A bit late perhaps, but I stumbled upon it when searching pictures for the photographic guide. This is a Mediterranean Gull, I think an adult non-breeding (but I can't see the wing clear enough to exclude a second winter bird).
Ohh that is great news, new species for my life-zoo-species-list and also good for my species photo archive as until now I only had a pic of a taxidermy museum specimen! Thanks a lot Mr Zootycoon :*
Mediterranean gull indeed, recognizable, among other criteria, by its black mask (wider than the parotical spot Black-headed gull has in winter) and its totally white wing (while Black-headed has black and white tips to its primaries)
