Climate and land-use change are projected to significantly impact global bird diversity. Using the Millennium Ecosystem Assessment scenarios, researchers evaluated the exposure of 8,750 land bird species to projected land-cover changes. Under even environmentally benign scenarios, at least 400 species are expected to lose over 50% of their range by 2050, with over 900 species projected to experience similar losses by 2100. Species most at risk are narrow-ranged and endemic to the tropics, where land-use changes drive range contractions. These species are not currently recognized as imperiled. While climate change affects biodiversity, land-use change in tropical countries is expected to cause greater species loss. A vast reserve network in the tropics and ambitious climate change reduction goals are needed to minimize global extinctions. The study used the Millennium Ecosystem Assessment scenarios to project environmental futures. Four scenarios were considered, representing different approaches to development and ecosystem management. Land-cover changes due to climate and land-use were modeled, and the resulting range size reductions were analyzed. The results showed that range loss varies significantly across species and scenarios. By 2100, the mean expected range contraction is 29–35%. Species with restricted ranges are most vulnerable, as they are more likely to experience significant range loss. These species are often not currently classified as threatened. The study highlights the importance of considering both climate change and land-use change in conservation strategies. While climate change will affect biodiversity, land-use change in tropical regions is expected to have a more significant impact. The findings emphasize the need for expanded protected areas in the tropics and more ambitious climate change mitigation efforts to prevent global extinctions. The study also notes that the geographic patterns of range loss vary across scenarios, with tropical regions experiencing more severe impacts due to land-use changes. The results underscore the urgency of addressing both climate change and land-use change to protect global bird diversity.Climate and land-use change are projected to significantly impact global bird diversity. Using the Millennium Ecosystem Assessment scenarios, researchers evaluated the exposure of 8,750 land bird species to projected land-cover changes. Under even environmentally benign scenarios, at least 400 species are expected to lose over 50% of their range by 2050, with over 900 species projected to experience similar losses by 2100. Species most at risk are narrow-ranged and endemic to the tropics, where land-use changes drive range contractions. These species are not currently recognized as imperiled. While climate change affects biodiversity, land-use change in tropical countries is expected to cause greater species loss. A vast reserve network in the tropics and ambitious climate change reduction goals are needed to minimize global extinctions. The study used the Millennium Ecosystem Assessment scenarios to project environmental futures. Four scenarios were considered, representing different approaches to development and ecosystem management. Land-cover changes due to climate and land-use were modeled, and the resulting range size reductions were analyzed. The results showed that range loss varies significantly across species and scenarios. By 2100, the mean expected range contraction is 29–35%. Species with restricted ranges are most vulnerable, as they are more likely to experience significant range loss. These species are often not currently classified as threatened. The study highlights the importance of considering both climate change and land-use change in conservation strategies. While climate change will affect biodiversity, land-use change in tropical regions is expected to have a more significant impact. The findings emphasize the need for expanded protected areas in the tropics and more ambitious climate change mitigation efforts to prevent global extinctions. The study also notes that the geographic patterns of range loss vary across scenarios, with tropical regions experiencing more severe impacts due to land-use changes. The results underscore the urgency of addressing both climate change and land-use change to protect global bird diversity.