Acoustic community structure and seasonal turnover in tropical South Asian birds

Birds produce diverse acoustic signals, with coexisting species occupying distinct “acoustic niches” to minimize masking, resulting in overdispersion within acoustic space. In tropical regions of the world, an influx of migrants from temperate regions occurs during winter. The effects of these migrants on acoustic community structure and dynamics remain unstudied. Here, I show that in a tropical dry forest bird community occurring within an urban area in India, the influx of winter migrants is accompanied by a change in species composition of the acoustic community. However, in spite of this, the acoustic community remains overdispersed in acoustic niche space. The winter community of vocal birds at this study site additionally exhibits lower energy in the 4–7 kHz frequency bands (consistent with species singing less continuously), as well as lower phylogenetic diversity. My data are thus indicative of seasonal turnover in acoustic communities but suggest that acoustic niches and community structure are stable across seasons. Migrants occupy similar regions of acoustic space as residents and are relatively closely related to some of these species. Their arrival, therefore, leads to greater phylogenetic clustering in the winter and thus lower phylogenetic diversity, although the acoustic community remains overdispersed. Studying seasonal dynamics of acoustic communities thus provides valuable insight into assembly processes, as well as a potential framework for long-term monitoring of urban ecosystems. Tropical bird acoustic communities exhibit stable acoustic niches in spite of seasonal change in species composition. Here, I present evidence that winter migrants occupy similar acoustic niches to resident breeding birds in the tropics. Their arrival coincides with species turnover and decreased overall singing activity, but each species still occupies a distinct acoustic niche from others.