Thread the needle: Depth perception in most birds

From: Nicholas Bodley (
Date: Wed Mar 28 2001 - 18:17:18 PST

Loved that one about stretching string from mid-face away from you.
No string handy just now, though...

Someone really knows about this; I'm partly guessing. Many species of
birds (but not owls!) have eyes that share no, or almost no, common
field of view. Seems to me that their double-frequency head motion
while walking allows their brains to store an image from before the
head-jump, and compare it with that from afterward. Brain perhaps
compares the two to give a sense of depth.

Science fair project: Try to use a telescopic lens to take videotapes
of walking birds. See whether their eyes remain fixed with respect to
the background as their bodies move forward.

Much more difficult (Not a school project!): Mount a large-screen
display next to a bird*, and update the display in synch with its
head movements to fool its brain. Update flicker has to be allowed
for. *So to speak...

Nicholas Bodley |@| Waltham, Mass.
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