[6][7] Hillstars of this genus are distinct among the hummingbird family Trochilidae because of their preference for high-elevation environments, and the development of many behavioral and physiological adaptations in order to survive the cold climate of the high Andes.
[8] 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.
[8] Hummingbirds (Trochilidae) such as the green-headed hillstar are considered members of the Apodiformes bird order, along with swifts (Apodidae) and treeswifts (Hemiprocnidae).
[8] 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.
[7] Females are more commonly found in gorges and valleys with more densely packed flora as these are some of the best nesting areas for high rates of clutch survival.
[8] 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.
[6] It is thought that this roosting behaviour exists to combat very cold nights at such a high altitude and as a way to evade nocturnal predators.
[8][7] Additionally, while hummingbirds are distinct for their ability to hover by producing power on both the forward and back wing beat,[14] in order to save energy the green-headed hillstar rarely hovers and instead clings to flowers to feed on their nectar, as well as only flying short distances.
[7] The other recognisable vocalization of the green-headed hillstar is the melodic twittering and note fluctuation that occurs mostly during displays and chases with other members of their species.
[8] The vocalization of the green-headed hillstar is high in pitch, as hummingbirds communicate and hear in the range between 2 and 5 kilohertz (kHz).
[15] Hillstars on average produce higher frequency vocalizations, believed to be a result of high-altitude habitats and eliminating acoustic competition.
Like other hummingbirds, the green-headed hillstar is a specialized nectarivore, and feeds preferably on the nectar and pollen of Puya, Cacti, Chuquiraga, and Cajophora/Caiophora.
[4] Like most hummingbirds, the green-headed hillstar uses its long and protractible tongue to collect small amounts of nectar from flowers.
[7] 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.
When the eggs hatch, the chicks are generally dark with two dorsal rows of grey natal down or plumulaceous feathers.
[7] 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.