Passage 3
Owl Secrets
A.
It always appeared to fly in the face of logic. But now, the biological secrets
that allow owls to rotate their heads without cutting off their blood supply have
finally been unravelled. Scientists have discovered four major adaptations in
owls designed to prevent injury when the animals rotate their overly large
heads by up to 270 degrees.
B.
The study found that the birds' unique bone structures and vascular
systems let them move with increased flexibility. Scientists at John Hopkins
University School of Medicine in the US studied snowy, barred and great
horned owls after their deaths from natural causes. They found that the
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 the blood to be exchanged between
the two blood vessels. This creates an uninterrupted blood flow to the brain,
even if one route is blocked during extreme neck rotation.
C.
The adaptation gives the birds a huge range of vision without having to
move their bodies and arouse detection by prey. The lack of similar
adaptations in humans could explain why humans are more vulnerable to
neck injury, the experts concluded. When humans attempt sudden and violent
twists of their neck they risk damaging the lining of their blood vessels, which
can result in a fatal blockage or stroke. Study senior investigator Doctor
Philippe Gailloud, said: '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 neck 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.'
D.
To solve the puzzle, the researchers studied the bone and blood vessel
structures in the heads and necks of the birds. An injectable contrast dye was
used to highlight the birds' blood vessels, which were then dissected, drawn
and scanned to allow detailed analysis.
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