When Leon Edelaar sent me the following pictures of a “herring gull sp.” that he had photographed at Ijmuiden, the Netherlands, on 2 February 2013, I was very hesitant to put a name to it. The pictures had been gathering dust on Leon’s hard drive, but they recently sparked his attention because he noticed a “grey mirror” on the underside of the ninth primary (see American Herring Gull: new ID feature), which made him wonder…
At first sight, the bird in the pictures did not strike me as very unusual. Surely, in shape and overall plumage aspect, it looked rather like any run-off-the-mill (subadult) European Herring Gull!? However, a closer look reveals a few interesting features. At rest, the bird shows quite impressive blackish and oval shaped ‘ink spots’ on the tertials, while the rest of the plumage looks basically adult. Many European Herring Gulls show dark marks on tertials, of course, but it is quite rare to see one that looks adult except for such large, oval shaped and well-defined, black(ish) spots. That is something much more commonly seen in American Herring Gulls. Then, in flight, the bird reveals an isolated grey spot in the black pattern on underside of primaries (at least in right wing). Again, this is more common in American Herring Gull. So far so good. An interesting bird, yes, but nothing impossible for a European Herring Gull. However, then we look closely at the secondaries, and they show the most alarming feature: two small but well-defined black ‘ink spots’. Such isolated black spots on adult secondaries are not seen in European birds, and have been considered a key feature of 3rd and 4th cycle American Herring Gull ever since the identification paper by Mullarney and Lonergan (2004).
Other characters are less helpful. The primary pattern includes a complete, black ‘W’ on P5, and black “bayonets” on P6-7 (see Adriaens & Mactavish 2004) – good for American Herring, but equally possible for European birds. The tail shows a few small, solid black spots – better perhaps for American birds, as blackish markings in the tail usually do not look very solid in subadult European Herring Gulls. The bill shape and length look ok to me for either species, as does the colour of the upperparts. I would have expected heavier brown blotching on the neck and breast for an immature American Herring Gull, but there is a lot of variation.
So what does it all mean? It seems that, on current knowledge and for the time being, this bird should be considered an American Herring Gull, even though it is certainly not an obvious example! Here is one from North America that is similar:
The identification of such birds relies heavily on the pattern of the secondaries. There are many people closely studying and ringing gulls in the Low Countries, and it seems that such a pattern has never been documented in the local Herring Gulls.
If anyone has ever photographed such a secondary pattern in argenteus or argentatus, both Leon and me would be very interested to hear from you…