Pufflegs (Erionemis) are small hummingbirds with a straight, black bill, glittering green plumage, and very large "puffs" of feathers on the tibia; these leg tufts usually are white, but are black in one species (Black-thighed Puffleg Eriocnemis derbyi). Golden-breasted Puffleg is a relatively large species of Eriocnemis. It is mostly glittering green, but is glittering coppery green on the breast, upper belly, and the sides of the neck. The vent and undertail coverts are dull brownish in the male, and shining green in the female. The tail of Golden-breasted Puffleg is relatively long, deeply forked, and greenish black.
Golden-breasted Puffleg is a distinctive species, and is not likely to be confused with other species. Sapphire-vented (Eriocnemis luciani), Glowing (Eriocnemis vestita), Turquoise-throated (Eriocnemis godini), and Coppery-bellied (Eriocnemis cupreoventris) pufflegs all have blue or purplish vents and undertail coverts, and bluish black tails. These species also have a green breast and sides of the neck (although Coppery-bellied Puffleg has a coppery orange lower belly).
The following description is based on Fjeldså and Krabbe (1990) and on Heynen (1999):
Adult male: Upperparts shining green; the nape and rump are a bronzier green. Central rectrices blue green; remaining rectrices dark green to almost blue black on the two outer pairs. Underparts generally glittering golden green. Feathers of the throat basally white (not showing in the field). Lower throat and upper breast coppery bronze; undertail coverts dull brownish, the more anterior coverts tipped with metallic green. Tibial tufts large, white.
Adult female: Similar to male, but smaller (see Measurements); undertail coverts greener.
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Bare parts color data from personal observations.
Total length: 11.4 cm (Hilty and Brown 1986), 11.5 cm (Ridgely and Greenfield 2001b), 13 cm (Fjeldså and Krabbe 1990)
Linear measurements (from Schuchmann et al. 2001):
Mass: mean 5.3 g ± 1.8 g (n = 11, sexes combined, maximum 6.2 g; Dunning 2008).