Age, Movements and the Management of the Wedge-Tailed Eagle, Aquila-Audax, in Arid Western Australia

Abstract

Four populations of wedge-tailed eagles were studied from 1967 to 1976 in the arid zone of Western Australia, and compared with data from the rnediterranean zone. The overall colour of eagles and the width of the pale bar on the dorsal surface of the wing were used to estimate ages in the field. Breeding usually started at 6-7 years old. The proportion of eagles of breeding age in the population varied between a quarter and two-thirds. A total of 355 eagles were banded (50% as nestlings) and 29 were recovered, 12 at >100 km, the furthest at 784 km away. Eagles of breeding age were probably sedentary even in drought, but as many as half those less than breeding age left the natal area. Most recoveries were within 2 years, but some bands were lost thereafter. Killing by man accounted for 54% of the recoveries in the arid zone. Such killing cropped the eagle population, the productivity of which varied according to its food supply. Killing was probably ineffective in reducing the numbers of eagles as it chiefly accounted for immatures, the birds most vulnerable to natural mortality. However, in habitats marginal for eagles and not used for sheep, such killing rates could have posed a threat to the species. Increases in land clearance and intensity of land usage could affect the wedge-tailed eagle in the future, even in the arid zone. Such effects would not be immediately obvious in such a long-lived, reproductively conservative species.