The Green-headed Hillstar (Oreotrochilus stolzmanni) is a species of hummingbird found in the Andes Mountains of South America. With its vibrant green head and throat feathers and long, curved bill, this medium-sized hummingbird is a sight to behold.
The green-headed hillstar is one of over 300 species of hummingbirds found around the world, the majority of which live in the Americas. Hummingbirds are known for their diminutive size, incredible speed and maneuverability in flight, and ability to hover in midair as they feed on nectar from flowers. The green-headed hillstar averages around 8-10 cm in length and weighs 5-8 grams.
The species was first described by the French ornithologist Jules Bourcier in 1851 after examining a specimen collected by the Polish explorer Jean Kalinowski in Peru. Bourcier named the bird Ornismya stolzmanni in honor of the Polish ornithologist Jean Stolzmann who extensively studied the birds of Peru. The green-headed hillstar is placed in the genus Oreotrochilus, which includes 4 other Andean hillstar species. They are specialized nectar-feeders found at high elevations in the Andes and are adapted to the relatively cold, arid conditions.
Distribution and Habitat
The green-headed hillstar occupies a range along the Andes Mountains in South America roughly 2,500 km long but only around 100 km wide on average. Their range stretches from central Peru south through Bolivia to northwest Argentina and far northern Chile.
They are found at elevations between 2,500-4,800 m, generally higher than other hummingbird species. Their preferred habitat is relatively dry, open grasslands and scrublands interspersed with rocky outcrops and hillsides that provide nesting sites. In the southern portion of their range they also inhabit meadows and along mountain streams.
Description and Identification
The green-headed hillstar is medium-sized for a hummingbird, measuring 8–10 cm in length and weighing 5-8 g. As their common name suggests, adult males have vibrant metallic emerald green heads and throats. The lower belly is also grayish-green. The crown often has a golden tinge. The upperparts are primarily bronzy-green. The tail is long and forked with feathers that have white tips and dark centers. Females are similar but have whitish undersides with scattered green spotting on the throat and lack the bold green head patch. The bill of both sexes is fairly long, slightly decurved, and black.
When perched, the green-headed hillstar sits very upright, and their long wings reach to just short of the tip of their tail. The wings produce a distinct humming sound in flight. They can be identified in flight by their swift, direct flying style along with the bold green head color.
Closely related to the green-headed hillstar are other hillstars in genus Oreotrochilus. The eared hillstar has black ear tufts, the Andean hillstar has a longer, red bill, and the white-sided hillstar is bigger with broader white flank stripes. Outside of their range, the green-headed hillstar could potentially be confused with the green violetear, but it has an entirely violet throat.
Diet and Feeding
Like all hummingbirds, the green-headed hillstar feeds on nectar from flowering plants. Their long bill is adapted for probing into flowers to lap up nectar with their extendible tongues. The curved shape helps them access nectar at the base of tubular corolla flowers. They use their slender bills to also capture small insects, which provide protein and nutrients to supplement their primarily sugar-based diet.
Flowers that green-headed hillstars are regularly observed visiting include species in the genera Chuquiraga, Barnadesia, Mutisia, and various others. They play an important role as pollinators of these high Andean flowers. They can lick up nectar at a rate of over 13 licks per second! They are aggressive at defending favorite flower patches from other hummingbirds.
In the early morning when temperatures are coolest, they enter a torpid state, lowering their metabolic rate to conserve energy. They perch puffed up with their bill tucked into their back feathers to retain body heat. When the air warms in the morning, they resume actively feeding on nectar.
Courtship and Nesting
The breeding season of the green-headed hillstar varies across their range, generally occurring from October to February. During courtship, the male performs aerial displays, flying in loops and dives to impress the female. The male and female may perch together singing before mating takes place.
The female hillstar is in charge of building the nest on her own. She uses plant materials like moss, grass, and feathers collected with her bill and bound together with spider webs. Nest locations are in protected rocky overhangs, crevices, or cavities in walls. The tiny cup-shaped nest has a diameter of only about 5 cm across and 3 cm deep.
The female lays just two tiny white eggs. She incubates them alone for about 16-18 days before they hatch. The chicks are born helpless, with eyes closed and only a bit of downy feathers. Both parents collect food and feed the chicks with regurgitation. After another 20-23 days, the young leave the nest and can fly skillfully.
Threats and Conservation Status
The green-headed hillstar is evaluated as Least Concern on the IUCN Red List of Threatened Species. Their population appears to be steady, and they occupy a relatively widespread range. However, high Andean ecosystems are vulnerable habitats, and climate change poses a potential threat to the hillstars in the future.
Some localized threats include overgrazing by livestock degrading habitats and irregular weather patterns that could reduce food sources. As with many unique species, habitat loss is an ongoing concern. Ecotourism and interest in photographing the hummingbirds may disturb nesting sites if not properly managed.
Conservation priorities are protecting key habitats through the creation of protected areas and working with local communities to sustainable manage grazing lands. Tracking population trends into the future will reveal whether climate change impacts become a more pressing threat. Luckily the remote, high peaks the green-headed hillstar inhabits offer some natural protection. Their unique adaptations allow them to thrive in the harsh conditions.
Significance to Humans
The green-headed hillstar’s small size and agility in flight make it a favorite among birdwatchers and nature photographers hoping to capture a glimpse and images of them accessing cliffside flowers. Their vital role as pollinators helps maintain the diversity and health of fragile Andean ecosystems that provide ecosystem services to human communities. They are impacted by and help indicate the effects of climate change occurring in the region. Their resilience surviving in extreme environments is admirable.
Overall, the green-headed hillstar is a magnificent species uniquely adapted to the high Andes. Though small, they represent the incredible diversity of life that has evolved on our planet. Their dazzling emerald colors and aerial maneuvers never cease to impress. They persist and blossom like precious gemstones adorning the mountainsides. Conserving their cloud forest habitats will ensure the green-headed hillstars continue to thrive for generations, providing enjoyment and valuable ecosystem services. Though often overlooked due to their remote range, they deserve recognition and protection as an important component of South America’s natural heritage.