Yellow-legged
Gull - Larus michahellis
(last update: October 08 2014)
Coordinators:
Delfín González
Gabriel Martín
Antonio Gutierrez
Amir Ben Dov
Mars Muusse
Larus michahellis - 4CY / sub-adult 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
August is one of the best months to study michahellis at Le Portel and Etaples, NW France. At the beach of Le Touquet, near Etaples, large 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 3CY birds and 4CY birds can best be checked by the outer primary, which may still be unshed by August: 4CY birds show a small but obvious white mirror on P10, while 3CY birds have the (second generation) outer primary all brown. Other clues can be found in the bare part coloration, with 4CY strongly resembling adults. Sub-adult michahellis has black in the old outer primary coverts and dark centres on the old secondaries. Furthermore, 3CY birds often have one or several second generation tail-feathers, showing a broad black band.
Complete moult in August:
As can be seen in most of the images,
sub-adult Yellow-legged Gulls look very untidy and mottled in their
August plumage, as was already the case in July. Simultaneous moult is in progress in the primaries,
wing-coverts, tertials, scapulars and the
tail-feathers.
By August, the median row and outer lower lesser coverts have been
renewed already a month ago. The inner greater coverts and upper
tertials have been replaced as well. Active moult is in progress in
the outer greater coverts (growing inwards, in descendant order) and
in the lesser coverts. The lower tertials are growing as well.
By the end of the month, the central greater coverts are still
missing and many lesser coverts are missing as well. In the carpal
edge, coverts may still be old and abraded.
The fresh grey median coverts
normally strongly contrast with the brown-hued and abraded lesser coverts and
old greater coverts (some central greater coverts are still present
by early August).
Moult stage and pace of remiges and rectrices:
Currently, we don't have sufficient data for detailed moult descriptions of sub-adult August birds. But in general, the primary moult stage of sub-adult birds averages P8-P10 remaining primaries in the first week of August. By this time, the new central tail-feathers are growing and the average bird has dropped the outermost secondaries S1-S2.
See Topography Section for explanation of feather tracts.
Tables:
None.
Yellow-legged Gull michahellis 2CY-4CY 255S July 27 2001, September 21 2002 & August 08 2003, Etaples, NW France. This
bird was recorded on the same spot in year 2000-2002.
Yellow-legged
Gull michahellis sub-adult, August 14 2009, Tarragona, Catalonia, Spain. Picture: Chris Gibbins. 
Yellow-legged Gull michahellis type 4CY, August 16 2014, Sevastopol, Crimea, Black Sea. Picture: Vitaly Giragosov.
Yellow-legged Gull michahellis 4CY, August 11 2008, Portalban, Switzerland. Picture: Stephane Aubry.
Yellow-legged
Gull michahellis sub-adult, August 10 2003, Etaples, France. 
Yellow-legged Gull michahellis sub-adult, August 09 2003, Etaples, France (50.44N,
01.35E). Picture: Ruud Altenburg.
Yellow-legged
Gull michahellis 4CY, August 23 2010, Malaga, Spain. Picture: Hans Larsson.
Yellow-legged
Gull michahellis 4CY, August 23 2010, Malaga, Spain. Picture: Hans Larsson.
Yellow-legged
Gull michahellis 4CY, August 23 2010, Malaga, Spain. Picture: Hans Larsson.
Yellow-legged
Gull michahellis 4CY, August 23 2010, Malaga, Spain. Picture: Hans Larsson.
Yellow-legged
Gull michahellis 4CY,
August 08 2003, Le Portel, NW France. 
Yellow-legged Gull michahellis sub-adult, August 10 2003, Etaples, France.