Time-sharing acoustic stream analysis to recognize multiple objects in space by echolocating bats

Abstract

Echolocating bats need to catch prey while they have to avoid obstacles and escape from their predators at the same time. Therefore, they have to perceive precise information about multiple objects from their surrounding space while they are flying. However, there are strong restrictions in the system; the neural system is too slow to perform real-time processing, and the bat has only one sound source emission and only two ears to receive echoes. The purpose of the present study was to investigate how echolocating bats perceive important information about different objects in space during their flight by analyzing acoustic characteristics of emitted pulses and returning echoes. Pulses and echoes of CF-FM and FM bats were recorded by a wireless telemetry microphone system (Telemike) on their head. In order to reconstruct their flight trajectory, a dual high speech video camera system was used. Obtained data showed multiple streams for temporal change in echo delay, Doppler-shift compensation, and echo intensity compensation. The present findings indicate that echolocating bats may adopt a time-sharing analysis, which is practically fast enough to recognize multiple objects in space during flight. [Work partly supported by the Innovative Cluster Creation Project promoted by MEXT and by a grant to RCAST at Doshisha University from MEXT.]