How Owls Spin Their Heads Around

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Fabian de Kok-Mercado (left) and Dr. Philippe Gailloud give a CT scan to a dead owl to learn how its blood vessels withstand the rapid, up-to-270-degree turns their heads make.
Fabian de Kok-Mercado and Dr. Philippe Gailloud

The large holes and "slack" at the bottom of the neck help explain why the vessels don't break. But they don't explain why the supply of blood isn't cut off when an owl turns its head — with so much twisting, the vessels are bound to become partially blocked.

Blood to the brain

The team noticed that the vertebral artery enlarges slightly as it approaches the brain, which is unusual and not seen in many other animals (like the trunk of a tree, vessels generally get smaller as they get farther from the heart). The authors think that these enlarged areas may function as reservoirs in which blood can pool, so that the brain has extra blood to work with as the head swivels around, de Kok-Mercado said.

The blood vessels near the brain are also highly connected. A vessel called the patent trigeminal artery connects the front and the back of the owl's brain, which helps supply the organ with as much blood as possible.

Why do owls need to crane their necks to such an extreme degree? It's because their eyes are tubular, built almost like telescopes, giving them amazing vision, de Kok-Mercado said. But unlike humans, who have roughly spherical eyes, owls cannot move them about easily, so they have to rotate their heads.

The finding is just another example of how the birds are perfectly adapted to suit their environment, enabling them to see despite having relatively fixed eyes.

"I hope it gives people more of an appreciation of the life on this planet," de Kok-Mercado said.