Overview

Brief Summary

Aerodramus cave swiftlets are best known as contributors of the key ingredient in bird’s nest soup, which is a coveted delicacy in many parts of Asia--the “caviar of the East”. True bird’s nest soup is made from the nests of any of several species of colonial Asian Aerodramus cave swiftlets, especially the Edible-nest Swiftlet (A. fuciphagus) and the Black-nest Swiftlet (A. maximus) of southeast Asia. These are swallow-like birds (although, like other members of the swift family, they are actually more closely related to hummingbirds) which are able to navigate through dark caves using echolocation, like bats. Their small cup-shaped nests, typically placed on the walls of caves, often quite high up, are composed largely or entirely of the hardened saliva of the male swiftlet.

Although they apparently hunt their insect prey relying mainly on vision, Aerodramus swiftlets are among the very few bird species to use echolocation to find their way, although, in contrast to typical echolocating bats, swiftlets appear not to use frequency modulation but rather rely only on temporal information (Fullard et al. 1993; Price et al. 2004; Price et al. 2005; Thomassen and Povel 2006). As a group, Aerodramus swiftlets are distributed very broadly, with species occurring in southern Asia, in Australasia, and on islands in the South Pacific and Indian Oceans (Chantler 1999).

Traditionally, swiftlet nests were harvested from natural populations in caves, the locations of which were often carefully guarded secrets. During the past couple of decades, demand for these nests, which command a very high price, has taken a severe toll on many swiftlet populations (e.g., Sankaran 2001; Gausset 2004; Hobbs 2004) and in some areas this high demand has even generated a criminal enterprise. On the brighter side, market demand has also stimulated the development of a successful cave swiftlet farming industry utilizing newly developed swiftlet husbandry methods and specially designed nesting structures situated largely in urban areas. In the meantime, some restaurants offer an imitation bird’s nest soup that uses noodles shaped like a bird’s nest in lieu of the real thing.

In some cases, counterfeit (or adulterated) edible bird's nests are marketed, either nests of other species or nest-shaped materials molded with fried pork skin, Tremella fungus, karaya gum from Sterculia trees, or red seaweed. Some of these versions are easy to distinguish from authentic nests of A. fuciphagus and A. maximus, but distinguishing the nests of other swifts can be another matter. Lin et al. (2009) investigated and discussed the effectiveness and limitations of a simple genetic analysis that could be an important tool in discriminating authentic and counterfeit edible bird's nests. (Marcone 2005; Lin et al. 2009) Marcone (2005) investigated the chemical composition of edible bird's nests. According to Goh et al. (1999), in a study of food allergens inducing anaphylactic allergic reactions in children seen at a general hospital in Singapore, bird's nest soup topped the list.

As swiftlet ranching has become big business, the marketing of information and equipment to individuals hoping to get in on the profits has itself become a business, as is apparent from the following sampling of links (note that inclusion of these links here in no way implies any sort of endorsement or determination of legitimacy!):

www.swiftletonline.com

www.swiftletecopark.com

nesttech.com.my

www.swiftletfarming.com.my

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Comprehensive Description

Aerodramus cave swiftlets are best known as contributors of the key ingredient in bird’s nest soup, which is a coveted delicacy in many parts of Asia--the “caviar of the East”. True bird’s nest soup is made from the nests of any of several species of colonial Asian Aerodramus cave swiftlets, especially the Edible-nest Swiftlet (A. fuciphagus) and the Black-nest Swiftlet (A. maximus) of southeast Asia. These are swallow-like birds (although, like other members of the swift family, they are actually more closely related to hummingbirds) which are able to navigate through dark caves using echolocation, like bats. Their small cup-shaped nests, typically placed on the walls of caves, often quite high up, are composed largely or entirely of the hardened saliva of the male swiftlet.

From a taxonomic perspective, the swifts are among the most challenging of bird families and, within this family, species boundaries and relationships among the swiftlets have proved to be among the most difficult to work out. At one time, all the swiftlets were placed together in the genus Collocalia, but based on a range of evidence ornithologists now divide these species among several genera--although some controversy remains regarding the composition of these genera (Chantler 1999; Price et al. 2004; Price et al. 2005; Thomassen et al. 2005). Although they apparently hunt their insect prey relying mainly on vision, Aerodramus swiftlets are among the very few bird species to use echolocation to find their way, although, in contrast to typical echolocating bats, swiftlets appear not to use frequency modulation but rather rely only on temporal information (Fullard et al. 1993; Price et al. 2004; Price et al. 2005; Thomassen and Povel 2006). As a group, Aerodramus swiftlets are distributed very broadly, with species occurring in southern Asia, in Australasia, and on islands in the South Pacific and Indian Oceans (Chantler 1999).

