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.