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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