Traditionally, swiftlet nests were harvested from natural populations in caves, the locations of which were often carefully guarded secrets. Diverse (and dubious) health and aphrodisiac properties are often attributed to swiftlet nests and, despite their odd texture and lack of much taste, they are also prized for their culinary value, prepared in a variety of both sweet and savory dishes. During the past couple of decades, demand for these nests, which command a very high price, has taken a severe toll on many swiftlet populations (e.g., Sankaran 2001; Gausset 2004; Hobbs 2004) and in some areas this high demand has even generated a criminal enterprise. On the brighter side, market demand has also stimulated the development of a successful cave swiftlet farming industry utilizing newly developed swiftlet husbandry methods and specially designed nesting structures situated largely in urban areas. It remains to be seen whether these farming efforts will be sufficient to relieve the unsustainable pressure on wild populations (or have unforeseen negative environmental impacts). In the meantime, some restaurants offer an imitation bird’s nest soup that uses noodles shaped like a bird’s nest in lieu of the real thing.

In some cases, counterfeit (or adulterated) edible bird's nests are marketed, either nests of other species or nest-shaped materials molded with fried pork skin, Tremella fungus, karaya gum from Sterculia trees, or red seaweed. Some of these versions are easy to distinguish from authentic nests of A. fuciphagus and A. maximus, but distinguishing the nests of other swifts can be another matter. Lin et al. (2009) investigated and discussed the effectiveness and limitations of a simple genetic analysis that could be an important tool in discriminating authentic and counterfeit edible bird's nests. (Marcone 2005; Lin et al. 2009) Marcone (2005) investigated the chemical composition of edible bird's nests. According to Goh et al. (1999), in a study of food allergens inducing anaphylactic allergic reactions in children seen at a general hospital in Singapore, bird's nest soup topped the list.

Langham (1980) reviewed the breeding biology of A. fuciphagus. Kang et al. (1991) investigated the impact of nest harvesting on nest construction and egg-laying in A. fuciphagus and A. maximus in Singapore and made recommendations on sustainable harvest frequency.

As swiftlet ranching has become big business, the marketing of information and equipment to individuals hoping to get in on the profits has itself become a business, as is apparent from the following sampling of links (note that inclusion of these links here in no way implies any sort of endorsement or determination of legitimacy!):

www.swiftletonline.com

www.swiftletecopark.com

nesttech.com.my

www.swiftletfarming.com.my

Creative Commons Attribution Non Commercial Share Alike 3.0 (CC BY-NC-SA 3.0)

© Shapiro, Leo

Source: EOL Rapid Response Team

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Molecular Biology and Genetics

Molecular Biology

Statistics of barcoding coverage

Barcode of Life Data Systems (BOLD) Stats
                                        
Specimen Records:8Public Records:8
Specimens with Sequences:8Public Species:4
Specimens with Barcodes:7Public BINs:4
Species:4         
Species With Barcodes:4         
          
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Barcode data

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Locations of barcode samples

Collection Sites: world map showing specimen collection locations for Aerodramus

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Wikipedia

Moluccan Swiftlet

The Moluccan swiftlets (Aerodramus sp.) are a group of three species of swift in the Apodidae family. They are endemic to Indonesia. They were at one time considered conspecific.

The three species that form the group are:

Their natural habitat is subtropical or tropical moist lowland forests and subtropical or tropical moist montane forests.

References[edit]

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Aerodramus

Aerodramus is a genus of small, dark, cave-nesting birds in the Collocaliini tribe of the swift family. Its members are confined to tropical and subtropical regions in southern Asia, Oceania and northeastern Australia. Many of its members were formerly classified in Collocalia, but were first placed in a separate genus by American ornithologist Harry Church Oberholser in 1906.[1]

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 are not fully resolved. These swiftlets can pose major identification problems where several species occur.

What distinguishes Aerodramus swiftlets from other swifts, and indeed almost all other birds, 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 of Aerodramus swiftlets are constructed with saliva as a major component. In two species, saliva is the only material used, and the nests are collected for the famous Chinese delicacy 'bird's nest soup', the over-collection of which puts pressure on the swiftlet populations.

