How Owls See and Hear
When looking at an owl, it’s easy to notice how large its eyes are, how much of its face is taken up with eyes. But what we see, is only a small part of the whole eye. The lid and the skull hide most of it. If humans had the same eye to head proportions that owls have, our eyes would be as big as grapefruits.
An owl’s eyes are fixed, so it cannot move its eyes from side to side as a person can; if an owl wants to look at something off to one side, it has to move its entire head. But what the owl can do, thanks to specialized neck bones and muscles, is move its head rapidly, far to either side, increasing its field of vision to 270 degrees. That’s almost 3/4 of a circle.
In the retina at the back of the eye, are cones and rods, tiny light-sensitive cells that act as receptors and form images. Cones distinguish colors, function in bright light, and are needed for sharp vision. Rods function in low light or at night. As would be expected with birds that hunt mainly at night, an owl’s eyes contain a lot of rods. But an owl’s eyes also contain enough cones to enable it to see quite sharply in the day; owls are by no means blind in the daylight. In fact, an owl’s ability to see sharply is as developed as in any kind of bird, including hawks.
Rods contain a pigment called visual purple, which is what enables an owl’s eyes to adapt to the dark. Owls can control the pupil of each eye separately, responding to different light intensities from different parts of its environment.
Another attribute that may help account for an owl’s extraordinary eyesight is the shape of its eye. It’s tubular, not spherical like ours. This tubular shape gives the owl good telescopic vision.
Owls have a balance between hearing and seeing. The eyes are in the middle of a disk of feathers, which are highly specialized sound conductors. The owl can flex these facial disks, channeling sound waves to the ears to catch even the faintest of sounds.
An owl’s ears are elaborate structures. They are large vertical slits bordered by flaps of skin in front of and/or in back of the opening. These flaps expand, contract, and adjust the ear opening size.
Many owls have asymmetrically developed ears, that is, the right external ear canal may be a different shape than the left external ear canal and each could be located higher or lower than horizontal on the side of the head. This design enhances depth perception.
With its ability, while flying, to swivel its head from side to side, individually control its pupils, make ear adjustments to accommodate changing sounds, and fly silently, due to its special feather design, the owl is a most formidable and perfect hunter.
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