[obol] Bird vision - (later)

[Dan Gleason]

A few days ago, Cindy Ashy asked many questions about bird vision in  
relation to UV light. I promised her that I would respond later when  
I had more time. I just wanted to let everyone know that I still plan  
to do this but life sometimes has its own ideas about where your time  
is needed that differ from what was planned. I don't have time to  
write the book (or do the years of research) to make a through  
response but I promise that I do plan to send more information along  
soon. Bird vision is a fascinating topic and I would like to share  
what I know with anyone interested.

Over the next two weeks, I have two articles to write and three  
public presentations to finalize and assemble in addition to my  
routine chores but I plan to write more about vision as holes in the  
schedule come up. A portion of this will be extracted from the new  
textbook that I am currently working on so I don't need to start  
completely from scratch. Cindy asked many interesting questions and  
I'm not sure that I can give a good answer to them all but as least I  
can give some input on some of them.

One thing is sure, our avian friends have the best visual systems of  
any vertebrates and we can never fully appreciate it because we  
simply don't see that well or in the same way. The discussion started  
with a comment about urine fluorescing in the UV and that Eurasian  
Kestrels find voles by this UV fluorescence. But avian vision is much  
more complex that UV fluorescence. The ability to see UV is  
independent of fluorescence.

Much more later but one brief aside. Humans also have retinal cells  
sensitive to UV light, at least some UV near the visible spectrum.  
Our cornea and lens filter out these wavelengths but if not filtered,  
the retina would see this light. I had a friend who had cataract  
surgery many years ago when the procedure was much less simple. The  
artificial lens that was implanted was defective and did transmit UV.  
He was offered a replacement lens to correct this but refused. He was  
a botanist and found this new ability to be useful. He was now able  
to see the nectar guides in some flowers. These are patterns on the  
petals or sepals that insects use as a signal to find the flower or  
entrance to the flower. These are often found on night-blooming  
flowers that are pollinated by moths and most insects also see UV.  
Since many of these patterns are only visible in UV, we do not  
usually see them but Don now could. What he did find distracting was  
the stage lights in a concert hall. The curtain would rise during a  
stage production. We would see a darkened stage before the lights  
came up. But the large, overhead stage lights produce stray UV light.  
He saw the details on the stage flooded in purple light.

Dan Gleason
-------------
Dan Gleason
dan-gleason at comcast.net
541 345-0450


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