Chart 2: Examples of calls recorded in each of the four settings: open, forest, entrance of the mine, and in the mine adit. Measurements were made of call duration and inter-pulse interval from the time amplitude and spectrogram displays. In the time-amplitude graph, the horizontal axis is measured in milliseconds (ms), and the vertical axis is measured in percent (%). In the spectrogram display, the horizontal axis is measured in milliseconds (ms), and the vertical axis is measured in kilohertz (kHz). Echoes and harmonics are also displayed in the FFT display.