Owl's feathers extract mechanical energy and convert it into heat to maintain silent flight

Owl 'stealth technology' could hold lessons for engineers

Stealth technology used by owls to help them swoop on prey undetected could hold lessons for engineers, say researchers.

Scientists from Dalian University of Technology in China used lasers and high-speed cameras to analyse and compare long-eared owl, eagle and pigeon feathers during flight.

While all three had a similar flapping style the researchers discovered that the feathers of the owls were able to both absorb aerodynamic sound caused by the wing travelling through the air as well as suppress the vibrations that occur when a bird flaps its wings.

They do this by extracting mechanical energy and convert it into heat resulting in near perfect silence as the bird approaches its prey.

Lead researcher Professor Jinkui Chu said: "Many owls have a unique and fascinating ability to fly so silently that they are out of their prey's hearing range, due to their feather structure. This behaviour has long been of interest to engineers, as we seek to apply the owl's noise-reduction mechanisms to other purposes and situations that benefit society.

"Now, however, we know the owls' silent flight ability is even more superior than we thought. You could say of all birds it is the 'king of acoustic stealth'. It not only manages to suppress aerodynamic noise when gliding, but also mechanical noise caused by vibration during flying.

"This is remarkable, considering the sudden jumping, bending and twisting the wings are subjected to when flapping and the noise that creates for other birds. In the scientific world, the process used to eliminate this mechanical noise is called 'damping' - which means the extraction of mechanical energy from a vibrating system usually by converting it into heat and allowing it to remain steady.

"Our research showed the Long Eared Owl has superior 'damping' skill, meaning it can remain mind-blowingly stable and eliminate mechanical noise caused by the movement of its feathers - quite a feat of engineering."

He added: "This study will hopefully provide further insight into the owls' silent flight mechanism and help engineers develop ideas for special materials or structures, such as on-shore wind turbines, where similar noise elimination can be applied."

The research is published in the Institution of Civil Engineers' Journal Bioinspired, Biomimetic and Nanobiomaterials.

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