To assess the extent to which species are affected by, it becomes increasingly important to develop reliable monitoring tools that can efficiently monitor changes in communities. Acoustic methods have been already used successfully to answer a range of ecological and conservation questions. However, it remains unclear whether the scale of the survey influences which index is most applicable.
Researchers from Xishuangbanna Tropical Botanical Garden (XTBG) measured the correlations between bird diversity and seven acoustic indices. They aimed to see whether it should matter if the survey is all conducted within a small area or different environments with different bird communities are sampled over a wider region.
The researchers tested the acoustic entropy, acoustic diversity, acoustic evenness, acoustic richness, acoustic complexity, bioacoustic index, and normalized difference soundscape index (NDSI) at two forested and highly biodiverse regions in Yunnan Province, in south China, located approximately 290 km apart and at different elevations.
They measured each index’s correlation to bird species richness and diversity, estimated using conventional point-count surveys conducted by an expert observer at the same time as the recordings.
Further, they tested whether the indices perform better when the analysis included only samples with similar environments and similar species compositions, compared to analyses in which samples with dissimilar environments and compositions are also included.
They found that although no index showed a very strong correlation with species richness or diversity, three indices (the acoustic entropy, acoustic diversity and acoustic evenness indices) performed consistently better than the other four, showing moderate correlations. The levels of environmental dissimilarity among the sites did not seem to affect the performance of any of the indices tested, suggesting consistency − an important property for the indices to have.
Their results support the idea that although the acoustic indices have the potential to be used for monitoring bird communities, there are still limitations to be overcome before they can be widely adopted.Meanwhile, they should be tested in more environments to reveal fully their potential and limitations.