Black-thighed Puffleg

Quick Facts

• Scientific Name: Eriocnemis derbyi
• Spanish Name: Zamarrito muslinegro
• Family: Trochilidae
• Known Nicknames: Derby's Puffleg
• Average Length: 10 cm / 4 in
• Average Weight: 5.5–6.1 g / 0.19–0.22 oz
• Wingspan: 11–13 cm / 4.3–5.1 in
• Key Feature: Dense black feather puffs on the thighs and a deeply forked blue-black tail
• Primary Diet: Nectarivore (Nectar and small insects)
• Range: Central and Eastern Andes of Colombia and Northern Ecuador
• Habitat: Humid montane forest edges, elfin forests, and páramo shrublands
• Social Structure: Solitary and highly territorial
• Nesting/Breeding: Cup-shaped nests made of moss and lichen, usually in dense vegetation
• Conservation Status: Near Threatened (NT)
• Population Trend: Decreasing

The Black-thighed Puffleg (*Eriocnemis derbyi*) is a captivating hummingbird native to the high-altitude cloud forests and paramo edges of the northern Andes in Colombia and Ecuador. It is most famously distinguished by its namesake feature: dense, velvety black feather tufts surrounding its legs, a stark and rare contrast to the white or buff-colored "puffs" seen in most other puffleg species. Its plumage is primarily a shimmering bronze-green that glints under the mountain sun, paired with a deeply forked, dark tail and conspicuous white undertail coverts. As a high-altitude specialist, this agile flier is known for its rapid, darting movements as it forages for nectar among mountain blooms, making it a unique and visually striking gem of the Andean peaks.

Faits amusants

The Black-thighed Puffleg stands out from its relatives thanks to its namesake "boots"—dense, fluffy tufts of feathers on its legs that are a unique charcoal black rather than the typical white. These stylish leg warmers serve a practical purpose, acting as essential insulation against the biting cold of high-altitude Andean peaks. Despite its small size, this bird is a fierce territorial defender, often seen dive-bombing much larger hummingbirds to protect its preferred feeding patches. It also exhibits a peculiar habit of perching with its wings held slightly aloft, a posture that highlights its brilliant, iridescent green underparts and sets it apart from other forest-dwelling species.

Habitats et répartition

The Black-thighed Puffleg is restricted to the Central Andes, ranging from southern Colombia into northern Ecuador. It primarily occupies high-altitude environments, typically occurring at elevations between 2,500 and 3,600 meters, though it can occasionally be found slightly lower in certain regions. Within this geographical belt, it is found in localized populations across humid montane landscapes. Its preferred habitats include the edges of humid montane forests, stunted elfin forests, and the shrubby transitions bordering paramo grasslands. It is frequently encountered in dense undergrowth, clearings, and along forest margins where it can access flowering shrubs. These cool, misty environments provide the specific nectar sources and dense cover necessary for its survival.

Comportements & Reproduction

This hummingbird is primarily solitary and exhibits highly territorial behavior, aggressively defending nectar-rich floral patches from competitors and other hummingbird species. Outside of the breeding season, individuals remain independent, focusing on foraging across high-altitude Andean shrublands and forest edges. Their social structure is characterized by these competitive interactions rather than communal living, as they rely on specific territories to maintain their high-energy requirements. During the breeding season, males perform specialized aerial displays to attract mates, likely utilizing their distinctive black leg tufts as visual signals during courtship. The mating system is polygynous, meaning males do not form long-term bonds or assist in parental care. Females take full responsibility for reproduction, constructing small, cup-shaped nests from moss, lichen, and spider silk tucked away in dense vegetation. They typically lay two white eggs and handle all incubation and feeding duties until the fledglings are independent.

Alimentation

The Black-thighed Puffleg primarily subsists on nectar gathered from a variety of flowering plants, showing a particular preference for species within the genera Bomarea, Fuchsia, Macleania, Palicourea, and Tristerix. To supplement its high-energy sugar intake with necessary proteins and minerals, this hummingbird also consumes small insects and spiders, which it captures through aerial hawking or by gleaning them from leaf surfaces. An interesting behavioral trait of its diet is its classification as a trap-liner; instead of aggressively defending a single territory, it follows a regular, repeating circuit of specific flowering plants to ensure a steady food supply. Additionally, while it often feeds at lower to middle heights within its high-altitude habitat, its specialized foraging allows it to exploit nectar sources in both humid forest edges and more open sub-paramo scrub environments.

Couleurs

The Black-thighed Puffleg is defined by its shimmering golden-green plumage and a deeply forked, dark steel-blue tail. Its most distinctive feature is the pair of dense, velvety black feather tufts around its legs, which unique among pufflegs that typically have white tufts. This iridescent green coloration provides effective camouflage within Andean cloud forests, while the contrasting black "boots" serve as a primary species identifier.

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