Acoustic cues for female choice and male competition in Tettigonia cantans

Song of the bush cricket Tettigonia cantans were analysed, and synthetic song models constructed, to reproduce both the natural variation in the song parameters and the modified spectral balance (high-frequency attenuation) seen after songs are transmitted through the natural habitat. In the laboratory, song models were replayed to female insects in a series of two-choice trials and the phonotactic response was used as the criterion for song preference. Controlling single variables in the models showed that females orientated preferentially to lower-pitched songs, louder songs and models with a relatively louder high-frequency content. Further trials confirmed song frequency to be an important cue and demonstrated spectral balance to be a more effective stimulus than intensity per se. Song models replayed in the field to established (‘territorial’) singing males produced different behavioural responses depending on the song frequency. To low-pitched songs, males were more likely to reduce their singing activity and move away from the sound source. High-pitched song often resulted in an increase in the singing rate and an approach to the loudspeaker. A model without the high-frequency band elicited no detectable response, the subject continuing to sing normally from the same perch. These results support the hypothesis that the spectral balance of the song can be used for range determination. The poor correlation between the measured song variables and morphology suggests that song in this species advertises the status of the male rather than other single attributes such as size or weight.