From: jespah@carson.u.washington.edu (Kathleen Hunt)
Newsgroups: sci.bio
Subject: Re: Are most deer colorblind???
Date: 16 Nov 92 19:39:18 GMT
Article-I.D.: u.1992Nov16.193918.19728
Organization: University of Washington, Seattle

>
>	I've often wondered how most deer hunters can get away with 
>wearing outrageously flashy clothes, such as fluorescent orange jackets,
>and not (presumably) have any effect on their tracking down deer. Can't
>the deer see them more easily with such gaudy attire? I have assumed
>that most vertebrates have color vision; are deer an exception? More 
>general, I'd like to know more about color vision among vertebrates. 
>What mammals, in particular, cannot see color?

One of my physiology texts here says "Color vision has been demonstrated
in all classes of vertebrates", but I think the only class it is
really widespread in is the birds.  Most birds have superb color vision, with
tons of cones, visual pigments, and special colored oil droplets for 
contrast, in addition to UV sensitivity.  Gill's "Ornithology" text says flat
out "The richness of avian color perception is probably beyond that of 
human experience."   Mammals on the other hand usually don't have very good
color vision -- especially nocturnal mammals.  Diurnal mammals, like squirrels
and primates, especially fruit-eaters, tend to have very good color vision
but a lot of the other mammals have some poor excuse for color vision or
none at all.  Usually careful studies reveal *some* sensitivity to color but
it's usually not comparable to what we're used to.  For instance cats can
distinguish pink from grey, but that's about it. (Of course they can 
distinguish all different shades of grey, too.)

Deer are often said to be color-blind, but they actually have
a bit of color vision.  Here in "The Natural History of Deer", Rory Putman 
says that fallow deer have "crude and partial color vision" AT CLOSE RANGE.
"Beyond 60 meters, however, it is unable to distinguish color at all," says
Putman, adding that fallow deer can't even distinguish shape at 60m, but
are excellent at detecting movement.  I've heard this book was sloppily 
put together, though, so you may want to hunt down a better reference.

A general rule of thumb for figuring out if an species has color vision is,
do they eat brightly colored things (fruits, flowers) or communicate with
each other with color in some way (bird plumage, lizard dewlap displays)?
In other words would color vision be useful for them in some way?
For instance, bees, which are attracted to flowers by vision (and scent) have
great color vision, including UV (but apparently not including long wavelength
reds that we can see).  I've heard that coral reef fish have good color
vision, too, which makes sense given the environment they live in and their
colorful mating displays.  Lizards may have good color vision, as they have
a lot of cones in their retinas.  I don't know about amphibians.

Some other notes:  Birds & many insects can see UV light.  Surprisingly the
human retina is also sensitive to UV light, but the UV gets filtered out
by the lens.  People who have had their lenses removed because of cataracts
report that they are suddenly able to see UV.

Many animals can detect the plane of polarized light, most famously the
honeybees (navigation, the waggle dance, all of that), but also horseshoe
crabs, octopi, some fishes, pigeons, lizards, & more.  Seems to be important in
orientation in a lot of animals.

Rattlesnakes & their relatives have directional sensitivity to infrared
(heat) radiation, so in essence they can see in infrared.    

Stop me or I'll start babbling about homing pigeon experiments and bee
cognitive maps and toad movement detectors.  :-)

Kathleen
-- 
Halfway round the course, up spoke the noble rider:  
 "I fear we must fall back, for she's going like a tiger."
Up spoke the noble horse:  "Ride on, my noble master,
  For we're halfway round the course, and now we'll see who's faster."