I've just googled, and herring gulls are indeed the birds I was referring to here in Norway, good catch. We have the same, actually, when tourists/guests of the city are easier targets. A few times I had to "defend" (mostly, by hiding) my lunch sandwich or bun as well, if I wanted to eat somewhere with a view over the sea. However, even a few kilometers from the sea, they can still be on a "hunt". Very interesting creatures!