Mysterymeeuw in Katwijk aan Zee

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De binnengekomen suggesties heb ik in een bericht op EuroBirdNet samengevat (19 November 1999). Dit was als volgt:

I received eleven answers to my question as to what (sub-)species birders thought this bird could belong. Generally, those who responded thought that the choice was between Herring L. argentatus and Yellow-legged Gull L. michahellis. Two thought Lesser Black-backed L. fuscus graelsii was another possibility and even Greater Black-backed was suggested, but then more as a candidate for one of the parents of this bird, thus being a hybrid. The scapular pattern could indeed suggest some Greater Black-backed influence. But as I stated, most went for argentatus or michahellis. Some were just sure that it was the latter species (see the pictures published in Limicola: Gruber 1995, Klein & Gruber 1997). Most others, however, were cautious and warned for the obvious difficulty that exists when trying to identify birds of this age. Apparently, both species are notoriously variable in this (first-summer/second-winter) plumage, although the knowledge of argentatus appears to be somewhat more extensive under gull watchers than that of (1S/2W) michahellis. The bird's jizz, although it can be a useful character, was considered right for michahellis by some, but just as right for argentatus by others. Plumage details were hardly mentioned in the discussions, most probably because of the variability in both species. People from areas where michahellis is common were quite positive that it was this species, although it was acknowledged that a michahellis should show more grey in the upperparts by this time. Slightly as a surprise to me, Lesser Black-backed Gull L. fuscus graelsii was also mentioned as a candidate (by 2), but others pointed out that this species would show darker and less patterned upperparts. However, a picture that has been published in British Birds (vol. 90, 1997, no. 9, p. 374, pl. 110) depicts a graelsii of similar age that shows a striking similarity to the mystery bird. Although the underparts and the greater coverts are quite darker than those of the mystery bird, the pattern and ground colour of the scapulars and especially tertials are just right. It was stressed by one observer that these rather pale greater coverts generally fit argentatus better than any other of the candidates. Another birder described ths plumage to be not uncommon under argenteus Herring Gulls. This is sometimes retained throughout the whole of the second winter. They often also produce very colorful bare parts (e.g., brighter pink bill base). Too bad the bird wouldn't stay around to check this! In conclusion, I cannot but say that the puzzle just hasn't been solved. Thanks everyone who responded!! And keep on gulling!   Teus

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