Forest type consistently shapes bird communities across seasons: Insights from passive acoustic monitoring

Forest management affects forest-dwelling taxa, such as birds, which play diverse roles in ecosystem functioning. While birds are frequently studied, surveys typically are conducted during the breeding season, overlooking non-breeding periods during which birds may have different resource requirements. Understanding year-round dynamics of habitat use is essential to inform management practices that support bird communities. We used passive acoustic monitoring to study bird assemblages across a gradient from deciduous broadleaved to coniferous forest stands around the city of Jena (Thuringia, Germany). We investigated how season, forest type, and environmental variables influence species taxonomic diversity, community composition, and functional diversity. Birds were monitored in 30-day periods during winter, spring, summer, and autumn 2024 using AudioMoth recorders and BirdNET for species identification. Species diversity varied significantly by season, peaking in spring and summer and declining in autumn and winter; forest type had no effect. Community composition was primarily driven by season, but within seasons, birds clustered by forest type. Season influenced functional dispersion and dissimilarity, but not evenness; forest type influenced only functional dispersion. Overall, seasonality, especially migration dynamics, most strongly impacts bird diversity. Within seasons, forest type structures community composition but does not affect taxonomic or functional diversity. Persistent functional diversity despite taxonomic shifts suggests functional redundancy, indicating resilience to habitat change. Coniferous stands emerged as harbouring distinct, but equally diverse bird species compared to deciduous stands. Forest managers should prioritise a mix of forest types to sustain rich bird communities and ensure long-term ecosystem functionality.