Who who whoo can turn her head 270 degrees?

Sunday, October 14, 2018

Eyes front!

Text and Photos by Gloria Zmuda Nagler 
Edited by John Wiley Lewis

As Douglas Main notes in his useful essay on owls, owls don’t need eyes in the back of their heads. One of the first things I noticed when our local Barred Owls showed up in our yard was that, as advertised, they can turn their heads from front to back without much effort.

Here are two photos of our neighborhood Barred Owl, and in both her body is facing toward the camera — in one of the two pix, though, her head is turned to look behind her. Can you do that? How do they do that?! Fortunately, avian researchers were curious as well, and did some research.

First, though, why did evolution need to come up with a head that can swivel 270 degrees? Owls have comparatively large eyes for their size, which allows them to attain a large image of prey; however, the round eyeballs humans have would result in too heavy an eye for owls, so nature came up with a tubular eye. Weighs less, takes up less space. Three cheers for Mother Nature!

No design is perfect, though, and the price for smaller, lighter eyes is that owls’ tubular eyes are fixed in position and cannot rotate. Owls, therefore, can’t look quickly to the side — bad news for a predator; hence, the need to revolve their heads! But if you and I tried to revolve our heads 270 degrees we would tear the lining of our arteries, producing dangerous blood clots.

I found two (among many, I’m sure) articles from 2013 on recent research as to why owls can rotate their necks so far. Coincidentally, barred owls were one of the species studied!

Eyes to the rear!
 

Dr. Fabian de Kok-Mercado and Dr. Phillipe Gailloud (see article citation below) looked at CT scans and other evidence to see what happens when the owls’ heads are rotated. They made several findings, and among them: the owls’ neck vertebrae have larger holes than usual (10 times larger than the artery rather than the same size, which is apparently often the case, e.g., in humans) giving the arteries a cushion when they are twisted. They also discovered blood vessels at the base of the owls’ heads which expand to hold more blood to sustain brain function.

If there is magic in the world, it’s evolution!

Sources:
All photos copyrighted by Gloria Z. Nagler

“Owls of the United States and Canada, A Complete Guide to Their Biology and Behavior”, by Wayne Lynch, The Johns Hopkins University Press, 2007

“Solving the Mystery of Owls’ Head-Turning Abilities”, by Marina Koren, Smithsonian.com, discussing the research of Kok-Mercado and Gailloud.

“Biological Twist: How Owls Spin Heads Around”, by Douglas Main, in cooperation with OurAmazingPlanet.com


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