Appearance

The Green-breasted Mountain-gem is a fairly large hummingbird with a straight black bill, a white postocular stripe and metallic greenish upperparts and cheek. The eyes are blackish. The tail is dark and cleft, with whitish outer tail feathers. The adult male has a bright green iridescent throat and dense green mottling on whitish breast and belly; the green mottling is densest on the upper breast and on the sides of the breast. The upperparts are dark metallic green throughout, except for the uppertail coverts, which are blackish blue. Remiges are dusky. The tail is cleft and grayish, with the central rectrices blackish gray and the outer rectrices whitish gray. The adult female is similar to the adult male but has a white throat with variable yellow or buff tinge, metallic green uppertail coverts, and less extensive whitish gray in the tail than the adult male. Recent fledglings with shorter, flesh-based black bill (Newell et al. 2007), have dark green mottling on throat, and extensive rufous tips on greenish feathers of upperparts; often with rufous spot above eye. Flesh color at base of bill changes to black soon after fledging; bill corrugations and rufous feather edging on head and lower back remain present throughout much of first year. Dark uppertail coverts (typical of the adult male) also present in immature male.

The Green-breasted Mountain-gem is very similar to the closely related Green-throated Mountain-gem (Lampornis viridipallens), but the two species are parapatric, so separation from this species in the field is usually not necessary. The male Green-throated Mountain-gem lacks greenish mottling on the breast, while the female Green-throated Mountain-gem has a completely white throat. Note however that a small percentage of adult female Green-breasted Mountain-gems show little or no yellowish tinge on a white throat, thus appearing quite similar to female Green-throated Mountain-gem in that respect. Separation of such specimens in the hand is still fairly straightforward, based on differences in the amount of whitish gray in the outer rectrices, which is greatly reduced in the female Green-throated Mountain-gem.

The following description is based on Ridgway (1911) and personal inspection of birds in the hand for the adult plumages, and Newell et al. (2007) for the juvenile and immature plumages.

Adult male: Upperparts primarily deep metallic grass green, more bronzy on the rump. Uppertail coverts black. Conspicuous white postocular stripe extends back from the eye and curves down around the upper margin of the auriculars. Auriculars and sides of neck deep metallic grass green. Thin white stripe between auriculars and throat, parallel to white postocular stripe. Remiges dusky. Central rectrices grayish black; outer rectrices pale gray or grayish white margined (on both webs) with dusky. Underparts mostly metallic grass-green, but the green is interrupted by an abundance of white or grayish white feather margins; feathers of the throat have a white subterminal bar. Leg tufts, lower belly, and vent white; inner undertail coverts green with white edges, outer undertail coverts  dusky gray with broader white edges. Underwing coverts metallic green in both sexes; greater primary coverts on underwing blackish dusky.

Adult female: Similar to the male, but chin and throat are buff, or white tinged with buff. The remaining underparts are mostly grayish white, the sides of the breast mostly metallic green. The outermost rectrix is white or grayish white (without gray margin), and with a more or less distinct subterminal dusky gray bar on the inner web. The next to outermost rectrix has a similar subterminal dusky gray bar across both webs. Some adult females show a green sheen on the dark upperside of the central rectrices, a character shared with some female Green-throated Mountain-gems but absent in the male of either species.

Juvenile: Has dark green mottling on throat. Feathers of crown and lower back with pale buffy to cinnamon tips; often with cinnamon spot above eye.

Immature: The diagnostic differences in throat color between the sexes are apparent in the first plumage acquired after the juvenile plumage. Juvenile feathers on chin often the last to be replaced. Tail patterns similar to adult plumages, although some immature males show whitish tip on gray inner flag of r6.

Little information. Juveniles apparently undergo a preformative molt, involving feathers of the throat and body (Newell et al. 2007). Post-breeding molt of remiges in adults occurs mostly Feb and Mar, into June (SalvaNATURA unpub. data).

Bill medium long, straight, and black (with pink or fleshy base in fledglings); legs and feet usually dusky, soles of feet light flesh (legs and feet sometimes entirely pale flesh in fledglings); toenails black. Extensive bill corrugations or striations along sides of upper mandible in HY individuals (up to 90% in recently fledged birds aged <2 months). Bills of adults smooth.

The following mensural data are from Ridgway (1911):

total length, male: mean 10.8 cm (range 10.4-11.3 cm, n=8)

wing length, male: mean 65.2 mm (range 62.5-67.5 mm, n=8)

tail length, male: mean 39.8 mm (range 38.5-42 mm, n=8)

culmen length, male: mean 21.1 mm (range 20-22, n=5)

total length, female: mean 10. cm (range 9.9-10.2 cm, n=5)

wing length, female: mean 58.4 mm (range 56.5-60 mm, n=5)

tail length, female: mean 35.7 mm (range 34.0-37.5 mm, n=5)

culmen length, female: mean 22 mm (range 22-22 mm, n=5)

Data for live birds trapped in the field are slightly larger, which Newell et al. (2007: 735) suggested may reflect geographic variation. But these mensural differences are consistent with the expected difference in size when comparing measurements of live birds against those from study skins (e.g., Winker 1993).

Mass (data from Newell et al. 2007 and from unpublished data SalvaNATURA)

Population La Tigra national park, Honduras, from Newell et al. 2007:

male, adult: mean 6.0 g (range 5.3-7.3 ± 0.4 g, n=51)

male, immature: mean 5.9 g (range 5.1-7.0 ± 0.5 g, n=33)

female, adult: mean 4.9 g (range 4.3-6.0 ± 0.3 g, n=58)

female, immature: mean 4.7 g (range 3.9-5.7 ± 0.4 g, n=65)

Population Reserva Biológica Monte Uyuca, Honduras, from SalvaNATURA unpublished data:

male, adult: mean 5.9 g (range 5.0-8.0 ± 0.5 g, n=137)

male, immature: mean 5.8 g (range 5.0-7.0 ± 0.5 g, n=44)

female, adult: mean 5.1 g (range 4.0-7.0 ± 0.6 g, n=102)

female, immature: mean 5.5 g (range 4.5-6.5 ± 0.6 g, n=20)