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Edible-nest Swiftlet

(Aerodramus fuciphagus, Thunberg 1812)

Anticlockwise from top:  Edible-nest Swiftlet in flight

Footnote Macro

Photo by Lim Hong Yao (2017)

 , perched on nest

Footnote Macro

Photo by Lim Hong Yao (2018)

, harvested edible nest

Footnote Macro

Photo by Ediblebirdsnest (2016) on Wikimedia Commons, accessed from https://commons.wikimedia.org/wiki/File:Edible-birds-nest-bowl-shape.png

, prepared bird's nest soup

Footnote Macro

Photo by Crue (2010) on Blogger, accessed from http://ichikichikehem.blogspot.com/2010/01/thai-hatyai-bird-nest-soup-7ps.html

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1. Introduction
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1.1 General information
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Edible-nest swiftlets are small insectivorous birds from the swift family Apodidae. Weighing in at a mere 8·7–14·8 grams and measuring in at 11·5–12·5 cm in length, this species is known to be an excellent flyer and can spend the long periods foraging in the sky without rest

Footnote Macro

Chantler, P. & Boesman, P. (2018). Edible-nest Swiftlet (Aerodramus fuciphagus). In: del Hoyo, J., Elliott, A., Sargatal, J., Christie, D.A. & de Juana, E. (eds.). Handbook of the Birds of the World Alive. Lynx Edicions, Barcelona. (retrieved from https://www.hbw.com/node/55287 on 29 November 2018).

. Edible-nest swiftlets may be observed over a wide variety of habitats (even far out at sea) and are widespread throughout South-east Asia today. This bird is well known (and studied) in the region due to its nest being widely collected or farmed as a delicacy known as bird’s nest soup or ‘燕窝’ in Chinese. Natural populations nest in caves, such as the Niah and Gomantong caves in Borneo. However, due to the practice of farming swiftlets in nest houses, many Edible-nest swiftlets have adopted nesting in man-made buildings as early as the 1880s

Footnote Macro

Lim, C. and Cranbrook, G. (2002). Swiftlets of Borneo. Natural History Publications (Borneo).

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1.2 Identification
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A medium sized swiftlet with glossy dark brown upperparts

Footnote Macro

Chantler, P. & Boesman, P. (2018). Edible-nest Swiftlet (Aerodramus fuciphagus). In: del Hoyo, J., Elliott, A., Sargatal, J., Christie, D.A. & de Juana, E. (eds.). Handbook of the Birds of the World Alive. Lynx Edicions, Barcelona. (retrieved from https://www.hbw.com/node/55287 on 29 November 2018).

. Rump tends to appear paler grey, but variable and can appear uniform. Brown-grey underparts except almost black undertail coverts, significantly forked tail. Naked or lightly feathered tarsi.

In Singapore, difficult to distinguish in flight from slightly larger Black-nest Swiftlet (Aerodramus maximus), unless seen exceedingly well enough to determine the Edible-nest Swiftlet's slightly smaller (1-3 cm) size, relatively pointed tail ends with a deeper notch, and less bulky head and body. In hand, identification is possible as Black-nest Swiftlet has more extensive black feathering on tarsi.

1.3 Etymology
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The genus Aerodramus stems from two Greek words: ἀερο, "aero" which means 'air', and δρόμος,"dromos" which means 'path'

Footnote Macro

Sheard, C. (2015). Edible-nest Swiftlet: Aerodramus fuciphagus. [online] Name This Bird. Available at: https://namethisbird.wordpress.com/2015/09/27/edible-nest-swiftlet-aerodramus-fuciphagus/ [Accessed 15 Nov. 2018].

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The specific epithet fuciphagus originates from Greek as well, with φυκι, "fukos" meaning ‘seaweed,’ and φαγος, "phagos" meaning ‘to eat’. This is likely a result of the (false) historical belief that the swiftlets consume seaweed or substances from sea mist which allows it to produce a gelatinous substance with which it builds its nest with.

