Is the Frequency Content of the Calls in North American Treefrogs Limited by Their Larynges?

Figure 6

Spectral structure of natural and artificial calls in Pseudacris streckeri. Artificial calls were obtained with forced airflow through the passive larynx of a euthanized male frog, and the mouth was open or closed, and, in the latter case, the vocal sac would inflate. Notice the same fundamental frequencies but different distribution of energy in harmonics.