Thursday, 25 May 2017

Death by Drone?

Walyunga's PTT showed a cessation in movement last week which saw me drop everything and fly north to Onslow to investigate. After a 200 km drive and a 2 km walk I was sad to find the bird's carcass next to a large bend in the Ashburton River, about 1000 km north of his natal home range. Initial examination showed the PTT to be still securely attached to his back, with no visible signs of injury. Curiously, a recently broken dead branch lay on the ground just in front of Walyunga, and it appeared this may have snapped when the bird launch from the ground in an attempt to reach a low perch. I wondered why. It wasn't until I was back in Onslow that I noticed the eagle appeared to have had several wing feathers missing, and I considered that the bird may have been trying to jump up to a perch and take off, without success.

Back in Perth, I took Walyunga's carcass for closer examination by Murdoch Uni's pathology department, and it was then that we noticed a total of 9 severed flight-feathers: 4 primaries on the right wing, 3 on the left, and 2 retrices (tail-feathers). X-rays also showed the bird had a dislocated knee. Although there was no conclusive evidence to prove whether these injuries occurred before or after death, consideration of this eagle's tracking data helps to paint a probable scenario that lead to his death.

Walyunga's right wing showing four primary feathers cut cleanly off.

The below map shows Walyunga making short movements along a bend in the Ashburton River from 5th - 12th May, something consistent with an eagle that, after moving very large distances, has 'taken a few days rest' at a billabong which may be supporting ample food resources (we've recorded this before with other dispersing juveniles, including Kuyurnpa).

But after 19th May, as the below map shows, movement stopped completely.

It appears that Walyunga may have attacked a drone and in the process of grabbing it with his talons, wrapped both wings and his tail around the moving object (as eagles often do when taking prey), which resulted in several neatly cut feathers. Unable to stay airborne, he crash-landed at the site where I found his body and moved around on foot for over a week, before finally dying of starvation.

While it is always sad to lose birds we are studying, especially in these circumstances, the story this tells is a key reason why I am conducting this research. You can see a few more pictures and read the posts made during my trip to Onslow on my Instagram account. I am extremely grateful to Chevron and, the local folk in Onslow, and Lynwood Veterinary Clinic, all of whom assisted me greatly during this 'wildlife forensics' episode!

Friday, 5 May 2017

Perth to the Pilbara

It's now a month since Walyunga, a beautiful male Wedge-tail from our Perth study area, began his juvenile dispersal period and started flying north. Amazingly this bird decided to maintain this trajectory for the next three weeks, moving between 50 and 200 km per day until he hit the Pilbara coast! By midday on 30th April, Walyunga had arrived at Karratha, 1200km north of the nest on which he hatched. This remarkable journey is the longest continuous distance travelled ever recorded for a Wedge-tailed Eagle, a truly amazing feat considering Walyunga is only 7 months old! It is a similar movement pattern to that of Kuyurnpa, who also reached the Pilbara coast in her first few months of independence, and I suspect the recent wet conditions in this region are an attractant for young eagles seeking areas with high productivity. This is something that will hopefully become clearer as my research continues.

Meanwhile Malya, our single survivor from the Matuwa study site, conducted his first 'prospecting' flight on 6th April, drifting 12km north of his natal territory between 11 am and 3pm, before coming home to roost. Then, on 26th April the 9am flight departed Matuwa and Malya was on board! By sunset this eagle was roosting 140km north, and he continued in this direction for the next few days, reaching Lake Dora near Punmu Community by the end of the month. What amazing distances these eagles are capable of flying! More updates soon!