Bats as bioindicators – the need of a standardized method for acoustic bat activity surveys

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Abstract
Summary: 1. The species‐rich group of bats fills a wide range of ecological niches and provides ecosystem services like pest control. Bats are known to be sensitive to environmental stressors and could, therefore, be used in assessing ecosystem quality. To use bats as bioindicators, a standardized bat survey method needs to be established as the existing approaches vary in their methodology, and results are, therefore, often not comparable.2. Generally, there are two different acoustic bat survey methods: the transect walk and the stationary measurement. By conducting transect surveys and simultaneously using several stationary systems, we measured bat activity within a homogeneous habitat and evaluated which method assessed the spatial bat activity patterns with highest precision. Also the survey tool – the detectors themselves – can be grouped into devices with two different methods of triggering the recording of ultrasonic signals: actively by a fieldworker or automatically by a built‐in recording control algorithm of the detector. We measured bat activity simultaneously and side by side with both methods for direct comparison.3. Our results indicate that the transect survey fails to represent the heterogeneous bat activity patterns in a homogeneous landscape. Furthermore, errors occur based on the subjective hearing of the active triggering of the data recording by the human operator.4. The application of several stationary and automatic sampling systems has the highest potential for standardized acoustic bat surveys. The general use of such an approach would enable us to understand bat activity at landscape scale and could lead to an improvement of bats as bioindicators.

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