2. Range
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The Edible-nest Swiftlet has a large range starting from the South of Hainan island spanning southward along the coasts of Vietnam, Myanmar, Thailand and Cambodia, subsequently including Sumatra, Java, Lesser Sundas, Borneo, and West Philippines (Figure 1)

Footnote Macro

Chantler, P. & Boesman, P. (2018). Edible-nest Swiftlet (Aerodramus fuciphagus). In: del Hoyo, J., Elliott, A., Sargatal, J., Christie, D.A. & de Juana, E. (eds.). Handbook of the Birds of the World Alive. Lynx Edicions, Barcelona. (retrieved from https://www.hbw.com/node/55287 on 29 November 2018).

. Inland Peninsula Malaysia is part of its natural range but Edible-nest Swiftlets from house farms are currently inhabiting the area. 8 current subspecies are recognized. For more details, see subspecies taxonomy below.

Range map of Edible-nest SwiftletFigure 1: Range map of the Edible-nest Swiftlet, adapted from HBW (2018)

Footnote Macro

Chantler, P. & Boesman, P. (2018). Edible-nest Swiftlet (Aerodramus fuciphagus). In: del Hoyo, J., Elliott, A., Sargatal, J., Christie, D.A. & de Juana, E. (eds.). Handbook of the Birds of the World Alive. Lynx Edicions, Barcelona. (retrieved from https://www.hbw.com/node/55287 on 29 November 2018).

3. Human interactions
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3.1 Bird's nest soup
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The Edible-nest Swiftlet’s nests are frequently prepared in a manner known colloquially as ‘birds’ nest soup’, which has long been a Chinese delicacy of immense value since the T’ang Dynasty (618–907 A.D.)

Footnote Macro

Lau, A. and Melville, D. (1994). International trade in swiftlet nests with special reference to Hong Kong. Cambridge, U.K.: Traffic International.

. Like many other Chinese delicacies, birds’ nest soup is not especially tasty, and relies on other culinary additions to appeal to the palate

Footnote Macro

Thorburn, C. (2015). The Edible Nest Swiftlet Industry in Southeast Asia: Capitalism Meets Commensalism. Human Ecology, 43(1), pp.179-184.

. Its value lies in its rumoured nutritional value and health benefits instead; the broth is said to help reduce inflammation, alleviate gastric problems, boost the immune system, metabolism, and mental performance, as well as improve skin complexion

Footnote Macro

Marcone, M. (2005). Characterization of the edible bird’s nest the “Caviar of the East”. Food Research International, 38(10), pp.1125-1134.

. Several studies have shown that certain claims may hold some truth to them, as components such as sialic acid and other compounds that are purported to aid infant development and immunity were discovered to be present in the nests

Footnote Macro

Oda, M., Ohta, S., Suga, T. and Aoki, T. (1998). Study on Food Components: The Structure of N-Linked Asialo Carbohydrate from the Edible Bird's Nest Built by Collocalia fuciphaga. Journal of Agricultural and Food Chemistry, 46(8), pp.3047-3053.

Footnote Macro

Roh, K., Lee, J., Kim, Y., Park, J., Kim, J., Lee, J. and Park, D. (2012). Mechanisms of Edible Bird's Nest Extract-Induced Proliferation of Human Adipose-Derived Stem Cells. Evidence-Based Complementary and Alternative Medicine, 2012, pp.1-11.

(Oda et al. 1998; Wang and Brand-Miller 2003; Ng et al. 1986; Kong et al. 1987; Roh et al. 2012). The Black-nest Swiftlet (Aerodramus maximus) also produces nests that are being collected and consumed, but their nests contain inedible feathers that need to be removed.

Given the high value of the nests (about USD$20 per nest, nest harvesting naturally became highly popular

Footnote Macro

Marcone, M. (2005). Characterization of the edible bird’s nest the “Caviar of the East”. Food Research International, 38(10), pp.1125-1134.

. Despite efforts to keep nesting colonies secret and manage the harvest rates, wild populations of the Edible-nest Swiftlets have plummeted from once immeasurable numbers, and many colonies have now been wiped out, or are critically endangered

Footnote Macro

Lau, A. and Melville, D. (1994). International trade in swiftlet nests with special reference to Hong Kong. Cambridge, U.K.: Traffic International.

Footnote Macro

Sankaran, R. (2001). The status and conservation of the Edible-nest Swiftlet (Collocalia fuciphaga) in the Andaman and Nicobar Islands. Biological Conservation, 97(3), pp.283-294.

