Abstract
In recent years, biodiversity has declined faster than ever before in human history. Appropriate monitoring methods are needed to detect the decline of populations in time to be able to take conservation measures. Information on population dynamics can only be obtained by conducting standardised monitoring programmes, and the quality of the data depends on the survey method used. The present study aims to provide scientifically sound recommendations for the selection of a suitable survey method for emerging flights at greater mouse-eared bat (Myotis myotis) maternity roosts. For this purpose, three survey methods, namely infrared video recordings, counting by light barriers and visual counting of emerging bats, were used simultaneously for 4–5 nights at three different maternity roosts in 2019 and comparatively evaluated. Besides the quality of the counting data, the requirements and limitations of the different methods were compared and discussed. The results of this study showed that the number of emerging flights detected with all three survey methods were closely correlated, regardless of location, number of emerging flights per night (between 300 and 800) and season. Furthermore, it was shown that the presence of the observer and infrared video recordings had no significant influence on the emergence behaviour of the bats recorded by light barriers concerning the time of emergence, the duration of activity and the number of counts. As the three methods differed with regard to additional parameters, such as the need for technical equipment or qualified personnel, the time required, the costs and the error-proneness individual settings and requirements should be taken into account when deciding about the method used. However, for the continuous monitoring of greater mouse-eared bats at their maternity roosts, which is part of the monitoring requirements under the European Union Habitats Directive, the use of light barriers proved to be the method of choice, in particular as it allows to promptly detect changes in the bats’ activity as a basis for conservation measures.
Highlights
Biodiversity has declined faster in recent years than ever before in human history
The statistical analyses of the results of the three survey methods studied have shown that they provide comparable results and that the counts collected with Light barriers (LB) and Visual counting of emerging bats (VCE) differ only very slightly from those collected with Infrared video recordings (IVR), which was chosen as benchmark for the two others, as it assumed that these counts would be the most accurate (Revilla-Martín et al 2020)
As the comparison has shown that there are no significant differences in data quality between the three methods used and that the presence of the observer on site or the installation of infrared lamps do not influence the results in terms of disturbing the emergence of the greater mouse-eared bat from the roost, the choice of an appropriate survey method can be made on a case-by-case basis depending on the context, the possible sources of errors and objectives of the particular study
Summary
Biodiversity has declined faster in recent years than ever before in human history These massive species extinction has reached global proportions and can be attributed to factors such as habitat destruction, overexploitation and degradation, land-use change, invasive species and climate change (Barboza and Franz 2016; Kehoe et al 2020; BMU 2018; IPBES 2019). To create basic information experts of species are needed to collect data on the status of species and habitats as part of standardised monitoring programmes as well as on potential stressors and conservation measures, over extended periods of time and by using standardised methods (BMU 2018; Hausmann et al 2020; Beresford et al 2020). The insect decline identified by a long-term study and which is very likely caused by human activities, might have taken a different course if corresponding monitoring studies had been conducted earlier and on a large geographical scale (Hallmann et al 2017; Settele 2019)
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