The black-billed streamertail (Trochilus scitulus) is a captivating species of hummingbird endemic to eastern Jamaica. This article delves into the fascinating world of this unique bird, exploring its taxonomy, physical characteristics, habitat, behavior, and conservation status. By examining various aspects of its life, we can gain a deeper appreciation for this remarkable creature and its role in Jamaica’s ecosystem.
Watch The Black-billed Streamertail
Taxonomy and Classification
The black-billed streamertail belongs to the “emeralds” tribe Trochilini within the subfamily Trochilinae of the hummingbird family Trochilidae. Its taxonomic status has been a subject of debate among ornithologists. While the International Ornithological Committee (IOC), BirdLife International’s Handbook of the Birds of the World, and the Clements taxonomy recognize the black-billed streamertail and its close relative, the red-billed streamertail (Trochilus polytmus), as separate species, the North American Classification Committee of the American Ornithological Society considers them subspecies of a single species, the “streamertail,” under the binomial T. polytmus.
This taxonomic uncertainty is further complicated by the fact that these two forms interbreed in their narrow contact zone, highlighting the complex nature of speciation and the challenges in defining species boundaries. The genus Trochilus, to which the black-billed streamertail belongs, was introduced in 1758 by the Swedish naturalist Carl Linnaeus in the tenth edition of his Systema Naturae. The genus name is derived from the Ancient Greek τροχιλος/trokhilos, referring to a small bird.
Physical Description
The black-billed streamertail is a visually striking bird, with notable sexual dimorphism in size and appearance. Males are larger, measuring 22 to 24 cm in length, including their distinctive 10 to 13 cm tail streamers. They weigh between 4.0 to 5.8 grams. Females, in contrast, are smaller, about 10.5 cm long, and weigh 3.5 to 5.5 grams.
Both sexes are characterized by their black bill, which is a key distinguishing feature from their red-billed counterparts. The male’s plumage is particularly striking, featuring a dull black to blue-black crown and a deep velvety black crest. Their upperparts are a bright grass green, contrasting beautifully with a black tail that has a green to bronzy gloss.
Female black-billed streamertails lack the male’s long tail streamers, which are a hallmark of the species. Their upperparts are metallic bronze green to greenish bronze, while their underparts are white, spotted with metallic bronze green on the breast and flanks. This coloration likely serves a camouflage function, helping to protect females during nesting and rearing of young.
Distribution and Habitat
The black-billed streamertail is highly localized, confined to the easternmost part of Jamaica. This restricted range makes it a unique and valuable part of Jamaica’s biodiversity. The species’ distribution slightly overlaps with that of the red-billed streamertail, which inhabits the rest of the island, creating an interesting zone of interaction between the two forms.
In terms of habitat preferences, the black-billed streamertail shows a clear affinity for forested environments. It is commonly found in evergreen montane forests, lowland tropical forests, and secondary forests. Interestingly, it avoids mangroves and arid highlands, suggesting a preference for more humid and densely vegetated areas.
The species exhibits a wide altitudinal range, occurring from sea level up to 1,500 meters in elevation. It is considered fairly common in the lowlands and common at middle and higher elevations. This adaptability to different elevations likely contributes to its success within its limited geographical range.
Specific locations where the black-billed streamertail can be readily observed include Ecclesdown Road and San San, both situated within its eastern Jamaican stronghold. These areas have become important sites for birdwatchers and researchers interested in studying this unique hummingbird in its natural habitat.
Behavior and Ecology
Movement
One interesting aspect of the black-billed streamertail’s behavior is its status as an elevational migrant. This means that the species moves between different altitudes, likely in response to seasonal changes in food availability or breeding conditions. This behavior showcases the bird’s adaptability and its ability to utilize different habitats within its range.
Feeding
Like other hummingbirds, the black-billed streamertail is primarily nectarivorous, foraging for nectar from a variety of native and introduced flowering plants. It shows a particular preference for Besleria lutea, a flowering plant in the family Gesneriaceae. This dietary preference highlights the importance of maintaining native plant species for the conservation of specialized pollinators like the black-billed streamertail.
The species demonstrates remarkable versatility in its foraging behavior. It feeds at all heights from the ground to the canopy, showcasing its adaptability to different forest strata. Interestingly, it has been observed “robbing” nectar from holes in flowers made by bananaquits and visiting wells drilled by yellow-bellied sapsuckers. This opportunistic feeding behavior suggests a level of intelligence and adaptability that likely contributes to the species’ success within its limited range.
In addition to nectar, the black-billed streamertail supplements its diet with small insects. These are either caught while hovering or gleaned from foliage or spiderwebs. This insectivorous component of its diet provides essential proteins and other nutrients that may not be available in nectar alone.
Breeding
The breeding behavior of the black-billed streamertail is characterized by territoriality and elaborate courtship displays. Both sexes aggressively defend their territories, a common trait among hummingbirds. This territorial behavior likely serves to secure access to food resources and potential mates.
Male courtship displays are particularly impressive. They perform repetitive forward and back flights, followed by vertical flights in front of the female while displaying their tail streamers. These acrobatic displays not only showcase the male’s flying skills but also highlight the species’ most distinctive feature – its long tail streamers.
The black-billed streamertail breeds year-round, with peak activity between January and May. Females may raise up to three broods annually, indicating a high reproductive potential. This extended breeding season and multiple broods per year likely help to maintain population levels despite the species’ restricted range.
Nest construction is the responsibility of the female. The nest is a small cup made of fine plant fibers bound with spiderwebs and decorated with lichen. It is typically built on a twig 1 to 3 meters above the ground. This careful construction and camouflage help to protect the eggs and young from predators.
The female incubates two eggs for 17 to 19 days, with fledging occurring 19 to 24 days after hatching. This relatively long development period for such a small bird reflects the complex skills that young hummingbirds must develop before leaving the nest, including the ability to hover and perform complex flight maneuvers.
Vocalizations and Sounds
The black-billed streamertail has a diverse vocal repertoire. Its calls include a loud metallic “ting” or “teet” and a prolonged “twink-twink-twink” that drops in pitch at the end. These vocalizations likely play important roles in territorial defense and communication between individuals.
One of the most fascinating aspects of the black-billed streamertail’s acoustic repertoire is the distinctive whirring sound produced by adult males during flight. This sound is synchronized with their wingbeats and is generated by the bending of the eighth primary feather (P8) with each downstroke, creating a gap that produces the fluttering sound. This unique acoustic feature adds to the species’ charm and may play a role in courtship or territorial displays.
Conservation Status
Despite its restricted range, the black-billed streamertail is currently assessed as being of Least Concern by the International Union for Conservation of Nature (IUCN). This assessment is based on the species’ ability to occupy man-made habitats, which suggests that habitat loss is unlikely to be a significant threat in the immediate future.
However, it’s important to note that the population size and trend of the black-billed streamertail are not well-documented. This lack of detailed population data highlights the need for ongoing monitoring and research to ensure the species’ long-term survival.
