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Texas Zoo column: Animals see in variety of ways

April 10, 2011 at 8:03 p.m.
Updated April 9, 2011 at 11:10 p.m.

A burrowing owl scans the horizon with its large eyes while sitting outside its hole in Yuma, Ariz. Owls see in shades of gray and have fixed eyes, so they have to turn their heads to see.


When Little Red Riding Hood arrived at Grandmother's, she was not dressed for success!

The wily wolf in Granny's nightie was probably partially color blind and somewhat near-sighted, but he could see red. He had great peripheral vision and night vision far superior to ours.

Animals process images differently depending on the species and the make up of their eyes. Vertebrates (animals with a spinal column) focus on objects in a camera-like way. Photo receptors called rods and cones line the eye's retina and detect light and color. Rods allow vision of shapes in the gray tones of dim light. Cones are activated by brighter light, allowing more color vision. The shape of the eye and the placement and numbers of rods and cones all make a difference as to how color is perceived. Wolves have red/blue photo receptors, but not green, as people do. The grayscale receptors (rods) in their eyes outnumber the color receptors (cones) by 95 percent.

Some animals see color and patterns that humans cannot. Honeybees and butterflies see green, blue and ultra violet, but not red, even though they visit red flowers. They smell the nectar, but are able to see ultra violet patterns on flower petals. These patterns are invisible to our un-aided eyes.

Bulls are red/green color blind, so a matador's cape would appear gray, not red. It's most likely the movement of the cape that irritates the bull.

Many birds have high numbers of cones and see even more color and patterns than people. Nocturnal (night active) owls are an exception. They have mostly rods and see in shades of gray. Their eyes aren't a typical ball shape, but elongated tubes. They're very large and fixed in bony sockets with no room for muscles to move them. The owl must turn its head to see to the side, up or down. Owls tend to be far-sighted and slide their heads back and forth to help focus.

Deer can't see the color orange. Our pet cats and dogs have limited color vision. It's generally thought that most animals have at least some color vision. The more vivid the species; the more apt it is to be able to see a larger range of colors.

Diurnal (day active) animals are often more colorful. It's more important in their brighter world. Nocturnal (night active) animals have much less need for color in their dimly lit hours of activity. There are millions of animal/insect species with many variations of sight capabilities.

If you'd like to test your rod and cone abilities, try this - on a clear night, look at the stars head-on. Their image projects onto your cones. They'll be difficult to distinguish. Then look at the stars just a bit off center, allowing their image to fall on your rods. Suddenly, the stars will be much clearer. This is because rods are terrific dim light receptors - and if you happen to see Red Riding Hood, tell her to wear green!

Judie Farnsworth works for the Texas Zoo in Victoria.



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