Long-term monitoring of bird communities provides fundamental data to build population models which are valuable instruments to biodiversity conservation. The Saco da Fazenda aquatic avifauna was monitored monthly through three-daily visual censuses from January 1996 to December 2005, adopting the monthly average number of birds as a standard measurement of abundance. A total of 50 species were registered, and considering the frequency of occurrence, 34.0% were considered regular, 12.0% seasonal and 54.0% occasional. Resident birds represented 72.0% of the total species observed, seasonal visitors from the North Hemisphere (22.0%), South America visitors (4.0%) and a single species representing a possible new occurrence for Brazil. Seven were classified as shorebirds, 39 were limnic waterbirds and four species were border inhabitants or visitors coming from the Atlantic Forest. The families Ardeidae, Scolopacidae, Laridae and Charadriidae contributed with 64.0% of the species, being Phalacrocorax brasilianus(Gmelin, 1789) and Larus dominicanus Lichtenstein, 1823 the predominant ones. Despite the seasonal fluctuations observed, monthly average abundances of avifauna presented no differences, but when comparing the 10-year censuses data set, abundances were significantly different. While the diversity index showed significant differences for both monthly and annual values, the evenness index showed moderate fluctuations along the sampled years, remaining statistically similar but monthly distinct. Long-term uninterrupted studies involving waterbird communities are unique and support the need to consider seasonality, time of the day and the number of censuses to adequately determine population's size. The continuity of such long-term monitoring, could give a substantial contribution to understand interactions among species and to evaluate the importance of the estuarine populations, in a regional context.
Community structure; seasonal fluctuations; waterbirds
