The breeding status of Peregrine Falcons Falco peregrinus in the UK and Isle of Man in 2002

Abstract

Capsule: Numbers of breeding Peregrines are now higher than ever recorded and the recovery of the species within the UK has continued since 1991. Aims: To estimate the current Peregrine breeding population and its changes over time by recording breeding evidence and nesting range occupancy at known and potential Peregrine eyries. Methods: Attempts were made to check all potentially suitable Peregrine nesting locations for signs of Peregrine occupation. Causes of nest failure were documented where possible. Estimates of occupancy of nesting ranges that could not be visited were based on the proportion of ranges occupied from visited nesting ranges in the same region. Results: In 2002, 1530 Peregrine nesting ranges were estimated to be occupied, comprising 1456 pairs or single birds confirmed as in occupation, and 74 estimated extras (5% of total occupied nesting ranges) that were not visited. Including non-breeding singletons holding nesting ranges, the UK and Isle of Man figure of 'Ratcliffe pairs' was 1437. This showed a 12% increase from 1991 and a 64% increase from the 1930s. However, there were geographical differences in change, with rapid expansion in the south of England tempered by declines in northern Scotland. Conclusions: The primary reasons for the population increase is primarily because of range expansion driven by a plentiful food supply and perhaps an increased tolerance of human disturbance. In areas where the species has declined, various factors (separately or in combination) including reduced food supply and persecution are likely to be involved. © 2010 British Trust for Ornithology.