Long-term change in the avifauna of undisturbed Amazonian rainforest: Ground-foraging birds disappear and the baseline shifts

How are rainforest birds faring in the Anthropocene? We use bird captures spanning >35 years from 55 sites within a vast area of intact Amazonian rainforest to reveal reduced abundance of terrestrial and near-ground insectivores in the absence of deforestation, edge effects, or other direct anthropogenic landscape change. Because undisturbed forest includes far fewer terrestrial and near-ground insectivores than it did historically, today’s fragments and second growth are more impoverished than shown by comparisons with modern ‘control’ sites. Any goals for bird community recovery in Amazonian second growth should recognize that a modern bird community will inevitably differ from a baseline from >35 years ago. Abundance patterns driven by landscape change may be the most conspicuous manifestation of human activity, but biodiversity declines in undisturbed forest represent hidden losses, possibly driven by climate change, that may be pervasive in intact Amazonian forests and other systems considered to be undisturbed. 

Methods
These count data were collected using a standard operating procedure of avian mist-netting across time (1980-1984 and 2007-2016) and space (70 unique mist net lanes) at the Biological Dynamics of Forest Fragments Project, ~80 km north of Manaus, Brazil (2º20’S, 60ºW). For specifics about field protocols, data quality control, subsetting, and categorization, we refer the reader to the pertinent sections of the Methods: Site selection, Bird sampling, and Bird data.