Talamanca Hummingbird is a large hummingbird with a long, straight bill. This species is sexually dimorphic. Males are very dark, with a small white spot behind the eye; the forecrown is iridescent purple, the upperparts are dark green, the gorget is glittering bluish green, and the rest of the underparts are dark green. The tail of the male is bronze green, and is slightly notched. Female Talamanca Hummingbird lacks the iridescent gorget and crown; the upperparts are green, and the underparts are pale grayish white. The outer rectrices have a broad blackish subterminal band and small white tips.
Male Talamanca Hummingbird is distinctive within its geographic range, and is unlikely to confused with any other species. Males of allopatric Rivoli's Hummingbird (Eugenes fulgens), which occurs from the southwestern United States south only to northern Nicaragua, are similar, but its gorget is purer green, and its breast and belly are black.
Female Talamanca Hummingbird also is distinctive, by virtue of its large size and long bill. Female Green-crowned Brilliant (Heliodoxa jacula) is smaller, with a shorter bill, and its underparts are flecked with green. The bill of starthroats (Heliomaster) are even longer than the bill of Talamanca Hummingbird; starthroats also have white flank patches, and longer white postocular streak.
The following description is based on Ridgway (1911) and Wetmore (1968):
Adult male: Forecrown dull black, glossed with dark green; feathering extends anteriorly, covering the nasal operculum. Crown metallic violet blue to purple. Nape and upper back dull black. Sides of crown and auriculars dark green. Postocular spot white. Rest of upperparts, including rectrices, bronze green or golden green; rectrices sometimes pale grayish at tip. Primary coverts very dark green. Remiges dark brownish slate or dusky, faintly glossed with purple. Lores deep black. Chin and throat (gorget) metallic bluish green. Breast dark bronze green; belly similar but mixed with brownish gray. Undertail coverts dull bronze green, feathers edged with pale buff.
Adult female: Upperparts, including the two central pairs of rectrices, dull dark green. Postocular spot white. Lores and auriculars sooty black. Basal half of the three outer pairs of rectrices bronze green, with a black subterminal band and a brownish gray or grayish brown tip, broadest on the outer pair. Remiges dark brownish slate or dusky, faintly glossed with purple. Throat brownish gray, feathers tipped with dull buff; lower underparts dull brownish gray, washed with dull green. Flanks dark green. Undertail coverts dull brownish gray, washed with dull green.
Immature ("Young"): Similar to the adult female, but underparts darker and browner (especially on the throat), and scaled with pale buff; the feathers of the upperparts have buffy fringes, especially on the crown and neck.
Talamanca Hummingbird probably follows the Complex Basic Molt strategy, although molts in hummingbirds require further research (Howell 2010). Molts in this species apparently are undescribed. In the closely related Rivoli's Hummingbird (Eugenes fulgens), the Preformative Molt is partial, involving the body plumage but not the flight feathers, and is very protracted; and the Definitive Prebasic Molt is complete (Powers 2013).
Iris: undescribed?, presumably dark brown
Bare parts color data from Wetmore (1968) and Stiles and Skutch (1989).
Total length: 13 cm (Stiles and Skutch 1989)
Linear measurements (from Ridgway 1911):
male (n = 10)
wing length, mean 77.8 mm (range 76-81 mm)
tail length, mean 46.8 mm (range 43.5-48.5 mm)
culmen length, mean 31 mm (range 29-33 mm)
female (n = 10)
wing length, mean 73.5 mm (range 68-74.5 mm)
tail length, mean 42.3 mm (range 36-43.5 mm)
culmen length, mean 36.3 mm (range 35-37.5 mm)
Mass: male (n = 10), mean 9.91 ± 0.35 g (range 9.4-10.4 g; F.G. Stiles, in Powers 2013); female (n = 12), mean 8.45 ± 0.32 g (range 7.9-9.0 g; F.G. Stiles, in Powers 2013)