Understory bird assemblage in a riparian environment dominated by Cecropia membranacea (Urticaceae) in southwestern Amazonia

Abstract

Studies on bird assemblage structure in pioneer environments allow us to understand the use of space, distribution patterns, ecosystem services, and population dynamics of these ephemeral habitats. However, studies on the bird community related to these types of habitats in the southwest of the Brazilian Amazon are rare. We compared the bird assemblage structure of an area dominated by embaúba-da-várzea (<em>Cecropia membranacea</em> Trécul) with the adjacent alluvial rainforest along the Chandless River, a right-margin tributary of the Purus River, in the southwest Brazilian Amazon. Birds were captured with mist nets and banded (with a metal ring) along trails in both habitats. The following environmental variables were measured: temperature, humidity, and canopy openness. Understory bird assemblage was similar in the two habitats, with no influence from the environmental variables sampled. Average similarity of understory species composition between the two habitats was 77.6%, <em>Pipra fasciicauda</em> being the species that most contributed to this similarity (10.76%). Despite their almost homogeneous canopy and inconspicuous understory composed of short life cycle plants, due to the impact of river dynamics, areas dominated by <em>C. membranacea</em> have an understory bird assemblage composition similar to that of the adjacent alluvial rainforest. Understory species move horizontally and easily between these two habitats. Habitats dominated by <em>C. membranacea</em> on the lower Chandless River, contrary to expected, harbor a rich bird fauna. Given its importance to biodiversity maintenance, the protection of this habitat is recommended, as well as the undertaking of further biological studies on this unique Amazonian ecosystem.