Fig. 1. Examples of chirps produced by a male Apteronotus leptorhynchus in response to stimulation with sinusoidal electric fields. (A) Instantaneous electric organ discharge (EOD) frequency plot during stimulation with a -4Hz difference frequency (DF) stimulus field. Temperature 26.5°C. (B,C) Instantaneous frequency and EOD waveforms during the type-I (left) and type-II (right) chirps indicated by the asterisks in A. (D,E) Histograms of chirp peak-to-peak frequency change (D) and duration (E) for chirps made by this male during one experimental session. Black columns, type-I; grey columns, type-II chirps.