Distribuição de aves de sub-bosque ao longo de gradientes ambientais na Amazônia central

Abstract

Riparian zones are recognized by their importance to maintaining the regional biodiversity. Several studies compared the bird distribution between riparian and non-riparian zones to evaluate the conservation value of riparian zones. However, no study aimed to establish how wide is the riparian zone recognized by birds in relation to distance from the stream. We investigated the distribution of understory birds along the environmental gradients of distance from the stream, clay content and slope of the terrain in a terra firme central Amazonian forest. We sampled understory birds using mist nets in 45 plots, sampling each plot three times. We used Non-metric Multidimensional Scaling (NMDS) to reduce the data dimensionality of species quantitative (abundance) and qualitative (presence-absence) composition in one multivariate axis. In 9720 mist-net hours, we captured 1506 birds belonging to 98 species in 28 families. Estimation of the width of riparian zone as indicated by understory birds in Reserva Ducke depended on the community attribute considered: species quantitative composition (100 m), species qualitative composition (140 m). The species distribution was related to clay content, but it was not related to slope of the terrain. In Reserva Ducke, distance from the stream is correlated with clay content, but it is not correlated with slope of the terrain. Clay content affects the plant species composition, which in turn could affect the bird species composition. However, the distribution pattern of birds in places near to and away from the stream is consistent among the studies carried out in diverse geomorphologies in both temperate and tropical regions, indicating an effect of distance from the stream itself. The protection of strip s adjacent to streams is one of the most used conservation strategies. In Brazil, the protected strip around the stream extends to 30 m. We demonstrated that the width of the protected strip should be increased considerably for the Brazilian environmental legislation to be effective in fulfilling its role of protecting the biodiversity associated with the riparian zones.