The first great promoters of the subspecies concept were the American ornithologists of the latter half of the nineteenth century. The concept is inherently problematic, however, the main issue being that subspecies do not all fall into a neat category – some are highly distinctive and potential candidates for treatment as full species, while others are barely diagnosable, at least in the field, and may represent little more than an arbitrary point in a complex pattern of clinal variation. 

There was initial opposition to ‘trinomialism’ from the European ornithological establishment. Nevertheless, the concept eventually gained acceptance in Britain, becoming a fundamental building block of the ornithological literature from the early years of the twentieth century (including in British Birds). Today, the notion of the subspecies is alive and well and still widely recognised as a useful framework within which to document geographical variation in species. Subspecies are fully embraced by modern handbooks and by all the leading taxonomies. 

However, despite the widespread adoption of the subspecies concept in ornithology, interest amongst birdwatchers has long been more subdued. The reasons for this are not hard to discern. For most observers, it is the species that remains the most important taxonomic unit. It gives structure to field guides, forms the basis of recording regimes and provides the raw material for listing. This means that, with some exceptions, we are not recording and valuing subspecies as comprehensively as we might. The identification criteria and particularly the status of many subspecies are not well understood and little discussed. They therefore represent some of our most fascinating but under-explored field challenges. Here, I discuss some of these issues in more detail and argue for a renewed engagement with, indeed a celebration of, subspecies, whether common, scarce or rare.

The British and Irish avifauna contains a high number of native subspecies. Following IOC taxonomy, there are 12 endemic subspecies in Britain alone, four of which are Eurasian Wrens Troglodytes troglodytes, with another 17 confined to Britain and Ireland. The British endemics range from the rather distinctive ‘St Kilda Wren’ T. t. hirtensis to the much less distinct (and not universally recognised) ‘Scottish Linnet’ Linaria cannabina autochthona and the increasingly rare ‘British Willow Tit’ Poecile montanus kleinschmidti. Those shared with Ireland include some of our commonest woodland birds such as ‘British Long-tailed Tit’ Aegithalos caudatus rosaceus and ‘British Blue Tit’ Cyanistes caeruleus obscurus. These are all birds to treasure, not just because we can enjoy trying to discern their subspecific differences but because of our special responsibility for them. 

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121. Hooded Crow Corvus cornix, Islay, Argyll, December 2023. Once universally considered a subspecies of Carrion Crow C. corone, Hooded Crow is now acknowledged by virtually all authorities as a species in its own right.

Andy Stoddart

Our common migrant species also exhibit great subspecific diversity. Amongst these, we already routinely note the subspecies of, for example, Brent Geese Branta bernicla and (male) Yellow Wagtails Motacilla flava,almost as though they were full species. So why do we not apply this approach more systematically? Instead of just noting, for example, ‘male Northern Wheatear’ Oenanthe oenanthe and ‘Snow Bunting’ Plectrophenax nivalis, why do we not try to record them more precisely? Is that Wheatear a European-breeding nominate oenanthe or a Greenland-breeding leucorhoa? Is that Snow Bunting an Icelandic-breeding insulae or a Scandinavian- or Greenland-breeding nominate nivalis?

Identification to subspecies level will not always be possible but, by studying individual birds closely and knowing their seasonal and geographical patterns of occurrence, we can, for many polytypic species, make a good assessment of their likely subspecific identity. This more finely grained approach will help county recorders and bird-report editors to document their local avifaunas more precisely and will also maximise the value of our records to conservation. In the context of accelerating habitat and climate change, detecting shifts in range, status or migration patterns at population level can be highly important.

We should also have scarcer subspecies on our radar. Here lie many still-unanswered questions. For example, what is the real status of ‘Russian Common Gull’ Larus canus heinei in Britain, how rare is ‘Icelandic Redwing’ Turdus iliacus coburni in eastern England, and how often does ‘Greenland Redpoll’ Acanthis flammea rostratawander south of northern Scotland? 

There are inevitably identification issues, however. Some scarce subspecies, such as ‘Greenland White-fronted Goose’ Anser albifrons flavirostris, are quite distinctive and can be identified with confidence; but for others, such as ‘Siberian Lesser Whitethroat’ Curruca curruca blythi, the subtle nature of their identification features or the clinal nature of their variation means that a precise geographical origin can be hard to prove. The potential for conflict between such ambiguity and the burden of proof demanded by a records committee is obvious. Claims of scarce subspecies may therefore sometimes challenge local committees but submissions should still be actively encouraged. Although it seems to have fallen out of favour in recent years, using the term ‘showing characters of’ can still be a very useful way of acknowledging the ambiguity inherent in some subspecific attributions.

At a national level, there has been a welcome embracing of the rarest subspecies by BBRC. Not long ago, only one or two readily identifiable taxa – such as ‘Black Brant’ B. b. nigricans –were considered at a national level; but, today, a much more comprehensive approach is taken. A guide to BBRC’s policy on subspecies, together with a detailed assessment of the issues associated with all currently occurring and potential future forms, is in Stoddart (2016) and at www.bbrc.org.uk/subspecies-information. Rare subspecies now take their rightful place alongside full species in BBRC Reports, while BOURC has always included subspecies recorded in Britain in the full version of the British List (https://bou.org.uk/british-list).

