How do birds see?

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Wilf James

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How do birds see?
« on: 19/04/2011 16:30:03 »
Wilf James  asked the Naked Scientists:
To The Naked Scientists

I usually hear the podcasts a week or two after they are are posted on your website.  This is why my thoughts about the way birds see could be way out of date.

The birds that I am most familiar with are pigeons and chickens.  Both these birds have a similar way of bobbing their heads backward and forward as they walk.  It seems that they obtain still sideways views as the backward head movement cancels the effect of the bird's forward movement momentarily - long enough to obtain a still image.  Since it seems reasonable for a bird to see in a similar way to us humans, it follows that it concentrates on one thing at a time. This means that the bird's concentration is on the view from one eye for one moment and the view from the other eye at the next moment. This means that the bird is momentarily blind on one side or the other as it walks along the ground.  (This reminds me about the way dolphins sleep.They can apparently sleep with one half of their brains at a time.) It is obvious that a bird to has some binocular vision when stationary.  It is clear that a pigeon or a chicken can aim its peck at a very small object in front of it.

This leads me to an aspect of vision that I am very familiar with. I have a mixture of slight short sight and astigmatism. (About a dioptre on both.)  I therefore hypothesise that a bird like a pigeon is short sighted when using binocular vision and long sighted or normal sighted when looking sideways.  If my hypothesis is correct it accounts for the fact that birds can't see large vertical objects  in front of them very easily.

I don't know how fast birds can switch the left-right concentration when flying but I imagine that it could be at a rate of around ten times a second.  They take snapshots of the views as quickly as humans blink or even more quickly.  This could cause a form of stroboscopic effect with rotating obstacles like turbine blades.  With some birds the switch rate could be comparable to the rotation speed (times 3 with a wind turbine) giving the effect to the bird that the blades are moving slowly or even stationary.

Another possibility is that when flying a bird still takes short snapshots on either side but reduces the frequency at which it takes fresh views.  If the snapshots are short enough, relatively slowly moving objects will appear to be stationary as happens when an electronic flash is used to freeze movement in photography.
A further point is that a string of wind turbines will turn at exactly the same speed because they are designed to synchronise with the frequency of the electricity grid.  Thus all the turbines in a set will appear to be slow moving if the stroboscopic effect is active or stationary if the bird takes very short snapshot views.

I offer these ideas as possible bases for further research on the ways birds see.

Wilf James

What do you think?
« Last Edit: 19/04/2011 16:30:03 by _system »