The rainbow-bearded thornbill is long. Males weigh about and females . Both sexes have a short, needle-like bill. Adult males of the nominate subspecies are mostly bottle green with a white dot behind the eye and rufous forecrown and crown. It has black primaries, a coppery rump, and white undertail coverts. The forked tail is blue-black with prominent white tips at the corners that are most easily seen from below. Its gorget ("beard") is a rainbow of colors from celadon-green through turquoise to yellow and red at the lower end. The feet are black. Adult females are generally similar to males, but with pale yellowish-ochre from lower the belly to the undertail coverts and a much reduced gorget. Juvenile birds are similar to the adult female, but the male has an entirely dark throat. Subspecies C. h. tolimae is very similar to the nominate but is darker overall and its gorget is longer.Schulenberg, T. S. and C. W. Sedgwick (2020). Rainbow-bearded Thornbill (Chalcostigma herrani), version 1.0. In Birds of the World (T. S. Schulenberg, Editor). Cornell Lab of Ornithology, Ithaca, NY, USA. https://doi.org/10.2173/bow.rabtho1.01 retrieved February 25, 2022