Of course, nationally rare subspecies also range from the relatively distinctive to the extremely subtle. As a consequence, BBRC has proposed for each rare subspecies (or sometimes a subspecies pair or group) an indicative ‘acceptance threshold’. Field notes or photographs might be sufficient to document some taxa such as ‘Steppe Grey Shrike’ Lanius excubitor pallidirostris but others may be provable only through additional categories of evidence such as biometrics, a sound recording, a ringing recovery or DNA analysis. These acceptance thresholds are adjustable in the light of new knowledge and may become less rigorous over time.

‘Baltic Gull’ Larus fuscus fuscus and ‘Central Asian Lesser Whitethroat’ Curruca curruca halimodendri are good examples of more problematic subspecies. Both are on the British List, and birds which ‘look the part’ appear to be occurring relatively regularly. However, proving the identity of the former requires a ringing recovery from a breeding colony (or photographs showing the primary moult state of a second-calendar-year bird in spring or early summer), while DNA analysis is required for the latter. These subspecies are therefore clearly being under-reported and any accepted records comprise merely the tip of a larger iceberg. 

Even more problematic are a number of other subspecies that appear to be occurring here too, some perhaps even regularly, but which are not on the British List. These include ‘Siberian Dunlin’ Calidris alpina centralis, ‘Siberian Common Tern’ Sterna hirundo longipennis, ‘Russian Jackdaw’ Coloeus monedula soemmerringii, ‘Russian Peregrine’ Falco peregrinus calidus and ‘Continental Stonechat’ Saxicola rubicola rubicola. However perfect any candidate might look, acceptance of any of these would probably also require evidence from the additional categories list, such as DNA, biometrics or a ringing recovery.

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122. Dunlin Calidris alpina, Cley, Norfolk, May 2015. The striking individual front right in the photo showed a white, very finely marked face and breast, contrasting white nape, large solid black belly-patch, bright fiery-orange hues in the upperparts, whitish tips to the rear scapulars, plain orange lower scapulars and worn, faded wings. These features all indicate a Siberian rather than a European origin. Birds showing Siberian plumage traits are seen relatively regularly in Britain, mainly in May, but neither centralis nor sakhalina is on the British List. 

Andy Stoddart

In all the above-noted cases, and particularly for first records, a high acceptance threshold is entirely appropriate. Unfortunately, however, this can have the unintended consequence of stifling our interest in and enjoyment of these subspecies. This is not, of course, the fault of BBRC or BOURC – it is simply the result of seeking to apply high standards of evidence-based recording. 

However, this need not engender a defeatist attitude. Instead of giving up on rare subspecies, we should take up the challenge, embrace the attendant ambiguities and search for them regardless. Good-looking candidates that show all the necessary characters in the field might not always be ‘provable’ in a records committee sense, but they can still be enjoyed and celebrated. They should also be documented as fully as possible in our personal records. Indeed, the best documented amongst them might still merit formal submission, even if they then sit ‘on file’ awaiting future insights. In time, these submissions might prove to be of real value in highlighting new identification features or elucidating occurrence patterns. 

Few of the subspecies featured here will translate into a tick. However, if we must have lists, why not keep them at subspecies as well as species level? Gantlett (1998) set out just such a framework. This would certainly take some of the heat out of our constant preoccupation with ‘splitting’ and ‘lumping’. 

There will always be taxonomic change at the relatively porous species/subspecies boundary – some of today’s subspecies will inevitably become tomorrow’s species and some species pairs or groups will go the other way; athough with the current trend of splitting rather than lumping, cases of the former will far outweigh cases of the latter. When this happens, the affected taxa do not suddenly become more (or less) interesting. They continue to exist just as before and merit our time and attention just the same. For example, ‘Siberian Chiffchaff’ Phylloscopus collybita tristis, ‘just’ a subspecies under IOC taxonomy, is treated as a full species by HBW/BirdLife. Do followers of the latter really have more rewarding encounters with this delightful leaf warbler? And what if, in future, all redpoll populations are treated at subspecies level rather than comprising two or three species?  Does this really mean that we needn’t bother looking for Arctic Redpolls A. hornemanni anymore?

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123. ‘Siberian Chiffchaff’ Phylloscopus collybita tristis, Blakeney Point, Norfolk, November 2021. The identification features of this subtle but attractive Phylloscopus are today well understood and it is now recognised as a regular scarce migrant, mainly in the Northern Isles and on the east coast of Britain in autumn, and as a winter visitor to southwest England. There are still questions as to its taxonomic status, however, and it is treated as a subspecies by IOC and as a full species by HBW/BirdLife. 

Andy Stoddart

Taking more notice of subspecies recognises the full diversity in the encounters we make. It also increases the value of our birdwatching, both in terms of recording and, potentially, in terms of its contribution to conservation. Above all, it provides us with a host of exciting challenges. Subspecies and their precise identification may sometimes deny us certainty, but they give us more things to look for and make us look harder at every bird.

References

Gantlett, S. 1998. Bird forms in Britain. Birding World 11: 222–239.

Stoddart, A. 2016. From the Rarities Committee’s files: Rare subspecies in Britain. Brit. Birds 109: 46–58.

Volume: 
Issue 4
Start Page: 
174
Authors: 
Andy Stoddart
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