Smallest organisms
With a mass of approximately and a length of 5 centimetres (2.0 in), the bee hummingbird ("Mellisuga helenae") is the world's smallest bird species and the smallest warm-blooded vertebrate. Called the "zunzún" in its native habitat on Cuba, it is lighter than a Canadian or U.S. penny. It is said that it is "more apt to be mistaken for a bee than a bird". The bee hummingbird eats half its total body mass and drinks eight times its total body mass each day. Its nest is 3 cm across.
Inaccessible Island rail
The Inaccessible Island rail ("Atlantisia rogersi") is a small bird of the rail family, Rallidae. It is the only species in the genus Atlantisia. Endemic to Inaccessible Island in the Tristan Archipelago in the isolated south Atlantic, it is notable for being the smallest extant flightless bird in the world. The species was described by physician Percy Lowe in 1923 but had first come to the attention of scientists 50 years earlier. The Inaccessible Island rail's affinities were a long-standing mystery; in 2018 its closest relative was identified as the South American dot-winged crake ("Porzana spiloptera"), both of which are nested within the genus "Laterallus".