Barn owl wings adapted for silent flight

Their screech is one of nature's eeriest sounds, but barn owls hunt in almost total silence.

Now researchers in Germany have revealed how the predators' wings are specially adapted to allow noiseless flight.

Their supreme stealth is thanks, largely, to their ability to fly so slowly - with relatively little beating of their wings.

And the shape and size of the owls' wings enables this very slow flight.

Dr Thomas Bachmann from the Technical University Darmstadt in Germany recently presented his study of barn owl wings at the Society for Integrative and Comparitive Biology's annual meetingin Charleston, South Carolina.

He explained to BBC Nature that barn owls were highly specialised nocturnal hunters.

"They hunt mainly in the dark, so visual information is very limited.

"They use acoustic information to locate their prey."

Their silent flight helps them listen for the scurrying of the voles they hunt for, and also reduces their chances of being heard by the prey as they approach.

To find out how they managed to fly so slowly and quietly, Dr Bachmann examined the birds' wings in minute detail.

He examined the plumage and took 3-D medical scans of their skeletal structure.

The wings' most important features, he explained, were the high curvature or "camber" of the wings. This curvature means that each wing beat produces more lift.

This is because, Dr Bachmann explained, the air flow is accelerated over the upper surface the curved wing. "So the pressure drops," he said. "[And] the wing is sucked upwards into the lower pressure on the upper wing surface."

"Friction noise between single feathers is also reduced [by] their velvety surface," he told BBC Nature.The feathery edges of each wing are also extremely fine - reducing any loud turbulence during flight, explained Dr Bachmann.

Continued:  http://www.bbc.co.uk/nature/16593259

Study: Optical clues help flying birds

BRISBANE, Australia, Oct. 28 (UPI) -- Australian scientists say they've discovered how birds avoid collisions with objects and each other as they perform their aeronautic maneuvers.

The graceful flight of birds, even in crowded environments, is a result of their perception of something called optic flow, Partha Bhagavatula of the University of Queensland said.

"Our findings show, for the first time, that birds regulate their speed and negotiate narrow gaps safely by balancing the speeds of image motion, or optic flow, that are experienced by the two eyes," Bhagavatula said in a university release.

In a study, researchers trained parakeets to fly through a 23-foot corridor lined with varying combinations of thick black horizontal and vertical stripes, and then filmed their flights.
They found birds flew down the center of the corridor when optic flow cues were balanced -- with identical, vertical stripes on either side of the corridor -- but flew more closely to one wall or another when the cues were unbalanced, for example, when one wall was lined with horizontal stripes and the other with vertical stripes.

Also, the birds flew faster when the tunnels were lined with horizontal, rather than vertical, strips, suggesting they were using optic flow cues to regulate their flight speed.

While similar flight behaviors have been demonstrated in flying insects, this is the first time the use of optic-flow signals has been demonstrated in birds, the researchers said.


Read more: http://www.upi.com/Science_News/2011/10/28/Study-Optical-clues-help-flying-birds/UPI-21391319845211/#ixzz1cMc1TuBS