Differences in diversity and habitat use of avifauna in distinct mangrove areas in São Sebastião, São Paulo, Brazil

Mangroves are an important ecosystem for many bird species for breeding, roosting and feeding, but habitat use depends on the area and vegetation structure. Avifaunal diversity studies are essential to establish baseline knowledge, identify impacts on communities, and for the effective management of ecosystems, especially in coastal areas under intense anthropogenic pressure. In this study, we: 1) characterized the mangrove vegetation structure on a former landfill (Ferry's site) from the expansion of São Sebastião Port, on the southeast coast of Brazil, 2) compared bird richness, abundance, and seasonal diversity of waterbirds and terrestrial birds at Ferry's site, with four sites located on natural land at Araçá Bay, a small semi-enclosed coastal bay, and 3) analyzed birds' habitat use. Ferry's site and Araçá Bay both border the port in the São Sebastião municipality. Overall, 52 bird species were detected in Ferry's site and 78 species in Araçá Bay. The waterbird community showed a higher average richness, abundance, and diversity in Ferry's site (A1) than in the Araçá sites (A2-A5). There were significant differences in these variables among sites, but not among seasons. For terrestrial birds, average richness and diversity were higher at Ferry's site, but average abundance was higher at Araçá Bay. These differences may be explained by habitat heterogeneity in the areas, however no pattern in these variables was found among A2-A5, because A5 has less human traffic and has more edge vegetation, which attracts birds. Ferry's site was used mainly for roosting throughout the year and as a breeding site for four heron species in summer, whereas Araçá Bay was used mainly as a foraging ground for waterbirds. Differences in habitat use were probably due to the higher density and maximum height of mangrove vegetation at Ferry's site, even though mangroves of Araçá Bay had a greater structural development. Furthermore, Araçá Bay has a large tidal plain, with high invertebrate diversity, which could explain why waterbirds used it mainly for foraging. This study highlights the importance of mangrove in the life cycle of several bird species and their aggregation. Therefore, protection of these coastal habitats should be prioritized in conservation measures.