Blue-tailed Emerald (Chlorostilbon mellisugus) - HBW 5, p. 573

Taxonomy: Trochilus mellisugus Linnaeus, 1758, Cayenne.
Forms superspecies with C. olivaresi, which may be merely a race of present species (see page 474). Taxonomy highly complex and uncertain: present species has been considered to comprise from two to as many as eight different species by some authors, mainly on basis of differences in bill colour, together with shape of tail and overall coloration. The different forms sometimes raised to full species are: auriceps; forficatus; canivetii; salvini (including osberti); assimilis; melanorhynchus (including pumilus); and gibsoni (including chrysogaster and nitens). Alternatively, on the basis of bill colour, the five northernmost races have been lumped under canivetii as one species, assimilis recognized as a separate species, gibsoni (including chrysogaster and nitens) as a third species, and the remaining eight southern races retained as present species; this arrangement has at times been varied by some with the lumping of assimilis within the mellisugus group, or a transfer of melanorhynchus (including pumilus) to the gibsoni group. However, length of tail and depth of tail-fork appear to decrease consistently from N to S, while red-billed forms appear in both N and S groups; also, the different forms replace each other geographically, with ranges consistently meeting, and until further study produces convincing evidence to the contrary it may be best to treat them all as conspecific. Several of the presently accepted races may be invalid; further study required, especially in zones of possible contact. Proposed race nanus of upper and middle Orinoco Valley, at one stage placed in canivetii group, may be best considered a synonym of caribaeus. Form napensis (= vitticeps) of Napo Valley (E Ecuador) indistinguishable from phoeopygus. Species formerly known as C. prasinus, when name mellisugus was erroneously thought to apply to Saucerottia saucerrottei braccata. Seventeen subspecies currently recognized.