American Herring Gull (smithsonianus)

(last update: October 30, 2015)

American Herring Gull 4cy October

The issue of Dutch Birding 26: 1-35, 2004 contained a very comprehensive paper on the identification of smithsonianus, titled: Identification of American Herring Gull in a western European context. It was written by Pat Lonergan & Killian Mullarney. The outstanding text is copied on this webpage, with links now added to various Canadian birds photographed throughout the months. When appropriate, more details from recent field research has been added as well. Full PDF download: HERE.

"we" in the text below refers to the original authors.
Description of juvenile plumage: HERE
Description of 1st winter plumage: HERE
Description of 2nd winter plumage: HERE
Description of 3rd winter plumage: HERE

If any errors occur in this text, please let me know and mail to marsmuusseatgmaildotcom.

Identification of American Herring Gull in a western European context
- Pat Lonergan & Killian Mullarney -

left: smithsonianus sub-adult, April 18 2007, Halifax, Nova Scotia. Note black spot on tertial. right: smithsonianus) sub-adult, February 09 2008, Dryden, NY. Black spots on tertials.
left smithsonianus sub-adult, July 25 2012, Vinalhaven, ME (Keith Mueller). right smithsonianus sub-adult, May 26 2011, Merritt Island, FL (Hart Rufe). Again, both birds much adult-like, except for ink-spots on tertials.

Description of Fourth-winter and older plumages

A surprisingly high proportion of the essentially adult-like smithsonianus we observed in Massachusetts in January-February exhibited features indicative of immaturity such as dark markings on the bill, dark-centred primary coverts or dark spots on the secondaries, tertials and rectrices.
One explanation for the comparative abundance of ’near-adult’ types amongst the birds we studied in Massachusetts might be that, for some reason, this is a preferred wintering area for four- to five-year-old birds. The high proportion of ’near-adu|t’ types might also indicate that smithsonianus, on average, takes significantly longer to acquire a fully adult appearance (without vestiges of immaturity) than does European Herring Gull. Whatever the reason, we have no way of knowing the precise age of these birds but, in view of their overall similarity to adults, we assume that most are at least in their fourth winter and we prefer, therefore, to include them in an ’adult-type' category. At present, these individuals exhibiting certain characteristic vestiges of immaturity in combination with an otherwise essentially adult-like appearance may be the only adult-type smithsonianus that can be conclusively identified in Europe.
There has been some suggestion that adult smithsonianus have paler upperparts than argenteus. Never having had a chance to compare adult smithsonianus directly with European
Herring Gulls, it is difficult to evaluate the practical usefulness of this feature in the field. In general, the upperparts of smithsonianus are pale grey (Kodak grey scale 4.0-4.5), similar in tone to argenteus and Ring-billed Gull and clearly paler than mean argentatus (Howell & Elliott 2001).
However, we did note some variation in upperpart colouration, even in small groups of birds, with a few individuals slightly darker than the majority The paleness of the upperparts in many smithsonianus may, however, be of greater significance when compared with argentatus.
The following features may be of more practical use in identification of near-adult and adult smithsonianus.
Tertial-spots One feature that was a surprise to us was the presence in a small percentage (5-10%) of near-adults (and possibly a few adults?) of discrete black ’ink-spots’ on one or more of the tertials. These spots appear to be linked to the extensive dark markings shown by many third-winters, and are similar in extent to the dark spots exhibited by some second-winter Common L canus canus and Ring-billed Gulls. They can, at times, be hidden by the overlying tertial(s) and may only become visible if the feathers are displaced by wind or while preening. In other individuals, they are extensive and can form a regular ’stepping stone-like' pattern across the tertials. While this pattern is usually associated with other traces of immaturity, such as a band on the bill or dark-centred primary coverts, a few apparently ’perfect’ adults may show one or two small black tertial-spots. We have never observed equivalent markings in adult or near-adult European Herring Gulls although it appears that similar markings may occur in some forms of Yellow-legged Gull L michahellis (plate 22 in Dubois 2001, pers obs). We recommend that any ’light-mantled’ herring gull in Europe exhibiting this character should certainly receive detailed scrutiny.
Secondary-spots Occasional individuals in this age category show small, well-defined black spots on otherwise adult-like secondaries. This feature is much more likely to be detected in photographs than in the field but, when present, may be a diagnostic indicator of smithsonianus.
Wing-tip pattern Attention has been drawn to a potential difference in wing-tip pattern between smithsonianus and European Herring Gulls (Millington & Garner 1998), with at least some birds, apparently originating in north-eastern Canada, having paler and longer grey tongues along the inner web of the outer primaries than in typical argenteus (but not unlike some argentatus). Wing-tip pattern of smithsonianus is known to be variable: Jonsson & Mactavish (2001) described significant differences in wing-tip pattern between Newfoundland and Niagara smithsonianus and proposed that these populations represent two distinct types. In the original draft of this paper submitted to the editors of Dutch Birding we made an attempt to identify potentially useful differences in wing-tip pattern between smithsonianus and European Herring Gulls. However, aware of the fact that long-term studies of known-age argenteus and graellsii in Britain (Martin Elliott pers comm) indicate that wing-tip pattern can continue to change well beyond the point at which they acquire ’adult' plumage, we doubted that any of our conclusions on this particular aspect of smithsonianus identification would prove to be of much practical value. More recently, we became aware that a detailed paper on wing-tip pattern differences between adult smithsonianus and European Herring Gull was being prepared by Peter Adriaens and Bruce Mactavish. We are confident that these authors will demonstrate the potential usefulness of wing-tip pattern differences far more successfully than we managed to do and we eagerly await publication of their findings in a forthcoming issue of Dutch Birding.
Primary coverts A rather high proportion (10-15%) of ’adult' and near-adult birds exhibit dark markings on the primary coverts. These vary from extremely fine black shaft-streaks to broader, more obvious, black lozenge-shaped marks. Dark primary-covert-markings are sometimes shown by a few adult and often by near-adult argenteus (Grant 1986) but they tend not to be as well defined and neat, or as black, as in many smithsonianus.
Winter head-markings The pattern of winter head-streaking in adults and near-adults often appears different in smithsonianus - being blotchier with less well-defined streaks than in argentatus/argenteus. However, as with many of the other features, this is variable and should be used with caution.
Bill pattern A high proportion of the near-adult smithsonianus we studied in Massachusetts in January-February had more extensive blackish markings around the gonydeal area of one or both mandibles than we are used to seeing in European Herring Gulls at the same time of year. Dark markings on the bill in all of these large gulls are linked with both immaturity and with season (with adults developing a dark spot in winter), so their significance in the context of identifying a vagrant in Europe is doubtful.
Voice While at this stage we do not anticipate voice characteristics having a major bearing on the identification of vagrants, we have registered a distinctly deeper tone, and possibly a subtly different repertoire compared with argenteus with which we are most familiar. Whether this is primarily a function of body size and whether the differences are as pronounced in comparison with argentatus is unclear and requires further research.

