Herring Gull - Zilvermeeuw (argentatus & argenteus) sub-ad September

(last update: 31 januari 2005)

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Herring Gull 5.352.702 (argenteus) sub-adult, September 18 2004, IJmuiden, the Netherlands (52.27N, 04.33E).

This 4cy bird resembles an adult argenteus in many respect, but the black markings on the bill are too extensive for full adult birds. Note the pink-based bill and dark orbital ring. The primary moult score: P7 fully grown (over P6 tip) and P10 still old. See also NLA 5.352.700. It is a local bird and was ringed as pullus on July 02 2001 at IJmuiden, the Netherlands (52.28N 04.35E).

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-September, P6 and P7 are fully-grown as well. At the same time, almost all 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.