Green-headed hillstar

The green-headed hillstar is a species of South American hummingbird ranging in length from 12 to 13 cm and weighing between 7.9 and 8.4 g. The green-headed hillstar is a sexually dimorphic species. The males are more brightly colored than females. Males have a bronzed-green posterior, including the forehead, crown, back, sides and rump. Their wings are a dark contrast to their back. The primaries and secondaries are typically a dark black/brown and green. On their anterior, they have a metallic emerald green gorget that may appear bronze or blue in certain angles. Their underparts are white with a black streak down the center. At certain angles, the gorget of the adult male will have a slight blue gleam. The females share a similar physique to males, primarily differing in gorget and tail feathers. Their gorgets are white with dotted lines of green to grey spots. Females also have darker tails than males. Their tails are green and black with white webbing along the base of the outer rectrices. The wings of adult males are larger than those of adult females by approximately 3.5mm. This is a common trait for species in the hillstar genus, excluding the wedge-tailed hillstar. Juveniles resemble adult females. There is no significant difference in measurements to the Andean hillstar, Ecuadorian hillstar, black-breasted hillstar or blue-throated hillstar. It is believed this is due to the commonality of a high altitude, cold Andean climate with similar diets, which has stabilized measurements specifically of the size of the bill, wing and rectrices. == Taxonomy ==

Hummingbirds (Trochilidae) such as the green-headed hillstar are considered members of the Apodiformes bird order, along with swifts (Apodidae) and treeswifts (Hemiprocnidae). Within the hummingbird family, Hillstars (Oreotrochilus) are a genus of hummingbirds that inhabit the alpine and temperate Andes in South America between the altitudes of . First described in 1895, After the recent discovery of a new hillstar species (Oreotrochilus cyanolaemus), studies think the green-headed hillstar is a sister species to O. cyanolaemus. This supports the green-headed hillstar's differentiation from the Andean hillstar. The binomial name commemorates Polish ornithologist Jan Sztolcman (Jean Stanislaus Stolzmann). There are currently seven species in the genus Oreotrochilus. • Green-headed hillstar (Oreotrochilus stolzmanni) • Andean hillstar (Oreotrochilus estella) • Ecuadorian hillstar (Oreotrochilus chimborazo) • Black-breasted hillstar (Oreotrochilus melanogaster) • Wedge-tailed hillstar (Oreotrochilus adela) • White-sided hillstar (Oreotrochilus leucopleurus) • Blue-throated hillstar (Oreotrochilus cyanolaemus) This species radiation is hypothesized to be a result of allopatric speciation. == Habitat and distribution ==

The green-headed hillstar is distributed across north and central Peru, and extends up to the southernmost portion of the Ecuadorian Andes. Its habitat includes rocky alpine grasslands, meadows, and scrublands populated by Puya and Polylepsis stands. Males also inhabit these gorges and valleys, but frequently occupy the rocky, more barren areas as well. Jimbura is the only region in Ecuador acknowledged to have an occurrence of the species. It is a location that produces the Chuquiraga plant, one of a few food sources for the species. == Behaviour ==

The green-headed hillstar is usually sighted alone or in pairs, except during night-time, when groups gather in crevices and caves along the mountainside to roost. and therefore must consume a large quantity of sugar everyday in order to sustain this high metabolism. To reduce the metabolic cost of energy during the night when they are not feeding, hummingbirds are one of the few bird species that enter a state of torpor, or deep sleep, to reduce their metabolic rate to 1/15 of its normal rate. Hillstars on average produce higher frequency vocalizations, believed to be a result of high-altitude habitats and eliminating acoustic competition. They produce their highest frequency vocalizations when they are perched on the stems of Chuquiraga plants. Its long and thin bill is a morphological characteristic correlated with a diet of nectar and pollen. Reproduction The green-headed hillstar will begin breeding during its second year of life, with the breeding season usually starting in February and ending in June, though sometimes continuing into August. A cup-shaped nest is built out of plant fibers and moss in protective places like rock cavities, under overhangs, in roofs or houses, or inside old open buildings like barns. The female lays a clutch of two white eggs, and incubates them for 19 to 21 days. When the eggs hatch, the chicks are generally dark with two dorsal rows of grey natal down or plumulaceous feathers. Fledglings of these young birds occurs approximately 36 to 40 after hatching. Courtship in the green-headed hillstar is not well studied, but evidence suggests males display using various postures to enhance their iridescent green gorget, and this is display is accompanied by melodious twittering. == Conservation and potential threats ==

According to the IUCN Red List of Threatened Species, the green-headed hillstar is ranked as least concern due to it being locally common in its extensive geographic range throughout the Peruvian Andes. The green-headed hillstar also has a relative extent of occurrence greater than 20,000 km2 and therefore is not classified as 'Vulnerable' or 'Near Threatened'. It is believed the species' extent of occurrence is actually closer to 108,000 km2. While their population has not been thoroughly quantified, evidence suggests that the total number of mature individuals is greater than 10,000 and their population trends are stable, Due to the rocky and arid nature of their habitat, agriculture does not pose a threat to their habitat at this point in time. == References ==