Eavesdropping on echolocation: Recording the bat´s auditory experience

Insectivorous bats are able to locate and capture insects in complete darkness while flying at high speeds. They may consume hundreds of insects each night while avoiding obstacles in a complex environment. To investigate the processes associated with bat echolocation, we have developed instrumentation that allows us to record and visualize what a bat hears while flying through its natural environment. Recordings were made using a miniaturized radio telemetry system mounted directly on the back of the bat. This paper describes the design and testing of the components of this system, presents echolocation data collected from bats and discusses issues associated with the visualization and analysis of echoes recorded in a natural setting from the bat´s point-of-view. It presents a new tool for visualizing a bat´s experience by generating call sequence sonograms (CSSs) based on various signal parameters. CSSs based on time series amplitude, band-limited spectral magnitude and Q-factor are presented. This work demonstrates that CSSs based on Q-factor (computed by dividing a peak frequency estimate by a bandwidth estimate) provides a relatively clear representation of the objects producing echoes encountered by a bat during a continuous flight.