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

(last update: 08 december 2003)

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Herring Gull sub-adult (argenteus), October 20 2003, IJmuiden, the Netherlands (52.27N 04.33E).

A sub-adult argenteus: the primary coverts are obvious immature and show some black markings and a few inner greater coverts have immature markings as well. The primary moult score: P9 fully grown, P10 already visible with a white mirror on both webs. 
From June (often mid-May in France, Belgium and the Netherlands) to October, a complete moult will bring birds in so-called "sub-adult winter" plumage. A new set of primaries will grow during the summer months and by October, the old primaries are all shed in argenteus in the Netherlands and northern France. In most adults (!), the new primary P6 is just visible beneath the tertials and shows a clear sub-terminal band. By late-October, P7 and P8 are fully-grown as well. At the same time, the wing-coverts have been renewed. In summer, the head is still largely white, but by September, most birds develop extensive 'winter streaking', in sub-adults strongly mottled brown contrasting with the white breast as in an executioner's hood. The tertials show obvious white tips. The iris is white-yellow with extensive speckling. The bill has a red gonydeal spot confined to the lower mandible. The orbital ring is yellow-orange in most argenteus, but often dark in autumn.