Audouin's Gull, Spain.
Larus audouinii

Audouin's Gull was one of the rarest gulls in Europe but has undergone somewhat of a recovery in the last decade, with a large colony spreading out from the Ebro delta along the coast of Spain and beyond. They occur in small number in the rest of the Mediterranean where the other large gull present is the Yellow-legged Gull and they are easily told apart: Audouin's has a red bill, greyish-green legs, dark eyes and is noticeably smaller (44-52 cm in length, 117-128 wingspan) while the Yellow-legged has a yellow bill, yellow legs and light eyes.
 

1-2: Valencia, Spain, 11/09/2012.