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 orientalis/albiventris. A ringing recovery would provide additional evidence. (updated April 2015 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 perhaps as many as twenty 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. The subspecies 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 caudatus and the darker southern European forms. The vast majority are close to rosaceus (though fractionally paler) but some exhibit caudatus-like characters, including a partially or largely white head. Whether all such birds represent intergrades with 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 caudatus x europaeus intergrades have been recorded here.

Nominate caudatus is a striking subspecies but it needs to be separated with care from caudatus x europaeus intergrades/’white-headed europaeus’. 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’ caudatus is the subject of debate, however, some authors (e.g. Jansen & Nap 2008) advocating that the merest hint of grey on the head excludes caudatus whilst most (e.g. Kehoe 2006) consider some faint grey streaking in the head to be compatible with caudatus. More clearly-defined head streaking forming faint ‘ghosted’ coronal bands and grey streaking in the ear coverts or across the breast would, however, definitely exclude 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 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 to the identity of either of these subspecies.

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 April 2015 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.

 

Greenish Warbler Phylloscopus trochiloides

Greenish Warbler comprises five subspecies – viridanus (eastern Europe to western Asia), ludlowi (southeast Afghanistan to Kumaon), nominate trochiloides (central and eastern Himalayas), obscuratus (central China) and plumbeitarsus – ‘Two-barred Greenish Warbler’ – (eastern Russia) (Collinson 2001). Variation across these subspecies is clinal, each interbreeding with its neighbour with the exception of viridanus and plumbeitarsus which show no intergradation where their distributions overlap. Here, they are clearly differentiated in terms of morphology, vocalisations and genetics and do not recognise each other as conspecifics (Irwin et al. 2001). The group has been proposed as the classic example of a ‘ring species’ (Collinson 2001, Collinson et al. 2003) although this interpretation is not universally accepted. Some authors, notably Cramp et al. (1992), regard plumbeitarsus as a separate species – ‘Two-barred Greenish Warbler’ P. plumbeitarsus. The former subspecies nitidus (from the Caucasus and therefore not forming part of the proposed ‘ring’) is now generally recognised as a full species – Green Warbler P. nitidus.

The subspecies viridanus is a scarce migrant to Britain, mainly in early autumn but also in late spring. The only other subspecies on the British List is plumbeitarsus, with four now accepted, all in mid to late autumn. A further candidate has also been documented (Stoddart 2003).

The identification of plumbeitarsus can be relatively straightforward. Observers should focus on the strength and shape of the greater covert wing-bar, the presence of a median covert wing-bar, the face pattern (resembling Arctic Warbler P. borealis) and leg colour. Vocalisations are very useful, the call being similar (though not identical) to viridanus and therefore clearly different from that of Arctic Warbler (van der Vliet et al. 2001).

Claims of plumbeitarsus are welcomed if accompanied by detailed notes and preferably good photographs. Biometrics should be recorded for a trapped bird. A ringing recovery would of course provide additional evidence. (updated April 2015 AMS).

References

Collinson, M. 2001. Greenish Warbler, ‘Two-barred Greenish Warbler’, and the speciation process. British Birds  94: 278-283.

Collinson, M., Knox, A. G., Parkin, D. T. & Sangster, G. 2003. Specific status of taxa within the Greenish Warbler complex. British Birds 96: 327-331.

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

Irwin, D. E., Bensch, S., & Price.T. D. 2001. Speciation in a ring. Nature 409: 333-337.

Stoddart, A. 2003. From the Rarities Committee’s files: The Holme wing-barred Phylloscopus warbler. British Birds 96: 74-78.

van der Vliet, R. E., Kennerley, P. R. & Small, B. J. 2001. Identification of Two-barred, Greenish, Bright-green and Arctic Warblers. Dutch Birding 23: 175-191.

 

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 April 2015 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.

 

Lesser Whitethroat Sylvia curruca

The Lesser Whitethroat demonstrates significant clinal variation and there is little consensus on the number of subspecies recognised. As few as five and as many as thirteen have been proposed but those most widely recognised are nominate curruca from Europe and western Russia, blythi (‘Siberian Lesser Whitethroat’) from central and southern Russia and northern Kazakhstan, halimodendri (‘Central Asian Lesser Whitethroat’, ‘Steppe Lesser Whitethroat’ or ‘Desert Lesser Whitethroat’) from southern Kazakhstan, north-west China and south-west Mongolia, minula (‘Desert Lesser Whitethroat’) from western China, margelanica (‘Margelanic Lesser Whitethroat’) also from western China and althaea (‘Hume’s Lesser Whitethroat’ or ‘Mountain Lesser Whitethroat’) from the montane regions of Central Asia. Cramp et al. (1992) also recognise caucasica (Caucasus and South-east Europe), telengitica (western Mongolia) and jaxartica (Transcaspia). Some authors, notably Shirihai et al. (2001) and Parkin & Knox (2010) , express doubt over the validity of blythi, treating it as synonymous with nominate curruca, whilst others, notably Svensson (1992), do not recognise halimodendri, treating it as synonymous with blythi.

Though treated by many authors (e.g. Cramp et al. 1992), as comprising a single species, the potential for multiple species within the Lesser Whitethroat complex has long been recognised, with a three-way split into a ‘Northern’ species, a ‘Desert’ species and a ‘Mountain’ species widely proposed. Shirihai et al. (2001) tentatively proposed four allospecies within a single superspecies. There is, however, little consensus on which subspecies constitute any proposed species.

