This tiny endemic bird inhabits open brushy areas, paramo, and edges of elfin forest at altitudes from 1850 m to the highest peaks. It is only 7.5 cm long. The male weighs 2.5 g and the female 2.8 g. The black bill is short and straight.
The adult male volcano hummingbird has bronze-green upperparts and rufous-edged black outer tail feathers. The throat is grey-purple in the Talamanca range, red in the Poas-Barva mountains and pink-purple in the Irazú-Turrialba area, the rest of the underparts being white. The female is similar, but her throat is white with dusky spots. Young birds resemble the female but have buff fringes to the upperpart plumage.
The female volcano hummingbird is entirely responsible for nest building and incubation. She lays two white eggs in her tiny plant-down cup nest 1–5 m high in a scrub or on a root below a south or east facing bank. Incubation takes 15–19 days, and fledging another 20-26.
The food of this species is nectar, taken from a variety of small flowers, including Salvia and Fuchsia, and species normally pollinated by insects. Like other hummingbirds it also takes some small insects as an essential source of protein. In the breeding season male volcano hummingbirds perch conspicuously in open areas with flowers and defend their feeding territories aggressively with diving displays. The call of this rather quiet species is a whistled teeeeuu.
This species is replaced at somewhat lower elevations by its relative, the scintillant hummingbird, Selasphorus scintilla.
- Stiles and Skutch, A guide to the birds of Costa Rica ISBN 0-8014-9600-4