A toolkit for the dynamic study of air sacs in siamang and other elastic circular structures
Fig 7
Significant correlations between air sac inflation (as air sac radius in pixel) and acoustic parameters.
The figure is divided into results of adult siamangs (left; panel a and b) and immature siamangs (right; panel c and d). The top panel shows the pooled data. Air sac radius in pixel on the x-axis is shown against four different acoustic parameters (from left to right): sound amplitude, f0 or fundamental frequency in Hertz, Wiener entropy and spectral Centroid in Hertz. For adults, we find clear correlations: The more the air sac is inflated, the higher the sound amplitude produced. This is in line with model predictions (see [34]). The fundamental frequency (f0) is also positively correlated with the air sac inflation, and seems to be the only stable relationship reflected in both the male and female individual. Mean Entropy is negatively correlated with air sac inflation, meaning, the more inflated the air sac is, the more tonal the produced sound. The Spectral Centroid is negatively correlated as well, indicating the higher the inflation, the more energy in the lower frequencies. We do not see those relationships in immature not fully grown individuals. In the middle panel significant correlation coefficients for all tested acoustic parameters are shown. Notice, that none of the acoustic parameters showed a significant relation in immatures (indicated by white circles). The bottom panel divides the pooled data. For adults we divide by sex into male and female, for the immatures we divide by ageclass into subadult and juvenile.