ACOUSTIC INFORMATION AVAILABLE TO BATS USING FREQUENCY-MODULATED SOUNDS FOR THE PERCEPTION OF INSECT PREY

Through the present study, the acoustic information available to an ec holocating bat that uses brief frequency-modulated (FM) sonar sounds f or the pursuit and capture of insect prey has been characterized. Comp uter-generated sonar pulses were broadcast at tethered insects, and th e returning echoes were recorded on analog tape at high speed for off- line analyses. Echoes from stationary and fluttering insects were disp layed using time waveform, spectrogram, power spectrum, and cross-corr elation representations, The results show echo signatures for the diff erent insect species studied, which change with the angle of incident sound. Sequences of echoes from fluttering insects show irregular chan ges in sound amplitude and time-frequency structure, reflecting a rand om temporal relation between the changing wing position and the arriva l of incident sound. A set of recordings that controlled the temporal relation between incident sound and insect wing position suggests that information about the spatial profile of a flying insect could be enh anced if the bat were to produce a sequence of sounds that synchronize d briefly with the moving target's wing-beat cycle. From this study, i t has been proposed that the FM bat receives stroboscopic-like glimpse s of fluttering prey whose spatial representation depends on the opera tion of the bat's sonar receiver.