That's the finding of new research into the eating habits of urban gulls.
Those feeding along the Merseyside coast are now said to be eating more and more human food such as discarded burgers, pastries and other fatty snacks.
And the study carried out by the University of Liverpool says this could lead to them putting on weight and developing health problems.
Marine biologist Dr Jonathan Green said: “The urban birds are eating more human food – and it’s possible they could gain weight or suffer chronic illnesses or heart disease in the future.”
The warning came after researchers studied the food consumed by black-headed gulls at 11 feeding points along the Merseyside coast.
They were offered a choice of man-made white bread or natural fish.