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

(last update: 09 maart 2004)

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Herring Gull C656R 5cy (argentatus), August 11 2002, Tampere, Finland (61.31N,23.43E).

A 5cy argentatus, ringed white C656R as pullus on June 30 1998 in Sysmä Finland. This bird shows only limited immature characteristics and much resembling adult argentatus, with relatively large tips on the outer primaries, but note the dark outer primary coverts. C656R is in active complete moult with the median coverts replaced and the outer greater coverts growing; the central greater coverts are shed. The inner primaries P1-P5 are fully grown with a broken thin sub-terminal band on the new P5. Primaries P8-P10 are still old, with a  large mirror on both P9 and P10.

From June to December, sub-adult argentatus undergo a complete moult resulting in so-called "winter plumage". By August, the first neat streaks can be found on the crown and hind-neck. After the complete moult is finished by late autumn, the head will show extensive 'winter streaking', often neat fine streaking in sub-adult argentatus
By the end of the complete moult (first week of December), the scapulars, mantle and all the wing-coverts will be replaced and near-adult argentatus will be indistinguishable from full adult plumage. From June onwards, the new plain grey wing-coverts are moulted in, starting with the outermost median coverts. 

During the summer, the primaries are moulted. In argentatus, the last outer primary P10 will be fully grown by early December, slightly later than in West-European argenteus. First data from Tampere, Finland, indicate that 3cy argentatus from this region are not delayed in primary moult compared to argenteus

Adult northern argentatus show a different pattern in the outer primaries, compared to argenteus. In argentatus, especially from northern Scandinavia, the black marking on P5 is very limited and, if black on P5 is present, this black has diffuse edges. But often, these black sub-terminal markings are completely lacking on P5. In Baltic argentatus populations, black on P5 is confined to the outer-web, with sharply defined edges.
Argenteus
normally has a black sub-terminal band on the top of p10, 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 completely lacks sub-terminal markings, also on the outer-web of P10. Some argentatus completely lack black on the edge of the inner-web, creating a so-called "thayeri pattern". 

The iris is clearly yellow in summer in most argentatus, but some sub-adult argentatus will keep the iris amber to dark brown.