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Spatial and temporal dynamics of bird assemblages in Pre Delta National Park, located in Diamante department, southwestern Entre Ríos (32o03’S 60o38’W), were studied between March 2006 and March 2008. The objectives of this study were to: (1) characterize the bird community in terms of species richness, abundance and diversity (alpha and beta); (2) relate the parameters of the assemblages with spatial and temporal environmental changes related to vegetation, hydrology and human disturbance; and (3) identify groups of species that respond in similar ways to a given environmental impact and which could, therefore, be effective indicators of environmental disturbance. A mean abundance of 3417 individuals was recorded, corresponding to 163 species, 41 families and 14 orders of birds. Among the total recorded species, 39 were aquatic birds belonging to 12 families. The remaining 124 species were typical of terrestrial habitats and / or the transitional area between terrestrial and aquatic habitats. Species richness, mean abundance and diversity differed among the three environmental units included in the study. Species were classified into 19 trophic guilds, which reflected the wide range of microhabitats and food resources of the floodplain that support a variety of diets and foraging methods. Overall richness and average abundance were mainly determined by wetlands, which supported the highest number of species in relation to the total and to each of the environmental units. This high number of species likely could be attributed to its spatial heterogeneity. Wetlands support a wide diversity of aquatic habitats, including bodies of open water, floating vegetation, and patches of emergent shrubs and trees. The latter contribute greatly to the overall spatial heterogeneity of this environment. The non-flooded and flooded riverine forests exhibited a relatively low number of species compared to wetlands. This difference may be partly attributed to the fact that wetlands cover larger areas than riverine forests; the latter are narrow and fragmented strips of vegetation. Richness and overall abundance of assemblages of birds did not differ significantly among wetland transects. Nevertheless, significant changes in species composition were observed along different stretches of wetland transects. In contrast, the only significant temporal change in bird assemblages was species richness, especially between years. Although many factors might explain the above changes, probably the most important were water regime, size and heterogeneity of the site, and vegetation structure. Guild abundance remained relatively constant between years and among seasons. Carnivores of aquatic shorelines as well as soil insectivores were, however, better represented in the first year of study. Conversely, arboreal herbivore– granivores differed significantly between years and, unlike other guilds, were better represented during the second year. Seasonal variation in the abundance of trophic groups could be attributed to migration patterns, food availability and / or reproductive behavior. Availability of habitats and spatial and temporal heterogeneity of resources for birds are governed by the geomorphological and hydrological dynamics of the river. When comparisons were made among forest types and seasons, only species richness showed significant variation. In contrast, abundance did not vary among forests or seasons. Similarly, there were no differences among years in richness, overall abundance and diversity. Among guilds, arboreal herbivoregranivores, foliage insectivores, ground insectivores, bark insectivores, short-or-long flight insectivores and aerial insectivores all differed according to forest types. Groundgranivores, insectivore-frugivores and foliage insectivores varied in abundance between years; insectivore-frugivores, short-or-long flight insectivores and nectarivores varied among seasons. Non-flooded riverine forest and flooded riverine forest, the two major forest types found in the study area, supported a variety of bird species, including migrants and residents. These forests differed in several important features associated with the topography and vegetation. Spatial and temporal variation in species richness and composition observed in flooded and non-flooded forests could be related to differences in vegetation and temporal changes in the floodplain. The obtained results underpin the greater importance of structural complexity of vegetation in comparison to floristic composition as a factor influencing bird species richness. Migratory species were important components of bird communities in the studied assemblages and contributed to the temporal variation of species richness and composition in both types of forests. The composition of the guilds was similar in non-flooded and flooded riverine forests with differences primarily related to habitat changes rather than to diet or substrate. The flood pulse was the main factor governing the structure and dynamics of the dominant biota. We addressed the relationship between hydro-sedimentological pulse regime and bird assemblages, particularly considering the frequency and duration of the high water phase. Hydrological attributes of flood pulses in the National Park markedly and differentially affected species assemblages and guilds, depending on the group considered. The results supports the idea that low-water phases would allow a wider range of microhabitats, as negative relationships were found between the full pulse frequency and number of days on which the study transects remained flooded, with respect to richness of the assemblages. Anthropogenic disturbances are another factor that influenced the structure and composition of bird assemblages. However, sites outside the protected area, despite being inhabited, are well preserved. Results found in the present thesis are of great current relevance, since wetlands have received much attention due to their importance as centers of biodiversity. Further research on stream ecology in floodplains could provide additional information for conservation of these systems.

Composición y distribución de los ensambles de aves de la planicie de inundación del Paraná inferior (Entre Ríos, Argentina)