Distribution[edit]

The range of these swiftlets is confined to tropical southern Asia, Oceania, northeastern Australia and the Indian Ocean, with the greatest diversity in Southeast Asia, Indonesia and Papua New Guinea.[2] Several of the species are restricted to small islands, and their limited range can make them vulnerable, like the Seychelles, Whitehead's and Guam swiftlets.[3][4][5] The Mangaia swiftlet is a recently extinct species known only from fossils.[6][7]

Description[edit]

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 the flight feathers.[2]

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 long primary 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 as Borneo, New Guinea and the Philippines, may not be separable in the field.[2]

Behaviour[edit]

These juvenile German's swiftlets have fallen from nests, and are being reared by hand.

Aerodramus swiftlets are aerial insectivores, which take prey like flies 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.[2]

Clutch size depends on the location and the food source, but generally Aerodramus swiftlets lay one or two eggs.[2] 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.[2]

Most Aerodramus swiftlets live in the tropical Indo-Pacific region and do not migrate. These birds usually remain in one cave or other roosting/nesting site. Examples of cave sites include the Niah Caves and Gunung Mulu National Park, which are both located in Sarawak, Malaysian Borneo.

Characteristics of behaviour, such as what materials apart from saliva the nests contain, can be used to differentiate between certain species of Aerodramus.[8]

Echolocation[edit]

Niah cave, a swiftlet nesting site

The genus Aerodramus is of special interest due to its use of echolocation. The swiftlets use this technique to navigate in darkness through the chasms and shafts of the caves where they breed and roost at night. Apart from swiftlets, the only other avian species to use echolocation is the unrelated oilbird.[9][10]

The Aerodramus swiftlets' echolocating double clicks are within the normal human hearing range and up to 3 milliseconds apart, with the interval becoming shorter in darker locations. Unlike the rest of the genus (for those species which have been studied), the Atiu swiftlet, Aerodramus sawtelli, and the black-nest swiftlet, A. maximus, emit only single clicks. Interestingly, the former species also uses echolocation outside its caves.[11]

The use of echolocation was once used to separate Aerodramus from the other non-echolocating cave swiftlet genera Collocalia and Hydrochous (virtually nothing is known about Schoutedenapus). However, recently, the pygmy swiftlet, Collocalia troglodytes, was discovered making similar clicking noises both inside and outside its roosting cave.[12]

It has recently been determined that the echolocation vocalizations do not agree with evolutionary relationship between swiftlet species as suggested by DNA sequence comparison.[13] This suggests that as in bats, echolocation sounds, once present, adapt rapidly and independently to the particular species' acoustic environment.

A study[14] suggested that the echolocation subunits were mainly located in the central 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 in Aerodramus and Collocalia, 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 some prehistoric nocturnal ancestor.

It has been suggested that the giant or waterfall swiftlet, Hydrochous gigas, which cannot echolocate, may be descended from an echolocating ancestor.[2]

Saliva nests[edit]

An edible nest

The intricately constructed saliva nests of this swiftlet genus, which in some species contain no other material, are collected to make the 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 swiftlet (or white-nest swiftlet), Aerodramus fuciphagus, and the black-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 these Aerodramus species has had an adverse effect on their populations.[15][16] The Niah caves population of black-nest swiftlets plunged from around 1.5 million pairs in 1959 to 150,000–298,000 pairs in the early 1990s through over-harvesting.[2]

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.[17]

Lice[edit]

As with other taxonomically difficult groups, ectoparasites can give information on relationships.[18] A study of swiftlet parasites in northern Borneo involved transferring lice between closely related swiftlet species.[19] 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.

Papuan swiftlet[edit]

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 or crepuscular and uses echolocation while active outside at night. It uses single, not double, clicks.[2][20] DNA sequence data provides strong support for a basal relationship between A. papuensis and other Aerodramus taxa and suggest that this species and the waterfall swift Hydrochous gigas, are sister taxa, a relationship that would indicate paraphyly of the genus Aerodramus.[20]

Species in taxonomic order[edit]

John Latham figure of the "Esculent Swallow and its Nest"

References[edit]

