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.
Goldcrest
The goldcrest is the smallest European bird, in length, with a wingspan and a weight of . It is similar in appearance to a warbler, with olive-green upper-parts, buff-white underparts, two white wing bars, and a plain face with conspicuous black irises. The crown of the head has black sides and a narrow black front, and a bright crest, yellow with an orange centre in the male, and entirely yellow in the female; the crest is erected in display, making the distinctive orange stripe of the male much more conspicuous. The small, thin bill is black, and the legs are dark flesh-brown. Apart from the crest colour, the sexes are alike, although in fresh plumage, the female may have very slightly paler upper-parts and greyer underparts than the adult male. The juvenile is similar to the adult, but has duller upper-parts and lacks the coloured crown. Although the tail and flight feathers may be retained into the first winter, by then the young birds are almost indistinguishable from adults in the field. The flight is distinctive; it consists of whirring wing-beats with occasional sudden changes of direction. Shorter flights while feeding are a mix of dashing and fluttering with frequent hovering. It moves restlessly among foliage, regularly creeping on branches and up and down trunks.