Study traces evolution of acoustic communication
(PHYSorg.com Biology)

Imagine taking a hike through a forest or a stroll through a zoo and not a sound fills the air, other than the occasional chirp from a cricket. No birds singing, no tigers roaring, no monkeys chattering, and no human voices, either. Acoustic communication among vertebrate animals is such a familiar experience that it seems impossible to imagine a world shrouded in silence.