Geese, a little story . . - a photo on Flickriver

            How do they know to retract and fold up their (swim)feet and keep them in line with their streamlined bodies to reduce drag when flying ?

How do they know that a V-formation is best for them to reduce aerodynamical drag ?
They (birds of passage, geese, storks, pelicans, swans etc.) only fly like that during long distances.

If these birds fly short distances in a group of families, they fly all over the place, and don,t care about their feet or flight formation.

It all has to do with the fact that somewhere in the grey past migrating birds found out that they could fly longer and more easily, using the vortex their frontman created by his downwards wingflap.

Imagine the sinusoid that this vortex creates, on a line-time base behind the first bird.

When that first bird flaps a wing downwards, it compresses the air underneath it, keeping the bird in flight.

But that air (being a gas) wants to recover its former state, and expands again, filling up the relative void it just left behind, forced by the airmasses underneath it that act like a "ground".

That is a dynamic proces on a stationary spot.

But the second bird flies through that stationary spot where this dynamic expanding of air is taking place and benefits from the upgoing air particals hitting the underside of its downgoing wing.

This system can only work for the second (and third, and fourth etc.) bird if he or she keeps a precise distance wherein this natural fenomenon (restoration of the static gas pressure) is taking place. 

For a good understanding, you will have to appreciate, that all of this takes place as a dynamic situation on a static place in the air, where the second bird flies through.

Come to think of it, it even should matter if this process happens in weather with a high pressure field or a low pressure field.

At least theoretically, they would have to fly closer to each other under high pressure weather conditions.

And don't forget that the birds themselves are subject to their frontal area, and that their air resistance depends upon the square of their velocity.

And yes, their downwards stroke is more effective because of the thicker air, but there is a (more streamlined, and the wing feathers open up) upgoing stroke as well, in that same air.

It will cost them more energy, so they fly shorter before having to eat again. (but having covered more land)

They inhale the oxygen more easily that gives them power because of the higher airpressure, but exhaling costs extra energy in the thicker air.

The list of variables is endless, but maybe, in the end, everything equals out to zero . .

Or does it ?

Taken on: February 26, 2018

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Sets appears in: • Airplanes, Kites & Balloons, with a little story here and there . . • KLM more » • Birds . . « less

Camera: Pentax K-5, f/8.0, 1/1600 sec, 150mm (=225mm), ISO 400 (more info) (hide info)

Camera:	Pentax K-5
Lens:	smc PENTAX-DA 50-200mm F4-5.6 ED WR
Aperture:	f/8.0
Exposure Time:	0.001 sec (1/1600)
Focal Length:	150mm (35mm equivalent: 225mm)
ISO:	400
Exposure Bias:	-0.3 EV
Flash:	Off, Did not fire
Exposure Program:	Aperture-priority AE
Exposure Mode:	Manual
Metering Mode:	Spot
White Balance:	Auto
Contrast:	High
Sharpness:	Hard
Color Space:	sRGB
Software:	Adobe Photoshop Lightroom 6.14 (Windows)
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