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.
Wren
Wrens are medium-small to very small birds. The Eurasian wren is among the smallest birds in its range, while the smaller species from the Americas are among the smallest passerines in that part of the world. They range in size from the white-bellied wren, which averages under and , to the giant wren, which averages about and weighs almost . The dominating colors of their plumage are generally drab, composed of gray, brown, black, and white, and most species show some barring, especially to tail and/or wings. No sexual dimorphism is seen in the plumage of wrens, and little difference exists between young birds and adults. All have fairly long, straight to marginally decurved bills.