Recoveries and Dispersal of Herring Gulls from the Isle of May

Abstract

SUMMARY (1) Recoveries of herring gulls ringed on the Isle of May between 1966-74 illustrated a high post-fledging mortality of young gulls, whereas adult mortality was greatest in the summer months. (2) Dispersal was predominantly in a southerly direction, with furthest recoveries reported in Germany and Denmark, gulls moving southwards dispersed significantly further than those flying westwards or northwards. (3) The rate of dispersal was greater amongst 2- and 3-year-old birds, but first year dispersal was further than in adult gulls. A contraction of range from the Isle of May in summer months illustrates a return to the Isle of May as gulls reach maturity. (4) There was evidence that a considerable proportion of herring gulls do not return to the natal colony to breed. (5) The dispersal rate of late hatching young was less than that of early hatching young. (6) There was no difference between the proportion of young and adult gulls recovered inland, except during the summer when adult birds had returned to coastal or island breeding sites.