We studied echolocation signals broadcast by free-flying naked-backed bats (Pteronotus davyi) from Panama. Calls consisted of a segment of constant frequency, followed by a downward frequency modulated sweep, and ended with a short segment of quasi-constant frequency. Up to three harmonics were detectable. The second harmonic usually was more intense, and mean frequencies in the constant and quasi-constant segments were 68.0 and 58.0 kHz, respectively. Most pulses showed the highest intensity in the frequency cone­ sponding to the constant segment of the second harmonic, but sometimes bats allocated most energy to the quasi-constant segment of that same harmonic or even to the constant or the quasi-constant segment of the fundamental harmonic. Pulses averaged 6.6 ms in duration and were repeated every 70.8 ms. The segment of constant frequency was always present, and its frequency changed little across extremely different behavioral situations

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