Using passive acoustic monitoring to examine the impacts of ecological restoration on faunal biodiversity in the Western Ghats

Abstract

Monitoring programs aimed at assessing ecological restoration have often relied on the response of a single taxon owing to the difficulty of sampling multiple taxonomic groups simultaneously. Using passive acoustic monitoring, we examined the impacts of ecological restoration on all vocalizing fauna simultaneously as well as a single indicator taxon, birds. In our study, acoustic recorders were programmed to collect data along a gradient of forest regeneration consisting of actively restored (AR), naturally regenerating (NR), and mature benchmark (BM) sites in a tropical biodiversity hotspot, the Western Ghats of southern India. For all vocalizing fauna, we calculated acoustic space use, a measure that reflects the amount and pattern of sounds within each frequency bin for a given time period. AR and NR sites were not significantly different from each other, and visual examination of the acoustic space showed a lack of sounds between 12 kHz to 24 kHz for AR and NR sites, suggesting limited insect activity. When we considered the response of birds alone (from manually annotated acoustic data), we found significant differences in the proportion of detections of rainforest bird species compared to open-country bird species across all treatment types, with the highest proportion reported in BM sites (mean ± SD: 0.97 ± 0.04), followed by AR sites (0.81 ± 0.12) and NR sites (0.71 ± 0.17). Considering the varied response of different taxa to habitat recovery over two decades, we highlight the need to take a multi-taxon approach while assessing restoration programs. We show that it is now possible to do so in tropical forests using passive acoustic monitoring.