Owl flight is not magic silence; measurements show the big win is hiding which sounds?

Answer: High-frequency flight noise

Low-frequency wing hum — Low-frequency sound is not where the cleanest owl advantage usually appears. Some measurements found owl gliding noise concentrated lower than duck noise, but comparisons with hawks and kestrels show a stronger reduction at higher frequencies. This matters because many prey-hearing cues and masking problems sit in kilohertz ranges. Owls are quiet, not physically soundless.

High-frequency flight noise ✓ — Right. Several measurements and reviews point to owl wings especially reducing higher-frequency flight noise, including ranges above about 1.6 to 2 kHz. That is a more useful trick than simply lowering total volume: it removes the sharp cues that prey and the owl's own hearing system are likely to notice. The surprise is that silence can mean spectral reshaping, not zero sound.

All flight noise equally — All-flight-noise reduction is the intuitive cartoon version, but measurements point to a more selective spectral story. Owl flight can remain physically audible while losing the higher-frequency cues that matter most for detection and masking. That distinction is useful: quiet design may target the most revealing frequencies rather than flatten everything equally.