (n 85) had a value lower than 10.0. The MCV is partly a function of an average slight difference in wing formula, abietinus having a slightly more pointed wing than collybita (for instance, male abietinus much more often having P2 = 6/7 than male collybita). There is, however, much overlap and little guidance from the position of P2 alone.

The above guidelines are aimed primarily at ringers and museum researchers, but should be of some use in the field. Apart from those listed, subtle and average differences exist in structure and proportions, e.g. collybita often appears larger-headed and/or shorter-necked, and abietinus somewhat more elongated and long-winged. However, these characters are more variable and 'personal' and should be applied with caution; they also depend significantly on the general size of each bird.

Descriptions often mention that abietinus has, on average, whiter underparts than those of collybita. It is true that an average difference exists, but the underparts coloration is more variable than often perceived, with near-total overlap between the two taxa when the very pale birds in the extreme northeast of the range are excluded. For these pale birds, though, the near-total lack of yellow beneath (except on the underwing) becomes an additional character for abietinus as opposed to collybita.


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