Partial recovery of primary rainforest bird communities in Amazonian secondary forests

Abstract

Loss of primary rainforest imperils species, communities, and ecosystem services. Secondary forests play a role in supporting primary forest species, making it important to assess how variation in landscape composition, sample area, and secondary forest age influence their value for maintaining biodiversity. We sampled bird communities in three 16-ha sites in 31-36-year-old secondary forest (SF) and three adjacent primary forest (PF) sites at the Biological Dynamics of Forest Fragments Project near Manaus, Brazil. SF sites were surrounded by vast, minimally broken PF. Spot-map surveys revealed 204 species, with 48 found only in PF (SF estimate 117–144 species/site, PF estimate 163–180). SF communities were distinct, but composed almost entirely of PF species and overlapped PF communities in functional attributes. Cavity-nesting species were slightly underrepresented in SF. Important differences in SF included much reduced abundance of canopy, terrestrial, and insectivorous species. Vegetation structure may limit canopy species: SF had a homogeneous canopy of 20–25 m, >10 m lower than the heterogeneous PF canopy. Sensitivity of terrestrial insectivores conforms to an expected pattern, perhaps exacerbated by a lack of colonists for these regionally declining species. Relatively better recovery of midstory and understory species does not align with some studies, perhaps because our landscape facilitated their colonization. In this system, SF bird communities appear to be recovering, with frugivores, nectarivores, and granivores (including game species) already well matched to PF. Complete recovery may be slowed not just by SF habitat suitability, but also by demographic processes in PF that limit availability of colonists.

Abstract in Portuguese is available with online material.