General description:

At the landfill of Dannes, near Le Portel, mixed flocks of mainly Lesser Black-backed Gulls (1.000's) from NW and N Europe can be found including 100's of adult and sub-adult Yellow-legged Gulls early October. Most individuals of this page were photographed at Dannes.

As can be seen in the images, sub-adult Yellow-legged Gulls look very tidy and neat again by the start of the month. Early October, almost all feather tracts have been replaced and active moult can be found in the outer primaries. Fresh moulted wing-coverts are plain grey, with neat fringes. The fringes may be slightly paler in very fresh condition. The most striking differences between those 4cy birds in September and adults is the dark bill-band, present on both upper and lower mandible in sub-adult birds. The legs are slightly paler yellow in 4cy birds, where adults show deep saturated yellow legs. Most striking differences between those 4cy birds in October and adults is:

• relatively pale bare part coloration compared to full adults, although differences are subtle. The base of the bill is rather pale yellow, often different from the deep yellow tip of the bill. The black bill-band is often well developed in most sub-adults. The legs are yellow with a whitish wash;

• black markings on the old rectrices. Often isolated limited black spots near the centre, although most rectrices are moulted to completely white tail-feathers by September and sub-adults with old rectrices are rare;

• the grey centres of the primary coverts show a brown hue and the shaft is often an accentuated black line over the centre of the outer primary coverts;

• 4cy birds have dark centres on the greater primary coverts.

Used as a single characteristic, the evidence is not very convincing, but individuals that combine these characteristics are probably 4cy or 5cy birds. 

Moult stage and pace of remiges and rectrices:

Regarding moult pace and timing, sub-adults much resemble full adult birds. 
Early October, the average sub-adult michahellis still show active moult in the inner secondaries. The tail-feathers were already fully grown by September and the complete moult is nearly finished, with sub-adults still growing the outermost primaries P9 and P10.
The table below shows the moult score on October 04 2002, with the fully grown primary score average of 8.1 (n = 23).

Complete vs partial moult in September:

The complete moult in the wing-coverts was finished in September. Although the outer primaries are still growing, partial moult starts again in the outer median coverts and the inner greater coverts. Upper tertials may be included in this moult as well. This partial moult started in the last week of August and continues in September. By October the partial moult in the wing-coverts is finished. In the September 2cy michahellis section this partial moult in 2cy birds is explained. The extend and timing of this partial moult in sub-adults may differ slightly. 

See Topography Section for explanation of feather tracts.

Tables: