Owls use 'stealth technique' to capture prey

Owls are equipped with sophisticated 'stealth technique' to help them swoop on prey undetected, according to new study that unveils the secret behind the nocturnal bird's silent flight.
Scientists have long been puzzled by the owl's ability to flap its wings hard enough to rise into the air without a sound while swooping silently on swift-moving rodents out of the still night.
The researchers crowned the owl the "king of acoustic stealth" after discovering that its wings absorbed the energy of flight vibrations and converted it to heat much more efficiently than other birds they examined.
Generating enough thrust to get aloft involves a large amount of force and disturbs a lot of air. Yet most owl species manage to do it at frequencies below 2 kilohertz (kHz), well out of their prey's hearing range, 'The Times' reported.

Researchers used the feathers of a long-eared owl, a golden eagle and a pigeon.
Simulating wing-beats, they measured the vibrations and found that the owl feathers trapped much more of the energy as heat than the others.

Scientists could copy the owl's noise-reduction mechanisms to quieten machine noises such as the thrum of onshore wind turbines, said Jinkui Chu, professor of mechanical engineering at Dalian University of Technology in China.
"The owl's silent flight ability is even more superior than we thought," said Jinkui.
"It not only manages to suppress aerodynamic noise when gliding, but also mechanical noise caused by vibration during flying. This is remarkable, considering the noise that creates for other birds," he said.

The study was published in the journal Bioinspired, Biomimetic and Nanobiomaterials.