(Updated on January 2, 2021) Ever gone owl-watching? You’ve probably seen our feathery friends rotate their heads in ways we can only dream of (or have nightmares about). Most owl species can safely turn their heads an incredible 270 degrees left or right; an owl can basically look at its right side by turning its head all the way to the left, and vice versa.
Humanoids that can turn their heads 180 degrees are the stuff of horror films, though, and with good reason: An ordinary human can only rotate their head about 90 degrees in either direction. Aside from breaking the neck, anything beyond that would also tear the carotid and vertebral arteries, forming clots and leading to a stroke.
Owls don’t have that limitation, though. They have multiple vertebrae in their neck and spine, giving them increased flexibility. Additionally, not all of their neck arteries thread through each vertebra. And when they do, the canals are about 10 times wider than the arteries, preventing arterial damage when owls twist their necks.
Furthermore, unlike other animals whose arteries generally narrow as they go farther away from the heart, owls’ arteries widen out as they reach the brain, making enough room for blood to pool. Experts believe that the reservoirs ensure a steady supply of blood for the brain, even when neck-turning pinches the arteries. Lastly, the patent trigeminal artery connects the front and back of the owl’s brain, keeping the blood flow consistent.
Which is all well and good, because that’s the only way an owl can see anything that isn’t directly in front of it. Owls can’t move their eyeballs; in fact, they don’t even have eyeballs in the traditional sense. Instead, they have tube-like eyes held in place by bones called sclerotic rings. While this means that owls have built-in binoculars in their heads, it also puts them at a disadvantage when it comes to trying very hard not to get killed by things outside of their limited field of vision. Hence, the need for near-The Exorcist levels of neck-twisting.
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Author: Mikael Angelo Francisco
Bitten by the science writing bug, Mikael has years of writing and editorial experience under his belt. As the editor-in-chief of FlipScience, Mikael has sworn to help make science more fun and interesting for geeky readers and casual audiences alike.