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Re: bird heads



I am not speaking against the stationary head necessary for visible
acuity.  

The simplest method of keeping things level is to rely on gravity to
keep things level for you.  Hanging something such as a plumb bob.  The
vision of birds is basically a slung camera operatus.

I'm contending that 'bobbing'/adjusting the head (specifically) for
visual acuity (new halloween party game?) was greatly reduced or
eliminated during flight.  Walking and hopping is a whole different
kettle of fish from flight.

With ground locomotion you have a shock/reverberation when a foot makes
contact with the ground.  These system shocks pass through the body. 
The bird 'bobs' it's head as a means of adjusting for this bounce to
it's vision.  I'm suggesting that during flight this gravity-induced
repeating vertical shock is reduced.  Wind and air pressure replace
gravity-induced vertical pressure as the biggest shocks to the system.

The bird is basically suspended in the air like a plumb bob is. Thus no
need to physically 'bob'/adjust the head to match body system shocks-the
system has to adjust as a whole unit as the wind/air pressure hits the
whole bird.  

The steady cam is still a good comparison.  A steadycam would use more
of it's steadying functions when filming while walking and less of it's
functions when filming while hang-gliding.  

-Betty Cunningham


Mickey Rowe wrote:
> 
> There seems to be some confusion about my comments on bird head
> movements...  When birds "bob" their heads while walking, the
> important part of the motion (in the hypothesis I described last week)
> is not the sudden forward jerk -- it's the relatively long periods of
> time during which the head is stationary.  Betty appears to think
> she's speaking against the hypothesis when she writes:
> 
> > If bobbing the head was integral to seeing during flight, these
> > would not happen.
> 
> when in fact everything she wrote supports the hypothesis that the
> promotion of retinal image stabilization is an important aspect in the
> control of bird head movements. 
-- 
Flying Goat Graphics
http://www.flyinggoat.com
(Society of Vertebrate Paleontology member)
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