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Context Some ecologists argue that nesting success and abundance of wedge-tailed eagles (Aquila audax) are strongly linked to the abundance of introduced wild rabbits (Oryctolagus cuniculus). Consequently, concerns were expressed about eagle population viability when the biological control agent rabbit haemorrhagic disease virus (RHDV) heavily reduced rabbit numbers. However, observations following the spread of rabbit haemorrhagic disease (RHD) in Australia and Spain (where Aquila adalberti is an equivalent of A. audax) question this assertion. Eagle numbers did not fall even though rabbits declined regionally by up to 90% in both countries. Aims To reconsider the assumption of a strong link between rabbit abundance and wedge-tailed eagle breeding and population maintenance. Dispelling misconceptions, if any, about the eagles’ dependence on rabbits would benefit the future management of both eagles and rabbits. Methods We reviewed the literature associated with claims that eagles were heavily dependent on rabbits and asked whether these views could be substantiated given the lack of changes in eagle abundance following the spread of RHD. Data on eagle egg-clutch size and nesting success were also reviewed. Conclusions There is little evidence that eagles depend heavily on rabbits as prey. Instead, as rabbits decline, more kangaroos, reptiles and birds are eaten, partly because more native prey becomes available. Eagles have a high proportion of rabbits in their diets mainly where degradation of natural ecosystems, including that caused by rabbits, results in native prey being rare or unavailable. There has been minimal variation in average clutch size following major perturbations in rabbit population size. Implications Rather than perpetuating the idea that high populations of rabbits are needed for wedge-tailed eagle conservation, resources would be better re-directed into understanding continental-scale eagle population dynamics. This would provide a more rational framework to assist decisions on future biological control agents for rabbits.

There is disagreement about whether Southern Boobooks Ninox novaeseelandiae duet. A recent review of the species concluded that duetting does occur, based on (i) observations of captives and (ii) two reports from wild birds, including one from New Zealand. We examined definitions of duetting, and attempted to collect evidence for it in the calling behaviour of three mated pairs on adjacent territories observed from October 1996 to October 1999. To identify callers, six adults were colour-marked, and four of the six were radio-tagged. Observations were made on 529 nights from just before the birds left their day roost each evening until one hour after. Of 255 bouts of calling in which Territorial Boobook and Por calls were used, 30 (11.8%) overlapped (owls called at the same time); two (6.7%) of 30 overlapping bouts were between mated pairs, but without the temporal precision or sequential ordering of elements normally found in duetting. The other 28 overlapping bouts (93.3%) were mostly between neighbouring males. We found no convincing evidence in the field, or in the literature , that Southern Boobooks duet. We comment on behaviours that some may interpret as duetting, and suggest caution when estimating, solely from vocalisations, the densities of territorial pairs and sizes of home ranges of Ninox.

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% fish and 1% insects by number, and 89% mammals (20% Rabbits, 38% macropods), 10% birds, and <1% reptiles, fish 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 fledglings, 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.

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