Yellow-legged Gull: Kensington Gardens, London A Yellow-legged Gull with quite heavily streaked head. The streaking is not as contrastingly blackish and is a little more smudgy than classic Azorean atlantis (photo: Fraser Simpson).
In August 1973 an interesting-looking adult gull was found on Madeleine Island, Quebec in the Gulf of St Lawrence just west of Newfoundland. The bird was collected (i.e. shot!) and the skin placed in the Canadian Museum of Nature. It was identified as being most probably a hybrid American Herring Gull x Lesser Black -backed Gull. Twenty years later the bird was confidently identified as the first North American record of Yellow-legged Gull and very specifically closest in appearance to birds from the Azores (known as both 'Atlantic Gull' and 'Azorean Yellow-legged Gull', but hereafter called Atlantic Gull). This ground-breaking paper by Wilds and Czaplak (1994) still remains a key article when considering vagrant 'Atlantic Gulls'.
When I first read the paper I was amazed at the extent of head streaking on the original specimen from Quebec and indeed of individuals from the Azores with which it was compared. So when Pete Morris sent me a photograph of his interesting-looking Yellow-legged Gull from Co. Kerry in September 1994 I pretty much had no hesitation in saying "it must be one of those things they had in Quebec!"
Since then about 20 of these hooded-looking Yellow-legged Gulls, with slightly darker mantles, have been claimed in Britain and Ireland, though very few have stayed and allowed close scrutiny.
However, an obliging Yellow-legged Gull present in Kensington Gardens (London) has recently been has been mooted as a potential Atlantic Gull or at least to use the BirdGuides phrase 'showing some characteristics of atlantis'. With its rather heavily streaked head, and extensively black-patterned wings, it is easy to see why. It also seems likely to be the same bird that was present in the spring and since August this year.
When presented with the photographs I found myself inevitably asking a series of questions. So just to be a bit different I thought I'd lead you through the kind of questions that have gone through my mind as I have looked carefully at the excellent photographs taken by Fraser Simpson.
Yellow-legged Gull: Kensington Gardens, London This bird is just completing primary moult and shows one white mirror on the part-grown outermost primary p10. The foreface is a little more whitish than on classic Azorean atlantis (photo: Fraser Simpson).
Yellow-legged Gull: Kensington Gardens, London) If this was the only photo it would be a scary bird indeed as the streaking looks different. A sobering reminder that both a range of photos, and good field notes, are crucial in vagrant gull identification (photo: Fraser Simpson).
Question 1: Why is it not just a heavily streaked michahellis?
Yellow-legged Gull: Kensington Gardens, London This individual shows the bill structure typical of Yellow-legged Gulls as well as the orange/vermilion orbital ring. The head streaking is heavy, but rather greyish, and a little smudgy — arguably within the range of heavily streaked michahellis (photo: Fraser Simpson).
Over 90% of Mediterranean Yellow-legged Gulls show head streaking between August to October (ish). The pattern of streaking is variable and occasionally some individuals have very extensive streaking not dissimilar to this individual over most of the head. They tend to have a white foreface, i.e. pale around the forehead, lores, chin and throat. My own gut reaction was that the Kensington bird does not have the blackish, more sharply defined, pencil marks that are present on the more obvious of Azorean birds. Rather, the head-streaking on the Kensington bird is slightly paler grey- (and grey-brown?) toned and more diffuse. Notwithstanding, some Azorean birds may have patterning like this but I would not call it the 'classic pattern'. Importantly, for easily identified Azorean birds, the streaking is as prominent in the malar region, below the gape line of the bill, as it is above it. Therefore, on Azorean birds really only the chin and throat are marked white. On this bird the strength of streaking is considerably reduced in the area below the gape and again, while similar, is not the classic Azorean pattern, and can probably be matched by heavily streaked michahellis.
Yellow-legged Gull: Kensington Gardens, London (photo: Fraser Simpson).
Question 2: What about the wing tip?
Having seen only photos of the perched bird with its head-streaking I was ready to dismiss it as just a heavily streaked michahellis. When photographs of the wing tip pattern appeared I became more interested. The bird has a combination of a single white mirror on the outermost primary and a small dark mark on the smaller inner primary known as p4. Whilst I have seen many examples of michahellis with only one primary mirror on p10, the combination of that and a dark mark on p4 is rather unusual. Such a combination is at least more frequent in birds from the Atlantic region rather than the Mediterranean Sea. The problem is that there is no clear line where one type of wing tip pattern ends and another begins. The differences are only ones of percentage, so arguably the bird could be from either population.
Yellow-legged Gull: Kensington Gardens, London (photo: Fraser Simpson).
Yellow-legged Gull: Kensington Gardens, London This wing tip pattern with one white primary mirror and black mark on P4 is more unusual for western michahellis and commoner in Atlantic populations. A really good Azorean bird, however, would have a solid black mark on p4 and wider black band on p5. Clinal variation and/or number of subpopulations make it hard to place exactly where this wing tip pattern has come from. Then there is the hybrid possibility. (photo: Fraser Simpson).
Essentially, the further west you go the amount of black increases and the amount of white decreases. So, while the wing tip pattern on the Kensington bird is interesting, it would be difficult to claim that it was diagnostic of one particular population. It may be that others with more time, and the critical information on the very minutiae of the wing tip pattern data, can comment more helpfully. Actually, this bird shows that the mark on p4 is not solid black but diffuse as it reaches the feather shaft. It is hardly outstanding and less indicative of an Azorean bird. The black band on p5 is solid but not massively broad. Certainly, some individuals of the Azorean population would have much more solid black on p4 and a broader band, particularly the outer web of p5. It is these latter patterns that are needed to help establish the occurrence of a real vagrant Azorean atlantis.
