How do bats use ecological technique??
Answers
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.
Introduction
Recently, Jones et al. (2009) argued that bats have great potential as bioindicators. Changes in bat populations or activity were related to climate change, water quality, agricultural intensification, loss and fragmentation of forest habitats, and habitat pollution (Jones et al. 2009).
Most current bat surveys rely on acoustic methods. Contrary to capture methods, telemetry and direct observations, the use of ultrasonic detectors is often the only logistically feasible and cost‐effective survey method. However, fundamental concerns regarding the basic methodological designs of many acoustic surveys were expressed as they often fail to address temporal and spatial variation in bat activity patterns (Hayes 2000; Sherwin, Gannon & Haymond 2000; Gannon, Sherwin & Haymond 2003). The assessment of variation in bat activity pattern and the comparability of independent studies are basic requirements for the potential use of bats as bioindicators. Consequently, a standardized bat survey method using a suitable detector system has to be established.
In practice, there are two different methods to survey bat activity: (i) line transects and (ii) the stationary measurement. The transect method is based on the assumption that the bat activity recorded along a transect is in accordance with the activity in the whole habitat of concern (i.e. the habitat is supposed to be homogeneous in regard to bat activity). In contrast, stationary systems are set up at a selected site to reflect the overall activity of the corresponding habitat. To test the transect survey assumption of evenly distributed bat activity within a habitat, we measured bat activity in an agricultural landscape dominated by cereal fields, a habitat assumed to be completely homogeneous, by conducting a transect survey while simultaneously recording with several stationary systems.
In addition to the two different survey methods, there are also two different methods of triggering the recording of ultrasonic signals: (i) actively by a fieldworker using heterodyne or frequency division systems [e.g. Pettersson D200 and D240X (Pettersson Electronic AB, Uppsala, Sweden) or S‐25 bat detector (Ultra Sound Advice, London, UK)] or (ii) automatically by the detector devices [e.g. Anabat II (Titley Electronics, Ballina, Australia) or ecoObs‐batcorder (ecoObs GmbH, Nürnberg, Germany)]. We measured bat activity simultaneously and side by side with a hand‐held Pettersson D240X detector in the heterodyne modus and an automatic ecoObs‐batcorder in open landscapes and forests to examine whether differences in data recording occur because of the subjective hearing of the operator of the active‐triggering system in comparison with a built‐in recording control algorithm of an automatic device.
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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