CONICET | Buscador de Institutos y Recursos Humanos

We compared the temporal variation of bird assemblages at three sites within a wetland of the Parana River. The final goal was to obtain an overview of the influence of spatial heterogeneity on communities in such a variable environment as the wetlands. We recorded 1662 individuals belonging to 139 species from 40 families. There were no significant differences between sites in richness, abundance or diversity. Species richness in the first year was greater than during the second year when comparisons were based on the same number of individuals (768 individuals).Number of resident and migrant species decreased in the second year, consistent with results for the general assemblages and the results of ANOVA. Community composition differed somewhat between the two years of study and was significantly different among seasons. Species were grouped into 19 trophic guilds. Aquatic carnivores, herbivores-granivores, soil-insectivores, and omnivores all varied significantly in abundance between years. Seasonal variation was noted for carnivores-insectivores, filter- feeders, herbivores- granivores, and aerial insectivores. In this study, number of species and their abundances were not significantly different among sites; there were differences in the composition of birds among sites. Thus, variation in the structure of the environments exerted a substantial influence on the composition of assemblages in different areas. Guild composition remained fairly constant between years and among seasons, with some exceptions. At this point, however, it is necessary to consider the depths of the river at which each particular site is flooded. Soil insectivores, whose feeding substrates also are affected by water levels, were recorded in higher numbers in the first year, in agreement with the pattern discussed above. The fact that their diet is based on resources very different from those of the other guilds that showed annual changes in abundance may indicate the existence of other processes that explain these differences. Geomorphological and hydrological dynamics of the river produce a heterogeneous availability of habitats and resources that affect the composition of bird assemblages. Annual and seasonal changes in meteorological variables, such as temperature and rainfall, can lead to changes in the structure and/ or composition of those assemblages.