1 research outputs found
Biases of acoustic indices measuring biodiversity in urban areas
Urban green infrastructure, GI (e.g., parks, gardens, green roofs) are potentially important
biodiversity habitats, however their full ecological capacity is poorly understood, in part due
to the difficulties of monitoring urban wildlife populations. Ecoacoustic surveying is a useful
way of monitoring habitats, where acoustic indices (AIs) are used to measure biodiversity by
summarising the activity or diversity of biotic sounds. However, the biases introduced to AIs
in acoustically complex urban habitats dominated by anthropogenic noise are not well
understood. Here we measure the level of activity and diversity of the low (0-12 kHz, l) and
high (12-96 kHz, h) frequency biotic, anthropogenic, and geophonic components of 2452
hours of acoustic recordings from 15 sites across Greater London, UK from June to October
2013 based on acoustic and visual analysis of recordings. We used mixed-effects models to
compare these measures to those from four commonly used AIs: Acoustic Complexity Index
(ACI), Acoustic Diversity Index (ADI), Bioacoustic Index (BI), and Normalised Difference
Soundscape Index (NDSI). We found that three AIs (ACIl, BIl, NDSIl) were significantly
positively correlated with our measures of bioticl activity and diversity. However, all three
were also correlated with anthropogenicl activity, and BIl and NDSIl were correlated with
anthropogenicl diversity. All low frequency AIs were correlated with the presence of
geophonicl sound. Regarding the high frequency recordings, only one AI (ACIh) was
positively correlated with measured biotich activity, but was also positively correlated with
anthropogenich activity, and no index was correlated with biotich diversity. The AIs tested
here are therefore not suitable for monitoring biodiversity acoustically in anthropogenically
dominated habitats without the prior removal of biasing sounds from recordings. However,
with further methodological research to overcome some of the limitations identified here,
ecoacoustics has enormous potential to facilitate urban biodiversity and ecosystem
monitoring at the scales necessary to manage cities in the future