Thursday, 26 December 2013

Finding Her Wings

Can you see the eagles there in the sky? Just squint and the dots become eagle-shaped! This amazing snapshot of Kuyurnpa (green dot on the right) shows how much she has progressed since fledging over a month ago. Today at noon, while most Australians tucked into those Christmas leftovers, Kuyu was soaring at 1600m above the ground, accompanied by her mother! This is the first time she has ever been recorded over 1 km up! The other green dots show her progress earlier today before reaching this altitude, and the red ones are those of Gidjee. This mother-daughter team were at the same height at noon today, although they were nearly 1 km apart (but could probably see each other with no problems!).

It seems like only yesterday that Kuyu was still sitting on her nest atop the ridge, seemingly marooned on this tiny island in the vast outback. The first few weeks of tracking data post-fledging showed her moving 'from tree to tree', in a south-easterly direction away from her nest - but now Kuyu is really expanding her home range and covering about one-quarter of the area that her mother Gidjee travels. Here's a quick map of Kuyu's progress, the pink icon showing the nest where her journey began. Where to next? More coming soon!

Saturday, 14 December 2013

And What of Wallu?

Today marks the 6 month anniversary of the day I was successful in capturing an adult Wedge-tailed Eagle, a male we named ‘Wallu’. He was released in a healthy condition and monitored closely for the next few weeks to ensure he coped with his new backpack. Wallu has since remained in the same territory (which we have determined to be about 32km2 in size – quite small for the desert environment in which he lives), giving us amazing insights into his life. He has regularly been clocked at over two thousand metres above the ground, usually soaring but occasionally performing fast dives at 90km/h!
Here is a three-dimensional map showing the ~2700 GPS fixes recorded by Wallu’s PTT since June 2013:

The two ‘outliers’ shown above indicate possible errors in the tracking device’s accuracy: the one at centre top showed an altitude of ~6000m, and the point at far right is about 3km out of Wallu’s territory (as shown by the rest of the fixes). Both fixes may indeed be accurate, but given their location in context of the other points, I am treating them with caution.

So far this data gives a solid backup to what we already know about this species: adults are resident in a fixed territory throughout the year. But what I’m really keen to find out is whether they may leave their home range at any given time. Such information cannot be unveiled without being able to identify individuals, and is another thing to look forward to as our study continues! 

Sunday, 8 December 2013

Spreading Those Wings

It’s now been nearly 2 months since I removed Kuyu from her nest and fitted her with a GPS/Satellite transmitter. About a month ago she made her first flight, and carried on moving away from her nest. Now she is beginning to spread out further and, as the above map shows, she is beginning to move down off the ridge and explore the lowlands.
How is she surviving, and what is she eating? Young wedge-tails like Kuyu are still very much dependent on their parents for food. Viewing her movements alone is interesting, but to provide some context, let’s see what her mother Gidjee has been doing. For a start, we need to zoom OUT! 

This map shows the area covered by Gidjee during over the same time period depicted in the first map above. Our powerful adult female eagle has covered most of her home range in just a few days, soaring as high as 2700m above the ground, and (during dawn and dusk), visiting regular hunting haunts, including some well-wooded areas inside the feral-proof mammal enclosure (possibly hunting for Burrowing Bettongs), and a number of rabbit warrens outside the enclosure. Kuyu is apparently left on her own for much of the day (although keep in mind we don’t have a tracker on Mulga, Kuyu’s father, so he may well be ‘guarding’ her while Gidjee is hunting), but her mother normally roosts within a few hundred metres of her each night, sometimes apparently sharing the same tree.

Take today for example. At 3pm Gidjee came in to meet Kuyu on a perch tree on the ridge, probably delivering some prey. She spent a few hours with her daughter, then between 6pm and 7pm, the two parted and roosted in different trees, with Gidjee moving south and Kuyu heading north. At 4am the next morning our diligent mother was already heading to a favoured hunting place nearly 2 km from her roost.