Yellow-legged Gull - Larus michahellis

(last update: May 16, 2011)


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This website deals with the Yellow-legged Gull taxon michahellis, which is a common migrant from July to December in NW Europe. After extensive expansion of the breeding population during the last three decades, it nowadays can be found breeding in Belgium, the Netherlands and Britain in mixed couples with both Herring Gull (argenteus) and Lesser Black-backed Gull (graellsii). There are subtle differences between the populations from the Mediterranean, Atlantic coast of Portugal and Morocco and from the islands in the Atlantic. Most pronounced differences can be found in the taxon atlantis, now regarded as full species by some authors.

L. michahellis: 1cy October

General description:

In the Netherlands, most michahellis can be found in October. October 10 2001, over 60 were present at a single location, the Maasvlakte, near the port of Rotterdam. Many local Lesser Black-backed Gulls leave the breeding grounds and migrate south, contra the northbound migration of michahellis. In the Netherlands, the majority of 1cy LBBG's now originate from Scandinavian populations and these fresh and neat looking birds contrast strongly from michahellis, which shows strongly worn juvenile covert fringes and tertials. Some 1cy michahellis at Le Portel (NW France) are metal-ringed or colour-ringed and they apparently originate from southern France (Marseille and islands in the Mediterranean), Italy, Croatia and Switzerland.

Moult stage and pace in the scapulars:

In 1cy michahellis, there are almost no birds left with juvenile feathers in the scapulars and mantle feathers. These feathers are almost completely replaced by second generation feathers (except probably three or four rear lowest lower scapulars). The last moulted scapulars show a brownish or buffish based centre between the dark bars or anchor pattern and the feathers have a broad white fringe.
The table below presents the results of scapular moult in early October 2002 at Etaples and Boulogne-sur-Mer, Pas de Calais, NW France. The complete table can be found here (140 kB). By early October, all upper scapulars have been replaced for second generation feathers in both samples (n = 21 and n = 30). In the lower scapulars, it's normally the last three or four rear scapulars in the lowest row (the ones covering the scapular coverts) which may still be juvenile. In most birds, these rear lower scapulars may be shed as well by the end of the month. As a result, the average 1cy michahellis have a complete second generation scapular region at the start of winter. It has to be said that birds with score C (50-74% moulted lower scapulars) by early October were on the far end of this class, so close to 75%.

Moult stage and pace in the wing-coverts:

The amount of replaced coverts and tertial vary to a large extend, just as it did in September. 2cy michahellis in spring may still show all the wing-coverts juvenile, so must have suspended moult in October in 1cy as well. But most 1cy birds have replaced at least a few (inner coverts) to second generation feathers. This moult started already in September and continues in October. A few birds may still start wing-covert moult and tertial moult in the last days of September and by the end of October, only 15-20% of the birds show complete juvenile wing-coverts and tertials. As a result: Over 80% has started partial moult (post-juvenile moult) in their first calendar year. 

The average moult stage by the first week of October is: almost all scapulars and mantle replaced completely for second generation feathers; 3 to 4 inner greater coverts replaced (with often a single inner greater retained juvenile); about 8 inner median coverts moulted (again sometimes one inner covert left unmoulted in some birds); the moult in the lesser and lower lesser coverts quite random, but concentrated in the inner half of the tracts and in some birds one tertial moulted (often the third). Some birds still show a complete juvenile wing, with abraded coverts (especially the inner coverts) and juvenile tertials. These 1cy michahellis birds strongly resemble graellsii when the wings are folded and the bird rests. For a nice example, see the Swiss-ringed michahellis in image 6773. This kind of 1cy birds (Sempach birds) are very hard to tell from graellsii, even more since they breed in the northernmost colonies of the michahellis range. They therefore may hatch slightly later in the season and in turn the abrasion in the coverts may appear to be more in line with graellsii which may breed at the same latitude.

The most advanced birds started wing-covert moult two months ago (August) and show many second generation coverts by mid-October; in some birds about 50% of the visible wing-coverts. Two examples can be found on this page, showing two colour-ringed birds from soutern Italy with very advanced wing-covert and tertial moult. 
Normally, the wing-covert moult is most advanced in the median covert row, notwithstanding the slightly higher score in the lesser coverts in the sample of October 03 2002 (n = 21). Advanced birds include the upper tertials in the autumn moult, but some birds may moult a central or a few central tertials (often starting with the third tertial). The juvenile tertials are plain brown centred and the fringes are completely gone, leaving a protruding shaft streak, where the new second generation tertials often show a barred pattern with neat fringes.

From the table below, the following results can be extracted:

  • by early October, about 75-80% of 1cy michahellis start moult in the tertials or wing-coverts (19-27% still shows a complete juvenile wing).
  • a minority of about 40% start tertial moult by early October.
  • about 10-14% of the wing-coverts and tertials is included in the partial moult by early October (missing, growing and fully grown feathers included).

Moult stage and pace in the rectrices:

Scanning flocks of 1cy michahellis, one may regularly encounter birds with moulted rectrices. Examples of such birds can be found here and here. Moult in the tail-feathers may start from early October (maybe already from late September?) to late October. By late October, about 5% of 1cy michahellis started moult in the rectrices. Of these birds, most are still missing tail-feathers (so actively growing feathers) and moult may continue in November. The complete extend of this moult is yet unknown, but by May, 2cy michahellis may show a completely moulted tail with all tail-feathers second generation. An example of such a bird can be found here


The moult stage of 1cy michahellis from October can be found in this spreadsheet

Juvenile michahellis moult score October 2002 at Pas-de-Calais, NW France: for the complete table of results click here (140 kB). The table below shows a summary.

