Figure 3. Fundamental frequency and air sac pressure measurements (mean ±1 standard deviation) in female and male calls before (“pre”) and after bilateral neurotomy (“post”).

Fundamental frequency and air sac pressure was also measured in the respiratory sounds (“rs”). ‘High’ and ‘Low’ fundamental frequency (F0) in male calls (“highF0” and “lowF0”) is explained in Figure 2. Means were calculated from individual means (number of individuals, N, indicated in each category) which are based on measurements in twenty calls. The probability levels that the slopes are greater than zero is P = 0.006 before and P = 0.012 after the nervecut.