Sites and Spacing of Nests as Determinants of Wedge-tailed Eagle Breeding in Arid Western Australia

Abstract

Wedge-tailed Eagles Aquila audax in the arid zone of Western Australia built their nests mainly in the top half of typical members of the commonest species of trees higher than 4 m. Most nests in the arid zone were 2-6 m from the ground, with a few at less than 1 m, and in the mediterranean zone at 4-16 m. Breeding success in the arid and mediterranean zones did not vary with the height of the nest and was similar in live and dead trees. Most temtories contained several nest-sites, used and re-used in different years. The availability of nest-sites did not limit breeding density in the arid zone. Mean size of temtories in the arid zone ranged from 30 to 100 km² and was probably related to long-term availability of prey. The smallest territories occurred in the areas of most erratic rainfall, where prey were very scarce for long periods and very abundant for brief periods. We conclude that terrtoriality sets an upper limit to the density of potential breeding pairs in any particular habitat.