Ten Thousand Fixes

Yup! TEN THOUSAND is the number of GPS fixes we have obtained from Wallu's PTT, which, as of today, has been tracking this very sedentary adult male wedgie for 700 consecutive days. The last time we checked in with Wallu we saw how he had not moved from his home range since the beginning of this tracking study. Not much has changed, and as you can see from the above 3D image, we have a very concentrated cluster of points clearly defining 'home'. As part of the process of publishing this preliminary research, I am now starting to look at this data in finer detail to analyse the points and look for patterns in daily behaviour, determine favourite roost sites, and search for other patterns in this eagle's behaviour. Watch this space for news of upcoming publications.

Settling In?

Has Kuyurnpa found a new home? It would seem so, for it has now been over 6 months since she settled in the one place in Western Australia's Pilbara region. Last year Kuyu visited Roy Hill station several times, spending about 10 weeks there in September, before heading back through Lorna Glen for another walkabout. But by the end of October, it was back to Roy Hill again, and that is where she has remained ever since.

The above map shows the collection of GPS points (nearly 2000 of them) which we have obtained this year. The cluster to the south-east occurs across a large area of relatively flat spinifex plain, and this is where Kuyurnpa has spent most of her time (i.e. all of February and March this year). Finer detail shows her movements in this period have often been very short, sometimes only travelling 1 - 2 km between roosts, which appear to be random with no favoured roost site selected. But throughout April she has ventured to the north west much more, moving 55 km between roosts on occasion.

This is the longest period our immature eagle, who is now approaching 2 years old, has spent in one location. Although it is much larger than her natal home range, which lies about 430 km to the south, and that of neighbouring eagles on Lorna Glen, it is still interesting to note this more sedentary behaviour after an initial wandering journey which covered about a quarter of WA's area (as shown on the map below - click to enlarge). I am hoping to find out more about Kuyurnpa's behaviour, and hopefully see what she looks like, when I visit Roy Hill Mine in early June this year to screen 'Where Do Eagles Dare?'. More soon!

Kuyurnpa's dispersal path in 2014. Roy Hill is shown with a green arrow. (Note that the northernmost and southernmost fixes are GPS errors.)

Refurbished PTTs

Today I am pleased to have received two refurbished PTTs which I plan to deploy on more eagles later this year. These came from two previously tracked wedge-tails: Gidjee, our adult female who died after unexpectedly leaving home in mid 2014, and Jarrkanpa who was killed in a heat wave earlier this year. I also plan to obtain some more funding to purchase additional transmitters with the hope to increase the sample size of tagged juveniles whose dispersal behaviour I plan to track. Watch this space!

An Early Death

Yesterday I received the sad news that Jarrkanpa was unfortunately found dead. Recent tracking data downloaded on 20^th January showed a lack of movement on the afternoon of 15^th and for the whole of 16^th January, but at the time of that download, no further data was available. As previous tracking data on a juvenile eagle (Kuyurnpa) had shown birds can remain stationary or show limited movement for more than a day, I made the decision to wait and see. But when the next set of data came in 3 days later, still no movement had been recorded. The Lorna Glen managers were away and out of contact but yesterday the caretaker managed to visit the location shown by Jarrkanpa's tracking data and confirm the outcome.

So what happened? A postmortem was unable to reveal the exact cause of death but it did conclude that the harness was still attached as normal and there were no injuries caused by the Teflon straps. What is most likely is Jarrkanpa died of heat exhaustion. Temperatures at Lorna Glen during the past fortnight have been exceptionally hot, with one daily maximum of 50.3˚C recorded at Lorna Glen during the week of 12^th January. The table below shows the temperatures recorded at Lake Carnegie (~60 km east of Lorna Glen) for the week in which Jarrkanpa died.

Date in January	Min. Temp (˚C)	Max. Temp (˚C)
12	18.5	36.6
13	20.6	38.5
14	24.0	40.5
15	25.9	42.0
16	23.7	43.5
17	27.2	43.8
18	29.0	44.4

 

Young birds not used to such conditions may not yet have learned the behavioural or physiological adaptations which help older, more experienced birds survive. For example, it is thought that one of the reasons adult eagles soar so high (as shown by altitude readings recorded in this study) is to keep cool and conserve energy. Considering he was on the wing for less that 2 months, Jarrkanpa may not have known that if he gets too hot, he can simply 'go up' to cool off. Also, premature death in juvenile eagles during extended periods of hot weather has been recorded previously at Lorna Glen. Two eaglets aged 7-8 weeks both died on their nests in October 2012 when the recorded temperatures at Wiluna and Lake Carnegie exceeded 40˚C for more than 10 days in a row. 

