24 August 2011

Every year an epic wildlife drama plays out high on Mt. Gillen, the red mountain ridge overlooking Alice Springs.

Each winter the same veteran pair of Wedge-tailed Eagles lay a couple of eggs in a car-sized nest. These hatch days apart but fledging two chicks is not part of the parents plan. The second egg is purely an insurance policy in case the first is sterile. The older of the white fluffy chicks resents sharing its nest and the stream of food from the attentive parents with anyone- even its own kin. So they fight, and the older, larger, stronger chick prevails, killing the smaller and sometimes even cannibalising it.

This practice is widespread among the Aquila genus of eagles and is interestingly known as ‘Cainism’, named after the siblicidal Cain of Biblical mythology. The eaglet, flush with success from its first murder grows rapidly.

This year's Mt Gillen Eagle Chick

By September the chick is getting large. Its white down has nearly been superseded by the brown contour feathers and it restlessly paces the nest. By October the wings will be ready for the first flight and one day, quite suddenly, the nest will be empty again.

The chick is taught to hunt rock wallabies on the rocky ridges, rabbits on the grassy flats, and ducks over the nearby sewage ponds. Then sometime in the hot summer the parents decide they have had enough. They drive the young bird from their territory and for a few months live for themselves again. But this retirement from reproduction is temporary: by March they are again adding branches to the nest. They show their fearsome commitment to each other and their territory with great swooping displays and tender moments of preening affection. They mate, and soon enough its time for more eggs to be laid.

I have watched this unfold each year I have lived in Alice Springs. It has been a privilege to know the adult birds, to see these peak predators become loving doting parents as they nurture another winged-terror to fledging and then drive it out to independence.

After months of following this year’s story through a scope from over a kilometre away I decided it was time to actually visit the nest in person to examine the new youngster at close range. It was a satisfying rough steep climb over scree and talus to the nest tree accompanied by songs of soaring Little Woodswallows and the contact ‘seeps’ of foraging Dusky Grasswrens. As I approached a fluffy white head peeked over the edge of the heaped branches. Climbing level with the nest we finally came face to beak- this really is a hearty great chunk of a chick! Its soft down whispered around its crown as it glared along its gore-splattered bill at me. There was no trace remaining of little Able the sacrificed sibling. This cruel youth will make a fine scourge of the skies one day.

Wedge-tailed Eagles are not rare or endangered in the outback, but despite this they always make even the most hardened twitcher stop in their tracks. These birds are true megafauna, top order predators which through fierce selection pressure have helped shape our wildlife into what it is today. Their annual life cycle is one of the eternal natural clocks of the desert, and I relish every minute of my time with them.