Bird Sounds

Practically all birds and other animals emit sounds that have a fundamental frequency and several harmonics. Some birds, however, can emit just the fundamental with no harmonics! Measurements inside the bird reveal that the original sound has harmonics. So how does the bird eliminate them before they escape into the great outdoors?

Answer

Some birds can emit just a fundamental frequency with no harmonics. Just how the bird eliminates the harmonics originally generated within is being investigated. The present conjecture is that a cavity resonance amplifies just the fundamental before the sound is emitted. If the fundamental frequency changes, then the cavity must change to accommodate the new fundamental in “live time.”