. Italy proposed to include the species under Appendix II of CITES to regulate trade in 1994, but opposition from the Southeast Asian nations prevented it, leaving it unlisted and thus unregulated

Footnote Macro

Thorburn, C. (2015). The Edible Nest Swiftlet Industry in Southeast Asia: Capitalism Meets Commensalism. Human Ecology, 43(1), pp.179-184.

3.2 "Blood nests"
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Some of the nests develop red stains in them, and were known collectively as “blood nests” under the false belief that the stains composed of swiftlet blood

Footnote Macro

Thorburn, C. (2015). The Edible Nest Swiftlet Industry in Southeast Asia: Capitalism Meets Commensalism. Human Ecology, 43(1), pp.179-184.

. These nests are rarer and used to fetch up to five times the price of a regular nest

Footnote Macro

Marcone, M. (2005). Characterization of the edible bird’s nest the “Caviar of the East”. Food Research International, 38(10), pp.1125-1134.

. Instead, the red was due to nitrifying bacteria reacting to ammonia vapour from decaying guano (swiftlet and/or bat excrement)

Footnote Macro

Thorburn, C. (2015). The Edible Nest Swiftlet Industry in Southeast Asia: Capitalism Meets Commensalism. Human Ecology, 43(1), pp.179-184.

. Some swiftlet farmers discovered this and induced these “blood nests” by treating the white nests with ammonia. Both artificial and natural red nests are found to have abnormally high levels of nitrite, up to 4400mg/kg, which can increase one’s risk of cancer, and potentially cause food poisoning

Footnote Macro

Chibber, A. (2011). China finds nitrite in edible bird's nests from Malaysia. [online] Food navigator-Asia. Available at: https://www.foodnavigator-asia.com/Article/2011/08/25/China-finds-nitrite-in-edible-bird-s-nests-from-Malaysia [Accessed 30 Nov. 2018].

. As a result, China, once the largest importer of swiftlet nests, banned the import of all birds’ nest from Malaysia and Indonesia. This caused a huge shock to the industry as demand of both "blood nests" and regular nests dropped significantly; China currently only imports from several Malaysian firms that meet strict regulations that were subsequently set up after the ban

Footnote Macro

News Asiaone. (2013). China lifts ban on bird's nest imports to Malaysia. [online] Available at: http://news.asiaone.com/News/Latest%2BNews/SoShiok/Story/A1Story20130621-431216.html [Accessed 30 Nov. 2018].

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3.3 House farming
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Two centuries ago, the Edible-nest Swiftlet nested solely on coastal habitats where caves were available, and there were no records of inland nesting colonies

Footnote Macro

Cranbrook, E., Goh, W. L., Lim, C. K., and Rahman, M. A. (2013). The species of white-nest swiftlets (Apodidae, Collocaliini) of Malaysia and the origins of house-farm birds: morphometric and genetic evidence. Forktail, 29, pp. 107–119

. Swiftlets were first reported to nest in houses near cliffs in the village of Sedayu in East Java in 1880, and entrepreneurs eventually began developing methods to attract swiftlets to nest in houses

Footnote Macro

Lim, C. and Cranbrook, G. (2002). Swiftlets of Borneo. Natural History Publications (Borneo).

. The industry grew as the use of broadcasting swiftlet calls to attract nesting birds became the norm, and a trade in swiftlet eggs began. House nesting swiftlets first appeared in the Malay Peninsula in the 1930s, reportedly first arriving in Singapore from Java, before spreading North across Malaysia

Footnote Macro

Cranbrook, E., Goh, W. L., Lim, C. K., and Rahman, M. A. (2013). The species of white-nest swiftlets (Apodidae, Collocaliini) of Malaysia and the origins of house-farm birds: morphometric and genetic evidence. Forktail, 29, pp. 107–119

. The swiftlets have a high degree of nest fidelity, and house farmed swiftlets and their young would return to man-made houses (preferably the same one) to nest again

Footnote Macro

Kang, N., Hails, C. and Sigurdsson, J. (2008). Nest construction and egg-laying in Edible-nest Swiftlets Aerodramus spp. and the implications for harvesting. Ibis, 133(2), pp.170-177.

