THE PEREGRINE FALCO-PEREGRINUS BREEDING POPULATION OF THE UNITED-KINGDOM IN 1991

A survey of Peregrines in the breeding season of 1991 gave an estimate d total of 1283 pairs occupying known nesting territories in Britain a nd Northern Ireland. 1214 territories were found occupied, 53 try appa rently singles birds, and 141 known territories (9%) were not visited. Overall territory occupancy was 83%. The figure of 1283 pairs represe nts 147% of the overall population level believed to exist in 1930-39, and 167% of that counted during the previous national survey, in 1981 . The net increase was geographically uneven, being greatest in a broa d zone from the eastern Grampians to South Wales, whereas numbers were still well below pre-war level in coastal south-east England. In coas tal and western inland areas of the northern Highlands, numbers have d eclined since 1981. Throughout the UK, many coastal populations have s ubstantial proportions of territories occupied by nonbreeding birds. P opulation growth has involved both an increase in breeding density and expansion of breeding distribution, the latter especially through inc reased use of nest sites on small cliffs, quarries, buildings, rocky b anks and even the ground. Both kinds of increase have been fuelled by a substantial increase in production and probably survival, reflecting the disappearance of pesticide problems, reduced persecution through protection efforts, and locally enhanced food supply through growth of pigeon racing. The failure of the northern coastal population to reco ver is attributed mainly to contamination by marine pollutants through the food chain, although this needs further research.