Herring
Gull - Zilvermeeuw (argentatus & argenteus)
(last update: 08 december 2003)
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Herring Gulladult (argentatus), November 16 2002, Westkapelle, the Netherlands (51.33N-03.25E).
An adult argentatus, with the sub-terminal band on
the outer primaries broken by the white shaft. The white eats in into the black area on the
outer-web of both P9 and P10, creating a complete thayeri-pattern
on these primaries, with hardly any black on P10. The band on
P5 is lacking and P6 has only an extremely limited faint streak, hardly
visible in the field.
A typical
argentatus, with the upper-parts dark grey, obvious darker than local Dutch argenteus
Herring Gulls, a coral red orbital ring, limited black in the outer
primaries and a more powerful, stronger head and neck. The inner wing-coverts and upper
tertials still have relatively fresh fringes, in much better condition than found in some
argenteus, which have
these feathers replaced about 4 months ago and show worn fringes by
November.
Note the missing central median coverts.
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 late November, the average argenteus in the Netherlands and northern
France has completely moulted all primaries. At the same time, the wing-covert moult is completed by the end
of the month. Argentatus from Scandinavia are behind in
primary moult.
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, slightly darker, orange-red or
coral red in argentatus.
The bird in the picture shows the characteristic 'thayeri' pattern in the outer primaries P9 and P10. This pattern is named after the Thayer's Gull, which often shows a particular pattern in the outer primaries: the mirror and the white tip merge and are connected to the pale inner-web. In other words: the black medial band of the outer-web doesn't fully reach the edge of the inner-web and there is no sub-terminal band. In Thayer's Gull this pattern may be very obvious and, together with the 'string of pearls' may be indicative for identification. A string of pearls refer to the white crescents, which can be found between the sub-terminal band and the grey patch on the inner-web. In the picture below, these white crescents can be found in P6-P8.
- This individual has no black sub-terminal band on P10 and limited sub-terminal black on the edge of the outer-web of P9. Full sub-terminal bands are only present on P7 and P8. A complete sub-terminal band on P10 is found in only 15% of argentatus. Adult argenteus normally shows a complete black sub-terminal band or reduced sub-terminal black at the edge of the inner-web and outer-web (broken sub-terminal band at the centre). Only a small minority of western argenteus completely lacks any sub-terminal markings. Extensive research on the P10 pattern of Scandinavian argentatus was done for Norwegian birds by the Norwegian ornithologist Edvard Barth, and is presented in the table below.
| Table 4 from E.K. Barth, The circumpolar systematics of Larus argentatus and Larus fuscus with special reference to the Norwegian populations, 1968. 200 Norwegian birds. (Notation converted to what we use in the texts, MM). | ||||||||||||||||||||
| locality | sample size | tip pattern P10 | tip pattern P9 | colour of P10 inner-web | black present from P10 to: | |||||||||||||||
| 1 | 2 | 3 | 4 | 1 | 2 | 3 | 4 | 5 | 1 | 2 | 3 | 5 | 6 | P7 | P6 | P5 | P4 | |||
| East Finnmark | 15 | n | 10 | 1 | 2 | 2 | 5 | 4 | 1 | 1 | 4 | 5 | 7 | 3 | 12 | 3 | - | 10 | 5 | - |
| % | 67 | 7 | 13 | 13 | 33 | 27 | 7 | 7 | 27 | 33 | 47 | 20 | 80 | 20 | - | 67 | 33 | - | ||
| Tamsöy in Central Finnmark | 33 | n | 17 | 7 | 6 | 3 | 10 | 10 | 6 | 0 | 7 | 12 | 20 | 1 | 23 | 10 | - | 19 | 13 | 1 |
| % | 52 | 21 | 18 | 9 | 30 | 30 | 18 | - | 21 | 36 | 61 | 3 | 70 | 30 | - | 58 | 39 | - | ||
| Troms | 29 | n | 17 | 8 | 3 | 1 | 11 | 9 | 4 | 1 | 4 | 3 | 20 | 6 | 24 | 5 | - | 24 | 5 | - |
| % | 59 | 28 | 10 | 3 | 38 | 31 | 14 | 3 | 14 | 10 | 69 | 21 | 83 | 17 | - | 83 | 17 | - | ||
| Bodö and Röst | 32 | n | 15 | 10 | 3 | 2 | 19 | 3 | 5 | 0 | 3 | 3 | 24 | 5 | 27 | 5 | 1 | 18 | 13 | - |
| % | 50 | 33 | 10 | 7 | 63 | 10 | 17 | - | 10 | 9 | 75 | 16 | 84 | 16 | 3 | 56 | 41 | - | ||
| Tarva | 20 | n | 8 | 7 | 3 | 2 | 11 | 5 | 4 | 0 | 0 | 10 | 8 | 2 | 12 | 8 | 1 | 7 | 10 | 2 |
| % | 40 | 35 | 15 | 10 | 55 | 25 | 20 | - | - | 50 | 40 | 10 | 60 | 40 | 5 | 35 | 50 | 10 | ||
| Stavanger and Lindesnes | 42 | n | 18 | 13 | 4 | 6 | 23 | 12 | 3 | 2 | 2 | 15 | 23 | 4 | 37 | 5 | - | 13 | 29 | - |
| % | 44 | 32 | 10 | 14 | 55 | 28 | 7 | 5 | 5 | 36 | 55 | 9 | 88 | 12 | - | 31 | 69 | - | ||
| Oslo Fiord | 29 | n | 19 | 6 | 3 | 1 | 20 | 1 | 4 | 1 | 2 | 12 | 14 | 3 | 24 | 5 | - | 17 | 12 | - |
| % | 66 | 21 | 10 | 3 | 71 | 4 | 14 | 4 | 7 | 42 | 48 | 10 | 83 | 17 | - | 59 | 41 | - | ||
| 1:
all white 2: trace of black near tip 3: incomplete black bar near tip 4: complete black bar or black tip |
1:
broad white band over both webs 2: white spot on both webs 3: white spot on inner web only 4: no white spot present 5: 'thayeri-pattern' |
1:
like mantle colour 2: slightly lighter than mantle colour 3: markedly lighter than mantle colour 5: relatively sharp border between black and grey 6: gradual transition from black to grey |
||||||||||||||||||
- This individual has no black on primary P5 and a very diffuse black line on P6, in line with what can be expected from north Scandinavian argentatus populations. In argenteus, the black on P5 is normally well-developed, either as a solid square mark on the outer-web or a complete black sub-terminal band. West-European argenteus have a well-developed black square sub-terminal mark on the outer-web of P5 or a complete sub-terminal band, extending over both inner and outer-web.
- The orbital ring is clear orange. Note the pale pinkish base of the bill.