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.
New Zealand wren
The relationships between the genera and species are poorly understood. The extant genus "Acanthisitta" has one species, the rifleman and the other surviving genus, "Xenicus", includes the New Zealand rock wren and the recently extinct bushwren. Some authorities have retained Lyall's wren in "Xenicus" as well, but it is often afforded its own monotypic genus, "Traversia". The stout-legged wren (genus "Pachyplichas") was originally split into two species, but more recent research disputes this. The final genus was "Dendroscansor", which had one species, the long-billed wren.New Zealand wrens are tiny birds; the rifleman is the smallest of New Zealand's birds. Their length ranges from 7 to 10 cm and their weight from as little as 5–7 g for the rifleman to an estimated 50 g for the extinct stout-legged wren. The New Zealand rock wren (and probably the bushwren) weighs between 14 and 22 g and the extinct long-billed wren weighed around 30 g.