Diets of Wedge-tailed Eagles ('Aquila audax') and Little Eagles ('Hieraaetus morphnoides') Breeding Near Canberra, Australia

Abstract

Recent concern about the decline of the Little Eagle ('Hieraaetus morphnoides') in southeastern Australia has raised questions about whether Wedge-tailed Eagles ('Aquila audax') might be implicated in this decline. The ecology, including the diet, of Little Eagles is rather poorly known. The diet of the Wedge-tailed Eagle is better documented, but the overlap in prey used by the two eagles has been little studied. Near Canberra between July 2002 and January 2008, we identified 1421 and 192 prey items from nests of Wedge-tailed Eagles and Little Eagles, respectively. Wedge-tailed Eagles' diet was similar to that reported elsewhere. In addition to European rabbits ('Oryctolagus cuniculus'), Little Eagles specialized on birds, but tended to avoid macropods, a main prey of Wedge-tailed Eagles, and there was little overlap in prey used by the two eagle species. Although Standardised Food Niche Breadth and Shannon Diversity Index were similar for the two eagles, Wedge-tailed Eagles captured significantly larger prey, as indicated by the difference in Geometric Mean Prey Weight, 1298 g for Wedge-tailed Eagles and 249 g for Little Eagles, which reflected the fivefold difference in mass between male Little Eagles and male Wedge-tailed Eagles. We suggest that direct competition for prey probably was not the cause of the Little Eagle decline.