Eriocnemis nigrivestis is an endemic species of Ecuador, found only in the temperate forests of the western face of the Pichincha volcano and the sector of Atacazo, between 2800 and 3500 meters in height.
This species reaches between 8 and 9 cm, and has a certain sexual dimorphism: the male exhibits a noticeable black coloration in the chest, unlike the female. A striking feature of this species (and in general of the genus Eriocnemis) is the presence of zamarros. The sandals are a pair of abundant white down on the thighs of the hummingbird, present in both sexes. It does not present characteristic vocalizations, in general it is silent. However, occasionally it can emit a monotonous and metallic "tseet tseet tseet" when it rises flight.
In the breeding season, the male's job will be restricted to courting and fertilizing the female, there is no monogamy. The courtship consists of small flights of the male in front of the female. Males can mate with several females. The construction of the nest, the empolle of the eggs and the care of the young are the sole responsibility of the female. The nest is built of moss and plant fibers, and even animal fur and feathers.
Nests have been found with webs of spiders and other sticky materials, quality that allows the nest to stretch even double its original size once the chicks are growing. Usually nests are found in low and horizontal branches.
The female incubates only two white eggs. Newborns are blind and immobile. The female feeds them regurgitating mostly insects, because nectar is not enough source of protein, necessary for the development of small.
Eriocnemis nigrivestis responds to flowering patterns by seasonality, being its main source of food blossoms of the family Ericaceae or genus Fuchsia . In areas that contain high amounts of flowers, the hummingbird will defend the territory, by chasing other intrusive hummingbirds.
Because of its restricted geographic distribution, the Zamarrito is critically endangered. The future of this bird depends on the conservation of key areas such as the reserve Yanococha and Verdecocha, one of the last remnants protected from temperate Andean western forest to the Pichincha volcano. Its habitat corresponds to cloud forest humid, including bushes bordering wooded areas.
In spite of its extremely limiting range, in 2006 a small population of E was rediscovered. nigrivestis in the Toisan mountain range, in Esmeraldas and another in the Imbabura volcano. It is believed that at present its range does not exceed 80 km, and hardly survives a population of 250 individuals, although by 2016 the population may be even smaller. One of the main threats to this bird was the construction of the Heavy Crude Oil Pipeline (OCP), whose route is interposed precisely by one of the last remnants of forest.
The response of E. nigrivestis to microhabitat and landscape variables is extremely sensitive. It is believed to be competitively disadvantaged by the same ecological niche with other species of hummingbirds, specifically, with Heliangelus strophianus, although further studies are needed on the subject.
On the other hand, the variability within a microhabitat, which does not correspond to the edge effect, does not seem to affect the Zamarrito. Previous studies on forage specificity suggest that E. nigrivestis does not react with microhabitat modulations. Therefore, it has been concluded that their eating habits are generalist and does not depend on highly specific blooms.