When I lived in Aberystwyth on the Welsh coast you could always tell a newcomer to the town because they'd eat outside without aerial cover. The herring gulls there are pterodactyl-like, massive and always watching for the slightest opportunity to fill their beaks. They're clever birds too, I've seem them work cooperatively to deprive some poor fresher of their lunch and hawks had little success in driving them away. I've actually come to miss them a bit having moved inland, I'm moving back to a city by the sea this year and I wonder how long that will last!

Depending on where you are, you may be thinking of the great black-backed gull.