| Aerodramus | |
|---|---|
 | |
| Australian swiftlet Aerodramus terraereginae | |
Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Aves |
| Clade: | Strisores |
| Order: | Apodiformes |
| Family: | Apodidae |
| Tribe: | Collocaliini |
| Genus: | Aerodramus Oberholser, 1906 |
| Type species | |
| Collocalia innominata (Himalayan swiftlet) Hume, 1873 | |
| Species | |
See text | |
Aerodramus is agenus of small, dark, cave-nestingbirds in theCollocaliinitribe of theswift family. Its members are confined totropical andsubtropical regions in southernAsia,Oceania and northeasternAustralia. Many of its members were formerly classified inCollocalia, but were first placed in a separate genus by AmericanornithologistHarry Church Oberholser in 1906.[2]
This is a taxonomically difficult group of very similar species.Echolocation,DNA sequencing andparasiticlice have all been used to establish relationships, but some problems, such as the placement of thePapuan swiftlet are not fully resolved. These swiftlets can pose major identification problems where several species occur.
What distinguishesAerodramusswiftlets from other swifts, and indeed almost all otherbirds, is their ability to use a simple but effective form of echolocation. This enables them to navigate within the breeding and roosting caves.
The nests ofAerodramus swiftlets are constructed withsaliva as a major component. In two species, saliva is the only material used, and the nests are collected for the famousChinese delicacy 'bird's nest soup', the over-collection of which puts pressure on the swiftlet populations.
The range of these swiftlets is confined to tropical southern Asia, Oceania, northeasternAustralia and theIndian Ocean, with the greatest diversity inSoutheast Asia,Indonesia andPapua New Guinea.[3] Several of the species are restricted to small islands, and their limited range can make them vulnerable, like theSeychelles,Whitehead's andGuam swiftlets.[4][5][6] TheMangaia swiftlet is a recently extinct species known only from fossils.[7][8]
Aerodramus swiftlets are in many respects typical swifts, having narrow wings for fast flight, and a wide gape and small reduced beak surrounded by bristles for catching insects in flight. They have dull plumage which is mainly in shades of black, brown, and grey. Members of this genus typically have dark brown upper wings and upper body, sometimes with a paler rump, light brown underparts, a paler throat, and brownish-white under-wings with dark brown "armpits". Males and female plumages are similar in appearance, as is that of the juvenile, for those species for which it has been described; in some species the juvenile shows pale fringes to theflight feathers.[3]
The legs, as with many swifts, are very short, preventing the birds from perching, but allowing them to cling to vertical surfaces. The flight is mainly gliding due to very longprimary feathers and small breast muscles.Aerodramus swiftlets, depending on species, weigh 8–35 grammes (0.28–1.23 oz) and are 9–16 centimetres (0.28–1.23 in) long. These swiftlets are very similar, and where several species occur, such asBorneo,New Guinea and thePhilippines, may not be separable in the field.[3]
Aerodramus swiftlets are aerial insectivores, which take prey likeflies on the wing. They roost and breed in caves; during the day they leave the caves to forage for food, and return to roost at night. They are monogamous and both partners take part in caring for the nestlings. Males perform aerial displays to attract females and mating occurs at the nest. The breeding season overlaps the wet season, which corresponds to an increased insect population.[3]
Clutch size depends on the location and the food source, but generallyAerodramus swiftlets lay one or two eggs.[3] The eggs are a dull white, and are laid every other day. Many, if not all, species are colonial nesters; some build their nests in high, dark corners on cave walls.[3]
MostAerodramus swiftlets live in the tropicalIndo-Pacific region and do notmigrate. These birds usually remain in one cave or other roosting/nesting site. Examples of cave sites include theNiah Caves andGunung Mulu National Park, which are both located inSarawak,MalaysianBorneo.
Characteristics of behaviour, such as what materials apart from saliva the nests contain, can be used to differentiate between certain species ofAerodramus.[9]
The genusAerodramus is of special interest due to its use ofecholocation. The swiftlets use this technique to navigate in darkness through the chasms and shafts of thecaves where they breed and roost at night. Apart from swiftlets, the only otheravian species to use echolocation is the unrelatedoilbird.[10][11]
TheAerodramus swiftlets' echolocating double clicks are within the normal human hearing range and up to 3milliseconds apart, with the interval becoming shorter in darker locations. Unlike the rest of the genus (for those species which have been studied), theAtiu swiftlet,Aerodramus sawtelli, and theblack-nest swiftlet,A. maximus, emit only single clicks. The former species also uses echolocation outside its caves.[12]
The use of echolocation was once used to separateAerodramus from the other non-echolocatingcave swiftlet generaCollocalia andHydrochous (virtually nothing is known aboutSchoutedenapus). However, recently, thepygmy swiftlet,Collocalia troglodytes, was discovered making similar clicking noises both inside and outside its roosting cave.[13]
It has recently been determined that the echolocation vocalizations do not agree with evolutionary relationship between swiftlet species as suggested byDNA sequence comparison.[14] This suggests that as inbats, echolocation sounds, once present, adapt rapidly and independently to the particular species' acoustic environment.
A study[15] suggested that the echolocation subunits were mainly located in thecentral nervous system, while the subunits in the vocal apparatus were already present and capable of use before echolocation even evolved. This study supports the hypothesis of independent evolution of echolocation inAerodramus andCollocalia, with the subsequent evolution of complex behaviour needed to complement the physical echolocation system, or just possibly that the vocal apparatus-parts of the echolocation system might even be inherited from someprehistoricnocturnal ancestor.
