IDBR: Acquiring a Bat's Perspective on Biosonar Echoes

Fitchburg State University, Fitchburg MA

Investigators

Abstract

A grant has been awarded to Drs. Kevin Austin and Howard Thomas at Fitchburg State College to develop instrumentation for recording and analyzing bat echolocation calls. The remarkable ability of bats to seek out, recognize and capture small flying insects while navigating at high speeds in total darkness is well-documented. Bats that eat insects generate loud, high-pitched bursts of sound that are beyond the range of human hearing. These "ultrasonic" bursts bounce off of various objects in the environment and carry information back to the bat. It has been suggested that bats' brains process the echoes to form an internal representation of space. Many bats are thought to be able to select particular insects from a wider array of prey. This suggests that a bat's experience of the environment, acquired through the perception of ultrasound echoes, must be quite rich. Indeed, controlled scientific experiments suggest that bats can distinguish physical properties of objects such as hardness, size and texture. Theories of how bats might accomplish this feat are numerous, but few have been empirically tested. Most theories make particular assumptions about the echoes associated with various environmental objects. One goal of this project is to provide data to validate the assumptions made about the character of ultrasound echoes from various environmental objects and prey insects. The investigators plan to do this by developing a light-weight device that will be attached to bats to record echoes in flight. The device will be equipped with two microphones (one for each ear) connected to radio transmitters. The goal is to eavesdrop on the echoes actually heard by the bat and send the signals to a ground-based computer for storage and analysis. Most of our knowledge of bat calls comes from recordings made using ground-based microphones. Field recordings of this kind are routinely made in wildlife surveys designed to quantify the distribution of particular bat species over a geographic area. This type of recording is not well suited to the detailed study of echolocation because ground based recordings are subject to Doppler shift, a well-known phenomenon, where the observed frequency differs from the actual emission due to the relative motion of the source with respect to the observer. To know the precise character of a bat call (and the echo) it is necessary to mount the recording device on the bat itself. Drs. Austin and Thomas have formed a interdisciplinary collaboration intent on developing instrumentation that will allow direct recordings of bat calls in flight by mounting small radio transmitters connected to microphones on the bats themselves. Additionally, these devices will, for the first time, enable investigators to analyze the actual echoes heard by bats. This information promises to provide a better understanding of how bats perform navigation and feeding in total darkness. A better understanding of how bats navigate using echolocation may allow the future development of devices that can navigate environments using auditory rather than visual information. Robots based on this technology may be of use in search and rescue operations associated with locating people trapped in dark places like mines or caves. A detailed understanding of bat echolocation may also lead to the development of assistive technologies for the visually-impaired. Undergraduate students from the Biology and Computer Science departments will participate in this research. In the process the students will have the opportunity to focus their talents on the solution of real-world research problems. They will learn how to work across disciplines and have the opportunity to present their work at professional conferences.