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The near-complete rotation of the head of a night-hunting owl has remained an object of mystery for several years and hence has been a favorite subject of horror stories. Now, a recent study has unraveled the mystery by performing medical examination on owls.

Dr. Philippe Gailloud of Johns Hopkins University School of Medicine was the senior investigator of the study, which was published in the journal Science.

In the research, scientists used angiography, CT scans and other medical tools to study the anatomy of around 12 birds. It was observed that owls have four distinct adaptations which are unique. All these adaptations are centered around the birds' bone structure and blood vessels that are needed to support the heavy head of an owl.

The scientists found that when the head of an owl is turned, the blood vessels present near the neck of the bird are able to expand outwards like a balloon, which acts a storage device to supply extra blood needed by the head and the eyes when the head is turned. The human neck, on the other hand, decreases the blood vessel size when the neck is turned, thus restricting the movement.

"Until now, brain imaging specialists like me who deal with human injuries caused by trauma to the 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. The carotid and vertebral arteries in the neck of most animals-including owls and humans-are very fragile and highly susceptible to even minor tears of the vessel lining," Gailloud said in a University news release.

A dye injection was passed through the blood vessel of owls that had died of natural causes and this caused a pseudo blood flow to mimic the natural blood flow of the animal. It was also found that the owls have exceptionally big cavities in their neck through which the blood vessels pass, thus giving them more room for neck movement. These cavities also ensured a smooth blood flow even when the bird rotates its neck to its highest capacity of 270 degrees.

"Moreover, our new study results show precisely what morphological adaptations are needed to handle such head gyrations and why humans are so vulnerable to osteopathic injury from chiropractic therapy. Extreme manipulations of the human head are really dangerous because we lack so many of the vessel-protecting features seen in owls," Gailloud added.