Ecoacoustic methods application for urban biodiversity monitoring

Passive acoustic monitoring (PAM) is an effective tool for ecosystem assessment. However, it is challenging to apply in an urban environment due to high levels of noise pollution. There is a lag in the number of studies applying PAM in an urban context, and such application therefore lacks proper methodological guidance. This study aims to fill this gap by examining the performance of acoustic methods for biodiversity and acoustic activity assessment. Over 1,000 h of audio data were collected in an urban green area in Moscow, Russia using four AudioMoth recorders and one SongMeter recorder. The sensors were installed at different distances from the road. The species lists obtained through PAM, a route census, and citizen science approaches were compared to evaluate the effectiveness of the acoustic methods. Of the studied methods, PAM produced the best results. Moreover, the correlations between species richness and four common acoustic indices were checked: the Acoustic Complexity Index (ACI), the Acoustic Diversity Index (ADI), the Normalized Difference Soundscape Index (NDSI), and the Bioacoustic Index (BI). None of the studied indices showed good performance as an indicator of species diversity. The biophony level and all acoustic indices were spatially heterogeneous; however, the nature of distribution requires further research. Finally, the dynamics of vocalizing animals' activity and its correlation with the ACI, ADI, NDSI, and BI was assessed. Both the NDSI and BI proved to be suitable indicators of the daily dynamics of acoustic activity in an urban environment, although with some limitations. The BI could also be utilized to assess the seasonal dynamics of biophony in urban green areas.