Australian Field Ornithology 2021, 38, 19–28 http://dx.doi.org/10.20938/afo38019028 Introduction Olsen & Fuentes (2004, 2005) frst signalled a decline since the 1990s in breeding Little Eagles Hieraaetus morphnoides in the Australian Capital Territory (ACT). The Little Eagle is now considered threatened in some southern Australian jurisdictions, being listed as Vulnerable in New South Wales (NSW), the ACT, Victoria and South Australia in relevant legislation. Further knowledge of its ecology and requirements, particularly in areas afected by human impacts (e.g. urban expansion in Canberra, ACT), will assist in its conservation and management. For instance, signifcant gains have been made on understanding its breeding-habitat and nest- site requirements (Larkin et al. 2020) and the home- range and roosting requirements of a fedgling (Olsen et al. 2017). The breeding diets of the Little Eagle and Wedge-tailed Eagle Aquila audax in various parts of Australia are now well known, especially for the latter species, whose diet has been studied comprehensively in every State and Territory (reviewed by Marchant & Higgins 1993; Debus 2017). Their diets have been compared quantitatively, using food-niche metrics, for contiguous territories in the ACT in 2002–2008 and again in 2008–2010, with a small change in dietary proportions as the number of European Rabbits Oryctolagus cuniculus increased (Olsen et al. 2010, 2013a). Rae et al. (2018, 2019, 2020) presented dietary data for the Little Eagle in the ACT and adjoining NSW (within 30 km of the ACT), but not separately for the ACT (i.e. peri-urban Canberra) and rural NSW although some dietary diferences may exist between the two areas. Here we compare the diets of the two eagle species in contiguous territories within the ACT over the period 2011–2019, to further investigate their diets in sympatry and any changes over time. The context for the study is controversy over the Little Eagle’s population and conservation status in the ACT, and the likelihood that interactions with the Wedge-tailed Eagle as well as urban sprawl, and perhaps secondary poisoning from pindone baiting to reduce Rabbit numbers, may be adversely afecting the Little Eagle (e.g. Olsen 2018, 2019). Study area and methods The general study area of peri-urban Canberra and surrounding rural ACT has been described in previous papers, i.e. eucalypt-dominated open forest (in Canberra Nature Parks), woodland, open woodland and tree-dotted pasture, with River She-oak Casuarina cunninghamiana gallery forest on the Molonglo River (e.g. Olsen et al. 2006a,b, 2010, 2013a; Fuentes et al. 2007). Dietary characteristics of breeding eagles (active nests to dependent fedglings) were determined by analysis of prey remains and pellets collected from under nests and roosts. Sampled were six Little Eagle territories from January 2012 to November 2018 (Table 1), and 13 Wedge-tailed Eagle territories from September 2011 to December 2019 (69 and 49 collections for a total of 232 and 256 prey items, over 15 and 33 nest-years, respectively). At least six (possibly seven) of these Wedge-tailed Eagle territories were individually contiguous with each of the six concurrently active Little Eagle territories or home-ranges, another two overlapped former but vacated Little Eagle nesting territories, and one was in an area inhabited by a pair of Breeding diets of the Little Eagle Hieraaetus morphnoides and Wedge-tailed Eagle Aquila audax in the Australian Capital Territory in 2011–2019 S.J.S. Debus 1 *, Jerry Olsen 2 **, Susan Trost 3 and Esteban Fuentes 4 1 Zoology, University of New England, Armidale NSW 2351, Australia 2 Institute for Applied Ecology, University of Canberra, ACT 2601, Australia 3 44 Wybalena Grove, Cook ACT 2614, Australia 4 Instituto Tecnológico y de Estudios Superiores de Monterrey Campus León, Av. Eugenio Garza Sada S/N, León, Gto. 37190, México *Corresponding author: Email: sdebus@une.edu.au **Deceased Abstract. The diets of the Little Eagle Hieraaetus morphnoides and Wedge-tailed Eagle Aquila audax breeding sympatrically in the Australian Capital Territory during 2011–2019 were compared by analysis of pellets and prey remains (six Little Eagle territories and 13 Wedge-tailed Eagle territories; 69 and 49 collections for a total of 232 and 256 prey items, respectively). Little Eagles took 33% mammals (29% European Rabbits Oryctolagus cuniculus), 44% birds, 6% reptiles and 17% insects by number, and 65% mammals (62% Rabbits), 27% birds, 8% reptiles and <1% insects by biomass. Wedge-tailed Eagles took 59% mammals (23% Rabbits and 19% macropods), 38% birds, 1% reptiles, <1% fsh and 1% insects by number, and 89% mammals (20% Rabbits, 38% macropods), 10% birds, and <1% reptiles, fsh and insects by biomass. Indices of dietary diversity (Shannon Index and Standardised Food Niche Breadth) were 2.57 vs 3.07 and 0.19 vs 0.24, respectively; Geometric Mean Prey Weights (GMPW) were 164 vs 1392 g, but discounting a biased sample of insects in many pellets from two fedglings, Little Eagle GMPW was more like 340 g. Dietary proportions and some metrics for both species appear to have changed little since the preceding decade, although Wedge-tailed Eagle dietary diversity increased slightly and dietary overlap (80%) increased greatly, concomitantly with some pairs of Wedge-tailed Eagles replacing pairs of Little Eagles. Intraguild predation occurred, including Wedge-tailed Eagle predation on Little Eagles.