I live on Long Island, NY. I boat, I chase them out of my garbage cans on land. Their favorite haunt is the town dumps. They are garbage processors and will eat anything they are often there at Wendy’s begging as I sit in my car eating a burger. I don’t give gulls anything. I know for a fact they will kill mammals and birds but have not seen them Do that I often see them eating thrown out burgers and fries and also road kill. On my boat I have seen them pluck eels and small sharks out of the shallows and fly them high then drop them on rocks or better yet in the middle of a parking lot to kill them.
The local commercial fishermen treat them with the same respect the ancient mariner should have treated that albatross. Seems they keep dead stinky stuff under control. I am familiar with herring gull, great black back gulls and I know of others but not their names.
Some years ago we were sailing in the Bahamas...a bareboat charter in the Abaco Keys...we had a charcoal grill on the boat we could hang over the rail...we were 8 of us on board, we were grilling 9 pork chops...a gull swoped down and grabbed one off the grill right ‘under my nose’, so to speak. They are aggressive, and not just for fish in the water. Kinda like Holder’s people...if it belongs to you, it’s mine if I can grab it...