Larus genei Breme, Slender- billed Gull
A stamp issued in a five-stamp sheet by Ukraine in 2002
The series is named BLACK SEA NATURE RESERVE, BIRDS AND FLOWERS.
I didn't find any reference to this bird in THE MEDITERRANEAN GARDEN but according to my bird book this one over winters around most of the Mediterranean.
Gulls are mentioned in BUSTER AND THE BIRD-BATH
By Leonard Pearcey
THE MEDITERRANEAN GARDEN number 36, April 2004