LAUSR

Abstract The critically endangered Brazilian Merganser Mergus octosetaceus is one of the rarest waterfowls in the world. Only three isolated populations remain in the Brazilian Cerrado, totaling less than 250 individuals. We evaluated the potential influence of small hydroelectric plants (SHPs) and Protected Areas (PAs) on the species’ conservation. We identified suitable areas by using recent presence records and environmental predictors, and overlapped it with the species dispersion zone and the SHP impact zone. Suitable areas for the species are limited to 4% of the geographic space (142,899 km2). Within the dispersion zone, we found 36 planned SHPs, which can impact 4.1% of the suitable area and 17.2% of the suitable area inside PAs. Our results expose the critical situation of the Brazilian Merganser, with few isolated suitable areas, high potential impacts for the three known populations, and a high proportion of suitable areas out of PAs. We highlight the need of considering SHPs impacts on the Brazilian Merganser in environmental impact assessment studies to reduce them. Furthermore, we appointed areas for search of new populations, and emphasize how urgent the implementation of effective conservation actions aiming to protect the remaining suitable habitats for the Brazilian Merganser is.