Yellow-legged Gull - Larus michahellis

(last update: October 08 2013)

Coordinators:
Delfín González
Gabriel Martín
Antonio Gutierrez
Amir Ben Dov
Mars Muusse

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Larus michahellis - 1CY August

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 and birds along the Atlantic coast of the Iberian peninsular: lusitanius. Both atlantis and lusitanius are treated in their own sections on this website.

General description:

Yellow-legged Gulls L.michahellis, which breed in southern Europe / the Mediterranean have a significant earlier breeding season than the large gulls breeding in western and northern Europe, Herring Gulls (HG) argenteus & argentatus and Lesser Black-backed Gulls (LBBG) graellsii & intermedius). As a result, most juvenile YLG's show more worn plumages than northern relatives by August (on average). Geographical latitude of breeding grounds probably is the main reason for these differences in feather conditions, but there may be many other aspects involved as well, like e.g. exposure to severe summer light condition.

Subsequently, the average moult timing to 1^st winter plumage commences earlier in the season (from late July-early August) than in LBBG and HG. By late August, almost all michahellis in the Calais Region, NW France already moult in second generation feathers. The mantle, scapulars and sometimes median covert, a few lesser coverts and tertials are involved. 
Herring Gulls with abraded fringes in the coverts and the same moult stage as michahellis are extremely rare, but some Lesser Black-backed Gulls also acquire new wing-coverts as early as August. However, in most cases the condition of the old feathers is different: michahellis have retarded feathers (the fringes of the feathers more abraded), while in graellsii the coverts are generally fresher. Of course it's interesting to find out how southern populations of graellsii adapt or change the egg-laying date in the near future now they expand their breeding area in France and further south.

Wing-covert moult in michahellis

The moult of the wing-coverts in michahellis may start in late July in a few individuals (see for details the tables presented in the July section). In the last week of August we scored moult stage in Boulogne-sur-Mer (NW France) in a group of 22 first calendar year (1CY) michahellis: 4 individuals (18%) had started the wing-covert moult (involving the median and lesser coverts). Late August, the most advanced individual showed c. 80% renewed median and greater coverts. Approximately 20% of the lesser coverts were moulted and the upper three tertials were missing. 

Most michahellis start moulting the wing-coverts in September and throughout the winter months wing-covert moult continues. About 80% of 1^st winter michahellis will show at least some moulted wing-coverts in spring next season (by then in 2CY).
The first birds with a 90-100% wing-covert moult score (all visible wing coverts replaced by second generation feathers) can be found as early as September. We have limited experience with "late winter covert score" (by then 2CY michahellis in spring), but we estimate less than 10% of michahellis to show all the visible coverts new. Probably, at least some wing-coverts will not be shed in 1^st winter and remain juvenile feathers until spring next season, when the complete moult-cyclus starts.

Yellow-legged Gull michahellis 1CY, August 14 2010, Île de Porquerolles, Huelva, Spain. Picture: José Enrique Larios López. Several scapulars replaced but all coverts and tertials juvenile. Note pattern of tail-band: wedge-shaped.

Armenian Gull armenicus 1CY, August 18 2010, Maagan Michael, Israel. Picture: Amir Ben Dov. Bird in juvenile plumage. Showing tail pattern and inner primary pattern. Obvious piano-key pattern on inner greater coverts. faint apical spots on P2-P4.

Atlantic Yellow-legged Gull atlantis 1CY, August 24 2010, São Miguel, Azores Islands. Picture: Richard Lowe. Overall brown tone. Typically, michahellis tail has single sub-terminal band on outerweb of R6; but often multiple in atlantis, like in this individual.

Yellow-legged Gull lusitanius 1CY, September 06 2009, Xove / Burela, Galicia, Spain. Picture Gabriel Martin. Flight shot to show the tail pattern. Typical wedge-shaped sub-terminal band on the tail associated with michahellis. But note the dark markings on the outer-web of R6 and the hint of an extra transversal bar over the tail. Tail pattern seems to be quite variable in 1CY lusitanius.

Lesser Black-backed Gull 1CY FH August 15 2012, Landfill Barneveld, the Netherlands. Picture: Herman Bouman. Ringed 1CY graellsii, ringed in SW Netherlands. All coverts and tertials juvenile.

Tables 

Yellow-legged Gull michahellis 1CY, August 12 2006, IJmuiden, the Netherlands.