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

(last update: 08 december 2003)

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Herring Gull C03S0 4cy (argentatus), August 06 2002, Tampere, Finland (61.31N,23.43E).

A 4cy argentatus, ringed white C03S0 as pullus on June 15, 1999 in Vkoski, Finland. This bird is in active complete moult with the inner primaries moulted to fourth generation. Primary P7-P10 are still juvenile. The median coverts are fresh adult-like grey and the central greater coverts are dropped, showing the old third generation secondaries underneath. Most obvious immature features can be found in the lower tertials and the inner greater coverts. Note also the brown immature primary coverts.

From June to December, 4cy argentatus undergo a complete moult resulting in so-called "fourth 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 and mantle and all the wing-coverts will be replaced and sub-adult argentatus will be hardly distinguishable from full adult plumage, except the black centres of the primary coverts in some sub-adults. 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 to fourth generation. The faded brown third generation primaries (with a mirror on P10) are replaced for true adult primaries. 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.