The Green-backed Hillstar (Oreotrochilus stolzmanni) is a species of hummingbird found in South America. With its vibrant green back and crown, white underparts, and long black bill, this small bird is a jewel of the Andes Mountains.
The green-backed hillstar is a medium-sized hummingbird that is a resident of the Andes Mountains in South America. Its range extends from central Peru south through Bolivia to northwestern Argentina. This striking hummingbird inhabits mountains at elevations between 10,000 and 15,000 feet.
At high elevations, the green-backed hillstar is found in areas of sparse vegetation called puna grasslands. This habitat provides the nectar resources it depends on, especially flowers from plants in the Asteraceae family. The long bill of the green-backed hillstar sets it apart from other Andean hummingbirds. This adaptation allows it to access nectar from flowers with long corollas.
The green-backed hillstar reaches lengths of 7 to 8 centimeters and weighs between 5 to 7 grams. As its name indicates, adult birds have vibrant green upperparts. The crown and back have a golden-green iridescent sheen. The tail is also golden-green. The underparts are snowy white from the chin backwards. A short white stripe extends behind the eyes. The wings are dusky brown. The long black bill curves slightly downwards. The legs and feet are blackish-brown.
Males and females have similar plumage. Juveniles have buffy edges to the green feathers of the back. The white underparts also have heavy buffy streaking. After the first year molt, young birds resemble the adults.
Diet and Feeding
Like all hummingbirds, the green-backed hillstar has a high-energy lifestyle and diet. It feeds mainly on nectar from flowers using its specialized long bill and tongue. It prefers flowers with longer corollas, such as species in the Asteraceae family. Some favorite nectar sources include plants like Barnadesia and Mutisia.
The hillstar supplements its diet with small insects including flies, beetles, and mosquitoes. It gleans insects from foliage or catches them in flight. The long bill helps it access insects deep in tubular flowers.
Several adaptations allow the green-backed hillstar to thrive in the cold, low-oxygen environment of the high Andes. Its small body size reduces heat loss in the cold. Rotating its wings in a figure-eight motion during hovering flight generates heat to keep the bird warm.
The hillstar also has adaptations to deal with the low oxygen levels at high elevations. It has a larger heart and more efficient lungs compared to other hummingbird species. This improves its oxygen intake and delivery while flying. Hemoglobin in its blood has a higher affinity for oxygen, allowing its blood to absorb oxygen more effectively.
Courtship and Breeding
The breeding season for green-backed hillstars coincides with peaks in flower abundance between October and April. Males perform elaborate courtship displays to attract females. Aerial displays reveal their colorful crown and back feathers. Dive displays demonstrate maneuverability and flying skills.
Females build a tiny cup nest on a rock ledge or cliff face using spider webs and moss. Two white eggs are laid. Only the female incubates the eggs for about 16 days. The chicks are fed regurgitated food by the female. They fledge at around 3 weeks old.
Green-backed hillstars do not migrate and remain resident in their Andean territories year-round. But they do make seasonal movements up and down mountain slopes tracking the flowering and fruiting of nectar plants. They move to lower elevations during the winter dry season and higher elevations during summer rains when flowers bloom at higher altitudes.
Taxonomy and Relationships
The green-backed hillstar is classified in the order Apodiformes, family Trochilidae. It is positioned in the genus Oreotrochilus along with 4 other Andean hillstar species. Its closest relative is the Andean hillstar. Genetic evidence suggests hillstars diverged from other hummingbird lineages around 5 million years ago.
The green-backed hillstar is evaluated as a species of Least Concern by the IUCN Red List. Its range covers over 500,000 square kilometers and the population appears stable. But some localized declines have occurred due to habitat loss and fragmentation in parts of its range. Global warming may also impact hillstars by altering plant communities and flower timing at high elevations. Continued protection of puna ecosystems will be important for this specialized high-elevation hummingbird.
– The green-backed hillstar has the second longest bill of any hummingbird, relative to its size. This allows it to reach nectar in long tubular flowers.
– To conserve energy in cold nights, hillstars enter torpor – a state of reduced body temperature and metabolic rate. Their body temperature can drop by up to 30 degrees Celsius.
– The wings of hillstars beat up to 15 times per second – one of the fastest wingbeat rates of any hummingbird. This helps power their flight in thin, low-oxygen air.
– The species name “stolzmanni” honors the Polish ornithologist Jean Stanislaus Stolzmann who collected natural history specimens in Peru and published the first description of the green-backed hillstar.
– Green-backed hillstars play an important role in pollinating high elevation flowers. Their specialized bill and tongue allow them to access nectar other birds cannot.
The green-backed hillstar is a remarkable hummingbird that is adapted to the harsh conditions of the high Andes environment. Despite its small size, this energetic bird survives year-round in cold, low oxygen habitats. Thanks to its distinctive bill, it can access nectar sources unavailable to other birds. As a specialized pollinator, it maintains mutually beneficial relationships with alpine plants. Conserving puna ecosystems will ensure the continued survival of this unique Andean jewel into the future.