THE EFFECT OF REMOVING LARGE NUMBERS OF GULLS LARUS SPP ON AN ISLAND POPULATION OF OYSTERCATCHERS HAEMATOPUS-OSTRALEGUS - IMPLICATIONS FOR MANAGEMENT

Predation on other breeding species has been used to justify culling a dult gulls at several colonies but few studies have been carried out t o assess the effects of gull control on these species. On the Isle of May, southeast Scotland, numbers of herring gulls Larus argentatus and lesser black-backed gulls L. fuscus increased rapidly during the 1960 s and large scale gull control was implemented in 1972 which continued , albeit at a reduced level, until 1988. Prior to the start of the coi l, there was a small breeding population of oystercatchers Haematopus ostralegus. In contrast to the British population which increased mark edly during the 1950s and 1960s, numbers on the Isle of May remained m ore or less stable during this time. However, immediately following th e start of gull control, the number of oyster catcher breeding territo ries rose and the increase continued throughout the period of control, with the rate of increase being above the British average over the sa me period Prior to the cull, oystercatcher breeding success was extrem ely low with most losses of eggs mid chicks attributable to gull preda tion. However, even after gull numbers had been reduced breeding succe ss remained low and gulls were the main cause of failure. The increase in numbers of oystercatchers could not have been sustained without su bstantial immigration. Thus, although the reduction in gull numbers ha d made the Isle of May more attractive to oystercatchers, breeding con ditions were not improved markedly. (C) 1997 Published by Elsevier Sci ence Ltd.