Respiratory vocal coordination increases as zebra finches prepare to sing
Complex vocalizations like human speech and bird song require precise coordination between respiration and vocalizations with most vocalization being produced during the exhalation phase of respiration. However, when this coordination is established each time animals vocalize remains poorly understood. Here, we addressed this question by recording respiratory pressure in adult, male, zebra finches during singing. Zebra finches begin their song bouts by repeating a short vocalization called an introductory note (IN), before producing song and these INs have been hypothesized to reflect motor preparation for song. We found that each IN is associated with a large amplitude expiratory pulse. Birds that did not produce INs had a few silent, large amplitude, IN-like, expiratory pulses just before starting song. Expiratory pressure and inspiratory pressure increased with successive repeats of the IN (silent or vocalized). Further, for birds with INs, coordination between respiration and vocalization increased with vocalizations beginning earlier in the exhalation and ending later in the exhalation, such that more of the expiratory pulse was filled with the vocalizaton. Overall, these results show that respiratory vocal coordination improves with each repetition of the IN and suggest that INs reflect preparation that involves coordination of respiratory and vocal neural circuitry.