Summary/Abstract
We present an overview of the global spatiotemporal distribution of avian biodiversity, changes in our knowledge of that biodiversity, and the extent to which it is imperilled. Birds are probably the most completely inventoried large taxonomic class of organisms, permitting a uniquely detailed understanding of how the Anthropocene has shaped their distributions and conservation status in space and time. We summarize the threats driving changes in bird species richness and abundance, highlighting the increasingly synergistic interactions between threats such as habitat loss, climate change, and overexploitation. Many metrics of avian biodiversity are exhibiting globally consistent negative trends, with the International Union for Conservation of Nature’s Red List Index showing a steady deterioration in the conservation status of the global avifauna over the past three decades. We identify key measures to counter this loss of avian biodiversity and associated ecosystem services, which will necessitate increased consideration of the social context of bird conservation interventions in order to deliver positive transformative change for nature.