Wow - this rapidly got all very technical !
OK - I really have to wrack my brain here (and I've been on a reasonable amount of opioid painkillers recently, so the memories are kind of like 3rd person! Actually I can't even remember if I had any painkillers that day (I probably would have had a bit of chocolate though), or was just really tired for not having them, and hence not much sleep after a rather bizarre spill on Friday night - the top hooks of my two hiking boots got locked together while I was walking up stairs - I was about to have a monumental stack and had to jump down 2 stairs with my feet stuck together - having 2 ruptured spinal discs the landing was mega painful - hence the treat on Saturday afternoon of two steak sandwiches with egg, bacon, and pineapple, and a brief, slow, and very careful walk along the short flat track under the beautiful tall trees to the waters edge for a relaxing late lunch, and a tiny bit of bino viewing.
The subject of were the birds flying clockwise, or anticlockwise circuits becomes very important. As far as I can recall, they were clockwise, and they were nearly all (90%+?) in that direction ...... I think ! :brains:
OK, let's set the scene here:-
* we are in the southern hemisphere.
* it was the first day of summer.
* the sun rises in the east, travels to north at midday, and then arcs around to set in the west. (actually this is all an inverse perception due to the earth's rotation, tilt, and orbit - but you get the drift
..... a surprising moment of brief clarity there !
* it was maybe about 3 or 4pm in the afternoon - meaning a sun approximately NW in the sky, at an elevation angle of 45°.
* I was sitting on the Northern shore.
* The birds were perched in a tall tree a few hundred meters away just back from the Eastern shore.
* My initial distance estimates were suprisingly accurate - so around about a ~200m or so circuit.
* The birds would fly in a Southern arc out of the tree, dropping down from the 30m or so altitude of the perch ("X" marks the spot in the diagram).
* They would then continue to arc around West, still dropping.
* As they are North/North-Nor-East toward me was when they would get serious about the 'bombing run'. So the sun was facing them from about 45-60° from their left (at an elevation angle of about 45°) if all of that has any bearing on their behaviour - just being a little silly now !
* When they were at the Western most point of the Arc (headed roughly N/NNE), they would honk along and drop from about 10m down to the water surface (or near as dammit). This is where I had trouble because I couldn't determine whether they were slightly skimming the surface to drink and I couldn't see the minor ripples, or whether they were fractionally above the surface.
* After this 'bombing run' they would use momentum to gain elevation back up to about the 10m mark as they arced to the Northerly most point of the circuit.
* Then they would bank and fly in an Easterly arc back up to the perch.
As far as any wind goes, records (at the weather station) show there was a gentle breeze of 10-5 km/hr, swinging around back and forth from NNE, in an arc from N, to NE, to E, to SE, and then back to NNE again - with quite a bit from that ~ NNE direction.
=> So yes, the birds were pretty much using gravity and tailwinds to gain speed, doing some high G tight turns, and then doing their 'bombing run' into the wind, and then using it further to bank and elevate in an arc back to the perch.
So there you have it ! It's very late here (and I'm rather impressed with the factual detail I could provide), but I'm still none the wiser as to what was actually going on.
Blame all of this on prescription drugs, iced coffee, Chewy Caramel Tim Tams and curiosity !
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I will try and include a bit of a diagram ......
Now - any ideas ??? :h?:
Chosun :gh: