Mystery unraveled: Scientists explain how owls swivel their heads

Monday, February 04, 2013
A little owl (Athene noctua), [PHOTO: Stemonitis/CC BY-SA 3.0]
Maryland, United States: A team of scientists has unraveled the ever-perplexing question of how night-hunting owls seems to be able to turn rotate their heads almost fully without damaging the delicate blood vessels in their necks and heads, and without cutting off blood supply to their brains.

The researchers of the team have picked up an international prize in the process.

The Johns Hopkins University’s team, led by medical illustrator Fabian de Kok-Mercado, M.A., a recent graduate student in the Department of Art as Applied to Medicine, found four major biological adaptations designed to prevent injury from rotational head movements.

The variations are all to the strigid animals' bone structure and vascular network needed to support its top-heavy head.

The reason for the neck-turning ability is this: an owl’s neck arteries don’t go through every vertebra and, where the arteries do go through a vertebra, the canal in the bone is up to 10 times wider than the artery inside it, meaning the arteries are less likely to get damaged during rotation.

De Kok-Mercado's award-winning poster, as featured in the journal Science
Now, even with the larger canals, there is still a possibility that the arteries could get pinched and stop the blood flow to the brain. But owls also have a way to get around this problem, the scientists discovered. The arteries that are at the base of an owl’s head widen and pool into reservoirs, whereas human arteries would narrow further away from the heart.

Researchers say these injuries are commonplace, often resulting from whiplashing car accidents, but also after jarring roller coaster rides and chiropractic manipulations gone awry.

“Until now, brain imaging specialists like me who deal with human injuries caused by trauma to arteries in the head and neck have always been puzzled as to why rapid, twisting head movements did not leave thousands of owls lying dead on the forest floor from stroke,” said study senior investigator Dr. Philippe Gailloud in a statement.

The scientists at Johns Hopkins made their discovery by testing dead owls (which died of natural causes) and injecting dye into their necks to mimic blood flow, while moving their heads in real-time in a scanner.

Owls can rotate their necks 270 degrees – more than twice as much as a human can turn. This ability is needed to help them hunt for prey because their large, tubular-shaped eyes cannot move.

The study helps shed light on why humans can so easily damage their fragile neck vessels, while owls can turn their heads almost completely around.

The team plans to test hawks next, to see if they share any of the same abilities that allow owls to turn their heads.
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