Herring
Gull - Zilvermeeuw (argentatus & argenteus)
(last update: 08 december 2003)
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Herring Gulladult (argentatus), October 20 2003, IJmuiden, the Netherlands (52.27N-04.33E).
This adult has an obvious 'thayeri' pattern in P10. Fine but extensive head streaking.
From June (often mid-May in France, Belgium and the Netherlands) to October, a complete moult will bring birds in so-called "adult winter" plumage. A new set of primaries will grow during the summer months and by October, all the old primaries are shed in argenteus in the Netherlands and northern France. In adults, the new primaries are visible beneath the tertials. At the same time, the wing-covert moult is completed by the end of the month. In summer, the head is still largely white, but by September, most adults develop extensive 'winter streaking', in sub-adults strongly mottled brown contrasting with the white breast as in an executioner's hood. The scapular coverts are plain grey, lacking white crescents. The tertials show obvious white tips. The iris is yellow. The bill is yellow with a red gonydeal spot confined to the lower mandible. The orbital ring is yellow-orange in most argenteus, but it is rather orange-red in this individual.
