How Owls Turn Heads...Without Tearing Arteries

When you jerk you're neck to one side, you're liable to hurt it. Owls, on the other hand, have no such problem. Now scientists have discovered how owls can almost fully rotate their heads without damaging blood vessels or cutting off the blood supply to their brains.

Owls can turn their heads fully 270 degrees--more than twice what humans can handle. In order to find out why, researchers at Johns Hopkins University examined 12 frozen owls. In order to obtain these specimens, one of the researchers, Fabian de Kok Mercado, contacted nature centers that happened to have a stash of frozen owls that had been killed by collisions with cars and other traumas.

The researchers thawed the owls and injected radio-opaque dye into their vessels. They then moved their necks in a scanner to track the flow in real time. They found that, unsurprisingly, owls had several different adaptations that humans didn't.

Owls have four major bone structures and blood vessel adaptations that prevent injury when they rotate their heads. Their neck arteries don't thread through every vertebra, unlike humans. In addition, the vessels that do go through bone have a much wider canal. This makes it less likely that bone will collide with the delicate tissue and injure it.

In addition to keeping their necks from being injured, owls can also keep the blood flowing to their brains. The arteries at the base of the head widen out into reservoirs--unlike in humans who have arteries that narrow the further they are from the heart. These reservoirs create more blood flow, even if they're pinched off elsewhere. A trigeminal artery that connects the front and back of the brain also keeps the blood flowing.

The researchers now plan to study hawk anatomy to see if they possess the same adaptations for the head rotation as owls.

De Kok-Mercado's drawings of this study won a first place prize in the National Science Foundation's annual contest for visualizing science.