Tuesday, 27 January 2015

An Early Death

Yesterday I received the sad news that Jarrkanpa was unfortunately found dead. Recent tracking data downloaded on 20th January showed a lack of movement on the afternoon of 15th and for the whole of 16th 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 12th 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)
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.

Tuesday, 20 January 2015

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?

Saturday, 10 January 2015

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.