Herring
Gull - Zilvermeeuw (argentatus & argenteus)
(last update: 08 december 2003)
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Herring Gull adult (argentatus), January 06 1992, Worcestershire, Britain. Picture by Peter Stewart.
From June to October, adult Herring Gull
have a complete moult to so-called "winter plumage". In
this moult all primaries, rectrices and secondaries are replaced; they
look still fresh by January. Adult birds from the western populations argenteus
show more black in the outer primaries, compared to northern argentatus.
In argenteus, P5 normally shows
small black sub-terminal markings, concentrated on the
outer-web as a clear-cut black angular spot and in some birds extending on
the inner-web as a diffuse streak. There may be some black on P4 as well,
although this might be a clue for near-adult birds. In argentatus, especially from
far northern Scandinavia, the black
marking on P5
is completely lacking or is very limited and diffuse.
Argenteus often has a black sub-terminal band on the top of P10, dividing the tip from the mirror. If
the black sub-terminal band on P10 is broken, there is often still black
on the inner and outer-web's edge of P10. Normally argentatus lacks sub-terminal
markings on the outer-web of P10.
In adult Herring Gull, 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
yellowish or yellow-orange in argenteus; slightly orange-red or
coral red in most argentatus; especially birds from the Baltic region
show a bias to reddish orbital rings. The legs are flesh-pink in argenteus, but
may show a yellowish hue or appear very clear yellow in some argentatus
(from either the Baltic region or far northern Finnmark). Furthermore,
adult argentatus from Finnmark also seem to develop
"bubble-gum" pink legs.
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.
Some features seem to point to a hybrid hyperboreus x argentatus. However, this bird may just be an adult argentatus, showing limited black in the outer-wing.
- This individual has no black sub-terminal band on P10 and only a small square, sharply defined sub-terminal mark on the edge of the inner-web. 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 broken sub-terminal band on P6, in line with what can be expected from northern 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 yellow-orange.