Warblers and Long-tailed Tit

Cetti’s Warbler Cettia cetti

Cetti’s Warbler comprises three subspecies. Nominate cetti occurs across western Europe. It is replaced by orientalis in Turkey, the Caucasus, the Levant and northern Iraq and by albiventris from the Volga delta through southern Central Asia to westernmost China, the latter two known collectively as ‘Eastern Cetti’s Warbler’. Variation is clinal, however, and the boundaries between the forms are not well defined (Cramp et al. 1992).

Only nominate cetti is on the British List but orientalis and albiventris are perhaps potential vagrants. The latter are more migratory than nominate cetti and birds resembling albiventris have reached Israel. An eastern bird, potentially orientalis, has been submitted from East Sussex but, although a promising candidate, it was found ‘not proven’.

Identification of vagrant subspecies is problematic. Birds become larger and paler towards the east but the differences are minor and only the most extreme examples will be identifiable. Western orientalis resemble nominate cetti but eastern orientalis are more similar to albiventris. Important features of the latter are a larger size/wing length, pale upperparts, pale underparts and virtually white undertail coverts. Biometrics would be useful for a trapped bird.

Claims of potential orientalis or albiventris are welcomed if accompanied by detailed notes and good photographs but only trapped birds with full biometrics noted are likely to gain acceptance, if not to a particular subspecies then at least to an orientalis/albiventris subspecies pair. A ringing recovery would provide additional evidence. (updated Dec 2017 AMS).

References

Cramp, S. et al. 1992. The Birds of the Western Palearctic Vol 6. Oxford University Press, Oxford.

Svensson, L. 1992. Identification Guide to European Passerines. Privately published, Stockholm.

 

Long-tailed Tit Aegithalos caudatus

Long-tailed Tit comprises seventeen subspecies. Of relevance here are three of these – rosaceus (‘British Long-tailed Tit’), endemic to Britain and Ireland, europaeus (‘Central European Long-tailed Tit’), breeding in western, central and south-east Europe, and nominate caudatus (‘Northern Long-tailed Tit’), breeding across Scandinavia, European Russia and northern Asia. Nominate caudatus and europaeus intergrade in a zone stretching from Denmark through eastern Germany and southern Poland to northern Romania and southern Ukraine, resulting in birds of intermediate appearance. This intergrade zone may be shifting southwards.

The subspecies europaeus is a contentious form, some authors regarding it as a fully valid (albeit variable) subspecies, others as an intergrade population between nominate caudatus and the darker southern European forms. The vast majority are close to rosaceus (though fractionally paler) but some exhibit nominate caudatus-like characters, including a partially or largely white head. Whether all such birds represent intergrades with nominate caudatus or whether some may represent variability within europaeus remains the subject of debate (Cramp et al. 1993, Harrap & Quinn 1996, Jansen & Nap 2008).

The subspecies rosaceus is common in Britain. Nominate caudatus is also on the British List, and although its historical status is a little obscure, it is now recognised as very rare. The subspecies europaeus was formerly on the British List on the basis of a specimen from Kent in 1882 but it has now been removed (BOU 2014). However, this subspecies is known to be dispersive and is a likely vagrant, indeed a number of birds resembling either this subspecies or nominate caudatus x europaeus intergrades have been recorded here.

Nominate caudatus is a striking subspecies but it needs to be separated from nominate caudatus x europaeus intergrades. The key feature is a wholly white head but the pattern of the tertials, scapulars and underparts should also be noted, although these are somewhat variable. Quite what constitutes a fully ‘pure’ nominate caudatus remains contentious, however, some authors (e.g. Jansen & Nap 2008) advocating that the merest hint of grey on the head excludes this subspecies whilst most authors (e.g. Kehoe 2006) consider some faint grey streaking in the head to be within the range of variation. More clearly-defined head streaking forming ‘ghosted’ coronal bands and/or grey streaking in the ear coverts or across the breast would, however, definitely exclude nominate caudatus.

