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.
Chatham Island merganser
The Chatham Islands merganser is known only from fossils and not much is known about the bird. It was the smallest of all "Mergus" species. Fossil records indicate it was widespread on Chatham Island but not on the smaller nearby islands.