Assessing the drivers of bird diversity in urban parks during winter: Insights from acoustic indices

As urbanisation accelerates, the biodiversity of urban ecosystems faces increasing challenges. Birds as indicator species, can reflect ecosystem health. Urban parks play a vital role in mitigating the pressures of urbanisation by providing critical habitats and breeding sites for birds. Passive acoustic monitoring (PAM) techniques have rapidly progressed in ecological research with automated data collection and big data development. PAM has been widely used in forest ecological monitoring and assessment, with acoustic indices developed to estimate faunal diversity. However, its application to urban bird activity, particularly under winter conditions, remains underexplored. In this study, PAM was used to assess the acoustic activity of winter birds in Nanjing, China. The study recorded at 30 sampling points in 10 urban parks for a duration of 24 h and used these data to calculate six common acoustic indices, vegetation characteristics and anthropogenic variables obtained through field surveys and GIS-based spatial analysis. The objective of this study was to identify the key vegetation and anthropogenic factors influencing bird acoustic activity in urban environments during winter, and to provide insights into urban ecosystem conservation strategies. We conclude that (i) acoustic indices can reflect the diurnal variation of bird biological activities, and the dawn chorus of birds in Nanjing during winter is delayed as temperatures decrease. (ii) Vegetation structure significantly influences bird diversity, with shrub-rich vegetation in urban parks during winter proving particularly favourable. (iii) Anthropogenic disturbances such as urban noise negatively affect bird diversity.