The identification of europaeus is problematic and it is not clear how most could be confidently distinguished either from a pale-looking rosaceus or, in the case of partially white-headed birds, from a nominate caudatus x europaeus intergrade. It is also possible that a leucistic or aberrant roscaeus might resemble europaeus, as might the offspring of any pairing of a continental vagrant with a British bird. Biometrics provide no useful clues.

Claims of nominate caudatus are welcomed if accompanied by detailed notes and preferably photographs. Claims of europaeus are welcomed if accompanied by a ringing recovery. (updated Dec 2017 AMS).

References

BOU. 2014. British Ornithologists’ Union 42nd Report. Ibis 156: 236-242.

Cramp, S. et al. 1993. The Birds of the Western Palearctic Vol 7. Oxford University Press, Oxford.

Harrap, S. & Quinn, D. 1996. Tits, Nuthatches and Treecreepers. Helm, London.

Jansen, J. F. J. J. & Nap, W. 2008. Identification of White-headed Long-tailed Bushtit and occurrence in the Netherlands. Dutch Birding 30: 293-308.

Kehoe, C. 2006. Racial identification and assessment in Britain. British Birds 99: 619-645.

Small, B. 2004. The Northern Long-tailed Tits in Suffolk. Birding World 17: 12.

Svensson, L. 1992. Identification Guide to European Passerines. Privately published, Stockholm.

 

Willow Warbler Phylloscopus trochilus

Willow Warbler comprises three subspecies – nominate trochilus from Britain, central Europe and southern Scandinavia, acredula (‘Northern Willow Warbler’) from northern Scandinavia, Russia and western Siberia and yakutensis (‘Siberian Willow Warbler’) from central and eastern Siberia. However, the subspecies are not well defined and there is extensive intergradation. Furthermore, variation is not linear, and birds showing the characters of one subspecies occur regularly within the range of another (Cramp et al. 1992).

Nominate trochilus is an abundant summer visitor and passage migrant to Britain, whilst acredula is a common pasage migrant, mainly to the east coast. The subspecies yakutensis is not on the British List but is a potential vagrant and birds showing its published characters have been noted in Britain.

The identification of yakutensis is problematic, however. This subspecies tends to be more grey-brown above and off-white below, with very little green and yellow in the plumage, but given the extensive intergradation with acredula and the appearance of yakutensis-like birds within the range of both acredula and nominate trochilus, it is not clear how a firm diagnosis can be made. Biometrics might be useful in some cases, yakutensis being on average longer-winged than the other subspecies.

Claims of potential yakutensis are welcomed if accompanied by detailed notes, good photographs and biometrics but a ringing recovery is probably necessary to secure its admission to the British List. (updated Dec 2017 AMS).

References

Cramp, S. et al. 1992. The Birds of the Western Palearctic Vol 6. Oxford University Press, Oxford.

Svensson, L. 1992. Identification Guide to European Passerines. Privately published, Stockholm.

 

Reed Warbler Acrocephalus scirpaceus

Reed Warbler comprises four subspecies but two are of most relevance here. Nominate scirpaceus breeds in Europe east to Ukraine, the eastern subspecies fuscus (‘Caspian Reed Warbler’) in central Turkey and the Caucasus east to north-west China and south to the Middle East. Nominate scirpaceus varies little across its range but fuscus exhibits extensive and complex though clinal variation. In general terms, birds become larger/longer-winged and paler towards the east but several plumage types (termed ‘warm’, ‘typical’ and ‘grey’) have been identified whilst birds from the Middle East are noticeably small. Genetic differences have also been identified between some of these types. It is therefore possible that further subspecies could be described within what is currently termed ‘fuscus’ (Kennerley et al. 2002). There is also moderate genetic distance between scirpaceus and fuscus, the former being more closely related to African Reed Warbler A. baeticatus. The taxonomy of this complex might therefore not yet be settled.

