The Pampas region of Argentina is dominated by shallow lagoons that may be either temporary or permanent and have complex ecological patterns driven by very local conditions. Birds are one of the most conspicuous fauna in these aquatic environments, and as a group they serve as both indicators of lagoon conditions and major players in lagoon nutrient cycling. Researchers proposed to study the structure and seasonality of waterbird assemblages in three lagoons with different limnological characteristics, and to characterize habitat use by these waterbird communities in reproductive colonies and roosting sites. In addition, they intended to estimate the seasonal contribution of waterbirds to the nitrogen, phosphorus and organic material profiles in the lagoons. As with many regions worldwide, the Pampas are becoming fragmented by human development while also being recognized for their intrinsic, tourism and recreational values. Knowledge of waterbird assemblages, diversity, habitat use, and role in nutrient cycles is essential to developing and updating conservation and management plans for habitats with resident and migratory species.
Researchers found that there was very high diversity across the entire region with the three representative lagoons providing roosting and breeding habitat for thousands of individuals and almost 130 species of waterbirds. Each lagoon had a characteristic assemblage of species with seasonal patterns that reflected both the roosting and breeding needs of the waterbirds, as well as local environmental conditions such as salinity, temperature and rainfall. Diversity was clearly related to level of disturbance: the lagoon closest to urban areas and with the highest degree of recreational use had the lowest diversity, while the lagoon closest to a large biosphere reserve area and most distant from major urban areas had the highest diversity. However, each lagoon had important assemblages of threatened and protected species.
The researchers also observed significant seasonal fluctuations in waterbird assemblages that were due to changes in the assemblage structure (species composition), not overall abundance. Differences in these fluctuations among lagoons also appeared to be related to local conditions; for example, the lagoon near agricultural centers attracted birds such as gulls that have adapted to human disturbance by shifting their diet to insects, worms and rodents associated with ploughing practices.
This study also revealed correlations between waterbird assemblages and nutrient cycling among lagoons. During the season that predators and omnivores used the lagoons, there were increased levels of phosphorus and nitrogen compared to the season in which insectivores dominated the species assemblages. These differences were attributed to the levels of these nutrients in the different diets represented as well as other factors such as temperature and residence time of the waterbird species.
The researchers hope to communicate the importance of waterbird communities, the underlying ecological patterns they may represent and the nutrient contributions that they make to management authorities that are currently attempting to develop conservation and management priorities and plans for this region. ($12,000)