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

(last update: 24 maart 2004)

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(2 images) Herring Gull HT-205231 sub-adult (argentatus), July 15 2003, Tampere, Finland (61.31N, 23.43E).

Sub-adult argentatus, probably 5cy, metal-ringed HT-205231, ringed in Finland, probably in June 1999 near Kanala. As soon as more data are available, this information will be added to this page.
The complete moult is well underway with many wing-coverts and the inner primaries recently moulted. Primary P6 has been dropped and P7-P10 are still old, with a large white mirror on P10. P4 has a complete black sub-terminal band. Note the dark outer greater primary coverts. All scapulars and replaced median and lower lesser coverts are plain grey, much adult-like. Most old wing-coverts show brown vermiculated patterns. The legs are pink. Note the mature colour of iris and bare parts.

From June to December, sub-adult argentatus undergo a complete moult resulting in so-called "winter plumage". From June onwards, the new plain grey wing-coverts are moulted in, starting with the outermost median coverts and followed by the inner medians, the inner greaters, and the rest of median and lower lesser coverts. 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' in argenteus, often neat fine streaking in sub-adult argentatus. Also, by the end of the complete moult, the scapulars, mantle and all the wing-coverts will be replaced and near-adult argentatus can hardly be distinguished from full adult plumage (except more black on the bill and often the dark centres in the outer greater primary coverts).

During the summer, the primaries are replaced. In argentatus, the last outer primary P10 will be fully grown by early December, slightly later than in West-European argenteus. However, 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 markings on P5 are very limited and, if black on P5 is present, this black often has diffuse edges. More often, these black sub-terminal markings are completely lacking on P5. In Baltic argentatus populations, normally black on P5 is confined to the outer-web, with sharply defined edges.
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".