Nominate scirpaceus is a common summer visitor to Britain. The subspecies fuscus has now been identified in Britain on the basis of DNA-tested birds in Lancashire in December 2011 and on Shetland in November 2012. These birds have now been accepted onto the British List. Further occurrences have been suspected although to date no others have been proven.

The identification of fuscus is highly problematic and there is also the potential for confusion with Marsh Warbler A. palustris and Blyth’s Reed Warbler A. dumetorum. Many, particularly ‘warm-coloured’ birds, are inseparable from nominate scirpaceus but birds of the ‘typical’ or ‘grey’ types might attract attention and would be worthy of close study. In describing the appearance of a fuscus candidate, observers should focus on the colour of the upperparts and underparts, the colour of the primaries (including any pale tips) and the extent of any pale in the fringes/tips of the tail feathers. Vocalisations offer no useful clues and biometrics are similarly of little value. Further research into the field identification of fuscus may enable progress to be made but, for the moment at least, this subspecies seems only to be provable in a vagrant context by DNA analysis.

Claims of fuscus are welcomed if accompanied by detailed notes, good photographs, biometrics and, crucially, DNA evidence or a ringing recovery. (updated Dec 2017 AMS).

References

Cramp, S. et al. 1992. The Birds of the Western Palearctic Vol 6. Oxford University Press, Oxford.

Garner, M. 2014. Challenge Series: Autumn. Birding Frontiers.

Kennerley, P. & Pearson, D. 2010. Reed and Bush Warblers. Helm, London.

Pearson, D. J., Small, B. J. & Kennerley, P. R. 2002. Eurasian Reed Warbler: the characters and variation associated with the Asian form fuscus. British Birds 95: 42-61.

Svensson, L. 1992. Identification Guide to European Passerines. Privately published, Stockholm.

 

Grasshopper Warbler Locustella naevia

Grasshopper Warbler comprises three subspecies – nominate naevia in west, central and northern Europe and western Russia, obscurior in the Caucasus and straminea (‘Eastern Grasshopper Warbler’) in western Siberia, Kazakhstan, north-west China and western Mongolia. The subspecies obscurior is an isolated population but nominate naevia intergrades with straminea.

Nominate naevia is a common summer visitor to Britain. A straminea on Fair Isle, Shetland in September 2012, its identity confirmed by DNA analysis, has now been accepted onto the British List (Hudson et al. 2014, Miles et al. 2015).

The identification of straminea is highly problematic, indeed on curent knowledge it is virtually indistinguishable from naevia/obscurior, whilst there is also the potential for confusion with Lanceolated Warbler L. lanceolata. It is polymorphic although the most easterly birds are small and grey, show well-defined upperparts streaking, pale lores and (often) little marked underparts. However, small and/or grey birds also occur in western populations. There are no vocal differences. Biometrics are potentially useful, straminea being significantly smaller than naevia/obscurior and having a more rounded wing but not all individuals are identifiable. In reality, straminea can only be proven in a vagrant context by DNA analysis.

Claims of straminea are welcomed if accompanied by detailed notes, good photographs, biometrics and, crucially, DNA evidence or a ringing recovery. (updated Dec 2017 AMS).

References

Cramp, S. et al. 1992. The Birds of the Western Palearctic Vol 6. Oxford University Press, Oxford.

Harvey, P. V., & Small, B. J. 2007. From the Rarities Committee’s files: Eastern Grasshopper Warbler – are there any confirmed British records? British Birds 100: 658-664.

Hudson, N. & the Rarities Committee. 2014. Report on rare birds in Great Britain in 2013. British Birds 107: 579-653.

Kennerley, P. & Pearson, D. 2010. Reed and Bush Warblers. Helm, London.

