Amazilia are medium sized hummingbirds with more or less straight bills that are extensively red, at least on the mandible. Azure-crowned Hummingbird is a relatively large Amazilia. The maxilla is blackish, but the mandible is pinkish red, with a dark tip. This species has a simple plumage pattern: generally it is green above, with a blue crown, and brownish green rump and tail; and white below, with dusky flanks. The subspecies of eastern Honduras and northern Nicaragua, chlorostephana, is similar, but the crown is glittering turquoise green, not blue. The sexes of Azure-crowned Hummingbird are similar.
Azure-crowned Hummingbird is similar to White-bellied Emerald (Amazilia candida), but the emerald is smaller with a shorter bill, has a green crown, and the underparts are more extensively white. Azure-crowned Hummingbird also is similar to Green-fronted Hummingbird (Amazilia viridifrons), but Green-fronted has a green crown, its bill is more extensively red, whiter flanks, and more coppery rectrices.
The following description is based on Ridgway (1911), and refers to nominate cyanocephala; see also Geographic Variation:
Adult male: Crown bright metallic blue. Nape, back, scapulars, and wing coverts metallic bronze green, becoming greenish bronze or bronze green on the rump, uppertail coverts, and rectrices. Remiges dusky. Suborbital region metallic bluish emerald green; auriculars and sides of neck mostly metallic bluish green (less bluish posteriorly). Chin, throat, malars, center of breast and belly, and tibial tufts white. Sides of breast metallic bronze green, becoming duller bronze green or greenish bronze on the flanks.
Adult female: Very similar to adult male, but blue of crown slightly duller or more greenish.
Immature: Similar to adult, but duller. Crown very dull greeenish blue. Feathers of rump and uppertail coverts narrowly tipped or margined with pale grayish buff. Tips of outer rectrices whitish. Underparts more or less washed with buff, especially on the chin, throat, and sides.
Little information. Dickey and van Rossem (1938) report a specimen from March, in El Salvador, undergoing the "annual" (prebasic) molt; this season, "during the late winter and early spring months", is when most species of hummingbird in that region undergo the prebasic molt (Dickey and van Rossem 1938). They also report a specimen from November with wing molt; "whether this was an aberrant individual or whether this species has two molts a year is not known" (Dickey and van Rossem 1938: 268). Wagner (1957) reports molt in Azure-crowned Hummingbirds in southern Mexico (Chiapas) from March to mid May.
Iris: dark brown
Bill: maxilla black; mandible dull pink, distal third to quarter black
Toes: dark brown
Bare parts color data from Dickey and van Rossem (1938).
Total length: 10-11.5 cm (Howell and Webb 1995)
Linear measurements (from Ridgway 1911):
male (n = 10)
wing length, mean 59.7 mm (range 57.5-62 mm)
tail length, mean 33.2 mm (range 31-34.5 mm)
bill length, mean 20.3 mm (range 19-22 mm)
female (n = 8)
wing length, mean 57.9 mm (range 54-61 mm)
tail length, mean 32.6 mm (range 31.5-34 mm)
bill length, mean 21.2 mm (range 19.5-23 mm)
Mass: mean 5.84 g SD 0.63 (n = 13, sexes combined?; Brown and Bowers 1985); one male, 6.1 g (Russell 1964); four females, mean 5.4 g (range 4.7-6.3 g; Russell 1964)