Disturbed Amazonian forests support diminished breeding bird communities

Abstract

Twenty percent of the Brazilian Amazon has now been deforested, and deforestation rates are increasing. This compels us to evaluate the conservation potential of human-modified landscapes; yet the ecological value of regenerating and fragmented Amazonian forests remains poorly understood. To date, most faunal studies in disturbed forests have examined metrics derived from presence or abundance. Although valuable, these data cannot tell us how old-growth species are using disturbed forests. In this study, we complement presence data with breeding observations to assess more comprehensively the habitat quality of disturbed forests in central Amazonia. We synthesized breeding evidence from standardized passive mist-netting, mixed-species flock-following, and opportunistic nest-searching across a full annual cycle in 30-35-year-old secondary forest, 10-ha fragments, and undisturbed forest. We then used multistate occupancy models to estimate the number of undetected breeding species in each forest type, which illustrated that fewer species bred in secondary forest (-43%) and 10-ha fragments (-17%) than in undisturbed forest. Both these losses are larger than the associated decrease in species richness alone (-17% and-10%, respectively). Notably, we confirmed breeding by only three terrestrial and near-ground insectivores in fragments and secondary forest combined (of the 9 species found in undisturbed forest). Disturbed forests also supported fewer breeding individuals (-35% to-50%) and, in secondary forest, fewer successful breeding attempts (-24%). Encouragingly, however, some forest-dependent birds are breeding and producing fledglings in disturbed forests, including representatives from almost every guild. This was especially apparent for mixed-species flocks and army-ant followers, two guilds that have historically been considered vulnerable to anthropogenic disturbance. Therefore, despite a loss of breeding habitat in disturbed forests, these data suggest that landscapes composed of regenerating forest and small fragments have conservation potential for forest bird populations. © Copyright © American Ornithological Society 2021. All rights reserved.