Washington: Scientists have discovered how night-hunting owls can almost fully rotate their heads without cutting off blood supply to their brains.
Researchers from the Johns Hopkins University, led by medical illustrator Fabian de Kok-Mercado, found four major biological adaptations in owls designed to prevent injury when the birds rotate their overly large heads by up to 270 degrees in either direction.
"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 and interventional neuroradiologist Philippe Gailloud.
"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," added Gailloud.
Sudden gyrations of the head and neck in humans have been known to stretch and tear blood vessel linings, producing clots that can break off and cause a deadly embolism or stroke.
To solve the puzzle, the Johns Hopkins team studied the bone structure and complex vasculature in the heads and necks of snowy, barred and great horned owls after their deaths from natural causes.
An injectible contrast dye was used to enhance X-ray imaging of the birds' blood vessels, which were then meticulously dissected, drawn and scanned to allow detailed analysis.
The most striking team 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, researchers said in a statement.
The supporting vascular network, with its many interconnections and adaptations, helps minimise any interruption in blood flow.
The study was published in the journal Science.