Figure 1. Sketch of the Zebra finch vocal system (A).

Sounds are produced in the syringeal valves, and then filtered through the vocal tract. In the syrinx, the labia oscillate modulating the airflow. They support two coordinated modes of oscillation: an upward propagating superficial wave, and an oscillation around their mass centers (C). In the vocal tract we highlight trachea, glottis, OEC and beak. Pressure is the subsyringeal pressure, stands for the pressure at the input of the tube and stands for the pressure at the output of the trachea. In order to compute the model, we write the equivalent circuit of the post-tracheal part of the vocal tract (B).