Tuesday, 13 June 2017
We know from research conducted by CSIRO in the in 1960's and 1970's that Wedge-tailed Eagles are capable of making long-distance movements of several hundred kilometres, but this important work was carried out during a time when banding/ringing was the only method available. The recovery rate of banded birds is usually very low (perhaps less than 10 percent), and the path flown between banding and recovery sites is not able to be determined. The satellite-tracking methods used in modern research, however, gives much more detail on eagle movement, and it’s been extremely exciting to follow the journeys of juvenile eagles satellite-tagged last year. The above map shows the movement paths of 4 birds from the Perth Hills: Walyunga (who made it all the way to the Pilbara) in pale red, Kala in yellow, Korung in orange, and Yirrabiddi (who only left her natal territory last week) in deeper red. It also shows in blue the northward journey of Malya, who moved 750 km north of Matuwa during dispersal.
The fifth bird, shown in green, is Kuyurnpa, the first juvenile eagle to be tracked using a GPS/Satellite transmitter, being fitted with this device in 2013. She is now nearly 4 years old, and has continued to move very long distances like those we detected in her early dispersal phase several years ago, frequently travelling the ~400 km between the Fortescue Marsh area and the expansive salt lake system of Lake Carnegie. It is clear from these maps that wedgies can certainly fly!, and Also of interest is the apparent pattern that birds seem to prefer going north - possibly due to cyclonic rainfall activity leading to ample food supply, conditions that may well attract young eagles. More insights about their habitat use at the landscape scale will be revealed as our tracking continues!
Thursday, 25 May 2017
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
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!
Tuesday, 11 April 2017
When I checked in on the most recent tracking data yesterday and found Wallu's transmitter showed no movement for 3 days, I was worried. This has in the past meant the transmitter's owner has died, and I dreaded to think of Wallu, our longest-tracked eagle, having lost his life. Given we have just moved into the 'new eagle year', and territorial behaviour will be heightening as the breeding season approaches, it would not be surprising to find a resident adult male killed by a usurper. It was at this time of year, 3 years ago, that our adult female Gidgee was ousted from her home range and later died.
Fortunately, however, this story does not have such an ending! I rang the Matuwa homestead and was delighted to talk to the current caretakers, John and Gail Grenville, who kindly offered to assist by investigating further. I later received an incomplete voice-to-text message on my phone, which said:
We found the tracker lying on the ground but no..."
This was enough info for me to realise what had happened, and that Wallu was not dead, and I rang Matuwa back instantly for more news. When John and Gail reached the GPS coordinates shown on my tracking map, they found his PTT on its side with one part of the harness frayed, causing it to dismount. This is a very interesting discovery, as this initial harness design was a 'permanent' mount, unlike the method used now which is made with a weak link, and I expected it may have lasted much longer. It appears the heat and harsh conditions in the arid zone (along with some encouragement from big, hooked beak!), caused the harness to weaken and eventually break on one of the main straps. So after 3 years and 10 months, the end of an era has arrived, and Wallu is wild and free again! We will check on him later this year during our eagle research trip during the breeding season (Wallu is still identifiable from his leg band), and possibly even catch him to give him a health assessment. Thanks so much to John and Gail for their wonderful help! More updates soon!
Monday, 10 April 2017
The last satellite-tagged Wailitj is the first to leave home! Walyunga, a late-fledging juvenile wedge-tail that we fitted with a transmitter in December, has made the bold move of 'leaving home', departing his natal home range last Tuesday. After not having moved more than about 4 km during the past 4 months of the post-fledging period, he suddenly flew east and spent the night near Wundowie, 35 km away. Then Walyunga travelled inland via York, turning north to reach Goomalling, then passing Wongan Hills and Dalwallinu as he moved nearly 200 km north of Perth!
|Walyunga's dispersal path into the WA Wheatbelt region (click to enlarge).|
It is so exciting to have reached the stage where our Perth eagles have begun dispersal, and I'm SO grateful to all who supported the initial crowdfund to pay for 3 of their transmitters. This is the first time the dispersal path of a 'wedgie' from south-west WA has been tracked, so it is very exciting to follow Walyunga's route, and anticipate where he might end up next! Don't forget to follow my Instagram account for the most recent updates of our satellite-tracked eagles!
Friday, 24 February 2017
While in Tasmania recently, I was very excited to receive a phonecall from my friend and expert wildlife journalist Vicki Laurie, who was keen to hear the latest news about my eagle-tracking research. My mind raced back to the above scene from October when I captured a photo of Malya's mother delivering a freshly killed goanna to feed her month-old chick, and we had a great chat about the most recently satellite-tagged Matuwa wedgies, and the findings from last season's research, whose current prime sponsor is the awesome Goldfield's Environmental Management Group (GEMG). Today the wonderful article that Vicki produced was printed in The Australian newspaper, and it was very exciting to see our Malya making his star appearance!
You can click the image below to enlarge and read the full article, or view the online version here. And if you are new to the eagle-tracking world, don't forget to zip back in time to read about the day we sat-tagged Malya.
If you are keen to read more of Vicki's wonderful wildlife writing, I thoroughly recommend her most recent book "The South-west: Australia's Biodiversity Hotspot," which you can find at the University of Western Australia's website.
Monday, 20 February 2017
Our most recently satellite-tagged Walluwurru Malya has continued to spread his wings and now appears to be ranging over most of his parents' territory, which, as you saw last time, is the 'neighbouring property' of our beautiful adult male Wallu. These two eagle territories are shown in red and blue on the above map. During the last few weeks, our 'teenage' wanderer Kuyurnpa drifted in from the east, homing in on a long-range (~300 km) exploratory loop to spend a single night roosting at Matuwa. This creates an exciting opportunity to summarise our three arid-zone eagles currently being satellite-tracked:
- Wallu, a ~10 year-old mature adult who remains sedentary in a fixed home range, where he has stayed for 3.5+ years;
- Kuyurnpa, a 4th year immature who is still in her dispersal/wandering phase, moving freely through the arid interior with occasional 'return visits' to her natal territory;
- Malya, a 1st year juvenile currently still in the post-fledging period in his natal territory, where he will be dependent on his parents until the dispersal phase begins in several months.
These birds represent the three different stages a Wedge-tailed Eagle's undergoes during its life, and it is exciting to be monitoring one arid-born eagle from each stage! I am super excited to know when Malya will begin dispersal, and when (if!?) Kuyurnpa will settle in a breeding territory. Let's keep on tracking and find out!
Sunday, 5 February 2017
It is now almost 2 months since Malya fledged, and his progress has been amazing! Initial movements of 50 - 100 m from the nest (shown by the pink pin on the above map) continued over the first fortnight, and soon the young male eagle was roosting in a tall tree just over 1 km from the eyrie (which, coincidentally, I had climbed the day of his tagging, to photograph an oncoming thunderstorm!).
These short bursts were rapidly replaced by longer flights of over 100 m, and in the last month of tracking, Malya has spread his wings widely and travelled across an area with a radius of just over 6 km. He has also been recorded soaring to great heights, reaching altitudes of over 2000 m on some of the warmer days.
Malya's parents' territory happens to be adjacent to that of Wallu, our 'founding member' of the eagle tracking family, and zooming out provides a comparison of the 2 birds' movements during the past 8 weeks. The dark, diagonal line shown on the below map (click to enlarge) is a ridge running north-west to south-east, a landform which appears to form the northern boundary of Wallu's territory. So far these two birds have not overlapped, but it is important to keep in mind a juvenile like Malya may be tolerated 'intruding' on another adult's patch, unlike one of his parents. It is great to be able to have this context of two arid-zone wedgies