Atlantic gull or Yellow-legged gull

http://www.rspb.org.uk/discoverandenjoynature/discoverandlearn/birdguide/name/y/yellowleggedgull/

There were plenty of these out in the Canaries: Yellow-legged gulls, Larus michahellis ssp atlantis. They are interesting because only recently were they recognised as a species in their own right. Prior to the 1990s people lumped them with the Herring gull or sometimes with the Caspian gull. British Birds magazine was the first to consider it a full species back in 1993 but the British Ornithologists Union waited until 2007 to do so. DNA evidence shows that it is more closely related to the Great Black-backed gull than the Herring gull. 
The Macaronesian subspecies is often referred to as the Atlantic gull and it may, in due course, be recognised as a full species. It seems that DNA analysis favours the splitters more than the lumpers.