Figure 3.

Ultrasonic vocalizations emitted during mating bouts are produced via an aerodynamic whistle mechanism. (a) Call types include frequency downsweeps and trills. Sound is depicted as a waveform (top panel; relative dB level) and a spectrogram (bottom panel). (b) Mean fundamental frequency (F₀) of frequency downsweeps in air and heliox. (c) F₀ of trills, low-amplitude calls, and agonistic barks (female) in air and heliox. Error bars indicate standard deviation. ‘Expected in heliox’ refers to the predicted frequency estimated from the frequency response of a whistle (see Material and methods).