Miles, W., Parnaby, D., Rosser, B., Moss, J. & Collinson, J. M. 2015. ‘Eastern Grasshopper Warbler’ on Fair Isle: new to Britain. British Birds 108: 231-236.

Svensson, L. 1992. Identification Guide to European Passerines. Privately published, Stockholm.

 

Lesser Whitethroat Sylvia curruca

Lesser Whitethroat comprises three subspecies – nominate curruca from Europe and western Russia, blythi (‘Siberian Lesser Whitethroat’) from central and southern Russia and northern Kazakhstan and halimodendri (‘Central Asian Lesser Whitethroat’) from southern Kazakhstan, north-west China and south-west Mongolia. Other forms traditionally included within Lesser Whitethroat are now treated as follows – Desert Lesser Whitethroat S. minula (with subspecies minula and margelanica) and Hume’s Lesser Whitethroat S. althaea (monotypic). Bioacoustical studies (Martens & Steil 1997) confirm the existence of three distinct song types within the complex corresponding with this three-way split. Recent genetic analysis (Olsson et al. 2013) identified six clades corresponding with curruca, blythi, halimodendri, minula, margelanica and althaea. These authors did not propose any new species limits but did indicate the potential for recognising perhaps as many as six species within the complex.

Nominate curruca is a common summer visitor to Britain and blythi is on the British List, categorised as a scarce migrant. The occurrence of blythi in Britain has long been recognised (e.g. Witherby et al. 1940) but its status was for a while obscured by a period of ‘taxonomic denial’ (e.g. Shirihai et al. 2001, Parkin & Knox 2010). However, with blythi now fully recognised once more as a valid taxon, an increasing number have been confirmed in Britain by DNA analysis (Collinson 2017) and field observations also suggest that this subspecies continues to be a regular scarce migrant, mainly to the Northern Isles and the east coast, in mid to late autumn but also in winter (and occasionally in spring). Significantly, all winter birds analysed to date have proven to be blythi.

The subspecies halimodendri is not on the British List but to date eight birds subjected to DNA anlaysis have proved to be of this subspecies. It still remains for halimodendri to be formally admitted to the British List but this process is in hand. It seems likely that this subspecies will prove to be a regular rarity in Britain.

The identification of halimodendri is not a straightforward task. Variation is clinal and age-related and a set of structural, plumage and vocal criteria has yet to be published although a paper is known to be in preparation. In the meantime, observers should focus on size, wing length/primary projection, tail length, bill size, the precise colour of the upperparts (including the nape), the colour of the underparts and, in first-year birds, the precise pattern of white in the outer tail feathers. However, even with all such details observed, a firm identification may not always be possible. Note also that photographs pose particular problems. The pale and subtle plumage hues of Lesser Whitethroats vary dramatically according to light conditions and are not reliably captured in images. Identifications relying on photographs rather than on field notes or other evidence will therefore be treated with particular caution.

Vocalisations offer useful clues and should be recorded where possible whilst full biometrics should be documented for a trapped bird. Any material from a trapped bird should be retained for DNA analysis.

Claims of halimodendri are welcomed if accompanied by detailed notes and good photographs. However, sound recordings, biometrics, a ringing recovery or DNA analysis would all provide more solid evidence and may be essential until field criteria can be defined. (updated Dec 2017 AMS).

References

Baxter, P. & Broadbent, I. 2004. The apparent Desert Lesser Whitethroat in Aberdeen. Birding World 17: 502-504.

Collinson, J. M. 2017. CSI: Birding. British Birds 110: 8-26.

Cramp, S. et al. 1992. The Birds of the Western Palearctic Vol 6. Oxford University Press, Oxford.

Garner, M. 2014. Challenge Series: Autumn. Birding Frontiers.

Holt, C. & Turner, S. 1999. The Desert Lesser Whitethroat on Fair Isle. Birding World 12: 281-283.

Martens, J. & Steil, B. 1997. Reviersgange und Speziesdifferenzierung in der Klappergrasmucken-Gruppe Sylvia [curruca]. J. Orn. 138: 1-23.

