Emu Emu Society
Journal of BirdLife Australia
RESEARCH ARTICLE

Trophic relationships between neighbouring White-bellied Sea-Eagles (Haliaeetus leucogaster) and Wedge-tailed Eagles (Aquila audax) breeding on rivers and dams near Canberra

Jerry Olsen A C , Esteban Fuentes A and A. B. Rose B
+ Author Affiliations
- Author Affiliations

A Applied Ecology Research Group, University of Canberra, ACT 2601, Australia.

B Australian Museum, 6 College Street, Sydney, NSW 2010, Australia. Present address: 61 Boundary Street, Forster, NSW 2428, Australia.

C Corresponding author. Email: Jerry.Olsen@canberra.edu.au

Emu 106(3) 193-201 https://doi.org/10.1071/MU05046
Submitted: 7 September 2005  Accepted: 12 May 2006   Published: 18 August 2006

Abstract

The diet of the White-bellied Sea-Eagle (Haliaeetus leucogaster) in Australia is poorly known, especially inland. The diet of the Wedge-tailed Eagle (Aquila audax) is better known, but the overlap in prey used by the two eagles has not been studied. In four inland territories of White-bellied Sea-Eagles, and five territories of Wedge-tailed Eagles nesting close to them (range 1.6–5.1 km apart) between July 2002 and December 2004, we identified 116 and 118 prey items from nests of White-bellied Sea-Eagles and Wedge-tailed Eagles respectively. There was little overlap between the diets, and that of Wedge-tailed Eagles was similar to that reported elsewhere. In addition to fish, White-bellied Sea-Eagles specialised in aquatic birds, such as cormorants, grebes or ducks, and aquatic reptiles, such as turtles or water dragons, but tended to avoid terrestrial birds and reptiles, such as ravens and skinks, or mammals such as European Rabbits (Oryctolagus cuniculus) and macropods that were the main prey of nearby Wedge-tailed Eagles. Though food niche breadth was almost identical for the two eagles, Wedge-tailed Eagles captured significantly larger prey, as indicated by the geometric mean prey weight. Our results indicate that closely located breeding pairs of riparian Wedge-tailed Eagles and White-bellied Sea-Eagles were not competing for food, owing to the differences in foraging preferences, at least during the breeding season. We found no evidence to support the claim that the spread of rabbits assisted the increase of breeding numbers of White-bellied Sea-Eagles.


Acknowledgments

Thanks go to Terry Dennis and Jeff Jolly for generating interest in White-bellied Sea-Eagles, Nick Mooney and Les Boyd for advice, and to Christie Gould, Michael Maconachie, David Mallinson, and Frank Barnes who found Wedge-tailed Eagle nests for the larger study. Thanks also go to Tony Bell, Mark Rodden, Marty Gardner, Trish D’Abrera, Kate Boyd and Monica Muranyi for passing along their observations at Googong Foreshores, and the ACT Parks and Conservation Service, including David Shorthouse, Murray Evans, Bernard Morris, Brett Macnamara, Paul Higginbotham and Darren Rosso. Particular thanks go to Walter Boles and John Disney of the Australian Museum for aid with the identification of some specimens, and Camilla Myers for helpful editorial advice. Special thanks to Ross Bennett, Enzo Guarino, Arthur Georges, Gabriela Peniche and the Kippax Veterinary Hospital for their assistance with prey weights. EF was supported by an International Graduate Scholarship from the National Council of Science and Technology (CONACYT) in Mexico. Thanks also to Stephen Debus for advice.


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Appendix 1.  Percentage of the total number of prey items (% #) and percentage contribution to the dietary mass (% mass) in the diet of Wedge-tailed Eagles (WTE) and White-bellied Sea-Eagles (WBSE) breeding near Canberra
Sources for biomass: (1) Higgins 1999; (2) McDonald et al. 2003; (3) Marchant and Higgins 1993; (4) Marchant and Higgins 1990; (5) Olsen et al. 2004; (6) Olsen and Tucker 2003; (7) Sharp et al. 2002; (8) Strahan 2004; (9) estimated based on remains located at nests; (10) unpublished data from injured animals taken to Kippax Veterinary Hospital, ACT; (11) R. Bennet, unpublished data
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