Figure 5.

The collar system can also trace differences in hyoid movement before (a) and after (b, c) nerve transection. Sound is depicted as time waveform (Amplitude, top panel) and spectrographically (second panel). Subsyringeal air sac pressure (panel 3) and the Hall effect sensor signal (panel 4) indicate that before nerve transection there is almost no hyoid movement during quiet respiration. Only a small shift in baseline associated with overall body movements can be noticed over 6 respiratory cycles in the Hall effect signal. At the beginning of the fourth expiratory phase, the bird produces a tet call, which is associated with a large Hall effect signal deflection indicating a prominent OEC expansion. b. Respiratory sounds from the same zebra finch indicate that nerve transection causes more OEC expansion during quiet breathing, but the main expansion occurs during inspiration. OEC size is smallest during expiration when sound is produced. The relative scale for OEC expansion is the same for a and b, indicating larger OEC expansion during sound production than during inspiratory expansion. c. The respiratory sounds of another zebra finch are also generated during expiration, and OEC expansion occurs during inspiration. Comparison of scale for OEC expansion between the birds (a, b and c) is not possible as explained in the main text. Panels as in Figure 4. I, inspiratory phase; E, expiratory phase; units as in figure 4.