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From: mjm@oliven.olivetti.com (Michael Mammoser)
Newsgroups: rec.birds
Subject: Re: HEAD JERKING OF WALKING BIRD
Message-ID: <49264@olivea.atc.olivetti.com>
Date: 13 Aug 90 20:23:21 GMT
References: <1990Jul28.033019.5059@ddsw1.MCS.COM> <63474@oliveb.atc.olivetti.com
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> 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.

	Well, I found a reference that disputes the idea about distance
judgement. It is in "Bird Behavior" by Robert Burton.

	"Birds other than owls have to judge distances by a number
of tricks,... Bobbing the head gives views from different angles and
makes objects move in relation to the horizon so their position can
be judged."

	"When pigeons and peacocks walk, they nod their heads to and
fro, but this has a fifferent function from head bobbing. They are
stabilizing the head, throwing it forward then keeping it steady while
the body moves up. With the head steady, the eyes are better able to
pick out tiny objects and slight movements."

Mike