Monday, 31 October 2016

Wedge-tailed Eagles in the Perth Hills

A nine week old wedge-tailed eagle Aquila audax chick on its eyrie

I have been over in Western Australia for the past week helping Simon Cherriman ring/band and satellite-tag wedge-tailed eagle chicks for part of his PhD study on the species'  behavioural ecology. As this is Simon's study, I will only post a few snippets here to give a picture of the birds; how we ring them, their habitat and prey. To read more on Simon's work please visit his website at

The wedge-tailed eagles' habitat in the Perth Hills is mostly woodland with open patches of heath, so there is considerable cover for potential prey species. This is quite different from the more open landscape of central Australia, or the open hillsides which golden eagles live in in Scotland. There is a chick in an eyrie on the right of the photograph.

Simon measures the bill of a young wedge-tailed eagle.The sex of even young birds can be determined by the size of their bills and feet relative to their age.The females are larger. Bill Brown, who has also been helping Simon, holds the chick firmly but gently. He is well-accustomed to handling eagles as he has studied them in Tasmania.

This chick was about four weeks old. At this age the chicks are still mostly covered with white down, with only the first brown feathers opening from their quills on their wings and tail.

Simon pulls himself up by rope to reach an eagle eyrie. Although this looks easy with modern climbing equipment, Simon also makes it look easy because he is one of the best, probably the best, tree-climber I have seen, whether free-climbing or with technical aid.

The Perth Hills eagle study area is only about 30 km from the city centre of Perth, less from the airport. A Qantas flight passes overhead; there seemed to be a flight like this every few minutes while we were at this nest site.

The eagles appear to select the largest trees in their territory to nest in. Often these are remnants of the once widespread forest which would have been mostly of such grand trees as Jarrah Eucalyptus marginata, Marri E. calophylla and Wandoo E. wandoo. This nest was about 25 m from the ground, similar to most of the nests in the area.

While at the nest sites, we searched around the base of the nest trees and any other perches in neighbouring trees, looking for the remains of prey. At this nest site there were remains of a minimum of two Red-tailed Black Cockatoos, three Kookaburras, one Australian Magpie, one Australian Raven, twelve Shingle-back Lizards and two young Western Grey Kangaroos. These are all woodland species and the eagles possibly catch the lizards after watching from perches in the high trees. We do not know if the birds are be able to see the understorey where the shingle-backs live from high in the sky. However, Simon's study should reveal just how the eagles hunt, as the tags measure the height that the eagles fly at. So for now this is only my supposition.

The four week old chick is here placed in a bag ready to be lifted back into its eyrie. This bird has a standard numbered metal ring on its right leg and a coloured metal ring with a unique number on its left leg which is more easily read in the field or caught on camera.

Simon checks that a larger chick, which has been fitted with a satellite-tag, is alright before he abseiled back down out of the tree and we left the bird to settle down. Satellite-tracking of eagles and other birds is a well-established method for finding out where birds move to, revealing where they hunt and whether they migrate or wander nomadic-ally, and if so where to. The full details of this birds movements will be analysed by Simon as part of his study, but meanwhile a sample of the information he has collected from previously tagged eagles can be read on his website as linked above. And I am sure Simon will post snippets of information on this bird's movements as soon as he can.  

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