Herring Gull - Zilvermeeuw (argentatus & argenteus): sub-adult Nov.

(last update: 07 april 2004)

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Herring Gull 5cy AVAWNovember 15 2003, Westkapelle, the Netherlands (51.33N-03.25E). 

A 5cy from the Belgian colour-ring program, ringed blue AVAW. Ringed as pullus at Zeebrugge, Belgium (51.21N 03.11E) on July 09 1999. The primaries are very adult-like, with the mirror merged with the tip on P10. The tail is completely white. The last vestiges of immaturity are shown by the bare parts, especially the bill.

From June to October, sub-adult Herring Gull have a complete moult to so-called "winter plumage". As long as the old outer third generation primaries are visible (until August), ageing as 4cy is rather straightforward. From November onwards, 4cy birds much resemble adult birds, except that the bare parts still show immature features: 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 in argenteus, concentrated on the outer-web as a clear-cut black angular spot sometimes extending on the inner-web as a diffuse streak in 4cy. There may be some black on P4 as well in sub-adults. 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.