Dear WW and Faldage: Here is a sensational URL about bird vision. I confess I haven't read it all yet.
http://www.biology.eku.edu/RITCHISO/birdbrain2.html

Just a brief glance looks fascinating. Thanks, Dr Bill.

I'd just like to understand how those fast fliers navigate through the woods so quickly without apparently hitting themselves in the head with so many branches. I sure as heck have problems sometimes woods navigating at a lethargic pace.

another great site, Bill! thanks!

Dear WW:One of the birds' secrets is the fact that their nerve pathways are relatively short. It takes an appreciable fraction of a second for nerve impulse to travel from brain to an extremity, so small animals can react much sooner than humans can.
I think the big dynasaurs must have had to wait a week for message from brain to reach their hind legs.
Remember the old parlor trick of telling a kid he can have a dollar hung vertically between his thumb and index finger, if he can close them before dollar drops through them? Kids look very much amazed.

Oh, many thanks, wwh, for that explanation. I have often wondered how in the world birds navigated so quickly through dense woods. The short nerve pathway does make some sense as a theory, so thanks for giving me that fodder to ponder!