dc.description.abstract | The Lagoon of the Fish constitutes one of the rare semi-closed estuary ecosystems of the country and, annually, it is connected with the Atlantic Ocean by the artificial opening of the estuary. We lead monthly censuses of birds in involved ecosystems in the estuary opening of the Lagoon of the Fish National Park, between November of 2007 and December of 2008. The studied environments had understood a sector of 12 km in the side of the beach, 3,5 km in the mouth of the estuary and 4 km in the flooding plain. We registered a total of 101686 individuals, pertaining to 99 species, distributed in 30 families and eleven orders. The more distinct secular variations had occurred between the hot stations and the cold stations, what it can be explained not alone by the migratory character of the species that occur in the region, as well as for the artificial handling of the estuary in the end of the winter, causing possible hydraulic variations in the lagoon. This way, we also evaluate the immediate effect of the artif | en |