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 - adult October

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

By October many michahellis can still be found at Le Portel and Etaples, NW France. At the beach of Le Touquet, near Etaples, groups congregate and use the beach as a resting place. They frequent the Dannes landfill as feeding place and many depend on the local fish-market of Etaples for food supply. The ports of Boulogne-sur-Mer and the beach of Le Portel are other good spots to find sub-adult Yellow-legged Gulls. See Le Portel page for locations.

The difference between sub-adult and adult birds is sometimes very difficult. We used the plain grey greater primary coverts as criteria in our scores. For details on differences between michahellis and cachinnans, see e.g. the article by R. Klein & D. Gruber in Limicola, April 1997.

Moult of remiges and rectrices

By October, the most obvious moult is in progress in the primaries. At the start of the month, the average moult score was 8.0 renewed fully-grown primaries, at the end of the month the average is 9.5 (so P10 halfway its final length). 
The secondary moult may still be halfway, with active moult at S8 approximately. In the first week of October, abraded inner secondaries are still not shed (and may be visible just beneath the tertials, as in image 6787). By the end of the month, the secondary moult is completed.
By the first week of October, some adults still show moult in the tail-feathers; often the outer pair of rectrices which have to grow an inch or so. 

Moult in the wing-coverts

The complete wing-covert moult is in progress throughout August and is finished by September. The ordinary moult strategy and sequence started in the outer median coverts, the innermost medians and innermost greater coverts, the upper tertial and the outer lower lesser coverts. By mid-August, the median and lower lesser coverts have been replaced. By late-August, the outer greater coverts have been replaced as well and the gap in the greater coverts will be closed at greater coverts #7-#8 in birds following the ordinary moult strategy. 
By September, most advanced birds have replaced all the wing-coverts and may start again a new additional cycles of wing-covert moult: the partial wing-covert moult in autumn. They normally start at the oldest wing-coverts, i.e. the median coverts and lower lesser coverts. Hence, the central coverts normally look much fresher than the adjacent coverts. Inner greater coverts or upper tertials may be included in the partial moult as well and birds may still grow new inner greater coverts in the first weeks of this month.

The tertial moult is finished by the end of September. Normally the upper two tertials show wear in the tips while the next four tertials are very fresh with broad white tips.

After completion of the scapular moult in the lowest row of scapulars, no obvious moult gaps are visible in October, but single feathers of the scapulars may be missing and some birds may continue moult in this tract at low pace.

The body feather moult has been completed. As can be seen in the images, the fresh feathers on the head show delicate fine streaks. It takes about 7 weeks to reduce streaking and by mid-winter (January) many adult michahellis show clean snowy white heads. 

See the Topography Section for explanation of feather tracts.

Naked parts

In full adult michahellis, the colour of the legs hardly turns paler in October. As can be seen in the images, the legs appear almost orangey-yellow or deep yellow, although the odd bird has a slightly pinkish cast over the yellow colour. It's hard to exclude 4CY birds in these cases, as the primary coverts have been moulted and black markings on the bill vary in adults.

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