The effect of removing large numbers of gulls Larus spp. on an island population of oystercatchers Haematopus ostralegus: Implications for management Original Research Article

Predation on other breeding species has been used to justify culling adult gulls at several colonies but few studies have been carried out to 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 1960s and large scale gull control was implemented in 1972 which continued, albeit at a reduced level, until 1988. Prior to the start of the cull, there was a small breeding population of oystercatchers Haematopus ostralegus. In contrast to the British population which increased markedly during the 1950s and 1960s, numbers on the Isle of May remained more or less stable during this time. However, immediately following the start of gull control, the number of oystercatcher breeding territories rose and the increase continued throughout the period of control, with the rate of increase being above the British average over the same period. Prior to the cull, oystercatcher breeding success was extremely low with most losses of eggs and chicks attributable to gull predation. However, even after gull numbers had been reduced, breeding success remained low and gulls were the main cause of failure. The increase in numbers of oystercatchers could not have been sustained without substantial immigration. Thus, although the reduction in gull numbers had made the Isle of May more attractive to oystercatchers, breeding conditions were not improved markedly.