Mediterranean Gull Praha ?E.15800 adult, January 03 2002, Le Portel /Boulogne-sur-Mer, France (50.42N,1.34E).

In the top image: two metal ringed adults, the right one being the most white-headed adult compared to other present birds (few tens) and ringed Praha ?E.158000, ringed in Slovakia. 
From late summer to September, a complete moult takes place, bringing birds into so-called "adult winter" plumage. The head pattern in wintering bird resembles "first winter plumage" after finishing the complete moult: a blackish mask behind the eye. The mantle, scapulars, tertials and all the wing-coverts have been replaced for plain pearl-grey feathers. 
The secondaries are completely white. The new adult primaries are shiny pearly-grey, flashing white at a distance. There is a black line along the outer-web of P10 (and sometimes on P9 as well). Secondaries, under-wing and tail are completely white. The bare part coloration: Iris brown, orbital ring red or orangey-red, the bill red or orangey-red with a black bill-band (and a yellowish tip) and the legs dull reddish or dark.

below photo 8622: Mediterranean Gull adult Praha ?E.15800, January 03 2002, Boulogne-sur-Mer, France (50.42N,1.34E).

Another picture of the same bird, the most white-headed adult compared to other present birds and ringed Praha E.15800.