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From: sonny@charybdis.harris-atd.com (Bob Davis)
Newsgroups: rec.birds
Subject: Re: HEAD JERKING OF WALKING BIRD
Summary: The head don't move, folks...
Message-ID: <4082@trantor.harris-atd.com>
Date: 5 Aug 90 22:52:26 GMT
References: <1990Jul28.033019.5059@ddsw1.MCS.COM> <63474@oliveb.atc.olivetti.com>
Sender: news@trantor.harris-atd.com
Reply-To: sonny@trantor.harris-atd.com (Bob Davis)
Organization: Advanced Technology Dept., Harris ESS, Melbourne, FL
Lines: 24
X-Local-Date: 5 Aug 90 15:52:26 PDT

In article <63474@oliveb.atc.olivetti.com> mjm@oliven.olivetti.com (Michael Mammoser) writes:
>
>This difference (parallax) is the way that we make accurate
>judgements of the distance that the object is at. Birds with 
>monocular vision are viewing a distant object with only one eye.
>They bob their heads back and forth to shift the position of
>their eye in order to provide this parallax. Sounds logical anyway.
>
>Mike
> 
NO, NO, NO. As another poster to this thread has already
accurately observed, THE HEAD IS RENDERED ABSOLUTELY IMMOBILE 
RELATIVE TO THE EARTH by the bird's "head bobbing" motion as it walks. 
Look at it closely. I often have marvelled at just how totally motionless the
bird is able to hold its head as it walks. What an effective biological servo
control system this is!


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