  1. ^ ITIS standard report page for Aerodramus
  2. ^ a b c d e f g h i Chantler, P., Driessens, G. (2000). Swifts: a Guide to the Swifts and Treeswifts of the World. Mountfield, East Sussex: Pica Press. ISBN 1-873403-83-6. 
  3. ^ Birdlife International species factsheet: Collocalia elaphra. Retrieved on 16 July /2007.
  4. ^ Birdlife International species factsheet: Collocalia whiteheadi. Retrieved on 24 July 2007.
  5. ^ Birdlife International species factsheet: Collocalia bartschi. Retrieved on 24 July 2007
  6. ^ "Aerodramus manuoi". Archived from the original on May 19, 2008. Retrieved 2008-02-29. 
  7. ^ Steadman, David W (July 2002). "A new species of swiftlet (Aves: Apodidae) from the late Quaternary of Mangaia, Cook Islands, Oceania". Journal of Vertebrate Paleontology 22 (22): 326–331. doi:10.1671/0272-4634(2002)022[0326:ANSOSA]2.0.CO;2. ISSN 0272-4634. 
  8. ^ Lee, P.L.M., Clayton, D.H., Griffiths, R., Page, R.D.M. (July 1996). "Does behavior reflect phylogeny in swiftlets (Aves: Apodidae)? A test using cytochrome b mitochondrial DNA sequences". Proc. Natl. Acad. Sci. U.S.A. 93 (14): 7091–6. doi:10.1073/pnas.93.14.7091. PMC 38941. PMID 8692950. 
  9. ^ ffrench, Richard (1991). A Guide to the Birds of Trinidad and Tobago (2nd ed.). Comstock Publishing. ISBN 0-8014-9792-2. 
  10. ^ Konishi, M., Knudsen, E.I. (April 1979). "The oilbird: hearing and echolocation". Science 204 (4391): 425–7. doi:10.1126/science.441731. PMID 441731. 
  11. ^ Fullard, J.H., Barclay, R.M.R. Thomas, D.W. (1993). "Echolocation in free-flying Atiu Swiftlets (Aerodramus sawtelli)". Biotropica 25 (3): 334–9. doi:10.2307/2388791. JSTOR 2388791. 
  12. ^ Price, J.J., Johnson, K.P., Clayton, D.H. (2004). "The evolution of echolocation in swiftlets". Journal of Avian Biology 35 (2): 135–143. doi:10.1111/j.0908-8857.2004.03182.x. 
  13. ^ Thomassen, H.A., Povel, G.D.E. (2006). "Comparative and phylogenetic analysis of the echo clicks and social vocalizations of swiftlets (Aves: Apodidae)". Biological Journal of the Linnean Society 88 (4): 631–643. doi:10.1111/j.1095-8312.2006.00648.x. 
  14. ^ Thomassen, H.A., den Tex, R-J., de Bakker, M.A.G., Povel, G.D.E. (2005). "Phylogenetic relationships amongst swifts and swiftlets: A multi locus approach". Molecular Phylogenetics and Evolution 37 (1): 264–277. doi:10.1016/j.ympev.2005.05.010. PMID 16006151. 
  15. ^ Hobbs, J.J. (2004). "Problems in the harvest of edible birds' nests in Sarawak and Sabah, Malaysian Borneo". Biodiversity and Conservation 13 (12): 2209–26. doi:10.1023/B:BIOC.0000047905.79709.7f. 
  16. ^ Marcone, M.F. (2005). "Characterization of the edible bird's nest the Caviar of the East". Food Research International 38 (10): 1125–34. doi:10.1016/j.foodres.2005.02.008. 
  17. ^ Rennie, James (1831). The Architecture of Birds. London: Charles Knight. pp. 288–306. 
  18. ^ Page, R. D. M., Lee, P. L. M., Becher, S.A., Griffiths, R., Clayton D. H. (1997). "A Different Tempo of Evolution in Birds and their Parasitic Lice" Text retrieved 12 Nov 2007
  19. ^ Tompkins, D.M., Clayton D.H. (1999). "Host resources govern the specificity of swiftlet lice: size matters". Journal of Animal Ecology 68 (3): 489–500. doi:10.1046/j.1365-2656.1999.00297.x. 
  20. ^ a b Price J.J., Johnson, K.P., Bush, S.E., Clayton, D.H. (October 2005). "Phylogenetic relationships of the Papuan Swiftlet Aerodramus papuensis and implications for the evolution of avian echolocation". Ibis 147 (4): 790–6. doi:10.1111/j.1474-919X.2005.00467.x. 
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