Kehoe, C. 2006. Racial identification and assessment in Britain. British Birds 99: 619-645.

Money, D. 2000. The Desert Lesser Whitethroat on Teesside. Birding World 13: 451-453.

Olsson, U., Leader, P. J., Carey, G. J., Khan, A. A., Svensson, L. & Alstrom, P. 2013. New insights into the intricate taxonomy and phylogeny of the Sylvia curruca complex. Mol. Phylogenet. Evol. 67: 72-85.

Parkin, D. T. & Knox, A. 2010. The Status of Birds in Britain & Ireland. Helm, London.

Pettersson, M. 2001. A Central Asian Lesser Whitethroat in Sweden. Birding World 14: 12-15.

Shirihai, H., Gargallo, G. & Helbig, A. J. 2001. Sylvia Warblers: Identification, taxonomy and phylogeny of the genus Sylvia. Helm, London.

Svensson, L. 1992. Identification Guide to European Passerines. Privately published, Stockholm.

Witherby, H. F., Jourdain, F. C. R., Ticehurst, N. F., & Tucker, B. W. 1940. The Handbook of British Birds. Witherby, London.

 

Whitethroat Sylvia communis

Four subspecies of Whitethroat taxonomy are recognised – nominate communis from western Europe and north-west Africa, volgensis from eastern Europe and western Siberia, icterops from Turkey, the Levant, the Caucasus and Iran and rubicola from Central Asia, southern Siberia and Mongolia, the latter three known collectively as ‘Eastern Whitethroat’. Variation is clinal, however, and the boundaries betwen the subspecies are not well-defined (Cramp et al. 1992, Shirihai et al. 2001).

Only nominate communis is on the British List but the other subspecies are potential vagrants and eastern birds have been suspected here (Cramp et al. 1992, Kehoe 2006).

Identification to a particular subspecies is problematic though there is a trend to larger size/wing length and paler, greyer and less rufous plumage from west to east. The subspecies volgensis is least distinctive, overlapping in appearance with nominate communis, but icterops and rubicola can be more striking. Vocalisations offer little help but biometrics would be useful for a trapped bird, particularly rubicola.

Claims of a potential vagrant subspecies are welcomed if accompanied by detailed notes and good photographs but biometrics or a ringing recovery are likely to be necessary for acceptance, either to a particular subspecies or to an icterops/rubicola subspecies pair. (updated Dec 2017 AMS).

References

Cramp, S. et al. 1992. The Birds of the Western Palearctic Vol 6. Oxford University Press, Oxford.

Kehoe, C. 2006. Racial identification and assessment in Britain. British Birds 99: 619-645.

Shirihai, H., Gargallo, G. & Helbig, A. J. 2001. Sylvia Warblers: Identification, taxonomy and phylogeny of the genus Sylvia. Helm, London.

 

Subalpine Warbler Sylvia cantillans

Subalpine Warbler comprises four subspecies. These are iberiae (Iberia, southern France and the north-west corner of Italy), inornata (north-west Africa), nominate cantillans (central and southern Italy and Sicily) and albistriata (Greece, western Turkey and the Balkans and the north-east corner of Italy). The first two of these form a subspecies pair known as ‘Western Subalpine Warbler’, the latter two a subspecies pair known as ‘Eastern Subalpine Warbler’.

Due to its increasingly regular occurrence (540 records published by the end of 2005), Subalpine Warbler was ‘dropped’ by BBRC at the end of that year though records of ‘Eastern Subalpine Warbler’ (then comprising just albistriata) were still sought. Due to taxonomic changes and a lack of clarity over identification criteria, the proportion of historical records assignable to each of the four subspecies now recognised is destined to remain unclear but the occurrence in Britain of albistriata, nominate cantillans and (presumed) iberiae (and therefore both ‘Eastern Subalpine Warbler’ and ‘Western Subalpine Warbler’ subspecies pairs) has now been confirmed by DNA analysis (Collinson et al. 2014). The subspecies inornata is not on the British List.

