Aquatic avifauna in a subtropical estuarine system, a World Heritage site (Paraná, southern Brazil)

The Paranaguá Estuarine Complex (PEC) is internationally recognized for its economic, social, and environmental relevance. It is designated as a World Heritage site and part of selected wetland areas that protect and conserve biodiversity, especially waterbirds. However, it has historically been under pressure from human activities, and the information about waterbirds that use the region is fragmented. Thus, with this study, we sought to establish a baseline for the waterbirds using the bays of the PEC, considering aspects such as species richness, abundance, and conservation status. On board a boat, we conducted monthly surveys from March 2020 to February 2021 along 36 transects equally distributed among the three main bays of the PEC. We recorded 46 species distributed across 17 families and eight orders. The order Charadriiformes displayed the highest number of species, totaling 19. Among them, the Neotropic Cormorant, identified as Nannopterum brasilianum, stood out with the highest number of occurrences. Furthermore, we documented eight migratory species from the Northern Hemisphere, including Calidris pussilla, the Semipalmated Sandpiper, considered near threatened by the International Union for Conservation of Nature Red List. Additionally, we observed seven other species classified under some threat of extinction. Our results revealed that the PEC harbors a rich and diverse assemblage of waterbirds consisting of resident and migratory species, many of which are at some risk of population decline. Therefore, we reinforce the importance of continuous monitoring in the region, which can serve as a basis for public policies, supporting management and conservation strategies focused on waterbirds and the wetlands on which they depend.