Is wedge-tailed eagle, Aquila audax, survival and breeding success closely linked to the abundance of European rabbits, Oryctolagus cuniculus?

Abstract

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.