Impact of grasslands grazed by cattle on taxonomic and functional aspects of bird assemblages in floodplain wetlands of the Paraná River

Abstract

Floodplain wetlands are frequently used for cattle grazing so understanding the impact of this activity is crucial for biodiversity conservation and management. Cattle grazing can lead to the replacement of tall natural grasslands with shorter, grazed ones, a structurally different habitat. Understanding the effects of this change on birds in floodplain wetlands is necessary for effective conservation efforts. Here, we assessed the relationship between presence-absence of grazed grasslands in the floodplain landscape and i) number of habitats per site, ii) taxonomic and functional bird diversities, iii) frequency and abundance of bird species, and iv) bird functional traits, using data from extensive bird sampling (via point counts) in the Paraná River floodplain. We found scale-dependent results. At point-count scale, presence of grazed grasslands led to an increase in number of habitats, bird species richness, and functional diversity per site. When we compared bird diversity indices based on the combination of all point counts using rarefaction curves, only functional diversity was higher in counts with grazed grasslands. One species (Geothlypis velata) was associated with the absence of grazed grasslands while 27 species (17%) were related to their presence. Thirteen bird traits (48%), including non-wetland dependency, were positively associated with grazed grasslands. Our results show that grazed grasslands increase bird diversities because a set of species, mainly birds typical of agricultural uplands, are associated with this cattle-created habitat. Further, birds associated with grazed grasslands modified the functional structure of assemblages, adding even exclusive traits such as brood parasitism that can pose a threat to floodplain birds.