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

(last update: 08 december 2003)

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(4 images) Herring Gull 5.325.398 (argenteus), February & October 2002, IJmuiden, the Netherlands (52.27N-04.33E). 

A 4cy argenteus ringed in the Netherlands: Vogeltrekstation Arnhem Holland 5.325.398. This individual was ringed as pullus on July 02 1999, at IJmuiden. This bird resembles an adult argenteus in many respect including the yellow-based bill, an orange-yellow orbital ring, an obvious mirror on P10 and white tips to the primaries. Nevertheless, a few immature features can be seen as well:

  • The brownish outer primary coverts, which would be plain grey in 5cy and older birds,
  • The arrow-head pattern on the old tertials,
  • The brown hue on the inner greater coverts,
  • The relative dense streaking on the head and the rather obvious black markings on the bill. The relatively well-developed dark bill-band is in line with near-adults.

From January to April, 4cy argenteus moult to so-called "third summer" plumage. By April, the head and under-parts will appear all-white. The tail-feathers, wing-coverts and primaries are not replaced, therefore most birds strongly resemble "third winter"  birds, although the white primary tips wear away and dark patches start to bleach. The iris is often yellowish, the orbital ring yellowish-orange and the bill predominantly yellow with a red gonydeal spot and limited black markings along the culmen by April.

2 images below: 5.325.398 4cy, February 04 2002, IJmuiden

image below: 5.325.398 4cy, February 07 2002, IJmuiden.

In general the upper-parts appear adult-like grey, but in the old tertials and inner greater coverts dark shaft-streaks are still visible. Note the dark outer primary-coverts. The primary tips are rather small and the mirror on P10 is almost limited to the inner-web. In immature birds the dark outer-wing continues further on the basal half than in adults.

image below: Herring Gull 5.325.398 4cy, October 22 2002, IJmuiden.

The primary moult score: P8 fully grown, P9 slightly longer than P8 and P10 visible in far wing. Note the head streaking. Note the relatively small mirror on P9.

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. 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.

Primary moult scores in adult Herring Gulls at Scheveningen.

. 05-10-2000 07-10-2000# 07-10-2000* 12-10-2000 14-10-2000 21-10-2000 26-10-2000
P5 1 1 - 1 - - -
P6 32 19 28 5 4 1 -
P7 51 69 82 69 106 32 24
P8 7 19 15 29 69 53 87
P9 1 - - 2 2 4 18
P10 - - - - - - -
n: 92 108 125 106 181 90 129
average: 6,7 7,0 6,9 7,3 7,4 7,7 8,0
95% CID: 0,14 0,12 0,10 0,12 0,08 0,12 0,10
SD: 0,66 0,63 0,58 0,61 0,55 0,58 0,57

# high tide at Scheveningen beach on October 07 2000,
* low tide at Scheveningen beach on October 07 2000,
95% CID: Confidence Interval of the Difference,
SD: Standard Deviation.