Behavioural adaptations of ground living bushcrickets to the properties of sound propagation in low grassland.

The acoustic behaviour of the closely related tetigoniid species Psorodonotus illyricus and Decticus verrucivorus have been invectigated by bioacoustical and behavioural methods. Both species show adaptations concerning the acoustic behaviour with respect to the biotope and the properties of sound propagation. These insects inhabit low grassland with an average vegetation height of about 20 cm which is also the general height for the song perches. Difficulties arise for efficient acoustic communication in such habitats. Sound propagation is influenced and limited by the strong ground attenuation and the excess damping by grass vegetation. Other limiting factors are the microclimatic conditions in the biotope. The two species counteract these difficulties by moving around in the biotope during stridulation. Both species mainly stridulate in the morning, avoiding problems of reduced sound transmission which often appear in the afternoon due to negative temperature gradients and resulting shadow zones. From the high mobility of these insects, it follows that individuals have no fixed territory and consequently no rivalry against conspecifics, which is very common among Orthopterans with a high degree of territoriality. It can be concluded that the preferred biotope influences and creates behavioural patterns in Orthopterans, especially here in the two investigated species of bushcrickets Psorodonotus illyricus and Decticus verrucivorus.