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.

Recovering Australia's arid‐zone ecosystems: learning from continental‐scale rabbit control experiments

“…Steele and Baker‐Gabb (2009) could not detect any effect of the introduction of RHD on the abundance of Wedge‐tailed Eagles or any other raptors that normally take rabbits. Olsen et al (2014) found that Wedge‐tailed Eagles exploited the increased abundance of gray kangaroos ( Macropus giganteus ) as the rabbit population fell and there was no sudden decrease in eagle egg clutch size or fledgling survival associated with the spread of RHD. Again, contrary to expectations by some researchers, there was no strong evidence that reduction of rabbit prey seriously compromised native predators.…”

Irrupting prey populations in the absence of a mammalian apex predator drive shifts in prey selection by eagles

“…Wedge-tailed eagles ( Aquila audax ) are the largest bird of prey in Australia and are common in arid regions of the continent. These birds are generalist predators that readily shift their diet in response to the availability of prey (Brooker and Ridpath 1980 ; Leopold and Wolfe 1970 ; Olsen et al 2014 ; Parker et al 2007 ; Silva and Croft 2007 ). In arid Australia, eagles prey heavily on rabbits and reptiles but also prey on larger species such as kangaroos and sheep (Brooker and Ridpath 1980 ; Fuentes and Olsen 2015 ; Sharp et al 2002b ).…”

Eastern Buzzard Buteo japonicus toyoshimai Breeding on the Ogasawara Islands Depend on Non-Native Rats as a Food Source

“…After European Rabbit eradication in Australia, several raptor species experienced reduced clutch sizes (Olsen & Marples 1992). However, the impact of such a reduction in non-native species on predators depends on the dependence of the predator population on the non-native prey and the availability of alternative foods (Tubbs 1974; Olsen et al 2014).…”