Using soundscapes to examine the impacts of urbanisation on spatial and temporal patterns of avian acoustic activity along a riparian corridor

Abstract Background Biodiversity may correlate with acoustic indices, potentially offering insights into urban soundscapes both spatially (identifying areas with higher or lower biodiversity) and temporally (depicting daily patterns of biological activity, such as the avian dawn chorus). We aimed to investigate how a habitat corridor may influence the impacts of urbanisation on patterns of avian acoustic activity, using three soundscape indices: Acoustic Complexity Index (ACI), Normalised Difference Soundscape Index (NDSI) and Bioacoustic Index (BIO). To do this we deployed passive acoustic loggers along a riparian corridor from farmland to the city centre of Glasgow, Scotland. Manual analysis of a subsample of audio recordings was used to ground-truth each acoustic index against manual identification of the contents of the recordings. Results ACI showed only a positive correlation with geophony diversity and duration and therefore was excluded from further analysis because of lack of correlation with ecologically relevant biophony or anthrophony measurements. NDSI was positively correlated with biophony duration while BIO showed the strongest relationship with both measures of biophony, and unrelated to anthrophony or geophony. NDSI results showed that reduced light pollution (lower streetlight densities) was associated with a more natural acoustic environment and BIO increased moderately with closer proximity to the river reflecting greater avian acoustic activity. The dawn chorus was reduced in more urbanised locations and greater diurnal fluctuation in avian acoustic activity occurred at lower levels of urban land cover. Acoustic activity was also lower at weekends than during the week, and peaked in early spring, coinciding with the onset of the avian breeding season. Conclusions This study suggests that soundscape indices can successfully be used for biodiversity monitoring within an urban environment. Soundscape indices revealed both spatial and temporal patterns in avian acoustic activity and were associated with anthropogenic factors driving these patterns. Avian acoustic activity increased with proximity to the centre of the riparian corridor highlighting the role of green corridors in reducing some ecological impacts of urbanisation. Similar approaches to bio-acoustic recording are recommended to inform planning and management of habitats in cities.