Question 3: How about the upperpart tone?
The bird can be compared with photographs of a Common Gull taken at the same time, but trying to assess the photographs in different light conditions can be a nightmare. Having assessed a range of photographs I came to the conclusion that the upperpart tone is unremarkable (though some reproduced her seem a little underexposed/over-saturated). In fact it doesn't look particularly darker than on a typical michahellis, though without direct comparison it would be hard to be sure. It doesn't however look the 'Laughing Gull' or 'Kittiwake' tone that would suggest an Azorean bird.
Yellow-legged Gull: Kensington Gardens, London) Here the upperpart tone is probably a little truer. An interesting and educational bird. True atlantis (from the Azores) is however an ocean-going pelagic feeder, not ideally suited to summering in a city park in London! However, such a locality would be normal for michahellis Yellow-legged Gulls (photo: Fraser Simpson).
Other features: It is sometimes said that Azorean birds have a paler, almost whitish-yellow, iris compared to Mediterranean birds (more golden-yellow). I see absolutely no difference in the iris colour between birds I've seen in Turkey, Menorca and the Canary Islands. Bare-part colours on all Mediterranean Yellow-legged Gulls become weaker in the winter. It would be difficult to glean any really useful information in focusing on bare-part colours on this particular individual at this time of year. While on average Azorean birds can be shorter-legged, I've seen many examples of apparent Mediterranean birds looking similarly short-legged, so find it hard to place too much significance to this feature.
Question 4: Why the heck is it in urban London?
Maybe it's just my own bias, but this is the question that made me most dismissive about it being an Azorean atlantis. Traditionally all the Yellow-legged Gulls of the Atlantic region have been considered sedentary. However, the North American record and observations of birds feeding hundreds of miles out at sea, together with the circumstantial evidence of birds reaching Ireland, suggest that Azorean birds are prone to wander.
However they are highly pelagic feeders. It is known that they feed on fish that live several hundred metres below the surface, which they obtain by seeking out the shoals of Tuna that push the small fish to the water's surface. In contrast Mediterranean Yellow-legged Gulls are littoral feeders, scavenging along shorelines and around human habitation. The behaviour and location of the Kensington individual does not tally in any way with that of an Azorean pelagic-feeding, ocean-going, seagull! It's not beyond the realms of possibility, but the location and situation do not add weight and favour to postulating a far-flung Atlantic-island origin. Rather it appears to be in the domestic, urban, surroundings, which are normal for michahellis.
The birds outside of the western Mediterranean are in taxonomic flux. So how can you claim that such a bird, which is not sufficiently extreme enough in its features (i.e. identifiable as an Azorean Atlantic Gull), can be an atlantis? What I mean by this is that there is a cline, or a least a number of subpopulations, lying anywhere between the edge of the western Mediterranean and the Azores. This includes Portugal, Spain, Northwest Africa, Madeira, the Canaries and possibly even coastal France. The Azorean birds are nowadays considers to be the taxon that is correctly assignable as atlantis. However, all the birds between the Azores and the Mediterranean could either be labelled as an atlantis, or michahellis, or a mixture of both. There is no clear view, partly because it is difficult to identify differing characteristics within the populations, never mind to try and name a vagrant.
In summary while the bird does look interesting I don't think it is distinctive enough in its features to be assignable to one particular origin. Gut Guess? It's probably from somewhere like the Berlengas Islands off Portugal at the starting point of darker wing tip patterns, more head streaking etc. Individuals from that area are already known to have reached the UK through a ringing recovery and I have suspected them in Essex and Belfast.
There is however another frightening and very real possibility. Normally the hybrid option is used as a get-out clause for an embarrassing misidentification. However, not far from the southern English coastline, the hybridisation between Yellow-legged Gulls and Lesser Black-backed Gulls, and various back-cross combinations, is a well-documented phenomenon. This, in my view, could easily produce a bird that looks just like the Kensington gull. Not only do Lesser Black-backed Gulls have more extensive head-streaking, and of a similar pattern to the Kensington bird, but they inevitably have more black and less white in the wing tip pattern. The key paper to read if you want in be really discouraged is to be found in Dutch Birding Vol. 26 no. 1.
The presence of an easily watched bird, together with the quality of pictures produced by today's digital camera technology, enables us to learn afresh about the possibilities, and problems, of identifying out-of-range large Gulls. In conclusion, I don't think this individual is assignable as a particular race, certainly not as an Azorean atlantis, although as ever it is highly educational.
Yellow-legged Gull: Dix Pit, Oxfordshire Streaky-headed adult michahellis in early November 2006 (photo: Ian Lewington).
Yellow-legged Gull: Menorca michahellis taken in Menorca June 2003 showing iris colour (photo: Martin Garner).
Des McKenzie, the bird's finder, sent these illuminating comments after this article was written: "The streaky-headed bird is now in its ninth month of residency (as of November) and was in fact paired off with a michahellis back in the spring. In terms of mantle shade, the gull in question didn't differ significantly to the Yellow-legged Gull and in direct comparison with Common Gull is a shade darker. Following the departure of one Yellow-legged Gull the remaining bird became paired with a graellsii Lesser Black-backed Gull and subsequently I ceased reporting the bird (at the time a presumed straightforward michahellis) throughout the breeding season for security reasons, though no young were ever seen. Once the pair bond had weakened I resumed reporting the bird. Vocally, the bird is more akin to Yellow-legged Gull/Lesser Black-backed Gull than to Herring Gull."
With many thanks to Fraser Simpson and Des McKenzie for useful feedback and photos of the bird and to Ian Lewington and Derek Charles.