, leaving the depleted natural populations and habitats unrestored

Footnote Macro

Cranbrook, E., Goh, W. L., Lim, C. K., and Rahman, M. A. (2013). The species of white-nest swiftlets (Apodidae, Collocaliini) of Malaysia and the origins of house-farm birds: morphometric and genetic evidence. Forktail, 29, pp. 107–119

. Furthermore, house nesting swiftlets are suspected to be a hybrid population of A. f. fuciphagus and A. f. inexpectatus or A. f. germani in what could be an ongoing case of domestication; the population of house farmed swiftlets have since spread Northward up to Myanmar, where it may be competing with local subspecies. More extensive regional genetic studies are required to confirm these suspicions.



Bird's nest soup prepared with red dates and rock sugar.
(Photo: Steamy Kitchen, 2017

Footnote Macro

Photo by Jaden Hair (2017) on Steamy Kitchen, accessed from https://steamykitchen.com/44260-chinese-birds-nest-soup-recipe.html.

)


Edible-nest Swiftlet "blood nest". 
(Photo: Lim Hong Yao, 2018)

Swiftlet house farm in Thailand
(Photo: Alexander Heitkamp, 2007

Footnote Macro

Photo by Alexander S. Heitkamp (2007) on Wikimedia Commons, accessed from https://commons.wikimedia.org/wiki/File:Nestinghouse_003.jpg

)

4. Ecology and behaviour
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4.1 Feeding
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Edible-nest Swiftlets are aerial insectivores that catch arthropods on the wing. Diet analyses have been conducted by examining regurgitated food boluses; hymenoptera (bees, wasps and ants), diptera (flies) and ephemeroptera (mayflies) made up majority of the food items, while arachnida (spiders and other arachnids), coleoptera (beetles) and hemiptera (true bugs) made up most of the rest

Footnote Macro

Lourie, S. and Tompkins, D. (2008). The diets of Malaysian swiftlets. Ibis, 142(4), pp.596-602.

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4.2 Reproduction
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The Edble-nest Swiftlets nest in natural caves, and man-made houses. Breeding has been observed to take place year-round but peak in October and February

Footnote Macro

Langham, N. (2008). Breeding biology of the edible-nest swiftlet Aerodramus fuciphagus. Ibis, 122(4), pp.447-461.

  • Nest building: Nests are made of salivary excrement that harden into a cement-like material. Each nesting pair will spend about 25 minutes a day to build the nest, which takes about 45 days to complete

    Footnote Macro

    Kang, N., Hails, C. and Sigurdsson, J. (2008). Nest construction and egg-laying in Edible-nest Swiftlets Aerodramus spp. and the implications for harvesting. Ibis, 133(2), pp.170-177.

    . Nests are re-used for subsequent nesting by the same pair in the future if not harvested

    Footnote Macro

    Langham, N. (2008). Breeding biology of the edible-nest swiftlet Aerodramus fuciphagus. Ibis, 122(4), pp.447-461.

    . Here is a video of the nest building process:

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urlhttps://www.youtube.com/watch?v=ngPs3kINUXE
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  • Chick development: Each pair of birds would usually lay two eggs and spend an average of 23 days incubating them. The chicks take about 43 days to develop and fledge, with an approximate 50% survival rate in nest houses when under observation (Nigel Langham 1979). Mortality is mostly attributed to eggs or chicks falling off the nests; it is not known why so many of them fall off the nest.


4.3 Echolocation
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As Edible-nest Swiftlets nest in places which are completely dark, they have evolved the ability to echolocate using clicking sounds, along with many other species from the genus Aerodramus

Footnote Macro

Jordan Price, J., P. Johnson, K. and H. Clayton, D. (2004). The evolution of echolocation in swiftlets. Journal of Avian Biology, 35(2), pp.135-143.

. This ability, however, is not diagnostic of the genus as the Pygmy Swiftlet (Collocalia troglodytes) has been proven to possess this ability too.

