How does cattle raising affect bird communities in the delta of the Paraná River?

Abstract

We hypothesize that the presence of cattle should increase environmental heterogeneity and therefore maintain more diverse bird communities. Therefore, we analyzed the changes in the structure of vegetation and diversity of bird species that inhabit the fluvial forests in the Delta region of the Paraná River in relation to the different cattle raising management (islands with cattle, islands without cattle, islands with recent cattle exclusion). In the islands with cattle we found lower height of the herbaceous layer, less coverage of the shrub layer and lower presence of climbing plants, which were associated with birds assemblages with greater richness, abundance and diversity. We consider that this region has evolved under a context of significant herbivory pressure, which in pre-Columbian times was possibly dominated by Blastocerus dichotomus and Ozotoceros bezoarticus (locally extinct at present), Hydrochoerus hydrochaeris and Myocastor coypus. In this context, the complete exclusion of cattle in protected areas and the absence of the cervids that inhabited this region in the past, would lead to deterioration the natural condition of the environment and seems to be generating a decrease in the diversity of these sites. We consider that a reintroduction plan for these cervids should be implemented in the area.