Although it is never nice to have a study bird die unexpectedly, it is an accepted part of research on wild animals that this sort of thing will happen, especially for a species for which, like many other large eagles, the juveniles have a high natural mortality rate (as shown by extensive research by the CSIRO in the 1970's). This event only reiterates how precious life is, and how difficult it is for animals to survive in one of the harshest ecosystems in the world. It also makes me think how amazing it is that Kuyurnpa not only survived her post-fledging period, but that she is still being tracked after dispersing from Lorna Glen over 12 months ago.

Flying Higher

In our last checkup on Jarrkanpa, he had shown a great deal of confidence gain in his soaring ability, moving beyond the 1000 m altitude mark. Today I checked the latest set of fixes and thought I'd post a 'day in the life' to show how he progressed even more. At 5 am he made his first movement from a roost in the woodland, not far from his nest. By 10 am the young eagle was stationary, probably sitting in a tree and digesting his breakfast. But by 11 am he had taken to the sky and was RIGHT up there, reaching nearly 5000 m above the ground! (click the above map to enlarge and see the altitude reading). At midday Jarrkanpa had begun to drop from the heavens, and he spent the next few hours roosting in a tree, avoiding the baking temperatures (which had also been responsible for helping him soar). The remaining afternoon fixes all showed much lower altitudes, indicating a few short flights from perch to perch in the woodland north of the lake.

If you cast your mind back to this time last year, you might remember that Kuyurnpa took similar steps with her learning to fly. This is obviously part of a young eagle's progression to independence, learning to ride the air currents and move about the landscape in the easiest possible fashion, before they one day leave home and fend for themselves. Kuyu left home at the end of March... when will Jarrakanpa make his departure?

To the South... then North

Jarrkanpa is flying high! Check out the GPS fix shown above on the left (click image to enlarge the map) - the altitude reading shows a very modest 2200m above sea level, which is about 1.7 kilometres high! Clearly this young male eagle is learning the ways of his wings, and after 6 weeks in the air is moving about the country with confidence. You can also notice how he has moved quite far away from the small cluster of points near his nest that we saw in the last update, roosting about 2.5km south-west on the second day of this New Year, then on 5th January, roosting ~3.5km north. The point far west into Wallu's home range can probably be explained by its altitude: when soaring on a thermal at such height, it is probably very easy to drift away on the wind and end up quite a distance off course!

It certainly has been a thrill to watch this young male eagle spread his wings with every week. It only seems like yesterday that Kuyurnpa was doing the same thing, branching out further and further from her days of nest confinement. What is she up to now?

Contrary to her normal behaviour of vast wanderings, Kuyurnpa has remained settled in a 'home range' since 31st October, when she sailed in after a fortnightly foray to Lake Carnegie. This small area north-east of the Pilbara town of Newman is about 100 km in diameter, and it's the second time Kuyu has spent more than a month here. The big question now is WHY? There are almost certainly other wedge-tails in this area, but it would seem too early for her to have paired up (previous research has shown most breeding wedgies are more than 5 years old). Perhaps the food supply is particularly good there... but we won't know for sure until I get out there for a look!

A map showing the location of Kuyurnpa's current 'home range', nearly 400 km from her natal nest.

Staying Put

Home is where the eagle stays! Today marks the 560th consecutive day that our wonderful Wallu has spent in a fixed home range at Lorna Glen in central Western Australia. Except for a few days where he was recorded about 60 km east of his territory for part of the afternoon, Wallu hasn't left home, roosting here every night for the past 18 months. This is a relatively small area for a large eagle, especially in such an arid environment, a sign that food supply in this habitat is ample. At the beginning of this study I expected the home range to be at least 100 km², but Wallu occupies an area less than half this size. In the future tracking more adult eagles will give us a better idea of the average home range in this landscape.