Taxonomy and systematics
The International Ornithological Committee (IOC), BirdLife International's ''Handbook of the Birds of the World'', and the Clements taxonomy treat the black-billed streamertail and red-billed streamertail (''Trochilus polytmus'') as separate species. However, the North American Classification Committee of the American Ornithological Society treats them as subspecies of the "streamertail" under the Binomial nomenclature, binomial ''T. polytmus''.Clements, J. F., T. S. Schulenberg, M. J. Iliff, T. A. Fredericks, J. A. Gerbracht, D. Lepage, S. M. Billerman, B. L. Sullivan, and C. L. Wood. 2022. The eBird/Clements checklist of birds of the world: v2022. Downloaded from https://www.birds.cornell.edu/clementschecklist/download/ retrieved November 10, 2022 The two species (or subspecies) interbreed in their narrow contact zone.Brokaw, J. (2020). Streamertail (''Trochilus polytmus''), version 1.0. In Birds of the World (T. S. Schulenberg, Editor). Cornell Lab of Ornithology, Ithaca, NY, USA. https://doi.org/10.2173/bow.stream1.01 retrieved September 5, 2022 The species as defined by the IOC is monotypic: no subspecies are recognised.Description
The male black-billed streamertail is long including the tail streamers and weighs . The female is about long and weighs . Both sexes have a black bill. The male has a dull black to blue-black crown; it and the nape form a deep velvety black crest. The rest of its upperparts are bright grass green. Its tail is black with a green to bronzy green gloss. The next to outermost pair of tail feathers is very long, giving the species its English name. The male's face and most of its underparts are metallic green; the undertail Covert feather, coverts are blue-black or black with a bluish gloss. The adult female's upperparts are metallic bronze green to greenish bronze that is duller on the crown. Its tail lacks the male's streamers. Its central pair of feathers are bright bronze green and the rest black with some bronze green gloss, and the outermost two pairs have wide white tips. Its underparts are white with metallic bronze green spots on the breast and flanks. Immature males are similar to the adult but lack the tail streamers; its tail feathers have bronze green tips.Distribution and habitat
The black-billed streamertail is found in far eastern Jamaica; its range slightly overlaps that of the red-billed which is found throughout the rest of the island. It inhabits evergreen montane forest, lowland tropical forest, and secondary forest. It shuns mangroves and arid highlands. In elevation it ranges from sea level to ; it is considered fairly common in the lowlands and common at middle and higher elevations.Behavior
Movement
The black-billed streamertail is an elevational migrant.Feeding
The black-billed streamertail forages for nectar at a wide variety of native and introduced flowering species; it especially prefers ''Besleria, Besleria lutea''. It forages at all heights from the ground to the canopy. It has also been observed "robbing" nectar from holes in flowers created by bananaquits (''Coereba flaveola'') and visiting wells drilled by yellow-bellied sapsuckers (''Sphyrapicus varius''). In addition to nectar, it feeds on small insects taken while hovering or gleaned from foliage or spiderweb.Breeding
Both sexes of the black-billed streamertail aggressively defend territories. Males court females that enter their territory. Both sexes make repetitive forward and back flights, after which the male flies up and down in front of the female while spreading its tail streamers. The species breeds at any time of year, mostly between January and May, and may raise three broods in a year. The nest is a cup of fine plant fibers bound with spiderweb with lichen on the outside. It is typically built on a fine twig between above the ground. The female incubates the clutch of two eggs for 17 to 19 days and fledging occurs 19 to 24 days after hatch.Vocal and non-vocal sounds
The black-billed streamertail's vocalizations include "a loud metallic ''ting'' or ''teet'' and a prolonged ''twink-twink-twink'' dropping in pitch at the end." Adult males in flight produce a distinctive whirring sound. The whirring is synchronized with the wingbeats and video footage shows primary feather eight (P8) bending with each downstroke, creating a gap that produces the fluttering sound.Status
The IUCN has assessed the black-billed streamertail as being of Least Concern, though it has a restricted range and its population size and trend are not known. No immediate threats have been identified. "The ready occupation of man-made habitats suggests that habitat loss is unlikely to be a problem."References
{{Taxonbar, from=Q1897577 Trochilus, black-billed streamertail Hummingbird species of Central America Endemic birds of Jamaica Birds described in 1901, black-billed streamertail Taxa named by William Brewster (ornithologist), black-billed streamertail Taxonomy articles created by Polbot