Extinct
Though simple in concept, determining extinction, i.e. knowing that every last individual of a species has disappeared, is incredibly difficult. Scientists rely on extensive and intensive surveys in the wild, and only if no solid evidence of life is found over an extended period of time will they conclude that the species is likely extinct. The primary forms of evidence used to confirm a bird species is still alive include capturing a live specimen, high-quality media captures (photographs, video or sound) that clearly include the bird's distinctive physical or vocalizing features , and genetic evidence (such as dropped feathers, unhatched eggshells, or active nesting materials, even trace cellular material that include a bird's specific DNA). If a bird species has gone ten or more years without any of the verifiable documentation listed above, it is officially classified as "lost to science".
All of the species below are classified as extinct because despite extensive surveying no evidence of the species has been found over a significant period of many decades or longer.