Abstract
Imagine solving a puzzle where half the pieces are missing: Acoustic bat monitoring, a key method for studying species distribution and population shifts, depends on purpose-specific parameters and clear documentation. Without detailed information on these specific parameters, mainly the employed hard- and software, reproducibility and cross-study comparability are not given. This comparability is imperative to address the gaps in bat population data, which have been described as one of the major threats to global bat biodiversity. We aimed to identify the parameters critical for the accurate interpretation and reproducibility of acoustic bat monitoring and assess how these parameters are communicated in existing studies. Using the PRISMA guidelines, we systematically reviewed studies that employed acoustic bat surveys or monitoring in European forests since 2008. Our review focused on three primary components: (1) recording devices and their settings, (2) call identification protocols, and (3) bat activity interpretation methods. Over 90% of the reviewed studies lacked basic methodological parameters. In all areas, we observed incomplete reporting of settings, unreproducible call identification protocols, and data interpretation methods that did not provide access to underlying data. We found a wide range of acoustic bat monitoring methods applied to diverse research questions. This variability underscores the fact that recommending a single approach is neither practical nor desirable. However, consistent reporting of equipment and methods is essential for improving transparency across studies. A standardized framework specifying key parameters for reporting would enhance comparability, support data reuse, and promote more robust bat monitoring and acoustic research. The lack of standardization does not reflect poorly on the researchers' competence or intent but emphasizes the need for a unified approach to bioacoustics methodology. We propose a standardized framework for reporting methodological parameters in acoustic bat monitoring to improve comparability, reproducibility, and transparency across studies.