LOS ANGELES, CA (Catholic Online) - Scientists have discovered four major adaptations in owls designed to prevent injury. The birds' unique bone structures and vascular systems let them move their heads with increased flexibility.

Studying snowy, barred and great horned owls, researchers at Scientists at the Johns Hopkins University School of Medicine examined the birds after they died from natural causes.

Researchers found a vertebral artery enters the neck higher than in other birds, creating more slack. Unlike humans, owls were found to have small vessel connections between the carotid and vertebral arteries, allowing blood to be exchanged between the two blood vessels, creating an uninterrupted blood flow to the brain, even if one route is blocked during extreme neck rotation.

This trait allows the owls to have a huge range of vision without having to move their bodies or arouse detection by prey.

Scientists concluded that the lack of similar adaptations in humans could explain why humans are more vulnerable to neck injury.

"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," Study senior investigator Doctor Philippe Gailloud said.

"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."

Researchers studied the bone and blood vessel structures in the heads and necks of the birds.

Using an injected contrast dye, researchers highlighted the birds' blood vessels, which were then dissected, drawn and scanned to allow detailed analysis.

The most striking finding came after researchers injected dye into the owls' arteries, mimicking blood flow, and manually turned the animals' heads. Blood vessels at the base of the head, just under the jaw bone, kept getting larger and larger. As more of the dye entered, and before the fluid pooled in reservoirs.

This contrasted starkly with human anatomical ability, where arteries generally tend to get smaller and smaller, and do not balloon as they branch out.

These contractile blood reservoirs act as a trade-off, allowing owls to pool blood to meet the energy needs of their large brains and eyes, while they rotate their heads.

The supporting vascular network, with its many interconnections and adaptations, helps minimize any interruption in blood flow.

"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," Gailloud said.

"Extreme manipulations of the human head are really dangerous because we lack so many of the vessel-protecting features seen in owls."

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