The rainbow-bearded thornbill (Chalcostigma herrani) is a species of hummingbird found in the Andes Mountains of Colombia and Ecuador. With its vibrant, iridescent colors and distinctive facial feathers, this tiny bird has captivated ornithologists and bird enthusiasts alike since its discovery less than 50 years ago.
Discovery and Taxonomy
The rainbow-bearded thornbill was first documented by scientists in 1977 near the town of Ricaurte in the Nariño Department of southwestern Colombia. The specimens were initially classified as a color variant of the bearded thornbill (Chalcostigma stanleyi), a closely related species. However, further study revealed distinct physical differences, including more vibrant plumage coloring and, most notably, the rainbow-hued “beard” of feathers covering the male’s throat. Based on these unique traits, the rainbow-bearded thornbill was designated as a new species, Chalcostigma herrani, in honor of biologist Hernando Herran who contributed to the research.
Since its discovery, no subspecies of the rainbow-bearded thornbill have been identified. Within the Chalcostigma genus, it is most closely associated with the bearded thornbill as well as the Longuemare’s sunangel (Heliangelus clarisse). All three belong to the mountain gem family (Trochilidae) of hummingbirds native to the Northern Andes.
The rainbow-bearded thornbill exhibits stark sexual dimorphism with the males boasting vibrant, shimmering plumage and elongated throat feathers while the females are comparatively drab brown in coloration.
**Males** have a predominantly green head and back with a bright yellow-orange breast. The throat and forehead are covered in iridescent, rainbow-colored elongated feathers that can be fanned out prominently during courtship displays. The tail feathers are also a mix of bronzy-green and purple. Their slender bill is mostly black and their eyes are brown.
**Females** lack the vibrant coloring of the males. Their plumage is primarily different shades of brown on the head, back, and tail with a lighter tan breast and belly. The throat and forehead lack specialized feathers. Females also have smaller bills and whitish eyes compared to males.
In terms of size, rainbow-bearded thornbills are relatively small, even for a hummingbird. Length ranges from 9–10 cm and body mass is roughly 5–7 grams. As is typical for its family, the rainbow-bearded thornbill has short legs and wings adapted for hovering flight.
Distribution and Habitat
The rainbow-bearded thornbill occupies a small range exclusively in the Andes Mountains of southern Colombia into northern Ecuador. Its extent of occurrence is estimated to be only around 12,000 sq km.
This species inhabites mountain forests and scrublands at elevations between 2000–3500 m. Typical habitat consists of patchy clearings, forest edges, and scrub interspersed with grasslands. Rainbow-bearded thornbills are most abundant in valleys with plentiful flowers and in proximity to stands of the giant rosette plant Espeletia which they rely on heavily for nesting sites.
The fragility of its niche mountain habitat has led the rainbow-bearded thornbill to be classified as Near Threatened on the IUCN Red List of Threatened Species. Areas protected under national parks status in both Colombia and Ecuador have been crucial for conservation.
Behavior and Ecology
Rainbow-bearded thornbills exhibit typical hummingbird behavior. They are diurnal, territorial, and feed almost solely on nectar. Their mating system is polygynous with males mating with multiple females.
These hummingbirds are active and energetic, constantly fluttering between flowers probing for nectar with their long bills. They utilize their specialized hovering ability to feed while suspended in air. Their wings beat approximately 15-80 times per second.
When not feeding, rainbow-bearded thornbills perch on branches, suspended nests, wires, or other surfaces. Males are highly territorial, using their iridescent plumage to chase intruders from feeding areas or display dominance. Aerial chases and dive displays are common against rivals or predators.
This species feeds opportunistically on a wide variety of Andean mountain flowers and plants. Some noted favorites include red trumpet vines, fuchsias, and the flowers of Espeletia plants. While nectar makes up the majority of their diet, rainbow-bearded thornbills supplement with small insects like flies, gnats, and spiders.
Breeding takes place in the months of April through July. The female builds a small, cup-shaped nest out of soft plant fibers and moss, typically on sheltered Espeletia plants. She lays 2 tiny white eggs. After about 16-19 days incubating, the eggs hatch and the female raises the chicks alone. Chicks fledge in roughly 3-4 weeks.
Relationship to Humans
Rainbow-bearded thornbills still remain relatively unstudied, although their allure among birdwatchers has grown since scientific documentation in the late 1970s. Ornithological groups occasionally organize expeditions into remote areas of the Andes specifically to observe and photograph this species in its natural habitat.
While not considered a significant pollinator species for agriculture, rainbow-bearded thornbills may play a role in pollinating native Andean plant species including their preferred Espeletia nesting sites. Local communities are generally fond of these vibrant hummingbirds and some indigenous groups consider sightings to be good luck.
There are not currently thought to be major threats to this species beyond habitat loss from logging and farming. Its popularity among bird enthusiasts helps raise awareness and protects critical areas from excessive development. Going forward, maintenance of undisturbed corridors between protected areas will be important to prevent population fragmentation.
With its restricted range and specialized habitat needs, the rainbow-bearded thornbill will remain a conservation priority in the Northern Andes. Further research into population dynamics and responses to climate change may shed light on this species’ resilience. But with proper habitat protections in place, the future continues to look bright for this colorful high-altitude hummingbird.