General description:

Early July and from July 26-30 2001 we did small surveys on Yellow-legged Gulls at Le Portel (near Boulogne-sur-Mer) and Etaples (near Le Tourquet). In these surveys, we scored moult stages to determine timing of moult in primaries (and wing- coverts and body-feathers) in 3cy michahellis.
The general appearance of 3cy michahellis is rather straightforward. Most birds can still be recognized by the plain grey upper-parts, combined with barred wing-coverts. The bare parts are typically a red orbital ring and yellow legs. An example of the average michahellis can be found in the first image, an individual ringed near Marseille, S France, showing active moult in the wing-coverts and only the outer two primaries are still old second generation.
For details on differences between michahellis and cachinnans, see e.g. the article by R. Klein & D. Gruber in Limicola, April 1997.

Moult stage and pace of remiges and rectrices:

The complete moult started by mid-May, when 3cy birds dropped the innermost primary P1. By early July, the average score has strongly increased: P7-P10 are still old secnd generation and all inner primaries are missing or new. Since the tips of P5 and P6 normally extend beyond the tertials (especially the abraded July tertials), the moult gap of missing P5 and P6 is obvious. 
3cy michahellis continue shedding primaries throughout the month, and by the end of July, the average primary moult score is 8.5, hence 50% have only P9 and P10 old, the other 50% has P8-P10 old. With this score,  3cy birds are about two primaries behind compared to 2cy birds (which have a score of 9.2: 45%of 2cy have shed all primaries by late July). 
As in adults, the gap between full-grown primaries and remaining old primaries is in general about three feathers, but often slightly more as the table shows. This large moult gap is typical for michahellis, and not found in e.g. Dutch argenteus.

By the time P4 is fully grown, 2cy birds normally start the complete moult in secondaries and rectrices. The ordinary moult strategy in 3cy birds may be slightly later (starting when P5 is fully grown. Note however that individual variation may exist, particularly in 3cy michahellis rectrices moult as this moult may follow an irregular pattern in earlier months. The partial spring moult has finished in June and a small minority of 3cy June michahellis have included some rectrices in this partial moult. Hence, it's not uncommon to find 3cy birds showing plain white tail-feathers, in some birds creating a 'blocked' tail pattern already, prior to the complete moult. On average, the common sequence is centrifugal moult: starting with the inner tail-feathers and continuing symmetrically outwards to both outer feathers.

Secondary moult hasn't started yet in late-July, but is initiated in early-August. The images on this page showing birds with open wings illustrate that all outer secondaries are still present. By early August, the outermost secondaries (S1 & S2, at the division between secondaries and primaries) are normally dropped individually, but the central secondaries are shed almost as in small groups, creating large gaps of missing secondaries, nicely illustrated by this flying 2cy bird and this stretching 3cy August michahellis.

Timing and strategy of body & covert moult in July

Wing-covert moult in 3cy and sub-adult michahellis vary between individuals. See e.g. 365D, showing extensive moult in the wing-coverts (the sequence is mentioned in the accompanying text). Such birds contrast strongly with e.g. this bird, which has almost all the wing-coverts old.

In general, conclusions based on average 3cy michahellis are:

• Moult of head feathers is in progress, creating a streaked head in the advanced individuals. See here (streaking) and here ("moth-eaten" head in 365D).
• 3cy birds show plain adult-like grey scapulars. It's difficult to score missing feathers in the complete grey upper-parts, hence we have no scapular moult scores. In general, the scapulars in the lowest row look very fresh, without abrasion at the fringes and lacking the faded grey tone, so scapular moult may be near its end in 3cy michahellis by the end of July. 
  In some individuals, the scapular region contains some old and abraded feathers (in the upper region of the upper scapulars), sometimes showing a brown hue, others are bleached white-grey with only a slightly darker shaft-streak. However, most birds have the entire back adult-like grey.
• The complete wing-covert moult is in progress throughout July. The ordinary moult strategy and sequence start in the outer median coverts, the innermost medians and innermost greater coverts, the upper tertial and the outer lower lesser coverts. Early July, the new median coverts are visible (first the outer median coverts), more so as the outer lower lesser coverts are dropped. By the end of July, the complete median covert bar is renewed, the lower lesser coverts are growing, the outer greater coverts are missing (exposing the secondaries underneath) and the innermost greater coverts have been renewed. In the tertials, the new upper two feathers are visible and the central tertials are dropped.

See Topography Section for explanation of feather tracts.

Tables:

The surveys were done at resting and preening 3cy sub-adults (with at least no white mirror at P10 and at least some obvious second summer feathers).