The green thorntail (Discosura conversii) is a small hummingbird in the "coquettes", tribe Lesbiini of subfamily Lesbiinae. It is found in Colombia, Costa Rica, Ecuador, and Panama.
Male green thorntails are about 9.5 to 10.2 cm (3.7 to 4.0 in) long and females about 6.6 to 7.5 cm (2.6 to 3.0 in). Five individuals whose sex was not recorded had an average weight of 3.0 g (0.11 oz). The adult male has a dark green crown and a lighter more metallic green back. The coppery bronze rump has bluish black inclusions and a white band across it. The bluish black tail is deeply forked and the outer feathers are very narrow, giving the species its common name. The throat is bright metallic green and the breast and belly mostly darker green with the center of the breast being metallic greenish blue. The adult female's upperparts are like the male's but for a darker rump. Its tail is notched but not elongated. All but the outermost pair of tail feathers are bluish black with dark green bases; the outmost have white bases, a blue-black middle, and white tips. Their face has a broad white cheek patch. The chin is dull black with white spots, the flanks dull green with a white spot, and the breast and belly dull black. Juveniles are like the adults but with a grayish white chin.
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The green thorntail forages for nectar mostly at the tops of flowering trees but also from epiphytes and shrubs. It appears to favor legumes. It nectars while hovering with its tail cocked at nearly a right angle to its body. Its diet also includes small arthropods such as flies, wasps, and spiders that it captures by hawking from a perch and gleans from the underside of leaves while hovering.
Breeding male green thorntails perch on high bare twigs and sometimes give a dive display. The species' breeding season appears to vary across its range but are not well defined. It is thought to span from November to April in Costa Rica, and displays have been noted in Colombia in June. All hummingbirds lay two white eggs that are incubated by the female alone, but no details of the species' breeding phenology are known and the nest has not been described.
