Responses of soprano pipistrelles, Pipistrellus pygmaeus, to their experimentally modified distress calls

To identify the key acoustic characteristics of distress calls that elicit behavioural responses in the soprano pipistrelle bat, Pipistrellus pygmaeus, we performed a series of playback experiments involving modifications to frequency and temporal parameters of a synthesized 'base' call resembling a typical natural distress call of this species. We Played experimentally modified distress call sequences and control sequences consisting of random noise and silence at foraging sites. To measure the bats' response, in terms of variation in the number of echolocation pulses, we simultaneously recorded ultrasound during playbacks and counted the echolocation pulses. Significantly more echolocation pulses were recorded during playback of the base call than during playback of control sounds and responses to modified base calls indicated that the interelement interval, element duration and consecutive element frequency may be important for distress call recognition. Changes to the interelement interval, consecutive element frequency and bandwidth may convey information about the affective state of the sender.