In urban national parks acoustic indices represent avian habitat quality better than avian diversity

Acoustic indices provide a statistical method to quantify and assess relationships between soundscapes and avian diversity; however, more testing is necessary before acoustic indices are accepted as suitable proxies for biodiversity. Our objectives were to assess relationships between two measures of avian biodiversity and five commonly used acoustic indices in eastern deciduous forests within an urban matrix in the Mid-Atlantic region, USA. First, we used linear modeling to determine if acoustic indices could be a proxy for species richness or a Bird Community Integrity index (BCI). Next, we used structural equation modeling to disentangle relationships among acoustic indices, avian diversity, and a suite of local habitat covariates relevant to avian and acoustic diversity. Linear models showed that among five acoustic indices, two were related to bird species richness, while four were related to BCI. Normalized Difference Sound Index (NDSI) showed the strongest relationship to avian diversity. The BCI had more explanatory power with acoustic indices showing the importance of integrating habitat, landscape, and biodiversity variables when using acoustic indices. Structural equation models showed that distance to road had the strongest effect on NDSI, followed by species richness. Together, the results of linear and structural equation modeling show the utility of NDSI for assessing habitat quality and the ecological consequences of noise pollution more than biodiversity patterns. In the context of integrating acoustic indices into biodiversity monitoring, our findings provide insight into how acoustic index choice and interpretation can be shaped by both biological and environmental factors, especially in developed regions.