The acoustic behaviour of the bushcricket Tettigonia cantans II. Transmission of airborne-sound and vibration signals in the biotope.
The airborne-sound and the vibratory signals produced by stridulating Tettigonia cantans males, and the transmission of these signals in the natural biotope were investigated. The song of T. cantans is composed of repeated uniform syllables with a rate of ca. 30/sec. Intensity approaches 100 dB SPL, 10 cm away from the animal. The spectrum shows three dominant frequency ranges around 8, 16 and 32 kHz. Airborne transmission of the song in such vegetation layers as are found in the biotopes of T. cantans shows an excess attenuation which increases with frequency. The relative intensities of the frequency components of the song vary as a result of the kind of vegetation, the positions of emitter and receiver, and the separation distance. These relative differences in intensity may be useful during the phonotactic approach to conspecific partners, providing a measure of the distance from the sound source. Stridulating males also produce vibratory signals in the plants they sit on. The spectrum of these signals includes frequencies up to 8 kHz, the first dominant frequency of the song: low frequency components are induced in the plants via the legs and abdomen of the animal. The vibratory signals are transmitted mainly in the form of bending waves. Near the animal, amplitude modulation corresponds to that of the song. At greater distances, reflections and frequency-dependent propagation velocities, cause distortions of this time pattern. Transmission depends greatly on the mechanical properties of the particular plant, attenuation values of 20-50 dB/m being found. Nevertheless, in most cases, vibratory signals may be perceived up to 1.5 - 2 metres away from a stridulating male.