An electronic system for monitoring activity of some echolocating bats in the field is described. An ultrasonic receiver is used to detect the bat cries. Audiofrequency signals from the receiver are processed and converted by the system to characteristic marks on the chart of an event recorder. The utility and limitations of the technique with respect to the echolocating characteristics of bats and analysis of recorder charts are considered. Quantitative data obtained in several habitats with this system are presented.

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