In an Exorcist-style display of flexibility, owls can rotate their necks a maximum of 270 degrees without breaking blood vessels or tearing tendons.
To the untrained eye, it looks like a case of movie magic, but scientists at Johns Hopkins University School of Medicine now have data to explain the eerie skill that has baffled birders for years.
Whereas people and other animals can simply move their eyes to follow an object or use peripheral vision to scan a room, owls must turn their heads for the same effect.
These birds have fixed eye sockets, which means their eyeballs can’t rotate, forcing them to stretch their necks—a seemingly supernatural feat.
“In the case of birds, their systems are designed to handle that amount of movement,” said Eric Forsman, a wildlife biologist for the U.S. Forest Service, who was not part of the study.
“The tissue, the blood vessels are designed to flex—things don’t just snap.”
Owls are more flexible than humans because a bird’s head is only connected by one socket pivot.
People have two, which limits our ability to twist, Forsman added. Owls also have multiple vertebrae, the small bones that make up the neck and spine, helping them achieve a wide range of motion.
Yet, even with these skeletal advantages, a bird’s body shouldn’t be able to withstand such extreme levels of movement. In people, a spinning head would cause all kinds of internal bleeding and breakage.
For the new research, the Johns Hopkins team obtained 12 dead birds from educational centers and created 3-D images of the animals’ blood vessels and bones.
The scientists also injected the carcasses with dye and liquified red plastic to preserve their arteries before dissection, according to a summary of their research on the U.S. National Science Foundation website.
The team discovered owls have backup arteries, which offer a fresh supply of nutrients when blood vessels get closed off by rapid turning. Their arteries also swell to collect any excess blood created in the process.