Day 3A: The Eyes Have It

Look carefully at these tiny birds. Before their feathers grow in to hide them, you can see how huge the bulges are where their eyes are hidden. Bird eyes are ENORMOUS compared to the size of their heads. Once the eyelids grow in, they will cover all but a small round part of the eye. Look at a partner's eyes, or at your eyes in a mirror. Our lids open to be oval-shaped and we can see the pupil, iris, and a lot of the white part or sclera. A bird's eyelids open to a round shape, and we can only see their pupil and iris.

Q: Why do human eyelids show more of the eye than a bird's eyelids show?
(Answer under photo.)

A. Human eyeballs can turn and roll to see up and down and to both sides. Our eyelids are shaped as they are so that our eyes can still see when they move side to side. Also, when birds fly, the rush of air has a drying effect. To protect their eyes from drying out, they cover as much of the eye as possible behind skin and feathers. And bird eyes can't roll like our eyes do. Because their eyes are much more "fixed" in the socket, there's no need to have eyelids made for turning eyes from side to side. Birds can't open their eyes any wider than their pupil and iris.

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