As now constituted, Subalpine Warbler sensu lato does not meet the threshold for BBRC consideration and any birds unidentified either to subspecies or subspecies pair should be considered by county and local records committees (as should any bird identified only to the level of ‘Moltoni’s or Subalpine Warbler’). However, each of its four subspecies (or either subspecies pair) do meet the criteria for consideration as rare subspecies whilst birds identified as either Moltoni’s Warbler or ‘Western Subalpine Warbler’ also fall within the rarity threshold and can be published as ‘either/or’ records.

In distinguishing these subspecies, spring males (especially adult males) represent the best opportunity though the differences are subtle and may only be apparent in good views in a variety of lighting conditions. Observers should pay particular attention to the precise colour of the underparts and upperparts, the strength of the malar stripe and the colour of the fringes to the wing feathers. The best submissions will include detailed notes on the precise plumage hues, in particular those of the underparts, and will ideally be supported by photographs. The committee is well aware of the difficulties in correctly assessing subtle hues in photographs so notes which comment on the degree to which any photographs correctly capture these hues will be important.

Call transcriptions/sound recordings will also be very useful in separating albistriata from the other subspecies (note, however, that there is some evidence that although close to albistriata in plumage, nominate cantillans has calls closer to western birds). For trapped birds, biometrics, moult stage information, details of the T5 pattern (the tip of the second outermost tail feather) and DNA analysis provide additional potential sources of evidence. With spring females, and all birds in autumn, these latter sources may represent the only sources of evidence (though it might be possible to photograph the tail pattern in the field). A ringing recovery would, of course, also provide solid evidence.

From 1st January 2015 BBRC welcomes submissions of any of the following:

Any bird identified as either Moltoni’s Warbler or ‘Western Subalpine Warbler’ (i.e. ‘Eastern Subalpine Warbler’ excluded) – confirmed by plumage and T5 pattern.

‘Western Subalpine Warbler’ S. c. iberiae/inornata subspecies pair – confirmed by plumage and T5 pattern and supported by call.

‘Western Subalpine Warbler’ S. c. iberiae – confirmed by DNA, supported by call, plumage and T5 pattern.

‘Western Subalpine Warbler’ S. c. inornata – confirmed by ringing recovery (genetic material is not currently available for comparison).

‘Eastern Subalpine Warbler’ S. c. cantillans/albistriata subspecies pair – confirmed by plumage and/or T5 pattern.

‘Eastern Subalpine Warbler’ S. c. cantillans – confirmed by DNA, supported by call, plumage and T5 pattern.

‘Eastern Subalpine Warbler’ S. c. albistriata – confirmed by DNA and/or call and/or wing length, supported by plumage including T5 pattern.

Pre-2015 claims are also sought where the evidence allows identification against the above framework. Any claims found ‘not proven’ by BBRC will be notified to county and local records committees and will not be published in the Appendix to the Annual Report. (updated Dec 2017 AMS).

References

BOU. 2015. British Ornithologists’ Union Records Committee: 44th Report. Ibis 157: 413.

Collinson, J. M., McGowan, R.Y. & Irestedt, M. 2014. First British records of ‘Eastern’ and ‘Western’ Subalpine Warblers. Brit. Birds 107: 282-285.

Cramp, S. (ed.). 1992. Birds of the Western Palearctic. Vol. VI.

Kehoe, C.  2006. Racial identification and assessment in Britain. Brit. Birds 99: 619-645.

Stoddart, A. 2014. From the Rarities Committee’s files: Assessing and recording Subalpine Warblers. British Birds 107:420-424.

Svensson, L. 2013. Subalpine Warbler variation and taxonomy. Brit. Birds 106: 651-668.