Recoveries and Dispersal of Herring Gulls from the Isle of May

Abstract

Recoveries of herring gulls [Larus argentatus] ringed on the Isle of May [Scotland, UK] between 1966-1974 illustrated a high post-fledging mortality of young gulls, while adult mortality was greatest in the summer months. Dispersal was predominantly in a southerly direction with furthest recoveries reported in Germany and Denmark. Gulls moving southwards dispersed significantly further than those flying west or north. The rate of dispersal was greater among 2 and 3 yr old birds, but 1st yr 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. There was evidence that a considerable proportion of herring gulls do not return to the natal colony to breed. The dispersal rate of late hatching young was less than that of early hatching young. 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.