Owls’ head-spinning secrets revealed

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A girl rotating her head 360 degrees was one of the scariest moments in the horror movie The Exorcist. But owls are capable of performing virtually the same feat without any help from a possessing demon.

Now scientists have solved the mystery of how the birds can swivel their heads almost in a complete circle without suffering serious injury. It has nothing to do with the supernatural, but is the result of uniquely evolved features of their bone structure and blood vessels.

The night-hunting owl can rotate its head up to 270 degrees as its eyes survey the ground for prey. If other animals tried to do the same, fragile arteries in the neck would stretch and tear, producing deadly blood clots.

“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 Dr Philippe Gailloud, one of the researchers from John Hopkins University School of Medicine in Baltimore, US.

The team looked at the bone structure and network of blood vessels in the heads and necks of snowy, barred and great horned owls that had died from natural causes. Dye was injected into the owls’ arteries to mimic blood flow, detailed X-ray scans conducted, and meticulous dissections carried out.

The researchers, whose work is reported in the journal Science, discovered several unusual structural features that appear to be unique to owls.

They included wide tunnels in the neck bones through which arteries ran to the brain. The cavities were around 10 times wider than the vessels passing through them, creating air pockets that allowed the arteries to move around when twisted.

Blood vessels at the base of the head ballooned as they branched out – meaning they could pool blood to meet the energy needs of their large brains and eyes.