Adaptive echolocation sounds in the bat Rhinopoma hardwickei - A field study

Abstract

1. Rhinopoma hardwickei were studied under natural conditions in the Madurai region of southern India. 2. Frequency modulated (FM) sounds of 3 ms duration were emitted shortly before landing and during times when 10-70 individuals were flying in clusters as they left their roosts. 3. Constant frequency (CF) sounds of 48 ms duration were produced in open space by single flying bats and by bats flying in a group. At these times the most intense component was the second harmonic. 4. When bats flew in a group the frequencies of the CF-sounds emitted by different individuals were in three different bands (30.0, 32.5, and 35.0 kHz) whereas single flying bats used only 32.5 kHz. Evidence is presented that shows that Rhinopoma hardwickei flying in groups regulate the frequency of their individual CF-components and in this way they avoid jamming one another. 5. After landing a pure tone multi-harmonic sound of long duration (maximally 100ms) is emitted. In this sound the fundamental frequency is dominant. Its significance, either communicative and/or echolocative, is not clear. 6. The possible role of different types of sounds recorded in different orientation situations is discussed. © 1981 Springer-Verlag.