"Revenge of the Seagulls". The Argus has its annual report on the aggressive behaviour of gulls in the breeding season.
Fifty years ago herring gulls were rare in Brighton. By comparison, in winter, large flocks of black-headed gulls were to be seen in their winter plumage, in which the black-cap shrinks to a small streak behind the eye. People would take their left-over crusts down to the seafront and, standing along the railings, throw them to the wheeling gulls to marvel at their aerobatics. Black-headed gulls were the 'common' gull in those days and it was only occasionally that one would see a true common gull (with its greenish legs), a black-backed gull or a herring gull, the latter two standing out from the others because of their impressive size.
It is remarkable how today the situation seems to have reversed, with the herring gull now completely dominant in the City. Various explanations have been offered for this: the cliffs to the east have been progressively smoothed to minimise the danger of falling chalk and the gulls have had to resort to nesting on buildings; while over the same period of time, the galvanised metal dustbin has been replaced by the easily plundered plastic binbag thus ensuring a ready supply of food throughout the year. It is said that the population of a species expands to meet the food supply available and perhaps, now that the Council has improved the system of refuse collection, we can expect to see a steady decrease in numbers.
This still doesn't explain what has happened to the black-headed gulls unless it a straight-forward case of competition and the more aggressive herring gull has simply bullied them away. . .