Population trends and breeding success of cliff-nesting seabirds in Orkney, 1976-98

Population trends of Northern Fulmars, Kittiwakes, Common Guillemots and Razorbills have been monitored in sample plots at five colonies in Orkney since 1976; several complete counts of these colonies were also made. Numbers of Fulmars, Guillemots and Razorbills attending the colonies in the breeding season increased from 1976 to 1997. However, for all three species, the overall increase was punctuated by a period of decline in the early 1980s; there was also some variation between colonies in population trends. In contrast to the other species, breeding numbers of Kittiwakes declined by an average of 2.5% per annum over the same period, the overall rate of decline being inversely related to colony size. Breeding success of Fulmars, Kittiwakes and Guillemots was onitored annually for varying periods from the mid 1980s to late 1990s. Breeding success of both Fulmars and Guillemots was close to or above national averages in most years. Kittiwake breeding success was generally very high in the past 10-15 years, so the declining population appears paradoxical. Large-scale mortality of fledglings in some years, particularly the late 1970s, may be partially responsible but the continuing decline of the Orkney Kittiwake population remains to be fully explained.