Listening for bats: the hearing range of the bushcricket Phaneroptera falcata for bat echolocation calls measured in the field

The hearing range of the tettigoniid Phaneroptera falcata for the echolocat ion calls of freely flying mouse-eared bats (Myotis myotis) was determined in the field. The hearing of the insect was monitored using hook electrode recordings from an auditory interneuron, which is as sensitive as the heari ng organ for frequencies above 16 kHz. The flight path of the bat relative to the insect's position was tracked by recording the echolocation calls wi th two microphone arrays, and calculating the bat's position from the arriv al time differences of the calls at each microphone. The hearing distances ranged from 13 to 30 m. The large variability appeared both between differe nt insects and between different bat approaches to an individual insect. Th e escape time of the bushcricket, calculated from the detection distance of the insect and the instantaneous flight speed of the bat, ranged from 1.5 to more than 4 s. The hearing ranges of bushcrickets suggest that the insec t hears the approaching bat long before the bat can detect an echo from the flying insect.