Heuglin's Gull (L. heuglini / antelius)

(last update: 6-3-2011)

adult heuglini: June

Is it possible to identify Baltic and Heuglin's Gulls?

By Chris Gibbins, IN: Birding Scotland 7(4), December 2004.

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THIS IS PART 4

Summary and discussion

Clugston et al. (2001) described fuscus as a passage visitor to Scotland, although they suffixed this statement with a question-mark. Because of the overlap with intermedius, at least some of the records upon which this statement is based may not hold up to critical scrutiny. For the moment, it may be best to regard the status of fuscus in Scotland as uncertain. There have been one or two claims of heuglini in both England (e.g. Yorkshire) and Scotland (e.g. Montrose) over the last few years but none of these records have yet been formally documented or accepted. Meinertzhagen (1950) reported collecting a Heuglin's Gull in Fife but of course his records have now been discredited. Continuing uncertainties over the taxonomic status of fuscus and heuglini should not deter us from undertaking field studies that aim to develop robust identification criteria; indeed, the development of such criteria may help future decisions over their taxonomic rank. The identification of these birds is certainly challenging and views on whether it is possible to identify them at all have changed over time.

The identification of adult fuscus was thought to be straightforward until Jonsson (1998a) illustrated the extent of overlap with intermedius. He suggested that adults could be identified in the autumn by their moult and proposed new criteria for the identification of immature birds during the summer months. However, more recent field studies have indicated that
some of these criteria may not be 100% safe. In particular, there seems to be more overlap in moult than realised at the time that Jonsson undertook his work. Rather than seeing Jonsson's paper as somehow flawed, it is preferable to recognise that it generated some very important testable hypotheses. By stimulating interest and subsequent detailed study, these
hypotheses have undoubtedly improved our knowledge of fuscus. Much of what Jonsson said remains insightful and valid and his work stands as a key paper on this taxon.

The story of heuglini is a very different one. Its field characters have only slowly and recently become known and there remains very little in the mainstream English language literature about this bird. There are now many web sites with images of 'heuglini' taken on the wintering grounds, particularly the Middle-East. For a number of reasons, these images are not particularly useful for birders looking for heuglini in Western Europe. Observers working on the wintering grounds do not have the problem of graellsii or intermedius to deal with, so the web sites tend to concentrate
on the separation of heuglini from other local taxa such as barabensis. Also, the separation of immature heuglini from barabensis is far from clear and in many cases it is difficult to demonstrate conclusively that images of 'heuglini' on the wintering grounds are not barabensis. The work of Visa Rauste made it clear that adult heuglini are extremely similar to graellsii and intermedius. He made the point that while many 2 cy heuglini are separable from fuscus in the field, some individuals can be difficult to tell with certainty. Heuglini is currently being studied in considerable detail in Finland. This work is painstaking and, consequently, slow to yield results. Quite rightly, field-workers are reluctant to publish until they have a clear understanding of heuglini and are thus able to present identification criteria with a high degree of confidence. This may take considerable time, so for the time being Visa Rauste's paper is likely to remain the most comprehensive account of the identification of heuglini. The heuglini section in the gulls monograph (Malling Olsen and Larsson, 2003) includes critical errors and should not be used as a primary source of reference for this taxon.

Separating typical fuscus from typical heuglini in Finland is not difficult, but in the UK the problem of graellsii and intermedius needs to be considered. So, could a heuglini or a fuscus be identified with confidence in Scotland? This is not an easy question to answer. It is clear from the material presented above that identification can be difficult and is complicated by intra-taxon variability. The following seven points attempt to summarise
current views on the identification of out of range fuscus and heuglini.

[1. - 4. About fuscus.]

5. On average, adult heuglini show a number of small structural, plumage and moult differences from graellsii. While these may be used at the population level to distinguish between these taxa, they are of little use in the identification of individual birds. Thus, based on current knowledge the confident identification of adult heuglini outside of its normal range does not seem possible.

