In North America, more than half of 529 bird species have declined, according to one study.
Another study of 378 European bird species estimates numbers fell by as much as 19% from 1980-2017.
There are birds on mountains, birds in cities, birds in deserts, birds in oceans, birds on farm fields and birds in parking lots.
Bird numbers are falling across a broad range of habitats, as these graphs from Europe and North America show.
A recovery program has boosted the species' numbers to more than 500, with several hundred living once more in the wild.
Persons:
—, Peter Marra, It's, Alexander Lees, Lees, Christopher Michel, Marra, we're, Lees et, Philip McGowan, Glenn Simmons, McGowan
Organizations:
Service, Penguins, Earth Commons, Manchester Metropolitan University, Cornell, of Ornithology, National Audubon Society, Survey, US Geological Survey, Environment Canada, European Union, International Union for Conservation, Environment, Resources, Newcastle University, IUCN, California condor, Recovery Initiative
Locations:
North America, Antarctica, ptarmigan, Everest, Georgetown, England, Canada, United Kingdom, Gould Bay, eBird, United States, Science, Costa, India, Europe, California, Arizona, Brazil