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nameT4254-Aerodramusfuciphagus-snd-1.mp3
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Sound recording of an Edible-nest Swiftlet's echolocating clicking calls. (Recorded by Lim Hong Yao, 2018)


5. Taxonomy
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5.1 Original description
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The Edible-nest Swiftlet was originally described by Carl Peter Thunberg, a well renowned Swedish naturalist from the 19th century. Thunberg collected the specimen in Java and described it as Hirundo fuciphagus in his Remarks about the Swallows that build jelly-like, edible Nests published in Kungl. Svenska vetenskapsakademiens handlingar (1812)

Footnote Macro

Thunberg. (1812). Remarks about the Swallows that build jelly-like, edible Nests. Kungl. Svenska vetenskapsakademiens handlingar, Vol. 1, pp.151-156. Accessed from https://www.biodiversitylibrary.org/page/47088095#page/165/mode/1up

(Figure 3), which, with help of Google Translate, roughly states that

  • he collected a specimen that appeared similar to Hirundo esculenta, but upon closer examination discovered it was an undescribed species. 
  • H. fuciphagus can be found in caves of the mountainous areas in Java and made jelly like nests that are a precious commodity.
  • The body of H. fuciphagus is black above and immaculate grey below, about four inches long
  • Tail is rounded and black above and below.
  • Wings black, twice the length of the tail and acute. Feet black and short.
  • Similar to H. esculenta but differentiated by the all black tail, chest and abdomen, no spots.

Figure 3: Scans of the original swedish description of H. fuciphagus in Kungl. Svenska vetenskapsakademiens handlingar by Thunberg (1812), obtained from Biodiversity Heritage Library

Footnote Macro

Thunberg. (1812). Remarks about the Swallows that build jelly-like, edible Nests. Kungl. Svenska vetenskapsakademiens handlingar, Vol. 1, pp.151-156. Accessed from https://www.biodiversitylibrary.org/page/47088095#page/165/mode/1up

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5.2 Phylogenetics of swiftlets
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Thunberg (1812) named the Edible-nest Swiftlets in Java Hirundo fuciphagus, mistakenly grouping them together with the swallows (Hirundo is a genus of swallows, which are passerines)

Footnote Macro

Thunberg. (1812). Remarks about the Swallows that build jelly-like, edible Nests. Kungl. Svenska vetenskapsakademiens handlingar, Vol. 1, pp.51-156. Accessed from https://www.biodiversitylibrary.org/page/47088095#page/165/mode/1up

. By the 1900s swiftlets were recognized as a separate taxon Collocalini 

Footnote Macro

Stresemann, E. (1931). Notes on the systematics and distribution of some swiftlets (Collocalia) of Malaysia and adjacent subregions. Bulletin of the Raffles Museum, 6, pp.83–101.

and all its members were initially lumped in the genus Collocalia, then subsequently divided into 3 genera: Hydrochous (Giant Swiftlets) are sister to Aerodramus (medium sized brownish swiftlets)and Collocalia (small glossy plumaged swiftlets). Multiple recent phylogenetic analyses have been conducted to establish that Collocalia are the basal group that are more related to the swifts, followed by Hydrochous and Aerodramus being sister genera

Footnote Macro

Cibois, A., Thibault, J., McCormack, G. and Pasquet, E. (2018). Phylogenetic relationships of the Eastern Polynesian swiftlets (Aerodramus, Apodidae) and considerations on other Western Pacific swiftlets. Emu - Austral Ornithology, 118(3), pp.247-257.

Footnote Macro

Päckert, M., Martens, J., Wink, M., Feigl, A. and Tietze, D. (2012). Molecular phylogeny of Old World swifts (Aves: Apodiformes, Apodidae, Apus and Tachymarptis) based on mitochondrial and nuclear markers. Molecular Phylogenetics and Evolution, 63(3), pp.606-616.

Footnote Macro

Price, J., Johnson, K., Bush, S. and Clayton, D. (2005). Phylogenetic relationships of the Papuan Swiftlet Aerodramus papuensis and implications for the evolution of avian echolocation. Ibis, 147(4), pp.790-796.

Footnote Macro
Rheindt, Frank E., Janette A. Norman & Les Christidis. (2014). Extensive diversification across islands in the echolocating Aerodramus swiftlets. Raffles Bulletin of Zoology, 62, pp.89-99.

. (Figure 3)



Figure 4: Phylogenetic tree of swiftlets obtained using nuclear and mitochondrial DNA analysis, estimated with Bayesian and Maximum Likelihood methods. Node support is denoted as posterior probabilities/bootstrap values. Adapted from Cibois et. al (2018)

Footnote Macro

Cibois, A., Thibault, J., McCormack, G. and Pasquet, E. (2018). Phylogenetic relationships of the Eastern Polynesian swiftlets (Aerodramus, Apodidae) and considerations on other Western Pacific swiftlets. Emu - Austral Ornithology, 118(3), pp.247-257.