top: smithsonianus sub-adult, March 26 2010, Merritt Island, FL, USA (Hart Rufe). below: smithsonianus 4th cycle (5CY) 0886-75788 January 26 2005, Corpus Christi, TX (Martin Reid). Adult-like plumage, except for the black spot in the tertial. Ringed bird with provenance on age and origin (east coast).

Hybrids

While ’larophiles’ on the West Coast of North America have had to make sense of an extraordinary variety of hybrid gulls for many years, and have now gained sufficient confidence to be able to guess the parentage of many of them, their equivalent in Europe is lagging behind in this particular field. With presumed hybrids apparently being of much more exceptional occurrence in Europe than on the West coast of North America it is difficult for any individual to gain a broad enough perspective on the problem to begin to make sense of it. The extent to which hybrid gulls in Europe may be complicating our attempts to identify smithsonianus on this side of the Atlantic can only be guessed at, and until we have a clearer understanding of the limits of variation within ’pure’ smithsonianus it is likely to remain so.

left American Herring x Glaucous Gull ("Nelson's Gull) juvenile (1CY) November 08 2009, Palmer Landfill, USA. Picture: Kirk Zufelt. right American Herring x Glaucous Gull ("Nelson's Gull) 2nd cycle (3CY) February 2009, Clallam County, Washington. Picture: Steven Mlodinow.

Some first-winter and second-winter presumed hybrids Glaucous x European Herring Gull bear a strong superficial resemblance to smithsonianus, especially when their mix of characters combines the size, rather uniform plumage, bill colouration and general demeanour of Glaucous with the dark wing-tip and tail pattern of European Herring. Most, however, possess obvious clues in their appearance to their hybrid origin, such as a much reduced or washed-out tail-band and secondary-bar, obvious pale fringes to the primary-tips or, at rest, a lighter overall tone to the tertials than a typical European Herring; others, however are not so obvious and correct identification may require very critical consideration indeed. In North America, hybrids Glaucous x smithsonianus (so-called ‘Nelson’s Gull') occur; these are usually more similar to Glaucous than to smithsonianus (Bruce Mactavish in litt) but there is evidence that different populations of smithsonianus and Glaucous produce different looking hybrids, some of which look more like pale smithsonianus but with low contrast between tertials and folded primaries and rest of upperparts (Bruce Mactavish in litt).
At least two birds believed to be second-winter smithsonianus recorded in Ireland were initially thought to be hybrids Glaucous x European Herring until more detailed examination indicated that their Glaucous-like character was quite compatible with typical second-winter smithsonianus.

