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The sword-billed hummingbird (Ensifera ensifera) is a neotropical species of hummingbird from the Andean regions of South America. It is the sole member of the genus Ensifera and is characterized by its unusually long bill size- the only bird to have a beak longer than the length of its body. E. ensifera uses its bill to drink nectar from flowers with long corollas and has coevolved with the species Passiflora mixta. It must also use its feet to scratch and preen feathers since its bill is so long. It is uncommon but one of the largest hummingbird species.

Taxonomy
The sword-billed hummingbird was first described by Auguste Boissonneau in 1839. Like all hummingbirds, it is apart of the Trochilidae family under the order Apodiformes. It is monotypic, meaning it is the only species within its genus. The name ensifera ("sword-wielder") is derived from Latin ensis (sword) and ferre (to carry), and refers to this hummingbird's remarkable beak length.

In 1939, there was a subspecies Ensifera ensifera caerulescens described, based on a specimen at the Royal Albert Memorial Museum. However, in 1990 ornithologist Gary R.Graves determined it was not a subspecies, but the same species with a slight discoloration due to the preservation process of the specimen.

Description


The sword-billed hummingbird are found perched on the mid to upper level branches of neotropical trees. Its length ranges 13 to 14 cm from the tail tip to the base of the bill, with males slightly larger on average than females. The bill can additionally be over 10 cm long. Individuals weigh between 10-15 g making it one of the largest species of hummingbirds. As is characteristic of hummingbirds, E. ensifera is able to fly backwards and hover in the air. It also exhibits higher than average wing-disc loading than other members of its family.

E. ensifera displays sexual dimorphism where plumage varies between males and females. Males have a coppery bronze head, bronze green back, bright green underbelly, blackish green throat, and bronze green tail. Females have a similarly colored head and back, a white belly speckled with green, a more olive colored throat, and grayish white edging around the tail.

Bill
The defining trait of this species is a beak longer than the rest of its body (excluding the tail). The tongue is also unusually long to span the length of the tube-shaped bill. The beak is black in color and curves slightly upwards. These adaptations help the hummingbird feed on flowers with long corollas that are inaccessible to other species.

Habitat and Distribution
Ensifera ensifera is a neotropical hummingbird found throughout tropical montane cloud forests of Bolivia, Colombia, Ecuador, Peru and Venezuela. It is found at higher elevations of 1700 to 3300 meters, but the most common occurrences are between 2400 to 3100 meter. It is a year-round resident of all 3 Andes ranges with no known migration patterns. This is a preferred habitat due to the concentration of nectar producing flowers. While the species is considered to have stable numbers and a wide geographic range (over 60,000 square km), it is unevenly distributed and hard to find, making the species difficult to research.

Diet and feeding
The sword-billed hummingbird is a specialist species, feeding on the nectar of specific flowers. Its abnormally long beak allows it to feed from flowers with long corollas, especially from the family Passiflora and Datura, which includes the most heavily hummingbird-pollinated plant species. E. ensifera usually drinks while in flight and is a trap-line feeder, visiting the same flowers in a consistent, patterned sequence. This promotes flower pollination and outcrossing.

Co-evolution with Passiflora mixta
A distinct factor of the sword-billed hummingbird is its extreme coevolution with the species Passiflora mixta. The two species evolved together during the early radiation of the Tacsonia clade, because the hummingbird exclusive pollinated P. mixta. The position of the flower's anthers and sigmas and the length of the corolla tube make it an inaccessible food source to nearly every species except E. ensifera. This mutualistic relationship, lets the passionflower depend on the birds for pollination, while the bird obtains a high-quality good source. To obtain nectar, the hummingbird will stick its long bill down the corolla tube (both are almost exactly the same length), drink, then retreat and hover for a few seconds before repeating the process. Other species, such as insects, may be able to access the flower's nectar but do so by puncturing the base and feeding through a hole instead of the corolla tube. Additional evidence of coevolution shows species also inhabit the same territory range along the Andean mountains. Ornithologist David Snow was the first to extensively described the relationship between E. ensifera and P. mixta. If sword-billed hummingbird populations were to decline, there would most likely be a negative affect on the abundance of passiflora mixta flowers due to their extreme coevolution.

Perching and Preening
The bird perches with its bill angled upwards to reduce the strain of the heavy beak and improve balance. The length of the bill is so long, it also forces the sword-billed hummingbird to use its feet to groom, even though this takes longer than traditional beak methods. Preening is important to remove ectoparasites and spread oil across the feathers.

Reproduction
Females and males are polygamous and may mate with several individuals to increase reproductive success. Eggs are laid usually between February and March and only the female stays to feed and guard the nest. Further research should be conducted on the number of broods and survival of offspring since little is known.

Vocalization
Other than a throated "trrr" sound, sword-billed hummingbirds make little noise. The sound is short, rapid, and usually repeated multiple times. Collections of recordings from the public show the bird may vocalize during foraging and flying, but much more research into the use and variations of their vocalizations needs to be done.

Status and Conservation
The sword-billed hummingbird is considered of "Least Concern" by the IUCN. There is no sign of population decline or visible threats to the species. There is also no census on global number of individuals, because of the large range of occurrence and uncommon sightings. Climate change and deforestation are the two most probable threats to E. ensifera in the future since this can lead to habitat loss and decreased food sources, especially of Passiflora mixta.

In Art and Media
BBC's documentary series Planet Earth II depicted the sword-billed hummingbird flying through the forest in the Jungles episode.

The sword-billed hummingbird is also frequently photographed by bird-enthusiasts and nature photographers due to its unique and colorful appearance.