Ecological Indicators (Feb 2024)
Influence of recording devices and environmental noise on acoustic index scores: Implications for bird sound-based assessments
Abstract
Passive acoustic monitoring serves as a minimally invasive and effective method for biodiversity assessment, particularly in bird monitoring through the application of acoustic indices. However, the use of different recording devices and different types of environmental noise (e.g., rain, wind, stream, traffic noise) lead to signal distortions that affect the application of ecoacoustics indices. Currently, there are no established guidelines specifying the technical requirements for recording devices and the signal-to-noise ratio (SNR) threshold for accurate calculation of acoustic indices. To enhance the accuracy of acoustic indices in bird biodiversity assessments, this study investigated the impact of different recording devices and environmental noise (rain, wind, stream, traffic noise) on acoustic indices. In this study, we selected six acoustic indices: Acoustic Complexity Index, Acoustic Diversity Index, Acoustic Evenness Index, Bioacoustic Index, Acoustic Entropy Index, and Normalized Difference Soundscape Index, and we used four different recording devices to simultaneously record 104 h of bird-sound data at the same location. In addition, 44 h of noisy bird signals with different noise types and intensities were artificially synthesized for comparison. The sound data were then used to analyze the effects of the recording devices and environmental noise on the acoustic indices used for bird biodiversity assessment. Our results showed that (a) all six acoustic indices were affected by the recording device used; (b) each acoustic index had different sensitivities to different noise types; and (c) there was a SNR threshold above which the effect of noise on the acoustic index was negligible. This study provides recommendations for recording device selection and determines SNR thresholds for noisy bird signals, contributing to the refinement of protocols for acquiring and preprocessing signals in the application of acoustic indices for bird biodiversity assessment. These findings aim to establish standardized protocols for signal acquisition and preprocessing in future application of acoustic indices.
