Herring Gull - Zilvermeeuw (argentatus & argenteus): 4cy June

(last update: 08 december 2003)

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Herring Gull 4cy (argenteus), June 24 2003, IJmuiden, the Netherlands (52.27N,04.33E).

A 4cy argenteus. The scapulars and wing-coverts appear completely adult-like grey. The primaries show a clear mirror on P10. Last autumn, this individual has replaced the all-brown immature primaries for more adult-like primaries, which show a white tip, a grey basal half and one or two mirrors (P9 and P10). But still the size of the dark patches and the amount of black in the outer primaries is more extensive when compared to adults: there is often a broad dark sub-terminal band on P5 and a dark faint spot on the outer-web of P4. The dark patches are not sharply demarcated as in adult, but the dark outer-web gradually dissolves in the grey inner-web.

During summer, from June onwards, a complete moult takes place in argenteus, bringing birds in so-called "adult winter" plumage. As long as the old outer third generation primaries are visible (until August), ageing as 4cy argenteus is rather straightforward. From November onwards, 4cy argenteus much resembles adult birds, except that the bare parts still show immature feathers: the black bill-band is obvious, extending over both upper and lower mandible. On average, this plumage develops a more pronounced winter 'hood' than in full adults: dense streaking on head, especially around the eye and in the hind-neck. The upper-parts, wing-coverts and tertials appear adult-like grey from 4cy October onwards. The fourth generation tail-feathers are plain white. 
The new fourth generation primaries are similar to the adult primaries, although the primary tips may appear slightly smaller, but otherwise similar in pattern: grey inner-wing and black outer-wing. Both P9 and P10 show a mirror. P5 shows small black sub-terminal markings, concentrated on the outer-web as a clear-cut black angular spot and rarely extending on the inner-web as a diffuse streak. There may be some black on P4 as well. Adult argenteus show a different pattern in the outer primaries, compared to northern argentatus. In argentatus, especially from northern Scandinavia, the black marking on P5 is very limited and diffuse or this is sub-terminal markings are completely lacking on P5. 
Argenteus
has more black in the outer primaries, including a black band on the top of p10 in most birds, dividing the tip from the mirror. If the black sub-terminal band on P10 is broken, the outer-web of p10 still shows black marking. Argentatus normally lacks sub-terminal markings on the outer-web of P10. 
The scapular coverts are plain grey, lacking white crescents. The tertials show obvious white tips. The iris is yellow. The bill is yellow with a red gonydeal spot confined to the lower mandible. The orbital ring is yellow-orange or orange-red. The legs are flesh-pink.