6. So far the pattern of black and the extent of white mirrors in the primaries of heuglini and graellsii have only been analysed in a simplistic way, dealing with one variable at a time. For example, various authors have looked for differences in the number of primaries with black pigmentation, the pattern of black on P4 or the number of primary mirrors. On the basis of these univariate analyses, there seems to be no diagnostic differences between heuglini and graellsii (i.e. no differences in either the number of primaries with black pigmentation or the pattern of black on P4 or the number of mirrors). However, our understanding would benefit from a multivariate approach which looked at whether a particular combination of these features allowed separation of these taxa. For example, a multivariate analysis may indicate that the combination of only one primary mirror, black on 8 primaries and a complete black band across P4 ruled out 95% of graellsii. This analysis is not possible from data currently published in the literature; it therefore requires new empirical studies, either from examination of museum skins, trapped birds or in-flight photographs. These are all difficult, not least because of the sample size required for a rigorous analysis. Nonetheless, until such analysis is undertaken it may be premature to say that no diagnostic differences between heuglini and graellsii exist.

7. Some 2 cy heuglini are extremely similar to some graellsii and intermedius. Anyone looking through large numbers of birds in the UK will come across individuals that match some of the heuglini illustrated here. Further work is needed to determine whether there are any consistent differences upon which confident identification of 2 cy heuglini can be based. Again, a multivariate approach that allowed features to be dealt with in
combination may be most fruitful.

This paper has concentrated on adults and birds in the summer to autumn of their second and third calendar years. For fuscus, this was because of the necessity to revisit the ideas put forward by Lars Jonsson concerning birds of these age groups during the summer to autumn period. This period is also relevant for heuglini because, like fuscus, perhaps the most likely chance of a vagrant appearing in Western Europe is during the summer, when birds return to northern areas, or in the autumn when they are migrating southward again.
However, an adult heuglini may be more identifiable in the winter when its late moult, compared to graellsii, may be useful – in February, a sleek, dark-eyed bird with only one small primary mirror and one or two regrowing outer primaries may be worthy of close attention. Of course it is now widely acknowledged that not all individuals conform to standard moult timing: illness or injury can delay moult, while it is increasingly recognised that out of range birds may track the moult cycle of taxa present in their new location. Vagrant Lesser Black-backed Gulls in North America, for example, moult at a different time to the birds in Europe. So, a displaced heuglini may not show late primary moult, particularly if it has been in Western Europe for some time.

The problem of separating heuglini, fuscus, graellsii and intermedius is complicated by the recent discovery that graellsii and intermedius occur occasionally in Finland. This was proven by the arrival in Finland of birds ringed as pulli in England, the Netherlands and Norway. Consequently, developing criteria to separate these taxa based upon observations in Finland may be problematic, since an unknown proportion of the fuscus and heuglini may be graellsii or intermedius. Thus, it could be argued that none of the Finnish 'heuglini' pictured here can be considered as proven. While this is a rather extreme stance (the breeding ranges of heuglini and graellsii suggests that graellsii should be much less abundant in Finland), it serves to illustrate this problem. An adult bird seen at Tampere in August 2004 with upperparts matching heuglini had the P10 mirror merged with the white tip, forming an extensive white tip to the feather. This is not proven to occur in heuglini but is frequent in graellsii. Although on range this individual
is more likely to be a heuglini, it would be unwise to argue that heuglini can have a wholly white tip to P10 based on this one bird observed in Finland. Clearly, more research is needed on the breeding grounds to determine the nature and extent of variation in the primary pattern of heuglini. Another adult heuglini-like bird seen at Tampere on 29 July 2004 showed five newly moulted primaries, so was more advanced in its moult than generally accepted for this taxon. Is this bird evidence that heuglini can moult early or was it a graellsii? These examples illustrate the problem thrown up by the proven occurrence of graellsii and intermedius in Finland when trying to assess patterns of variability of fuscus and heuglini and so clarify their identification.

