By Diane Darrow
As a big-city dweller, I often like to sit on a bench in my local community garden appreciating nature – the clean, fragrant air; the trees, plants, and flowers; and the many visitors that pass by on the paths and lawn.
I particularly enjoy looking at the avian visitors because the garden attracts many kinds of birds.
One day I was struck by the differences in eyes between people and birds. People have basically almond-shaped eyes, with a colored circle, the iris, in the center and whites tapering to the ends.
Most of the birds I see – such as sparrows, robins, blue jays, and doves – have tiny, round, all-black “boot-button” eyes. I wondered about that difference, so I did a bit of research.
Boy, did I learn a lot! For one thing, it seems that birds actually have very big eyes. They do have whites, but in most species, we can’t see them: Everything but the iris is covered by feathers. And birds’ eyeballs are huge in proportion to the size of their heads. If human eyes were in the same proportion, our eyes would be as big as tennis balls.
Next, birds’ eyes are positioned on their heads differently from the way ours are. Human eyes are set forward on the face, so we can see straight ahead with 3-D binocular vision. That’s true of only a few bird species (owls, for instance.)
Most birds have eyes that angle out to the sides of their heads, so their brains have to reconcile two separate, overlapping fields of vision to see what’s directly in front of them. Oh – so that’s why I often see a robin tilting its head sideways to focus its “good eye” on something on the ground!
Birds’ eyesight is also much sharper than ours. We think we’re doing great if we come close to 20-20 vision. Most birds would score at least 20-10 on our scale. That means, if I’m squinting to see an object lying some distance along a garden path, the blue jay on a branch above my head can see it as clearly as I could if it were only half that far away.
If it’s edible, he’ll grab it.
Moreover, birds’ eyes have at least twice as many light-sensitive cells as human eyes, letting them see much better than us in low light conditions. And beyond the top of our visible color spectrum (red-orange-yellow-green-blue-indigo-violet), birds can see ultraviolet light, which makes colors appear far more brilliant and differentiated.
So now whenever I see plain, dull brown or gray birds in the garden, I try to imagine what they might look like to each other – or what I must look like to them!