Tuesday, 18 June 2013

Tracking them Down



The excitement out bush continued today when we spotted an eagle perched in a dead tree not far from Trap 2, the location at which Wallu was trapped last week. A closer look at the bird revealed it was a large female – Wallu’s mate Wurru! I knew he couldn’t be far away, and minutes later I saw him perched in a live gidgee tree on an adjacent hill. He flew as soon as I left the vehicle, as did the female, but we noticed both birds settled in another dead perch tree a few hundred metres off the road. Although the odds were it was Wallu, I needed to sight his PTT (transmitter) to confirm. Neil and I stalked them, keeping hidden behind a small ridge, and managed to get within about 100m.

I set up my long zoom-lens and framed both birds – Wurru facing sideways, the male facing us front on. Where was the PTT!? I couldn’t see his back! As though hearing my thoughts, he suddenly turned around and revealed his back… and I saw it! The PTT sat perfectly, aerial probing skywards. He was alive and well!
Wallu's PTT is visible as he turns to fly from the perch tree.

A sighting of Gidjee earlier that morning revealed she was also doing fine, flying low over the pen not far from her release site. We now had a couple of records of our eagles since their release, making us confident they’ve resumed their normal lives. Tracking information from the PTTs also confirmed this, and for the first time we have been able to view the birds’ movements and ‘see’ what they got up to after we released them. Here’s a map of Wallu’s story…

 
You can see from this amazing imagery (thanks to Google Earth!), Wallu roosted on a hill about 1km from the trap site (green circle). First thing the next morning, he flew straight to an area bordering the lake system and spent a few hours there (blue circle). (Later inspection revealed this site was a rabbit hotspot, littered with piles of dung, diggings and a few large warrens. It wasn’t surprising – the day after trapping, Wallu was hungry, and flew nearly 4 kilometres to exactly where he knew he could get a meal). He then returned to the ridge to the north of the trap site and spent some time at one of his nest sites, roosting that night close by. The next day was spent close to this nest site, possibly because he was helping Wurru gather lining for it in preparation for the upcoming breeding season. Yesterday at mid-morning, Wallu again made a beeline to Rabbit Ridge, probably for another feed, before flying to perch near the road where we sighted him

'Rabbit Ridge', showing one of the perch trees Wallu has been using on the right.
The map from Gidjee’s territory also reveals her movements, shown in close proximity to the fenced enclosure (blue line) containing many reintroduced native mammals… 


We know Gidjee roosted not far from the trap the night of her capture (shown by the red circle just above 'Trap 1' in the above map). The next day she spent the morning on the ridge overlooking the enclosure, before perching in a tall patch of eucalypts on the plains below (yellow circle). Roosting nearby that night, she began her Monday morning with a flight above the nearby ridge, then spent the afternoon perching in patches of tall eucalypts, both in the enclosure (near an active Boodie warren), and then another patch further south of the enclosure. This behaviour may well be associated with investigating possible prey areas: these eucalypt areas are productive, usually supporting good numbers of rabbits, kangaroos and birds.
Later on we visited the area of tall eucalypts inside the pen and discovered Gidjee and her mate Mulga had built a new nest here! This is probably in response to an increase in prey density inside the fenced enclosure, as the native marsupials thrive in the absence of feral cats and wild dogs. More light will be shed on Gidjee and Mulga's breeding in this new nest as the year progresses.


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