A significant decline of breeding Peregrine Falcons in coastal north and west Cornwall, 2015–19

Published on 09 June 2020 in Main articles

Steve J. Watson and Richard G. Sale

Abstract The breeding population of Peregrine Falcons Falco peregrinus on the Atlantic coasts of north and west Cornwall appears to be declining dramatically. During 2015–19, both clutch size and the number of fledglings decreased significantly, yet neither can explain the decline in eyrie occupation. We suggest that the primary cause of the population decline is an increase in adult mortality or emigration. A reduction in the ‘quality’ of the local adult population, through mortality or emigration, would inevitably lead to a reduction in clutch size and fledgling rates, but we believe these to be second-order events. The adult Peregrine population of this coast seems to be declining catastrophically, perhaps as a result of presently unknown environmental factors. Early indications for 2020 occupation are that the observed decline is continuing.

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An adult Peregrine Falcon Falco peregrinus landing close to a nest site in the study area in north and west coastal Cornwall, June 2010. Ian McCarthy