The Search for Lost Birds, a collaboration between Re:wild, American Bird Conservancy and BirdLife International, has developed the most complete tally of bird species that are lost to science. Of the approximately 11,849 species of birds, 126 meet the criteria of being “lost.” These birds have not had a documented sighting in at least 10 years (meaning there are no photos, videos or audio recordings of them), and they are not assessed as extinct or extinct in the wild by the International Union for Conservation of Nature’s (IUCN) Red List of Threatened Species. Citizen scientists and birders’ enthusiasm for documenting birds provided important data that helped create the list of lost birds.