The "resplendent" in this quetzal's name characterizes the brilliantly glowing appearance of the bird, particularly the male, quite well. Its golden-green iridescence, uniquely long and flowing uppertail coverts, acute crest on its head, and contrasting deep red, black, and white plumage make this bird hard to misidentify. Yet its wariness (Skutch 1944, LaBastille et al 1972) and often soft (yet sometimes powerful) vocalizations may still cause the bird to be missed high in the trees. The female lacks the long tail coverts and some of the brilliant coloration of the male, yet she still is iridescent green and more showy than the female of any other species of trogon.
The bushy crest (due to elongated feathers of the crown and nape) of both sexes of the Resplendent Quetzal and the extremely long tail coverts of the male make the species unique in its family. In general, the female quetzal differs from other trogons in its range by the larger size and the rich green coloration, as opposed to a brown or gray.
No other quetzal species overlaps with the Resplendent Quetzal in its range. It is replaced in the highlands of eastern Panama (and in the Andes) by the Golden-headed Quetzal (Pharomachrus auriceps). The females of the two species are similar, but the female Golden-headed has a red belly and the under surface of the tail is dark (Johnsgard 2000). The red of the underparts of the female Resplendent is confined to the undertail coverts, and the under surface of the tail is barred black and white.
Adult male: The upperparts, head, neck, and chest are iridescent or golden green; the green may appear bluish in darker light. The lower breast, belly, and undertail coverts are bright red. The greater wing coverts are elongated with black at the ends, and the greater secondary and primary wing coverts and the six middle rectrices are black. The three outer rectrices are white with black shafts and black or gray bases. The thigh feathers are black, with lower ones showing some green. The feathers on the head form a crest, from the forecrown to the rear of the head. The uppertail coverts, also green, are greatly elongated beyond the tail. The coverts cross above the end of the tail.
Adult female: The appearance of the female is duller and less dramatic. The crown, head, back, scapulars, wing coverts, rump, and uppertail coverts are iridescent, golden green. The crest feathers are less developed than the male (Johnsgard 2000), with the northern subspecies mocinno exhibiting more of a crest than in subspecies costaricensis (LaBastille et al. 1972). The uppertail coverts of the female do not extend beyond the tip of the tail. Belly and sides mostly gray; undertail coverts red. The tail is black with the three outer rectrices on both sides barred in white and black. The primaries are edged with buff. The throat is gray-brown. The thighs are black with the gloss of green as in the male.
Immature: Similar to the adult female (Johnsgard 2000). The immature male is somewhat brighter and its bare parts appear the color of the adult male. The immature female is more bronzy to dull green than the adult female, and its bill is more yellowish. The rectrices of the immature male and female are more pointed than the adult female.
As do other trogons and quetzals (Trogonidae), the Resplendent Quetzal has the unique heterodactyl toe arrangement (third and fourth toes in front; first and second toes in rear).
The bill is smaller than other trogons (Skutch 1944). It is bright yellow in males and black in females (Skutch 1944) or darkish gray (LaBastille et al. 1972).
Feet and toes are olive to dull orange-brown in males and dull green to olive-brown in females (Johnsgard 2000).
The iris is black and "glittering" (Skutch 1944) or dark brown (Johnsgard 2000) with no orbital ring like other trogons.
Measurements of wing and tail taken from Johnsgard (2000):
Wings: 189-206 mm (mean 199 mm) in males; 193-208 mm (mean 198.4 mm) in females. Wings of male mocinno average 7 mm longer than those of costaricensis (as given).
Tail: 179.5-195.5 mm (mean 187.4 mm) in males; 184-216 mm (mean 196.8 mm) in females. Rectrices of male moccino average 20 mm longer than the costaricensis (as given). Longest uppertail coverts in males: 480-855 mm for costaricensis and 650-957 mm for mocinno.
Tarsus: 19.1-20.8 mm (mean 19.9 mm) in males; 19.4-21.2 mm (mean 20.1 mm) in females (Wetmore 1968).
Culmen (from base): 21.9-26.3 mm (mean 23.5 mm) in males; 21.0 - 25.8 mm (mean 23.3 mm) in females (Wetmore 1968).
Mass: 180-210 g (Collar 2001).