Appearance

Coronets (Boissonneaua) are stout, heavy-bodied hummingbirds with a relatively short heavy bill. Chestnut-breasted Coronet has a very simple plumage pattern: the upperparts generally are green, with a glittering green throat, all of which contrasts with the rufous chestnut lower breast, belly, and tail. The sexes are similar.

Chestnut-breasted Coronet has a distinctive plumage pattern, and is unlikely to be confused with any other species in its geographic range. Rainbow Starfrontlet (Coeligena iris) is larger, with a much longer bill.

The following description is based on Fjeldså and Krabbe (1990):

Adult: Upperparts metallic green, with a white spot behind the eye. The central rectrices are bronzy; remaining rectrices are chestnut rufous, with bronzy tips. The throat is heavily speckled with yellowish green. The underwing coverts, belly, flanks and undertail coverts are chestnut rufous, with a variable amount of green speckling on the flanks. The tail is notched, but not strongly forked.

Fjeldså and Krabbe (1990) do not describe sexual dimorphism. Ridgely and Greenfield (2001b) described the sexes as similar, but also report that the female has somewhat paler underparts, and with reduced green speckling on the throat, such that the buff base color of the throat is apparent. Zimmer (1951) noted similar differences in plumage color between the sexes, but also cautioned that "none of these characters is at all constant". Zimmer (1951) also pointed to a deeper notch in the tail in males as "a relatively reliable clue to the sexes", although he provided no comparative measurements.

Undescribed.

Iris: black, dark brown

Bill: black

Toes: brown, pinkish brown, grayish

Bare parts color data from specimens in the Louisiana State University Museum of Natural Science and the Field Museum of Natural History.

Total length: 10.5 cm (Ridgely and Greenfield 2001b), 11.4 cm (Hilty and Brown 1986), 11.5-12 cm (Schulenberg et a. 2010), 13 cm (Fjeldså and Krabbe 1990)

Bill length: 1.8 cm (Fjeldså and Krabbe 1990, Schulenberg et al. 2010)

Mass: mean 6.65 g (n = 4, sex?; Brown and Bowers 1985); 8.3 g (n = 1, male; Weske 1972)