Bird community associated to a gradient of grazing intensity and cattle exclusion in the southern Brazilian Pampa

Grazing intensity is one of the main factors that shape vegetation structure, influencing the grassland bird community. Tall grass birds, including several threatened species, are depending on low intensities or exclusion of grazing, which is rarely practiced in Pampa. In this study we evaluate how grazing intensities affects the bird community in Brazilian Pampa grasslands. We established three transect lines, one each grazing treatment (moderate and low intensity, and on an area with cattle exclusion). During 13 months, transects were sampled monthly to record the diversity and abundance of bird species. All three areas presented very similar species richness, ranging from 50 to 54 species, and diversity (H’) ranging from 2.79 to 2.95. The abundance was favored by the decrease in intensity and the exclusion of grazing. In general, shortgrass bird species were more representative in the area under moderate grazing, while tallgrass birds were favored by low intensity and grazing exclusion. The taller and denser vegetation, in areas less impacted by livestock, was especially important for endangered species, such as Culicivora caudacuta Vieillot, 1818 and Sporophila cinnamomea Lafresnaye, 1839, providing shelter, perches and substrate for building and fixing nests. We corroborate the need for areas with distinct grazing intensities, forming a mosaic with different heights of vegetation, maintaining the grassland bird diversity. However, more areas with low intensity or exclusion of grazing are needed, on which several threatened species depend. Although, even these areas must be managed, avoiding the encroachment of excessive woody vegetation, which can lead to the deterioration of grassland vegetation, affecting the associated birdlife.

KEYWORDS:
Avifauna; grasslands; livestock; diversity; abundance