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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

To determine the prevalence of European Bat Lyssavirus 1 (EBL1), antibodies plasma samples were obtained from 175 serotine bats (Eptesicus serotinus) from four colonies in southern Spain between September of 1991 and September 1992. Five bats were detected with EBL1 virus in one colony in 1989. The prevalence of antibodies rose to 74% in one of the colonies studied (Villarrasa) in the spring of 1992. After a few months the prevalence declined to under 10%. Individuals with a high antibody level in the spring (up to ED50 = 280) had very low titers or no antibodies in the following summer and autumn.