Bird Families

Atius salangan / Aerodramus sawtelli

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Aerodramus is a genus of small, dark, cave-nesting birds of the fast family Collocaliini. Its members are limited to tropical and subtropical regions in southern Asia, Oceania, and northeastern Australia. Many of its members were previously classified in Collocaliabut were ranked first in a separate genus by American bird watcher Harry Oberholser in 1906.

This is a taxonomically difficult group of very similar species. Echolocation, DNA, sequencing and parasitic lice have all been used to establish relationships, but some problems such as the placement of the Papuan swiftlet have not been fully resolved. These swiftlets can pose major identification problems where several species occur.

what distinguishes the swiftlet Aerodramus from other swifts, and indeed almost all other birds, is their ability to use a simple yet effective form of echolocation. This allows them to navigate through breeding and roosting caves.

Swifty nests Aerodramus built with saliva as the main component. In two varieties, saliva is the only material used and the nests are harvested for the famous Chinese delicacy 'bird's nest soup', the over-collection of which is putting pressure on swiftlet populations.

Distribution

The range of these swiftlets is bordered by tropical southern Asia, Oceania, northeastern Australia and the Indian Ocean, with the greatest diversity in Southeast Asia, Indonesia and Papua New Guinea. Several of the species are confined to small islands, and their limited range can make them vulnerable, like the Seychelles, White eels, and Guam's swiftlets. Salangana Mangaia is a recently extinct species known only from fossils.

Description

Salangan Aerodramus - typical swifts in many ways, having narrow wings for fast flight, and a wide yawn and a small reduced beak surrounded by bristles for catching insects in flight. They have dull plumage, which is mainly in shades of black, brown, and gray. Members of this genus tend to have dark brown upper wings and upper body, sometimes with a paler rump, light brown lower parts, a paler throat, and brownish white under the wings from dark brown "armpits". The male and female plumage are similar in appearance, as that of the juvenile, for the species for which it has been described, in some species the juvenile shows pale edges to the flight feathers.

The legs, as with many swifts, are very short, preventing birds from perching but allowing them to cling to vertical surfaces. The flight mainly glides due to the very long main feathers and muscles of the small chest. Salangan Aerodramus, depending on the species, weigh 8-35 grams (0.28-1.23 oz), and 9-16 centimeters (0.28-1.23 in) long. These swiftlets are very similar, and where several species occur, such as Borneo, New Guinea and the Philippines, may not be separable in the area.

Behavior

Salangan Aerodramus - aerial insectivores that take prey like flies on their wings. They roost and breed in caves, during the day they leave caves to forage for food and return to roost at night. They are monogamous and both partners take part in caring for the chicks. Males perform aerial shows to attract females and mating takes place in the nest. The breeding season is superimposed on the rainy season, which corresponds to the increased insect population.

The size of the clutch depends on the location and food source, but swiftlets usually Aerodramus lay one or two eggs. The eggs are dull white, and are laid every other day. Many, if not all, species are colonial nesting birds, with some building their nests in high, dark corners on the cave walls.

Most swiftlets Aerodramus lives in the tropical Indo-Pacific and does not migrate. These birds usually stay in one cave or another to roost / nest. Examples of cave territories include Niah Caves and Mulu Gunung National Park, which are both located in Sarawak, Malaysian Borneo.

Behavioral traits, such as what materials other than nest saliva contain, can be used to differentiate between certain species Aerodramus.

Echolocation

Genus Aerodramus especially interesting because of its use of echolocation. Salanganians use this technique to guide them in the dark through chasms and cavern mines, where they breed and roost at night. Apart from the swiftlet, the only other avian species to use echolocation is the unrelated oilbird.

Echolocation-detecting swiftlet double-clicks Aerodramus within the normal human hearing range and up to 3 milliseconds apart with an interval lacking darker locations. Unlike the rest of the genus (for those species that have been studied), the Atiu swiftlet, Aerodramus sawtelli, and the swiftlet of the black nest, A. maximus, emits only single clicks. Interestingly, the former species also uses echolocation outside of their caves.

The use of echolocation was once used to separate Aerodramus from other genera that do not detect by echolocation the cave swifters Collocalia and Hydrochous (in fact, nothing is known about Schoutedenapus). However, recently a pygmy swiftlet, troglodytes Collocalia, was discovered making a similar clicking noise both inside and outside of his roosting cave.

It has recently been determined that echolocation vocalizations do not agree with the evolutionary relationship between swiftlet species, as suggested by DNA sequence comparisons. It suggests that as in bats, echolocation sounds, once a present, adapt quickly and independently to the acoustic environment of particular species.

The study suggested that the subunits of echolocation were mainly located in the central nervous system, while the subunits in the vocal apparatus were already present and capable of being used before echolocation, even developed. This study supports the hypothesis of independent development of echolocation in Aerodramus, and Collocalia, with the subsequent development of complex behavior was to complement the physical echolocation system, or it is simply possible that the vocal hardware of the echolocation system might even be inherited from some prehistoric nocturnal ancestor.

It has been suggested that the giant or swiftlet of the waterfall, Gigas dough hydrotubesthat cannot be detected by echolocation may have come from an echolocating ancestor.

Saliva nests

The intricately constructed saliva nests of this genus of swiftlets, which in some species contain no other material, are collected to make a delicacy bird's nest soup. They therefore command extremely high prices.

Authentic bird's nest soup is made from the nests of the edible nest swiftlets (or white nest swifters), Aerodramus fuciphagus, and the swiftlet of the black nest, Aerodramus maximus... Rather than incorporating twigs, feathers and straw like others in the genus, these two swiftlets make their nest only from the strands of their sticky saliva, which harden when exposed to air. Once the nests are obtained, they are cleaned and sold to restaurants. Over the past twenty years, there is a high demand for the nests of these species Aerodramus had a negative effect on their population. Niah digs a population of black nest swiftlets, submerged from about 1.5 million pairs in 1959 to 150,000–298,000 pairs in the early 1990s through overharvesting.

Early writers had doubts about the material used to make the nest with whale and fish semen and sea foam suggested as a basis for construction. Even in the 1830s, when the use of saliva was fairly well established, it was believed that it was only the cement to bind the marine plant that provided most of the nest's gelatinous material.

As with other taxonomically difficult groups, ectoparasites can provide information on relationships. A study on the swiftlet parasites in northern Borneo included lice transmission between closely related swiftlet species. Lice survival in most of these transmissions has been significantly reduced in proportion to the average difference in feather tine size between the donor and recipient host species. Thus, adaptation to a particular resource on the host's body seems to govern the specificity of swiftlet lice. In transmissions where the lice survived, the lice moved to various areas on the host's body where the average diameter of the prong of the feathers on which the lice originated had the required value.

Papuan swiftlet

Papuan salangan, Aerodramus papuensis, three toes instead of the usual four in this group. It has the ability to detect by echolocation, but whereas other previously studied species use echolocation primarily when flying in their caves, the Papuan swiftlet appears to be nocturnal or crepuscular and uses echolocation while active outside at night. It uses single, not double, clicks. DNA sequence data provide powerful support for the underlying relationships between A. papuensis and other taxa Aerodramus, and assume that this species and the waterfall are fast Gigas dough hydrotubes, related taxa, a relationship that would indicate a paraphyly genus Aerodramus.

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