Fig. 13. (A) Cycle-by-cycle frequency analysis of a calling song. The fundamental frequency is more constant in the middle portion of the song, corresponding to the strong harmonics evident in the spectrogram of the same song (B). The blue trace represents the instantaneous velocity of the wing, calculated from the wing movement recordings. (C) Plot of predicted wing velocity (triangles, green line) for the song shown in A and B, and measured wing velocity (circles, blue line) for this song and three others from the same individual. Predicted wing velocity is calculated from the cycle-by-cycle frequency data and the measured distances between adjacent file teeth in this specimen. For each cycle of sound output, we obtained the period and calculated the wing velocity required for the scraper to traverse the corresponding inter-tooth gap in that time. This indicates the instantaneous wing velocity required for tooth-scraper impacts to occur at the same phase in every cycle of sound output. The blue and green lines are Lowess curve fits to the data. The harmonic portion of the song occurs when the actual wing velocity most closely approaches the predicted velocity required for consistent phasing of tooth impacts.