Re: Bird (Dinosaur?) vision

[Mickey Rowe <rowe@psych.ucsb.edu>]

Dann Pigdon <dannj@alphalink.com.au> wrote:

> Apparently night birds like owls that have a lot of rod cells in
> their retina but few cones (if any) can detect prey only if it moves
> or makes a sound.

Color me skeptical.  There was a series of articles published in the
1940's attempting to show the limits of illumination at which owls
could see.  By today's standards the experiments weren't
well-calibrated, but they did show that owls had more difficulty
finding their prey at lower illumination levels.  That strongly
indicated that the animals were using vision for the task whenever
possible.  The task was locating a dead mouse.  At the time, there was
no way to record the animal's behavior directly (cameras, IR image
converters were not sensitive enough), so they performed the
experiment by putting the mouse in an enclosure covered with sand.
The next day, they checked the sand for tracks to see what the owl
did.  At relatively high light levels the owls would pick up the mice
without landing.  At the lowest light levels, the tracks strongly
suggested that the owls walked around in the sand until they
accidentally bumped into the mouse, and I think that sometimes they
didn't find it at all.  I'd have to dig through the literature again
to verify this, but I think the animals tested were Strix and/or Bubo.

Anyways, more recently (e.g., see Animal Cognition 2003 6:39-55) barn
owls have received more attention because studies of their visual
systems suggest that they "see the world" very much like primates do.
Motion is a component of our visual world, but as Jeff Hecht pointed
out, it certainly isn't a necessary feature.

Now granted birds are dinosaurs and all that, but why is this
conversation going on here?

-- 
Mickey Rowe     (rowe@psych.ucsb.edu)