These juveniles were all photographed in the same location and at the same time (Porto Moniz September 19th). Whilst three of them look very similar I believe that they are actually four different individuals. If you look closely at the pattern on the tertials and greater coverts there are obvious differences. It would appear that the major identification problem is differentiating atlantis from Lesser Black-backed Gull (Larus fuscus). Most of the people who have commented have stated that they could not rule out graelsii on the basis of these photographs. I have added a new image (top right) which shows a bird starting to moult in its first winter scapulars which has similarities to the picture published in British Birds November 1999 page 613. That bird has a more advanced scapular moult and is labled as 1st Winter. I am hoping that this picture may help to resolve the problem. My identification of these birds relies heavily on the fact that they were in a group which involved adult Yellow-legged Gulls and no other species (see small image below).
