Measuring biodiversity with sound: How effective are acoustic indices for quantifying biodiversity in a tropical dry forest?

Large-scale biodiversity conservation and management necessitate rapid assessment tools and technologies. Indices derived from passive acoustic data offer a novel solution for rapid biodiversity monitoring. Although these indices quantify vocalizing biodiversity at a site, previous studies indicate inconsistencies in the indices' performance across different biomes. We tested the efficacy of seven acoustic indices-acoustic complexity index, acoustic diversity index, bioacoustic index (BI), acoustic entropy index, total entropy (H), normalized difference soundscape index, and number of peaks in an understudied biome, tropical dry forests, in central India. We measured the relationship between every index and a combination of these indices with a biodiversity metric, avian species richness. We found a weak correlation between individual indices and species richness (0.00 <= R <= 0.35), while a combination of indices was comparatively better at predicting species richness (R2 = 0.54). Although BI performed better than all other indices, our results indicate that acoustic indices do not accurately quantify avian species richness in this forest in central India. However, combining multiple indices increases their efficacy, limitedly. We recommend evaluating the efficiency of acoustic indices, especially in underrepresented habitats, before their application in avifauna-based rapid acoustic surveys. We assessed the effectiveness of acoustic indices for monitoring biodiversity in an underrepresented biome in ecoacoustic literature-the tropical dry forests in Central India. We found that, in our study region, the indices were limited in their capacity to measure avian species richness, which we used to represent overall biodiversity. We emphasise the need for further evaluation of these indices, especially in underrepresented habitats, before applying them for rapid acoustic surveys. image