It has been suggested that the giant orwaterfall swiftlet,Hydrochous gigas, which cannot echolocate, may be descended from an echolocating ancestor.[3]
The intricately constructedsaliva nests of this swiftlet genus, which in some species contain no other material, are collected to make the delicacybird's nest soup. They therefore command extremely high prices.
Authentic bird's nest soup is made from the nests of theedible-nest swiftlet (or white-nest swiftlet),Aerodramus fuciphagus, and theblack-nest swiftlet,Aerodramus maximus. Instead of incorporating twigs, feathers and straw like others in the genus, these two swiftlets make their nest only from strands of their gummy saliva, which harden when exposed to air. Once the nests are harvested, they are cleaned and sold to restaurants. Over the past twenty years, the high demand for the nests of theseAerodramus species has had an adverse effect on their populations.[16][17] The Niah caves population ofblack-nest swiftlets plunged from around 1.5 million pairs in 1959 to 150,000–298,000 pairs in the early 1990s through over-harvesting.[3]
Early authors had doubts about the material used to make the nest, with whale and fish sperm and sea foam being proposed as the basis for construction. Even in the 1830s, when the use of saliva had been fairly well established, it was believed that it was only a cement to bind a sea plant which provided the bulk of the gelatinous material of the nest.[18]
As with other taxonomically difficult groups,ectoparasites can give information on relationships.[19] A study of swiftlet parasites in northern Borneo involved transferring lice between closely related swiftlet species.[20] The survival of lice in most of these transfers was significantly reduced in proportion to the mean difference in feather barb size between the donor and recipient species of hosts. Thus, adaptation to a particular resource on the body of the host appears to govern the specificity of swiftlet lice. In transfers where lice survived, the lice moved to different areas on the body of the host where the mean barb diameter of the feathers on which the lice occurred had the required value.
The Papuan swiftlet,Aerodramus papuensis, has three toes instead of the usual four in this group. It has the ability to echolocate, but whereas other previously studied species use echolocation primarily while flying in their caves, the Papuan swiftlet appears to be nocturnal orcrepuscular and uses echolocation while active outside at night. It uses single, not double, clicks.[3][21] DNA sequence data provides strong support for a basal relationship betweenA. papuensis and otherAerodramus taxa and suggest that this species and thewaterfall swiftHydrochous gigas, are sistertaxa, a relationship that would indicateparaphyly of the genusAerodramus.[21]
The genusAerodramus was introduced (as a subgenus ofCollocalia) in 1906 by the American ornithologistHarry C. Oberholser. He designated thetype species asCollocalia innominataHume. This taxon is now considered as asubspecies of theHimalayan swiftlet (Aerodramus brevirostris).[22][23] The genus name combines theAncient Greekaēr meaning "air" with-dromos meaning "-racer" (fromtrekhō "to run").[24]
The genus now contains 25 species:[23]
| Image | Scientific name | Common name | Distribution |
|---|---|---|---|
| - | Aerodramus elaphrus | Seychelles swiftlet | Seychelles |
 | Aerodramus francicus | Mascarene swiftlet | Réunion andMauritius |
.jpg) | Aerodramus unicolor | Indian swiftlet | southwest India and Sri Lanka |
 | Aerodramus mearnsi | Philippine swiftlet | Philippines |
| - | Aerodramus infuscatus | Moluccan swiftlet | Sulawesi and Moluccas |
| - | Aerodramus hirundinaceus | Mountain swiftlet | montane New Guinea |
| - | Aerodramus spodiopygius | White-rumped swiftlet | Melanesia |
| | Aerodramus terraereginae | Australian swiftlet | northeastern Queensland |
.jpg) | Aerodramus brevirostris | Himalayan swiftlet | Himalayas, southern Chine and Myanmar ; winters to Malay peninsula |
| - | Aerodramus vulcanorum | Volcano swiftlet | montane Java |
| - | Aerodramus whiteheadi | Whitehead's swiftlet | Philippines :mount Data (Luzon) andmount Apo (Mindanao) |
| - | Aerodramus nuditarsus | Bare-legged swiftlet | sparsely montane New Guinea |
| - | Aerodramus orientalis | Mayr's swiftlet | New Ireland andGuadalcanal |
| - | Aerodramus salangana | Mossy-nest swiftlet | Indonesia |
 | Aerodramus vanikorensis | Uniform swiftlet | eastern Indonesia and Melanesia |
| - | Aerodramus amelis | Ameline swiftlet | Philippines |
| - | Aerodramus pelewensis | Palau swiftlet | Palau |
| - | Aerodramus bartschi | Mariana swiftlet | Mariana Islands |
| - | Aerodramus inquietus | Caroline swiftlet | Caroline Islands |
| - | Aerodramus leucophaeus | Tahiti swiftlet | Tahiti andMoorea |
 | Aerodramus sawtelli | Atiu swiftlet | Atiu (Cook Islands) |
| - | Aerodramus ocistus | Marquesan swiftlet | Marquesas Islands |
.jpg) | Aerodramus maximus | Black-nest swiftlet | Southeast Asia |
 | Aerodramus fuciphagus | Edible-nest swiftlet | Southeast Asia |
| - | Aerodramus papuensis | Three-toed swiftlet | sparsely montane New-Guinea |
The Mangaia swiftlet (Aerodramus manuoi) is a prehistoric species known from fossils.
A rightulna (MNZ S42799) found at theBannockburn Formation of theManuherikia Group near theManuherikia River inOtago,New Zealand. Dating from the Early to MiddleMiocene (Altonian, 19-16million years ago),[1] probably belongs toAerodramus.
Data related toAerodramus at Wikispecies
Media related toAerodramus at Wikimedia Commons