Despite the confusing morphological variation, bioacoustical studies (Martens & Steil 1997) confirm the existence of three distinct song types within the complex corresponding with the three-way split outlined above. The most recent genetic analysis (Olsson et al. 2013) has identified six clades corresponding with curruca, blythi, halimodendri, minula, margelanica and althaea. It has also identified a deeper divide, with curruca and minula well separated both from each other and from the other subspecies. Thus, somewhat counter-intuitively, blythi is not necessarily the closest relative of curruca. 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 where it is categorised as a scarce migrant. The subspecies was not listed as a rarity in Kehoe (2006) and BBRC has never assessed or published any records. The occurrence of blythi in Britain has long been recognised (e.g. Witherby et al. 1940) but its recent status has been obscured by a period of ‘taxonomic denial’ (e.g. Shirihai et al. 2001, Parkin & Knox 2010). However, an increasing number of blythi have now been confirmed in Britain by DNA analysis (M. Collinson in litt.) 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 occasionally in winter. The contemporary evidence therefore strongly suggests that its continued categorisation as a scarce migrant is probably correct.

No other subspecies is on the British List but Lesser Whitethroats resembling one or more Central Asian subspecies are also reaching Britain. Some appear (and sound) particularly striking and have in the past been attributed tentatively to minula but three such birds subjected to DNA analysis have proved to be halimodendri (M. Collinson in litt.). It still remains for halimodendri to be admitted to the British List but it seems likely that this subspecies will prove to be a regular rarity in Britain. The subspecies minula and margelanica are also potential vagrants but have yet to be proven by DNA analysis. It is worth noting here that Olsson et al. (2013) described a relatively restricted western Chinese range for minula, much smaller than that previously mapped, and a correspondingly larger range for margelanica and halimodendri.

The identification of Lesser Whitethroats to subspecies is not a straightforward task. Variation is clinal and age-related and a set of structural, plumage and vocal criteria aligned to the above taxonomy 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. This latter feature may be possible to photograph in the field. However, even with all such details observed, a firm identification may not always be possible. In this context it is worth noting that several birds identified even in the hand as blythi have proved, when subjected to DNA analysis, to be nominate curruca. 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 (though halimodendri is less biometrically distinct). Any material from a trapped bird should be retained for DNA analysis.

Claims of blythi are not sought but claims of Central Asian subspecies are welcomed. If not identifiable to a particular subspecies, some birds might be referrable to a subspecies pair or group if accompanied by detailed notes and photographs. However, sound recordings, biometrics, a ringing recovery or DNA analysis would all provide more solid evidence and potentially enable attribution to a particular subspecies. Submissions of Central Asian subspecies are currently stalled but it is hoped to make progress on their assessment in due course and also to put forward an example of halimodendri for admission to the British List. (updated Sept 2015).

References

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

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.

 

Subalpine Warbler Sylvia cantillans

Following the BOURC split of Moltoni’s Subalpine Warbler Sylvia subalpina (BOU 2015), Subalpine Warbler is now generally regarded as comprising four subspecies. These are iberiae (Iberia, southern France and the northwest corner of Italy), inornata (northwest Africa), nominate cantillans (central and southern Italy and Sicily) and albistriata (Greece, western Turkey and the Balkans and the northeast corner of Italy). The first two of these comprise a subspecies pair known as ‘Western Subalpine Warbler’, the latter two another 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, with a total of 61 records now published (as at September 2015). 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, 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 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 that there is growing 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 provide the only potential evidence (though in some cases it might be possible to photograph the tail pattern in the field). A ringing recovery could, of course, also provide solid evidence.

With effect 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 not 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 Nov 2016 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.

 

Whitethroat Sylvia communis

Whitethroat taxonomy is complex and there is little consensus on the number of subspecies. As many as eight have been described but four are most commonly recognised. These are 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). Not all authors recognise volgensis.

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 Sept 2015 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.

 

Grasshopper Warbler Locustella naevia

Grasshopper Warbler comprises perhaps four subspecies – nominate naevia in west, central and northern Europe and western Russia, obscurior in the Caucasus, straminea in western Siberia and Kazakhstan and mongolica in north-west China and western Mongolia, the latter two known collectively as ‘Eastern Grasshopper Warbler’. The subspecies obscurior is an isolated population but nominate naevia intergrades with straminea. The above taxonomy is debated, however, with mongolica not recognised by Kennerley & Pearson (2010).

Nominate naevia is a common summer visitor to Britain. A bird of the eastern subspecies group straminea/mongolica 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/mongolica  is highly problematic, indeed on curent knowledge they are virtually indistinguishable from naevia/obscurior, whilst there is also the potential for confusion with Lanceolated Warbler L. lanceolata. The eastern subspecies are 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/mongolica being significantly smaller than naevia/obscurior and having a more rounded wing but not all individuals are identifiable. In reality, straminea/mongolica can only be proven in a vagrant context by DNA analysis.

Claims of a potential vagrant subspecies are welcomed if accompanied by detailed notes, good photographs, biometrics and, crucially, DNA evidence or a ringing recovery. (updated Sept 2015 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.

 

Reed Warbler Acrocephalus scirpaceus

Reed Warbler comprises two subspecies. 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. Other forms of uncertain taxonomic status occur in north-west and north-east Africa. 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 are now being considered for admission to 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 undeparts, 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 Sept 2015 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.