Springtime spatio-temporal distribution of bird diversity in urban parks based on acoustic indices

Abstract

Human-dominated urban ecosystems have encroached on native habitats, positioning urban parks as crucial sanctuaries that support bird diversity conservation. Bird communities tend to act as significant indicators of habitat quality. Birds play a key role in generating soundscapes in urban environments, where a healthy acoustic environment is essential not only for human well-being but also serves as a core focus for environmental monitoring and landscape enhancement. Previous studies have pointed out that acoustic indices have great advantages and strong feasibility for long-term environmental monitoring. However, few studies on the comparative analysis of bird diversity across urban parks subject to varying degrees of urbanization have been published in this field. In this study we recorded the springtime soundscape across 8 urban parks in Nanjing (China) from March to April 2023 for 10 hours each day. Six acoustic indices of Acoustic Complexity Index, Acoustic Diversity Index, Normalized Difference Soundscape Index, Bioacoustic Index, Acoustic Entropy Index and Power Spectral Density were used to quantify the monitoring results. To investigate the influence of vegetation habitats on bird activity, we utilized K-means clustering analysis to categorize the parks based on their developmental gradient, while Principal Component Analysis (PCA) was employed to simplify the dimensions of 12 vegetation factors. The results revealed that the distribution of birds in urban parks is a complex interplay of variables including the gradient of urban development, the functions of park plots, and the characteristics of vegetation habitats, among others. Day-to-day, human and bird activities show similarities, yet birds' responses to urban environments vary by location. The daily movement of visitors exerts a discernible influence on park birds, even those adapted to urban life. In instances of heightened human activity, birds demonstrate a proclivity for seeking refuge in less disturbed areas, and their activity space tends to be concentrated on higher plants. Vegetation communities in areas of high human disturbance are found to provide substantial support to bird habitats. Specifically, vegetation communities featuring tall trees or ground cover that form buffer zones have a significant positive effect on weakening the impact of human activities on bird communities. In terms of monitoring bird diversity with acoustic indices, Bioacoustic Index and Acoustic Diversity Index show more consistent performance, rendering them more reliable than other acoustic indices.