Novel motor gestures for phonation during inspiration enhance the acoustic complexity of birdsong.

Sound generation based on a pulmonary mechanism typically occurs during the expiratory phase of respiration. Phonation during inspiration has been postulated for the calls of some amphibians and for exceptional sounds in some human languages. No direct evidence exists for phonation during inspiration in birds, but such a mechanism has been proposed to explain very long uninterrupted songs. Here, we report the first physiological evidence for inspiratory sound production in the song of the zebra finch (Taeniopygia guttata). Motor gestures of the vocal and respiratory muscles leading to the production of inspiratory phonation differ from those of silent inspirations during song as well as from those leading to phonation during expiration. Inspiratory syllables have a high fundamental frequency, which makes them acoustically distinct from all other zebra finch song syllables. Furthermore, young zebra finches copy these inspiratory syllables from their tutor song, producing them during inspiration. This suggests that physical limitations confine the production of these sounds to the inspiratory phase in zebra finches. These findings directly demonstrate how novel respiratory-vocal coordination can enhance the acoustic structure of birdsong, and thus provide insight into the evolution of song complexity.