Unfortunately, identifying individuals based upon the characteristics of ringed birds (whose origin is therefore known) also raises problems. The bird CYHP also looks very unlike typical fuscus, but it was ringed as a
chick in a fuscus colony and so should be a fuscus. So why does it not look like one?
Three possibilities exist. The first is that it is a fuscus, but a rare variant that is inseparable from western Lesser Black-backed Gulls at this age. The second possibility is that heuglini may be breeding in Finland and this bird, a heuglini, was incorrectly identified when it was ringed as a chick. Misidentification of this bird as a nestling is possible since gulls of this age are notoriously difficult to identify and its parents were not necessarily seen while it was being ringed. The third possibility is that it is a hybrid heuglini x fuscus, again ringed incorrectly as a nestling. One of these explanations could account for the unusually pale adult 'fuscus' ringed in Finland. Clearly, the possibility of birds ringed incorrectly being used develop identification criteria is alarming; the possibility of hybridisation as an explanation for the odd appearance of some individuals is also worrying, but it needs to be borne in mind. For the moment, it seems prudent to leave such individuals aside and develop identification criteria based on the more typical birds.

Ringing recoveries (listed in Yésou, 2002) prove the occurrence of fuscus outside of its normal range. The large proportion of Finnish fuscus that are ringed (approximately one in eight birds seen at Tampere in 2004; Markku Kangasniemi pers. comm.) raises the possibility that identification of a suspected vagrant fuscus may be clinched by the presence of a ring. For some, this is the only way that the identification of an out of range
bird can be made with 100% certainty. For others, the accumulation of a number of known fuscus features is sufficient. The caption to the plate of the 3 cy Cambridgeshire bird (Birding World 17 (5), p. 180) exemplifies the latter philosophy; the caption read "it has to be a fuscus". Those who spend a lot of time looking at gulls and are aware of their variability tend to be rather more cautious. The evidence presented above indicates that 3 cy intermedius can show one or two fuscus features, although it is yet to be
demonstrated conclusively that they can show the full suite apparently present in the Cambridgeshire bird. Of course the fact that no intermedius with the full range of fuscus features has yet been seen does not mean they do not exist. For this reason, some may argue that records of unringed vagrants should be shelved until the full range of variability shown by all taxa is known. It may appear a semantic point, but while the Cambridgeshire bird appears from the photograph to almost certainly be a fuscus, it does not 'have' to be one.
Overall, the work published in the late 1990s added much to our knowledge of fuscus and heuglini. However, there remains much to learn. As emphasised earlier, the current paper has been written to provide an update to the very detailed accounts given by Jonsson (1998a) and Rauste (1999). Hopefully it is judged and used in this context. It is important to reiterate that there are a number of issues that have not been considered here. First, the identification of 1 cy heuglini and fuscus and of 3-4 cy heuglini has not
been covered. Very little is currently known about how these age groups can be identified; their plumage is described in the literature but there is little in the way of critical comparative analysis, relative to graellsii and intermedius (note their treatment in Malling Olsen and Larsson, 2003). This comparative analysis is necessary for field identification.
Second, identification of birds during the winter months has not been considered. Like many large gulls, the identification criteria for fuscus and heuglini are very time-specific, so many of the features described here will not hold true during the winter. It is important therefore to not apply features carelessly at times when they may be inappropriate. Finally, issues of the taxonomic rank of fuscus and heuglini have intentionally been left aside. Both taxa have and continue to be treated in different ways in the literature; they are treated as subspecies of Lesser Black-backed Gull by some authors and as full species by others. Whatever their taxonomic rank, improving our understanding of their status in Scotland is only possible if observers are aware of what is currently known of their field characteristics and are encouraged to look in detail for candidate birds. Hopefully this paper has helped in a small way towards this goal.

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Acknowledgements

I (CG) would like to thank Visa Rauste, Annika Forsten, Mars Muusse and Markku Kangasniemi for invaluable comments that greatly improved this paper. Ideas on the ages of primaries in 3 cy fuscus are those of Annika Forsten, so my thanks to Annika for allowing me to discuss them here. Thanks also to Visa Rauste and Mars Muusse for allowing me to use some of their photographs and to Mars for the use of information from his web site. Peter
Stewart kindly allowed me to use his graellsii moult data. Ken Shaw and Micky Maher helped with information on the 1999 Shetland bird. Thanks to Paul Baxter for his company on trips to Sweden, Finland, Israel and UAE. Also to Phil Bloor and Hywel Maggs for their patience with me and my gull watching in UAE. I have learnt a lot from time spent with Mars and Theo Muusse, Visa Rauste, Markku Kangasniemi and Hannu Koskinen, particularly
to be always cautious when dealing with gulls.