Coeligena are medium sized hummingbirds with long, thin, straight bills. Male Black Inca is black and purple, with a white patch on each side of the breast, glittering blue wing coverts, and an iridescent blue-green gorget. Females have a similar pattern but are generally duller, with a longer bill and less blue on the shoulder. The tail is black, and is slightly more forked females than in males.
Black Inca is unmistakable. Collared Inca (Coeligena torquata) is similar but is distinguished by a white triangular patch on the breast, and a tail that is mostly white (with green tips) (Fjeldså and Krabbe 1990).
Adult male: Bill long, thin and straight. Purplish black, with a white postocular spot and a white patch on each side of the breast. Wing coverts dark metallic blue (Hilty and Brown 1986, Erize et al.2006, Restall et al. 2006). Gorget iridescent blue green. Undertail coverts edge with white (Hilty and Brown 1986). Tail black, forked.
Adult female: Slightly duller (grayer) than the male and with less extensive blue on the wing coverts (Fjeldså and Krabbe 1990, Daza & Villamarín 2006). The bill is longer, the wings shorter, and the fork of the tail less pronounced (Sánchez-Osés 2003).
Immature: Lack the gorget (Fjeldså & Krabbe 1990) and are duller than adults (Restall et al. 2006).
Some data on molt comes from a study conducted in the Reserva Biológica Cachalú, municipality of Encino, department of Santander (Daza and Villamarín 2006), during with 32 individuals were recaptured between August 2004 and March 2005. The majority of the individuals during this period showed signs of molt, although molt was initiated earlier in males tan in females. This period of molt coincides with a period of a relative abundance of flowering plants, with is suited to the increased energy demands during molt.
Toes: rosy red
Bare parts color data from Hilty and Brown (1986).
Total length 14 cm (Erize et al. 2006), and mass 6.6-7 g (Daza and Villamarín 2006). Snow and Snow (1980) reported the following mean measurements (sexes combined): wing length, 77.8 mm; bill length (exposed culmen), 29.8 mm; and bill length as a percentage of wing length, 38.3%.