Yellow-legged Gull, Gibraltar.
Larus michahellis

Yellow-legged Gulls replace Herring Gulls in the southern and central parts of Europe, but are now increasing in more Northern areas, including Britain. They have been variously considered subspecies of the Lesser Black-backed and Herring Gulls, but are considered by most authorities to be a separate species. In recent years, this species has been split again to give Yellow-legged Gull, Larus michahellis, Caspian Gull, Larus cachinnans and Armenian Gull, Larus armenicus, the last two of which are from Eastern Europe.
 

1: The Rock, Gibraltar, 02/2004. Photo by J. Keene