Sunday, 21 July 2013

Wallu feeding Wurru

Today I looked at our eagle data for the last 3 days, and noticed a slight pattern in Wallu’s daily routine. Around 10 or 11am, he is recorded as being AT one of his nest sites – Nest 57 – which, as we discovered early on, was in mid-June being freshly lined in preparation for use. Wallu’s fixes show us that he begins the day near the rabbit warren (probably hunting), then delivers a kill to Wurru, who I think is incubating eggs on Nest 57, and takes over sitting duties for a short period while she feeds away from the nest. When she is full of ‘roo or rabbit and ready to sit again, Wurru returns to incubate and allows Wallu to fly. Judging by the large distance between fixes, he might well be spending the rest of his day performing territorial duties at the far boundaries of his patch.
It really looks like our Wallu has his work cut out this year!
More updates soon.

Thursday, 18 July 2013

Gidjee nest update

Gidjee is still incubating!
Imagine sitting in a tree all day with this view. This is what our female eagle is doing at the moment during the incubation period.

Her movements today show, well… no real movement! This is a good sign that she has settled on her clutch of eggs and is well into the incubation phase of this year’s breeding season. Mulga is obviously doing a good job at providing her with food, allowing this dedicated incubator to focus on the task at hand.

Monday, 15 July 2013

Speed Dives

How fast does an eagle fly? It’s probably quite a common question, but not something that is easy to answer as wedgies don’t fly past multi-novas very often! Luckily, one of the many variables our sophisticated PTT devices have the ability to record is speed, measured in knots. I’ve been keeping track of the speeds recorded at each GPS fix and not noticed anything that exciting. Both Wallu and Gidjee are usually stationary (i.e. perched, or, in Gidjee’s case, incubating eggs), or when they are in flight, they cruise at relatively low speeds of 5 – 10 knots, roughly 10 – 20 km per hour.
But today something awesome came through.

Check out this fix:

It was taken on Wallu at 11 am 2 days ago as he dived from the sky. If we convert knots to km/h, it clocks him at nearly 70km/h!! For a large bird of prey this is quite impressive. I hadn’t really paid much attention to speeds prior to today, but this fix made me light up and scroll back through the last couple of weeks’ data, and notice a faster dive occurred on 5th July at the same time of day, when Wallu travelled at 80km/h! How cool is THAT!?

Why so fast?
Currently we are in the breeding season, and it’s known that male Wedge-tailed Eagles defend their territory with aggressive aerial displays. They dive from the heavens like a bullet, showing the two white dots which are clearly visible at the point where each wing joins the body, on the dorsal surface. To another eagle these dots would appear as bold markings, and in a display dive indicate to their neighbours that means ‘I’m a big scary object at high speed, so don’t come near my patch – it’s taken’!
There is also the possibility that such a fast dive is in response to a sudden appearance of a prey animal. Or, when deciding that he needs to be closer to ground level, he might as well do it in the quickest fashion possible! If you can – why not? I know that if I was capable of stooping from the sky in a controlled fashion, I certainly would!  

Monday, 8 July 2013

Gidjee in a nest – but nest in a gidgee!

By visiting some of the favoured roost trees of our two eagles, we have been able to see on-ground what these places look like, giving us a good idea of the birds’ reasons for being there. We discovered a couple of weeks ago that Gidjee was frequently roosting quite close to a small patch of gum trees inside the fenced enclosure, and the reason for this was she and her mate Mulga had built a new nest here. I could tell by its good condition that this nest had been newly constructed and was most likely the site at which Gidjee and Mulga would breed this year.
However, today I know my predictions were wrong.

The above tracking data shows Gidjee’s behaviour over the last few days has contracted to a small spot on a ridge overlooking the fenced enclosure. On the 2nd, 3rd and 4th July she spent most of each day at this location, only moving away a few times. This behaviour aligns with her making the final preparations at a nest by adding fresh leaves to the nest cavity, and spending more time there prior to laying. Considering we are expecting her to be laying eggs soon, we would assume she would be closing in on Nest 63, if this was her chosen nest in the 2013 breeding season. Apparently it isn’t!
I can now see that Gidjee and Mulga must have another nest, one we have not yet located, on the ridge, and THIS is where she is breeding! Being situated in this prominent location means the nest is almost certainly in a gidgee tree, hence the title of this blog post. Since the three days shown above, almost all the daily fixes have occurred at this same point, with Gidjee only leaving the nest briefly during late morning or mid afternoon, probably to receive a meal from Mulga (male wedge-tails usually feed their females on the nest during incubation). Each time we get a fix on her being away from the nest for some time, this almost certainly means her mate is incubating the eggs while she takes a break. Such is the cooperation present between well-bonded adult Wedge-tailed Eagles.

Tuesday, 2 July 2013

Altitude Findings

I am now back in Perth, 1200km away from the Lorna Glen eagle study site. But every 3 days, a nice little package of GPS coordinates streams into my computer telling me what our two adult wedgies, Wallu and Gidjee, have been up to. After just over a fortnight of tracking, we are starting to see some really amazing stuff! Here’s a little video to share with you the wonders of GPS PTT technology:

Wedge-tailed Eagle Satellite Tracking from Simon Cherriman on Vimeo.