Mediterranean Gull juvenile August 09 2003, Le Portel /Boulogne-sur-Mer, France (50.42N,1.34E).

A fresh bird in complete juvenile plumage from early August. Note that moult to second generation mantle feathers and scapulars have started already; a few scapulars are missing.

Mediterranean Gull carries a complete juvenile plumage for only a short period, as moult to second generation scapulars and mantle starts quickly after fledging. In juvenile plumage, the head is pale brown, uniform buffish-brown with slightly darker ear-coverts and a pale throat. Juvenile birds have dark blackish eye-crescents in front of the eye and white crescents behind the eye. The brown colour of the head extends in the neck, forming a barred collar running down along the sides of the breast to the flanks. The under-parts and rump are white. The scapulars and mantle feathers are deep brown with a dark sub-terminal band and a silvery-white fringe, creating a scaly pattern.
The pattern of the scapulars is repeated on the lesser coverts, lower lesser coverts, median coverts, inner four greater coverts and upper tertials which also show brown centres and neat silvery-white fringes. They contrast strongly with the central and outer greater coverts, which are predominantly grey, forming a pale bar in the dark inner-wing in flight, as the secondaries are dark blackish-centred as well (but with broad white tips). The inner primaries are largely white-grey, the grey slightly decreasing in the primaries outwards, strongly reduced to the inner-webs in the outer primaries P9 and P10. The under-wing coverts are all-white, but neat black tips on the under-wing greater primary coverts. The white tail has a clear-cut black sub-terminal band, very thin on the outer rectrices. The iris is dark brown, the bill and legs are blackish.
The partial autumn moult (post-juvenile moult into so-called "first winter" plumage) takes place right from the moment the nest is abandoned and will be finished by late September.

Note that the comments on moult are based on observations of juveniles from and in Western Europe in early autumn. More easterly fledged Mediterranean Gulls may postpone their moult to first winter until later in the autumn and very fresh looking juveniles may be encountered well into October.