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DollarBirds - Drinking? - or - Dining on DragonFlys??

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Old Sunday 2nd December 2018, 13:23   #1
Chosun Juan
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Question DollarBirds - Drinking? - or - Dining on DragonFlys??

I've always seen DollarBirds whizzing around the Eucalypt canopies - doing their mad aerobatics and going gaga for all the insects up there.

On the weekend I was at a large lagoon in the shade of some big surrounding trees for lunch on a 30+ day, and just happened to have my bins with me. About ~100m away I observed something I hadn't seen before ......

A couple of DollarBirds doing high speed circuits alternately one after the other from their high bare branch perch, right down to the water's surface. These circuits were more or less constant for about ~15mins, and then stopped. They were too far away for me to make out precisely what was going on, even through the 8x.

Were they having a drink? or dining out on something (not necessarily dragonflys)?
Can anyone positively advise based on previous up close observations?




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Old Sunday 2nd December 2018, 14:05   #2
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Could you see if they were making any ripples / splashes? If just picking insects off the surface, I doubt there'd be much of a splash, but if they were drinking or bathing, there probably would be.
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Old Monday 3rd December 2018, 00:41   #3
Chosun Juan
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Quote:
Originally Posted by Nutcracker View Post
Could you see if they were making any ripples / splashes? If just picking insects off the surface, I doubt there'd be much of a splash, but if they were drinking or bathing, there probably would be.
It was a fair way away and they were fairly honking, so it was difficult to see. I think I could safely rule out bathing (perhaps) as there seemed to be no full body splashes - they were also around about ~50m from shore when they were near the surface. I've never seen them bathe, but wonder if they wouldn't just land in the shallows close to shore and flap around?

As they are summer visitors here, I've only observed them a dozen or so times at various locations - a lot of them inland. Having such large mouths - I've mostly seen them going mad for Christmas Beetles, Cicadas, and Dragonflys, etc - large insects. It never occurred to me that they would also hunt smaller massed insects - hoover style - much the same way whales do with krill.

I had a quick search on the net, and could only turn up this reference in a brief time. https://www.google.com/amp/www.shepp...spirit%3famp=1

There did seem to be small swarms of 'midge' type insects at the surface of various parts of the lagoon. This didn't seem to be where they were diving/skimming, close though - maybe I just couldn't see clearly enough.

They seemed to do a circuit (maybe ~1-200m round trip?) one at a time, and then perch for less than a minute and then go again. Alternating in this way. One other snippet is that I don't recall hearing them call.

I don't know whether it was drinking or feeding, but I do remember thinking that if it was drinking, they certainly ended up with a fair gut full of water over time! Still puzzled ......

Any thoughts or experiences welcome :)




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Old Monday 3rd December 2018, 10:10   #4
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Hi Chosun,

Quote:
Originally Posted by Chosun Juan View Post
A couple of DollarBirds doing high speed circuits alternately one after the other from their high bare branch perch, right down to the water's surface. These circuits were more or less constant for about ~15mins, and then stopped. They were too far away for me to make out precisely what was going on, even through the 8x.

Were they having a drink? or dining out on something (not necessarily dragonflys)?
Did they fly a straight line out, or did they zig-zag? I'm asking because the birds I've seen chasing flying insects would manoeuvre continuously and fairly rapidly.

On the other hand, if the prey were weater insects, I'd expect the final approach before the "catch" to be flown into the wind, both to give the bird more time to spot its prey and to reduce the force of water contact.

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Old Monday 3rd December 2018, 12:51   #5
Chosun Juan
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Hi Henning, Nutcracker, these are actually excellent questions, and I should be able to dig around and get some geological and meterological data (though the weather station data comes from about 10kms away or so and down a mountain on the plains! so maybe not that relevant. From memory though, it was reasonably still and the birds were pretty much doing clockwise circuits.

I will get back to you with more details .......



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Old Monday 3rd December 2018, 14:36   #6
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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 !

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 ! :)

I will try and include a bit of a diagram ......
Click image for larger version

Name:	DollarBird flightpath over lagoon_01-12-2018.jpg
Views:	6
Size:	78.4 KB
ID:	681740

Now - any ideas ???





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Last edited by Chosun Juan : Monday 3rd December 2018 at 15:31. Reason: attach pic
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Old Monday 3rd December 2018, 23:50   #7
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Here's a link to a pic of a DollarBird with a more typical 'Christmas Beetle' for lunch ......
https://m.facebook.com/groups/140310...composer=false



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Old Wednesday 5th December 2018, 00:23   #8
Chosun Juan
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Question

Reviewing all of that detail, info, and diagrams, a further thought (question) has occurred to me.

The birds (as most usually do) were using the prevailing weather conditions to minimize the expenditure of energy for their flight, so the question is:

Q/. For those that have observed birds (of any species) drinking on the wing (especially in hotter environments), do they generally do this at a high speed? or a lower speed?

The only birds I have really seen do this are Swifts and Swallows, and they seemed to do this at a reasonably high speed (as they do most things! :) , interspersing it amongst their zig-zagging hunting circles - they may even have been switching between near water surface aerial prey, and surface or just under, prey - I don't know. ie. I don't know whether or not the birds are able to get all the moisture they need from their prey, or whether they require supplimental water?

The DollarBirds I have observed inland have been around woodland tree canopies and very late in the afternoon (understandable on ~40C days). I don't know if they were off for a drink at other parts of the day .....

Surely someone here is very familiar with DollarBird (or the similar Rollers elsewhere in the world) behaviour and observation .....




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