The black-legged kittiwake is a true seagull in the sense the phrase is usually misused for. It spends the non-breeding season on the open ocean, feeding at the surface on sandeels, capelin and other small shoaling fish and on zooplankton. It does not follow ploughs, work landfill sites or take food in towns.
That specialisation is the problem. Where forage fish near colonies have become scarcer or have shifted with warming water, kittiwake breeding success has fallen, and the species was moved to Vulnerable on the IUCN Red List while adaptable, omnivorous gulls have thrived. Nesting is equally particular: a mud and vegetation cup cemented to a ledge sometimes only a few centimetres wide, on cliffs and, in a growing number of places, on window ledges and bridges.
The useful correction is to the word gull itself. Gulls are not one ecological type, and the birds people complain about in car parks are not the ones in trouble. Which of the kittiwake's pressures dominates, prey availability or something else, differs by ocean basin and is not settled.