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Is Mediterranean a possibility...the angle is a difficult one.
My Flickr photos...
With only this photo for us to go on, I would tend to favour Med. Gull over Black-headed as the correct ID. The dark bill also (perhaps) points more to Med., but could just be an effect of the photo.
With a photo from this angle I wouldn't be keen on suggesting that it is a Med. Gull though.
This and another one. That´s the best i have. The light wasn´t perfect.
Lat/Lng: 38.706, -9.139