Characteristics of echolocation system in Japanese house bat, Pipistrellus abramus

Abstract

Japanese house bats, Pipistrellus abramus, emit harmonically structured downward FM sweeps for echolocation where the fundamental frequency changes from 80 to 40 kHz. Previous studies with an on-board telemetry microphone revealed that they conduct echo-amplitude compensation to stabilize amplitude of returning echoes. When they hunt preys in the field, emitted pulses are prolonged, and the fundamental frequency little change where the terminal fundamental frequency is fixed at about 40 kHz. About 40% of neurons in the inferior colliculus are tuned best to a frequencies range between 35 and 45 kHz, where higher frequency resolution than other frequency ranges is implied and suited for detecting wing beats of insects. However, their audiogram has not yet been known. The present study constructed their audiograms between 4 and 80 kHz by using the auditory brainstem responses evoked by tone pips. Results show that threshold around 40 kHz is lower than other frequencies except for frequency regions around 20 kHz. Findings suggest that Japanese house bats appear to have high sensitivity around 40 kHz, the terminal frequency, and around 20 kHz, corresponding to their communication frequencies. Characteristics of their cochlear microphonics will be discussed. [Work supported by ONR.]