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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