Reduction in taxonomic and functional bird diversity in an urban area in Southern Brazil

Urbanization is a globally process studied and considered one of the most drastic environmental disturb on biodiversity. This study aimed to evaluate how different intensities of urbanization act in the structure of birds in a medium size city inserted in a wetland area. In addition to the traditional metrics richness, abundance and taxonomic composition, it was found as the functional diversity and redundancy of birds are influenced by urban gradient. The urban area studied was the Pelotas city (31 degrees 46S, 52 degrees 20W) situated at the southernmost part of Brazil in a humid region of Pampa biome. A total of 216 fixed observation points along an urbanization gradient were used to sample the avifauna and four independent variables: number of trees, number of buildings with two or more floors, presence of aquatic habitat, and presence of open habitat. Functional traits of species characterized the biomass, diet, forage substrate and nesting substrate. The richness, abundance and functional diversity of avifauna were negatively related to the increase of urban intensity while the redundancy, different from the expected, did not respond to the urban gradient. The traits related to the areas with more intense urbanization (building with two or more floors) were: preference for foraging in the air, omnivory and cavity nesting. Areas with less intense urbanization (more trees and open habitats) were related to the preference for nesting on vegetation and in lower sites, and carnivory. The study showed the importance of the presence of open and aquatic habitats for the avifauna, landscape features typically not cited in urban studies, which highlight the need to adequate the mitigation actions for conservation efforts inside urban habitats according to the regional pool of species.