Is it true that some birds can see only movement -- that they cannot "see"
something that is not moving? I've recently had this suggested to me, but
I'm not sure I see the sense of it. Is there such a condition in nature?
If so, what is it called?
I can't imagine that this could be true as stated - how could birds build
nests accurately (say) if they literally could not see inanimate
objects? However, an increased acuity to movement could well be present (I
have heard it suggested that this is the chief advantage of the compound
eye structure of insects), or simply a hightened response to movement as
opposed to inanimate objects, with no difference in acuity. It has been
suggested that the pecten, a comb-like structure at the back of the eye,
serves to pick up movement, but it may have more to do with nutrient supply
and pressure regulation (the pecten is highly vascularized). There is a
good article on "Vision" in "A Dictionary of Birds" (Lack and Campbell,
eds, 1985).
--
Ronald I. Orenstein Phone: (905) 820-7886
International Wildlife Coalition Fax/Modem: (905) 569-0116
1825 Shady Creek Court
Mississauga, Ontario, Canada L5L 3W2 mailto:ron.orenstein@rogers.com