Neurological imaging experts at Johns Hopkins University, Baltimore, MD, have figured out how owls, which can rotate their heads by as much as 270 degrees in either direction, do so without cutting off blood supply to their brains and without damaging the delicate blood vessels in their necks and large, heavy heads. This could also help to explain why humans are prone to neck injuries.

By using angiography, CT scans, and medical illustrations to examine the anatomy of a dozen owls, the Hopkins team, in collaboration with a medical illustrator in the Department of Art, found four major biological adaptations designed to prevent injury from rotational head movements. The variations all apply to the bone structure and vascular network needed to support its head.

The team's findings are acknowledged in the Febuary1 issue of the journal, Science, and as first-place prize winners in the posters and graphics category of the National Science Foundation's 2012 International Science & Engineering Visualization Challenge.

The carotid and vertebral arteries in the neck of most animals are fragile and susceptible to even tears of the vessel lining. Sudden gyrations of the head and neck in humans, like whiplash injuries, can stretch and tear blood vessel linings, and produce clots that can break off and cause a deadly embolism or stroke.

In studying the bone structure and vasculature in the heads and necks of snowy, barred, and great horned owls, the researchers used an injectible contrast dye to enhance X-ray imaging of the birds' blood vessels, which were meticulously dissected, drawn, and scanned to allow detailed analysis.

What they discovered was that blood vessels at the base of the head, just under the jaw bone, got larger when the owls’ heads were turned. This contrasts starkly with human anatomical ability, where arteries tend to get smaller and smaller, and do not balloon as they branch out.