  03 Oct 2002 (n: 21) 04 Oct 2002 (n: 30)
  min (0) max (50) aver min (0) max (50) aver
tt 0 (62%) 21 3.6 0 (60%) 25 5.3
gc 0 (57%) 6 2.0 0 (47%) 16 2.5
mc 0 (38%) 22 6.8 0 (33%) 50 13.1
llc 0 (38%) 19 5.8 0 (40%) 45 7.7
lc 0 (29%) 22 7.2 0 (43%) 40 6.8
tot: 19% - 10% 27% - 14%
second generation scapulars: A (100%), B (75-99%), C (50-74%)
  A B C A B C
us 21 (100%) - - 30 (100%) - -
ls 1 (5%) 18 (86%) 2 (10%) - 28 (93%) 2 (7%)
tot 1 (5%) 18 (86%) 2 (10%) - 28 (93%) 2 (7%)
In this table the moult of wing-coverts and tertials is presented. For all feather tracts, a maximum score of 50 is possible, when all juvenile feathers in a tract are replaced by second generation feathers which in turn are all fully grown. Growing or missing feathers are valued half score. Hence, if all feathers in one tract are missing or growing, the maximum score is 25. If all feathers in a tract are still juvenile, the score is 0. In the total score, all class scores are added, so the maximum score is 250 (100% second generation tertials and wing-coverts).



adult michahellis in April. (61415 bytes) michahellis 1cy U8CA October 29 2010, Ramat Gan Safari, Israel. Picture: Amir Ben Dov.
adult michahellis in April. (61415 bytes) michahellis 1cy U9BH October 29 2010, Ramat Gan Safari, Israel. Picture: Amir Ben Dov.
5624ntt8.jpg (55149 bytes) YLG (L. michahellis) NTT8, October 11-17 2002, IJmuiden, the Netherlands. This bird was ringed on Mendes Island, NE Spain.
4704.jpg (62225 bytes)ILZB & IKZH YLG (L. michahellis) 1cy, October 26 2002, Etaples & Boulogne-sur-Mer, France.
7087.jpg (91420 bytes)YLG (L. michahellis) 453T, October 13 2001, Westkapelle, the Netherlands. 
This 1cy YLG is ringed 453T and was born in the Camarque colony, S France last year.
5313w793x.jpg (63004 bytes)YLG (L. michahellis) 793 X, October 03-04 2002, Etaples, France.
Ringed in southern France.
6773.jpg (104245 bytes)YLG (L. michahellis) Sempach 885629, October 01 2001, Le Portel, France.
Ringed individual from Switzerland, much resembling graellsii. This bird was seen again in June 2002.
5267sempach.jpg (51105 bytes)YLG (L. michahellis) Sempach 894231, October 03 2002, Le Portel, France.
Ringed in Switzerland.
5494sempach.jpg (69316 bytes)YLG (L. michahellis) Sempach 894333, October 04 2002, Etaples, France.
Ringed in Switzerland.

Tail-feather moult in 1cy:

5779ylg.jpg (76604 bytes)Photo 5779: YLG (L. michahellis) 1cy, October 18 2002, Westkapelle, the Netherlands. 

5264.jpg (77157 bytes)Photo 5264: YLG (L. michahellis) 1cy, October 03 2002, Le Portel, France.
unringed michahellis 1cy October:

6674.jpg (89392 bytes)Photo 6674: YLG (L. michahellis) 1cy, October 01 2001, Le Portel, France.

Photo 6623: YLG (L. michahellis) 1cy, October 01 2001, Le Portel, France.
All coverts still juvenile.
6744.jpg (82280 bytes)Photo 6744: YLG (L. michahellis) 1cy, October 01 2001, Le Portel, France.
6838.jpg (92833 bytes)Photo 6838: YLG (L. michahellis) 1cy, October 01 2001, Le Portel, France.
6896.jpg (91525 bytes)Photo 6896: YLG (L. michahellis) 1cy, October 01 2001, Le Portel, France.
6778.jpg (90558 bytes)Photo 6778: YLG (L. michahellis) 1cy, October 01 2001, Le Portel, France.
Another Swiss individual?
5359.jpg (55926 bytes)Photo 5359: YLG (L. michahellis) 1cy, October 03 2002, Etaples, France.
Only few coverts moulted.
5282.jpg (69593 bytes)Photo 5282: YLG (L. michahellis) 2cy, October 03 2002, Le Portel, France.
7252.jpg (90254 bytes)Photo 7252: YLG (L. michahellis) 1cy, October 14 2001, Westkapelle, the Netherlands. 
Some of these first winter scapulars already look abraded.
7164.jpg (89011 bytes)Photo 7157 YLG (L. michahellis) 1cy, October 13 2001, Westkapelle, the Netherlands. 
7402.jpg (85851 bytes)Photo 7402: YLG (L. michahellis) 1cy, October 22 2001, Westkapelle, the Netherlands.
7489.jpg (85623 bytes)Photo 7489: YLG (L. michahellis) 1cy, October 22 2001, Westkapelle, the Netherlands. 
Sunset gives a warm orange tone hue.
6068.jpg (58916 bytes)Photo 6068: YLG (L. michahellis) 1cy, October 24 2002, Etaples, NW France.
6079.jpg (51700 bytes)Photo 6079: YLG (L. michahellis) 1cy, October 24 2002, Etaples, NW France.
2cy michahellis in October. (66144 bytes)Photo 5429: michahellis 1cy, October 04 2002, Etaples, France.