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Saturday, February 9, 2013

How owls swivel their heads


1 February 2013 

How owls swivel their heads

By Jonathan Amos
Science correspondent, BBC News





It's the owl's greatest trick - turning its head almost a full circle.

The puzzle has been how the bird doesn't throttle itself in the process. If we did it, we'd cut the blood supply to our brains and pass out.

But according to two US-based scientists, the owl has some very smart bone and vascular structures running along its neck to the skull.

These features protect blood vessels from damage and maintain the flow even when the head is swivelled 270 degrees.

"They haven't developed just one answer to the problem; they have several answers," said Dr Philippe Gailloud from Johns Hopkins University School of Medicine.

"And it's because of this set of solutions that we don't see lots of owls lying on the forest floor having suffered strokes," the interventional neuroradiologist told BBC News.

Most birds have extremely flexible necks, but the owls are the avian species that have perhaps garnered the greatest attention for their neck-twisting exploits.

They must turn their heads in this extraordinary way because of their eyes' narrow field of view and relative immobility.

It's true they have double the number of bones in their neck compared with us - 14 versus seven cervical vertebrae. But it's really the way the animal manages the flow of oxygenated blood to its brain that underpins the impressive feat.

Dr Gailloud and science illustrator Fabian de Kok-Mercado used various imaging and dissection techniques to detail the anatomy of a dozen dead owls.

They showed that the big carotid arteries, instead of being on the side of the neck as in humans, are carried close to the centre of rotation just in front of the spine. As a consequence, these arteries experience much less twisting and stretching. The potential for damage is therefore greatly reduced.

This arrangement is not specific to owls, of course; it is seen in other birds as well. What does appear unique to owls, however, is the way the vertebral arteries - the vessels that travel through channels within the neck bones - are given extra space. (...)

See more: http://www.bbc.co.uk/news/science-environment-21279609

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