Multifunctional control of vocal output in the songbird syrinx

Songbirds produce complex vocalizations by coordinating neuromuscular control of syrinx, respiratory system and upper vocal tract. The specific involvement of individual syringeal muscles in achieving fine vocal control is still largely unknown. Here we investigate the contributions of the two main airflow controlling muscles, the dorsal and ventral tracheobronchial muscles in the zebra finch, through a new experimental approach. Ablation of the muscle insertion on the cartilage framework reveals detailed insights into their respective roles in the fine control of song features. Unilateral ablation of a tracheobronchial muscle resulted in mostly subtle changes of the air sac pressure pattern and song features. Effects of ablation varied with the acoustic elements, thus indicating a context-dependent specific synergistic activation of muscles. More pronounced effects on song features and air sac pressure were observed after bilateral ablation of the dorsal tracheobronchial muscles. The results illustrate that the gating muscles serve multiple functions in control of acoustic features, and that each feature arises through context-dependent, synergistic activation patterns of syringeal muscles.