The Juan Fernández Firecrown (Sephanoides fernandensis) is a hummingbird found solely on Isla Róbinson Crusoe, one of a three-island archipelago belonging to Chile. It is non-migratory and shares the island with the smaller Green-backed Firecrown Sephanoides sephaniodes (sic).

The population of this species has been in a general decline for years. A census made in October 2002 revealed fewer than 200 individual birds and of these only 60 females, although scientifically sound census methods have not yet been used to provide a reliable figure. The species is ranked Critically Endangered by Birdlife International. A conservation effort was begun in 2004 by a partnership of several organizations (The Hummingbird Society, American Bird Conservancy, and Juan Fernández Islands Conservancy, Oikonos - Ecosystem Knowledge) with the aim of preventing extinction of the species.

Contributing factors to the decline in population include destruction of native flora by man; invasion of exotic Rubus ulmifolius and Aristotelia chilensis, particularly by reducing the extent of the Luma trees used for nesting; predation by domestic and feral cats; and erosion by actions of introduced rabbits and goats.

This medium-sized bird inhabits forests, thickets, and gardens. In summer, males are frequently seen in the island's only town, San Juan Bautista, feeding on Dendroseris.

The male is 12 cm long and weighs 11 g. Its color is mostly cinnamon orange, excepting dark grey wings, black bill, and iridescent gold crown.

The female is 10 cm long and weighs 7 g. Its underparts are white with a dappling of very small green and black areas; the crown is iridescent blue, and upperparts are blue-green.

This species arguably shows the greatest degree of sexual dimorphism found among hummingbirds, so much so that in the 1800s the male and female were thought to be of different species until a nest was discovered with one of each gender.

The female lays two white eggs in a small cup-shaped nest typically 3-4 m above ground, nearly always in Luma apiculata.

The food of this species is nectar, often taken from the flowers of native Juan Bueno (Rhaphithamnus venustus) and Dendroseris litoralis. It also feeds on introduced Eucalyptus and Abutilon. Both genders defend their foraging territories. This hummingbird is also insectivorous. The call of the male is a loud, raspy staccato of rising and falling pitch.