An isolated jewel
On Robinson Crusoe Island, 667 kilometers off the coast of mainland Chile, lives the Juan Fernández Firecrown (Sephanoides fernandensis). This hummingbird is critically endangered and its entire global population exists on this single, remote island of just 48 square kilometers. The species has one of the most extreme cases of sexual dimorphism in the hummingbird family; the male and female are so different they were considered separate species during the 19th century.
The male measures 11.5 to 12 centimeters long and weighs about 10.9 grams. His body is almost entirely a cinnamon-orange color, with a fiery reddish-yellow iridescent crown. The female is smaller, at around 10.5 centimeters and 6.8 grams. Her plumage is different: her back is a bluish-green, her underside is white with green and black spots, and she possesses an iridescent blue-purple crown. A now-extinct subspecies, S. f. leyboldi, is thought to have once lived on the neighboring Alejandro Selkirk Island.
A precarious existence
The firecrown's survival is threatened by a combination of factors, primarily habitat loss and invasive species. Introduced plants like zarzamora blackberry (Rubus ulmifolius) and maqui wineberry (Aristotelia chilensis) have overrun native flora, degrading the forest the birds need to survive. The firecrown builds its cup-shaped nest almost exclusively in native luma trees (Myrceugenia fernandeziana), typically about four meters above the ground. Herbivores brought to the island, such as rabbits and goats, destroy the saplings of these essential native trees.
Predation from introduced animals like domestic cats, rats, and coatis poses a direct threat to eggs, nestlings, and adult birds. birds also compete for resources. The Green-backed Firecrown (Sephanoides sephaniodes), a relative from the mainland, colonized the island in the 19th century and now vastly outnumbers the endemic species. While the larger Juan Fernández Firecrown often wins one-on-one confrontations, the sheer number of competitors puts pressure on food sources, particularly for the smaller females. The population is currently estimated to be between 1,500 and 3,500 mature birds, and the number is decreasing. Conservation efforts, started in 2004, involve restoring native habitat, removing invasive plants, and managing predator populations.