Conclusion

With a total of around 70 accepted or likely to be accepted records of smithsonianus in Europe since 1986 (most of which have been found in under-watched Ireland), it is clear that smithsonianus is occurring regularly on the European side of the Atlantic Ocean. We hope this paper will form a baseline for further study on both sides of the Atlantic. The sporadic nature of our contact with large numbers of smithsonianus undoubtedly limits our work but we trust that readers of this paper who have more experience with this taxon will not be reticent about clarifying any aspects we may have unintentionally misrepresented. There is, in particular, a need to develop further and refine the criteria for identifying sub-adult and adult smithsonianus, age categories still hardly recorded in Europe but which, surely, must occur more frequently? The other major challenge, we feel, is to gain a clearer picture of variation in juvenile smithsonianus, particularly the birds at the lighter end of the range. This would help us determine the identity of a number birds already observed in Europe which have closely resembled what might be described as ’light smithsonianus’, but which have exhibited an ambiguous, or more argentatus-like tail pattern and/or upper- and undertail-covert markings. Some, it appears, may be hybrids but if so, what is the parentage? Is it possible that smithsonianus has already entered the European Herring Gull gene pool, and could this be the explanation for the appearance of some of the more perplexing birds? We suggest that a thorough investigation of morphological variation in the Icelandic Herring Gull population, combined with judicious sampling and analysis of genetic material could help answer some of these questions.
It is good to hear that smithsonianus is, at last, the subject of some new taxonomic studies being carried out by North American research teams (Pierre-André Crochet in litt). Of course, we do not know what this work will entail, but we can speculate as to the advances that might be made if it attempted to evaluate whether morphologically distinct ’types' (Jonsson & Mactavish 2001) warranted taxonomic distinction. We can also imagine how a large-scale colour-ringing project might stimulate great interest in observing what these (and other, yet-to-be-identified?) types look like as immatures, and where they go outside the breeding season, just as it has in Europe. Finally, we are very interested in receiving feedback, both positive and negative, from observers whose experience of any of the taxa discussed here is complementary to our own.
Increasingly, in recent years, it has been the pooling of information and exchanging of ideas that has been responsible for advancing our understanding of this most challenging group.

above: argenteus 4th cycle (5CY) breeding male mint 6T, 09 May 2006, Moerdijk, the Netherlands (Mars Muusse). European birds normally have diffuse borders on the pale brown markings.

above: argenteus 4th cycle (4CY) BLB H-136532 November 26 2006, Oostende, Belgium (Theo Muusse). Black markings in tail.

Herring Gull adult, March 21 2013, Noordwijk, the Netherlands (Mars Muusse). Not ringed, but probably local bird, argenteus. Just on 3 points it meets smithsonianus: pale grey upperparts, full sub-terminal band on P10 and small mirror on P9 only on innerweb. No good for smithsonianus and in favour for argenteus: pale innerweb on P10 only 50% and not square-ended, black on outerweb of P9 reaches coverts, short pale tongue on P8, black on P8 not bayonet-shaped but ending blunt square, this is repeated on P7, P6 no W-shape, P5 no W-shape, no white tongue-tips.

Acknowledgements

We wish to express our gratitude to the following people who helped in various ways, from providing photographs for reference to stimulating discussion and company in the field: Joe Adamson, Mashuq Ahmad, Paul Archer, Theo Bakker, Martin Elliott, Frode Falkenberg, Sean Farrell, Martin Garner, Peter de Knijff, Diederik Kok, Henry Lehto, Anthony McGeehan Richard Millington, Paul Moore, john Murphy, Rudy Offereins, Jari Peltomaki, Peter Pyle, Martin Reid, David Sibley, Roy Smith, Norman van Swelm, Alyn Walsh and Jim Wilson. We are especially grateful to Bruce Mactavish, who has been a constant and enthusiastic source of information related to the identification of smithsonianus. We also want to thank Peter Adriaens, Andre vanLoon, DK and Magnus Robb who, in performing their duties as members of the Dutch Birding editorial board, suggested many improvements to this paper. Visa Rauste was most helpful in providing an excellent range of photographs of juvenile Finnish argentatus, for reference. Pierre-André Crochet kindly advised us on the latest results in the field of mtDNA research on smithsonianus and related taxa.
Finally, we would like to dedicate this paper to the memory of Peter Grant, whose life-long dedication to clarifying the problems associated with gull identification was such a powerful inspiration, and ’opened the door' for the rest of us.

References

See PDF HERE

East coast birds

Great Lakes birds