Composição de bandos mistos de aves em fragmentos de mata atlântica no sudeste do Brasil

Abstract

Habitat fragmentation has been one of the most important subjects for conservation biology during the last years. However, few studies have evaluated the effects of forest fragmentation on mixed-species bird flocks. These flocks are associations of two or more species, which cohesion is related to networks of interactions between flock members. Decreased predation and increased foraging efficiency are two main selective advantages thought to explain the evolution of mixed-species flocking behavior. The aim of this work was to analyse mixed-species flock composition in relation to the size of Atlantic Forest fragments during rainy and dry seasons, at Zona da Mata region, Southeastern of Minas Gerais State, Brazil. Three distinct kinds of mixed-species flocks were identified at the study area: heterogeneous flocks, understory flocks and canopy flocks. The first one was observed in all forest fragments, although understory flocks were observed in only three. Canopy flocks were rare in all fragments. Some species were presente in two different kinds of flocks. The Black-goggled Tanager (Trichothraupis melanops) and the Golden-crowned Warbler (Basileuterus culicivorus) were nuclear species of heterogeneous flocks. The Red-crowned Ant-tanager (Habia rubica) was the most important species in understory flock formation and cohesion. In canopy flocks none of the species had similar characteristics. Here we analyzed the effect of season and forest fragment area on the composition of understory and heterogeneous mixed-flock based on two approaches: 1) - frequency of species and 2) - ecological traits of flocking species. In relation to species' frequencies, seasonality affected heterogeneous flocks composition more strongly than fragment area. Only two forest fragments differed slightly in heterogeneous flocks' composition. Both area and seasonality influenced understory flock composition. Excluding the category of canopy species of heterogeneous flocks, which decreased with fragment area in the rainy season, the overall proportion of species in the categories forest-dependence, foraging strata and foraging characteristics did not change in relation to forest fragment area or season, neither for heterogeneous nor for understory flocks.