Small territory sizes and high densities of insectivorous birds in an Atlantic Forest secondary fragment, Brazil

Rômulo Ribon,Miguel Â Marini

doi:10.1007/bf03544359

Abstract

Demographic parameters of birds are essential to understand their ecology and delineate conservation and management plans. This becomes especially important in highly altered biomes such as the Brazilian Atlantic Forest, since the few remaining fragments bear mostly secondary forests where demographic parameters might differ from old-growth forests. Few studies about territory sizes and density have been conducted for entire bird communities or groups of species in the Neotropical region, with a bias towards Central America and the Amazon. In this work we determined territories of Atlantic Forest birds in order to assess their size and density. We conducted spot-mapping in a rectangular 40-ha plot within a 384-ha of secondary semideciduous forest fragment in Vicosa region, state of Minas Gerais, Brazil. We identified 260 territories of 30 species of insectivorous birds. Mean territory size of all species was 2.4 ha, ranging from 0.5 to 7.5 ha. The mean density for all species was 21.7 pairs/100 ha, ranging from 2.5 to 72.5 pairs. The sizes of the territories of many Atlantic Forest birds were by far smaller, and the density higher, than those of conspecific or congeneric species from Amazonian or Central American forests. These geographical differences in territory size and density can be explained by at least two non-exclusive hypotheses: 1) higher primary and secondary productivity in advanced successional secondary forest fragments and; 2) density compensation, given the loss of other competitor species.

Highlights

Secondary forests are increasingly replacing pristine forests around the world (ITTO 2002) and are, important for conserving the remaining forest specialist species (Wright 2010)
In this study we focused on insectivorous birds as they have been reported to be highly vulnerable to forest fragmentation and degradation (Stouffer & Bierregaard-Jr. 1995, Barlow et al 2006, but see Anjos 2006)
Our study was conducted at Viçosa county, a hilly region in southeastern Minas Gerais, Brazil, that consists of a mix of semideciduous secondary forest fragments, immersed in a matrix of pastures consisting of non-native grasses, non-shaded coffee, Eucalyptus plantations, small corn and bean plantations, small vegetable gardens and orchards (≤ 0.5 ha), and narrow linear streams often bordered by cattail (Typha spp.)

Summary

Introduction

Secondary forests are increasingly replacing pristine forests around the world (ITTO 2002) and are, important for conserving the remaining forest specialist species (Wright 2010). Compared to secondary forests, Neotropical primary forests have more microhabitats, varying from very open understory under a higher and more closed canopy cover, to open vine tangles and bushes in older treefall gaps, and even to virtually impenetrable, shaded vine tangles in more recent treefall gaps (Robinson & Terborgh 1995, 1997) This mosaic of thicker and more open understory in primary Neotropical forests can result in a strikingly different use and distribution by birds in a given area (Robinson & Terborgh 1995, 1997, Jullien & Thiollay 1998). The knowledge of the size and distribution of their territories by habitat types allows a better estimation of their population sizes with respect to vegetation characteristics of forest fragments of a given area, and their use in population-based models (Millspaugh & Thompson-III 2009)

Methods

Results

Conclusion