The BTO winter atlas showed that Black-headed Gulls were present in all 10km squares during the winters of 1981-82, 1982-82 and 1983-84.
The darker the colour, the higher the relative total count for each 10km square. The darkest blue represents over 1,491 birds.
Found extensively using wet pasture and newly ploughed land but all roosts reported were around the estuaries.
Graham Rees