Metaltails (Metallura) are small, short billed hummingbirds of the high Andes with tails that are only slightly forked. Metaltails are named for the metallic sheen to the tail, which is glittering green, purplish, or coppery, depending upon the species. Coppery Metaltail primarily is very dark, reddish coppery, with a narrow, glittering green gorget. The upper surface of the tail is dark blue, but the underside is bronzy or golden green. Females are similar to the male, but are somewhat duller.
The dark reddish coppery color of Coppery Metaltail is unique among metaltails. Closely related species to which it is most similar, such as Neblina Metaltail (Metallura odomae) and Fire-throated Metaltail (Metallura eupogon), are greener, with redder gorgets, and also are completely allopatric. Shining Sunbeam (Aglaeactis cupripennis) is much larger, is brighter rufous with a tawny pectoral patch, and has a purplish rump.
The following description is based on Cory (1913), Bond (1954) and Fjeldså and Krabbe (1990), and refers to nominate theresiae; see also Geographic Variation:
Adult male: Upperparts reddish bronze or reddish coppery; lower mantle, rump, and uppertail coverts somewhat greener. Sides of head and neck reddish bronze. Small buffy white spot behind the eye. Upper surface of rectrices bronze green with violet reflections; undersurface of rectrices shining bronze green. Narrow, glittering golden green gorget on throat. Rest of underparts bronze green (somewhat greener, less reddish than the upperparts).
Adult female: Similar to male, but duller; gorget less extensive.
Juvenile: Lacks the gorget.
Toes: black, blackish brown, brown
Total length: 10-10.5 cm (Schulenberg et al. 2010), 10.5 cm (Fjeldså and Krabbe 1990)
Linear measurements (from Graves 1981):
male (n = 7)
wing length (chord): mean 63.3 mm (range 62.4-64.4 mm)
tail length: mean 42.1 mm (range 41.2-42.7 mm)
bill length (exposed culmen): mean 12.0 mm (range 11.6-12.6 mm)
female (n = 4)
wing length (chord): mean 57.6 mm (range 55.8-59.5 mm)
tail length: mean 39.5 mm (range 37.8-42.2 mm)
bill length (exposed culmen): mean 12.3 mm (range 12.1-12.4 mm)
Mass: mean 4.9 g (n = 2; Colwell 2000); mean 5 g (n =2; Brown and Bowers 1985)