The owl fly in perfect silence.

Inaudible even in headphones, despite passing a few centimeters from a large set of microphones in an already silent test environment. Its wings move the air without generating any spikes.

Please, note: NOT “any spikes at audible frequencies”, just no spikes. The record is a almost straight line (see the second video).

Taken from the BBC Two Natural World program. Reported by Lucia.

In the first video there is the essence of the experiment.

Here we have a more complete video with some comments.