The Green-breasted Mountaingem, known scientifically as Lampornis sybillae, is a hummingbird of striking beauty. This avian jewel measures approximately 10 to 11 centimeters in length and tips the scales at a mere 4 to 7 grams, with males being the larger sex. Its plumage is a resplendent metallic grass green on the upperparts, accented with bronze on the rump and black on the uppertail coverts. A distinctive white stripe elegantly curves behind the eye, complemented by similarly hued cheeks with a thin white stripe below.
To identify the male Green-breasted Mountaingem, look for underparts that mirror the metallic green of the upperparts, edged with white or grayish white. The lower belly, vent area, and leg tufts are white, while the tail feathers are a mix of grayish black and pale gray with dusky margins. Females, on the other hand, display a buff chin and throat with grayish white underparts and green flanks. Their tail feathers are predominantly white or grayish white with a dusky gray bar near the end, lacking the dusky margins seen in males. Juveniles can be recognized by their dark green mottled throat and buffy to cinnamon tips on their feathers.
This species thrives in the interior and edges of humid evergreen and pine-oak forests, as well as in the transitional zones leading into cloud forests.
The Green-breasted Mountaingem graces the central and eastern regions of Honduras and the northwestern territories of Nicaragua with its presence.
Seasonal elevational movements are thought to be part of this bird's behavioral repertoire, although the specifics of these movements are not well-documented.
The song of the Green-breasted Mountaingem is a soft, scratchy warble that may conclude with a trill. Males typically sing from concealed perches, but they may also vocalize openly or while in flight. Both sexes emit short, buzzy 'shrrrt' calls during feeding.
Details on the breeding habits of the Green-breasted Mountaingem are scarce, but available data suggest a breeding season spanning from November to February.
The IUCN has classified the Green-breasted Mountaingem as Least Concern. Although the population size is unknown and suspected to be in decline, there are no immediate threats identified. However, the bird's habitat is expected to shrink due to the effects of global warming.