Breeding of the Peregrine Falcon Falco peregrinus. I. Weather, Nest Spacing and Territory Occupancy

Abstract

The density of pairs of Peregrine Falcons occupying nest sites near Canberra was high (minimum of one pair per 343 sq. km). Nest sites were scarce. Falcon pairs were spaced no closer than 2 km apart and were clumped where there were suitable cliffs; within these clumps the spacing of cliffs used for nesting was fairly regular while that of all cliffs was random. Over 12 years, occupancy of nest sites was high and stable with between 82 and 100% of sites occupied annually by at least one Falcon. Variation in occupancy by pairs, and therefore breeding density, was not significantly correlated with the change in occupancy from the previous year (a density-dependent influence). Heavy rain during August, in particular, and October reduced occupancy of nest temtories by pairs and this reduced the potential breeding population (a density-independent influence). Occupancy of temtories by pairs was significantly correlated with rain intensity, which accounted for 77% of the variation in occupancy. Flooding of nests, more than a reduction in food (prey availability, hunting success, etc.), appeared to result in lower occupancy by pairs in wet years.