What do you think of this fact?
An owl sits on a branch, you walk around the tree, and its head just follows you. It can turn up to 270 degrees in either direction, well past three quarters of a full circle.
Why owls need to turn their heads at all
The owl has no choice. According to World of Owls, its eyes aren’t round eyeballs but long tubes held in place by a bony ring. It can’t roll its eyes and can only look straight ahead. If it wants to look left, it has to turn its whole head.
Its neck is built for that. It has 14 neck vertebrae, twice as many as yours, which makes it very flexible. But flexibility alone doesn’t explain why such a twist doesn’t cut off the blood supply to the owl’s brain.
What researchers found inside an owl’s neck
That is exactly what researchers at Johns Hopkins University wanted to know. According to Mental Floss, medical illustrator Fabian de Kok-Mercado and neuroradiologist Philippe Gailloud examined 12 owls that had died of natural causes, including snowy, barred and great horned owls. To make the vessels visible, they injected contrast dye into them.
They found several adaptations. Under the jaw, owls have blood vessels that can widen like small reservoirs, so blood keeps flowing to the brain and eyes even during an extreme turn. There are also small connections between the major neck arteries that let blood take a detour if one route gets squeezed. And the bony channels that carry an important artery through the neck are much wider in owls than they need to be, giving the artery room to move.
Bonus fact: According to the California Academy of Sciences, the illustrations from this project won first place in a 2012 National Science Foundation visualization challenge.
Not a trick, but engineering
What looks like a party trick from a horror movie is really a carefully built system of bone and blood vessels. Humans don’t have that package, so you’re better off sticking to a quick glance over your shoulder.
The owl can’t move its eyes, so evolution simply gave it a swivel head.