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!  

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