The Blue-tailed Emerald, Chlorostilbon mellisugus, is a hummingbird that breeds from Colombia south and east to the Guianas, Trinidad Bolivia and Brazil.
It is a bird of savanna, scrub, cultivation and similar semi-open woodland. The female lays her eggs in a small cup nest, similar to that of the Ruby-topaz Hummingbird, placed on a horizontal tree branch. Incubation is 13 days with a further 18 days to fledging.
The Blue-tailed Emerald is 7.4 cm long and weighs 2.6 g. The black bill is short and straight. The male has mainly brilliant green plumage, with white thighs and a forked metallic blue tail. The female differs from the male in that she has grey-white underparts, a blackish ear patch, a short white supercilium and white-tipped outer tail feathers.
Blue-tailed Emeralds feed on insects and nectar. The song is a pleasant twittering, and the call of this species is a pebbly tsip.