Fig. 1. Concurrent vocalization (A), tracheal flow rate (B) and cranial thoracic air sac (CTAS) pressure (C) signals for one coo. Grey bars beneath the spectrogram and grey areas in the flow and pressure plots indicate where sound is produced, as measured from the sound oscillogram (not shown). Arrows and broken lines indicate the location of frequency jumps. The flow rate recorded during the silent intervals of the amplitude-modulated part of e2 may not reach zero because the microbead thermistor fails to track the very fast and large changes in flow rate. Note that flow rate and pressure signals have been low-pass filtered at 100 Hz to remove acoustic components and higher frequency noise.