Fairies (Heliothryx) are two species of medium sized hummingbirds with long, strongly graduated tails and a relatively short, straight, black bills. Fairies have two-toned plumage, with bright green upperparts and immaculate white underparts; the outer tail feathers also are white. Additionally, fairies have a black band or "mask" across the sides of the head. The male Purple-crowned Fairy has a glittering violet purple forecrown; the crown of the female is green. Also, the tail of the female Purple-crowned Fairy is longer than in the male.
Purple-crowned Fairy is unmistakable across most of its range. It is extremely similar to Black-eared Fairy (Heliothryx auritus) of Amazonia, but the distributions of the two species apparently are allopatric. Male Black-eared Fairy has a green (not purple) forecrown, but the posterior portion of the black facial mask is purple. Female Black-eared Fairy has dusky speckling on the throat and breast; the underparts of female Purple-crowned Fairy are immaculate white.
The following description is based on Ridgway (1911), Wetmore (1968), and Howell and Webb (1995):
Adult male: Forecrown metallic violet. Lores and a broad black and through and below the eye, terminating, just posterior to the auriculars, in a metallic violet spot; sides of the face below this black "mask" are bright emerald green. Upperparts, from crown to uppertail coverts, and wing coverts, bright emerald green. Remiges dull black. Two central pairs of rectrices blue black; outer rectrices white. Throat, breast, and belly pure white.
Adult female: Similar to male, but crown green. Black on the side of the head somewhat reduced in extent, lacking the purple distal spot, and not bordered below with green.
Immature: Crown, nape, and upperparts broadly tipped with cinnamon. Throat and breast with sparse, fine, dusky spotting.
Iris: dark brown
Bare parts color data from Wetmore (1968).
Total length: 9-9.5 cm (Ridgely and Greenfield 2001b), 10.7 cm (Hilty and Brown 1986), 11.5 cm (Stiles and Skutch 1989), 11.5-13 cm (Howell and Webb 1995)
Linear measurements (from Wetmore 1968):
male (n = 11)
wing length: mean 66.9 mm (range 64.3-67.8 mm)
tail length: mean 44.5 mm (range 36.5-51.1 mm)
bill length (culmen from base): mean 20.7 mm (range 19.1-22.1 mm)
female (n = 12)
wing length: mean 65.4 mm (range 64.1-67.2 mm)
tail length: mean 60.2 mm (range 56.0-67.2 mm)
bill length (culmen from base): mean 20.8 mm (range 19.4-22.0 mm)
Mass: mean 5.47 ± 0.20 g (n = 9, sexes combined; Brown and Bowers 1985). Male, mean 5.46 ± 0.25 g (n = 3; Hartman 1961); female, mean 5.48 ± 0.20 g (n = 5; Hartman 1961).