Canberra's wedge-tailed eagles thriving on degustation menu

Rabbit scourge perpetuates the myth that our beloved wedge-tailed eagles rely on the pest for survival, writes Ian Warden.

Of course, like all commuting Canberrans, my heart is filled with joy as I drive, singing, to work in the mornings. Public servants I'm sure must be finding it especially fulfilling to scurry to work every day to serve the Abbott government. But for me there are several mornings a year when that routine joy of my drive to work is enhanced, turned to rapture, by the sight of wedge-tailed eagles gliding high in the sky.

Canberrans' blessings include the way in which we share our bird-blessed Bush Capital and its region with eagles.  New research  now enlightens us about some of what is going on gastronomically in these eagles' lives. In a  newly-published paper, raptor scholars associated with the University of Canberra's Institute for Applied Ecology ask the probing question (it is the paper's title) Is the wedge-tailed eagle, (Aquila audax), survival and breeding success closely linked to the abundance of European rabbits?

Jerry Olsen, Brian Cooke, Susan Trost and David Judge have given this popular belief a rigorous ogle and have concluded that it is a myth. They've thoroughly investigated what Aquila audax actually is dining on, and I know this column's bird-loving readership will be fascinated by the findings.

Back to the scholars in a moment, but first to how my daily commute is sometimes eagle-enriched. My route takes me from my humble cottage in a lower Garran frost pocket and along Hindmarsh Drive and on to Fyshwick. And as one ascends Hindmarsh towards the crest of the hill (with Red Hill to one's left and mount Mugga Mugga to one's right) there are sometimes eagles gliding to and fro in the vast blue empire of sky ahead of and above us. Eagles nest every year somewhere in the vast terrestrial empire far below the empire of sky that Hindmarsh Drive commuters sometimes see them patrolling.

Ths scholars say they wanted to ask their question because some ecologists argue that the success and abundance of Australia's native wedge-tailed eagles is strongly linked to the abundance of wild rabbits - an introduced pest.

This belief means that there are fears that when the biological control agent rabbit haemorrhagic disease (RHD) is used with great success against the accursed rabbits, our eagles, bereaved of an important food, are sorely afflicted. What this means, the scholars worry, is that because the wedge-tailed eagle is quite rightly seen "as an iconic species" there is rabbit-controlling inaction among conservation managers worried about doing harm to eagles. This is in spite of the fact that rabbits have such a proven severe impact on Australia's natural eco-systems.


The scholars note with impatience "continuing assertions" - unsupported by facts -  that use of RHD is reducing the breeding success of eagles. Scouring all the key publications on this subject the UC scholars find (in great detail we have no room for here) that there's simply no proof that even when RHD and warren-ripping are successfully inflicted on rabbits that this does the eagles any harm.

They say it emerges that eagles seem to have healthy appetites for such a smorgasbord of foods that they will usually thrive without  rabbits. When Esteban Fuentes, an indefatigable UC Masters student and researcher, and colleagues studied wedge-tailed eagles of Canberra and the region in 2002-04 he was doing it at the height of RHD's impact on rabbits. But what was discovered?

The paper reports that the search "not only detected many more eagle breeding territories, but found substantial changes [since a study 40 years earlier] of the prey species taken and evidence of higher productivity [more successful breeding] of eagle pairs". The eagles studied were eating 57 prey species, "including 19 mammals, 20 birds, seven reptiles and one crustacean".

Fuentes did this study by, among other techniques, forensically fossicking through the castings (big pellets of inedible parts of what they've just eaten) that eagles attractively vomit out.

Although 40 years earlier rabbits had dominated eagles' diets, by 2002-04 "macropods dominated the diet" with the eastern grey kangaroo "the most important prey". Yes, the eagles were still eating some rabbits, and lots of native birds, especially Galahs and (some of us will wince at this news) adorable Magpies.

Here the feral journalist in me wishes, for sensationalism's sake, that there was a finding of the Canberra eagles whisking away and eating the occasional suburban dog (Cavalier King Charles spaniels would be no great loss) but there is no evidence of that.

The scholars conclude that misinformed folk have to stop "perpetuating" the rabbit-dependancy myth.

"There is little evidence that eagles depend heavily on rabbits as prey. Instead, as rabbits decline, more kangaroos, reptiles and birds are eaten." And where eagles do have a high proportion of rabbits in their diets this is usually only because the rabbits have so buggered the landscapes in which they are teeming that there's no native prey there for the eagles to eat.

"Rather than perpetuating [this] idea ... resources would be better redirected into understanding continental-scale eagle population dynamics. This would provide a more rational framework to assist decisions on future biological control agents for rabbits."

We blush to show it again but our pornographic photograph of two well-nourished ACT eagles seen copulating a few weeks ago (they're beside the road to Tharwa) does reinforce the truth that we are living in an eagle-blessed Territory.