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5.3 Species taxonomy
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5.3

Many studies have attempted to resolve the phylogenetic relationships of the Edible-nest Swiftlet, but A. fuciphagus has often shown up as a paraphyletic clade with one or more individuals of A. fuciphagus are more closely related to A. salangana than other A. fuciphagus 

Footnote Macro

Cibois, A., Thibault, J., McCormack, G. and Pasquet, E. (2018). Phylogenetic relationships of the Eastern Polynesian swiftlets (Aerodramus, Apodidae) and considerations on other Western Pacific swiftlets. Emu - Austral Ornithology, 118(3), pp.247-257.

Footnote Macro

Price, J., Johnson, K., Bush, S. and Clayton, D. (2005). Phylogenetic relationships of the Papuan Swiftlet Aerodramus papuensis and implications for the evolution of avian echolocation. Ibis, 147(4), pp.790-796.

Footnote Macro
Rheindt, Frank E., Janette A. Norman & Les Christidis. (2014). Extensive diversification across islands in the echolocating Aerodramus swiftlets. Raffles Bulletin of Zoology, 62, pp.89-99.

. Even the most recent tree constructed using mitochondrial and nuclear DNA analysis depicts this (Figure 4). The low genetic divergence between closely related taxa is likely due to occasional hybridisation events, which have been reported in Sabah

Footnote Macro

Lee, P., Clayton, D., Griffiths, R. and Page, R. (1996). Does behavior reflect phylogeny in swiftlets (Aves: Apodidae)? A test using cytochrome b mitochondrial DNA sequences. Proceedings of the National Academy of Sciences, 93(14), pp.7091-7096.

, leading to genetic introgression in the form of mitochondrial DNA (mtDNA) sweeps that cause some individuals to appear closer to sister species than its own

Footnote Macro

Rheindt, F. and Edwards, S. (2011). Genetic Introgression: An Integral but neglected component of speciation in birds. The Auk, 128(4), pp.620-632.

Furthermore, some authors disagree with classifying all 8 subspecies under a single species A. fuciphagus. The eight recognised subspecies for A. fuciphagus are as follows (descriptions are relative to nominate race unless stated)

Footnote Macro

Chantler, P. & Boesman, P. (2018). Edible-nest Swiftlet (Aerodramus fuciphagus). In: del Hoyo, J., Elliott, A., Sargatal, J., Christie, D.A. & de Juana, E. (eds.). Handbook of the Birds of the World Alive. Lynx Edicions, Barcelona. (retrieved from https://www.hbw.com/node/55287 on 29 November 2018).

:

  • A. f. amechanus (Oberholser, 1912) – Anambas Is, off SE Peninsular Malaysia.
    • Darker upperparts with green sheen and paler underparts, with greyer rump than germani
  • A. f. germani (Oustalet, 1876) – Coastline from W Hainan S around SE Asia to Malay Peninsula, including Mergui Archipelago (off S Myanmar); coastal N Borneo and W Philippines (Palawan E to Panay and Ticao).
    • Paler underparts and whitish rump
  • A. f. inexpectatus (A. O. Hume, 1873) – Andaman Is and Nicobar Is.
    • Slightly smaller than nominate race
  • A. f. vestitus (Lesson, 1843) – Sumatra, Belitung I and Borneo (except N coasts).
    • Darkest upperparts, lack contrasting rump
  • A. f. perplexus (Riley, 1927) – Maratua I, off E Borneo.
    • Some purple sheen on rectrices and remiges, slight contrasting rump
  • A. f. fuciphagus (Thunberg, 1812) – Java, Kangean Is and Bali to W Lesser Sundas, and Tanahjampea.
    • Dark brown upperparts with slightly paler greyish rump. Underparts brownish-grey.
  • A. f. dammermani (Rensch, 1931) – Flores (EC Lesser Sundas).
    • Slightly paler rump
  • A. f. micans (Stresemann, 1914) – Sumba, Sawu and Timor (C Lesser Sundas).
    • Slightly greyer overall with contrasting rump

Differences amongst subspecies are often subtle and difficult to distinguish in the field due to variations in lighting as well as difficulty in observing constantly fast-moving subjects.

According to the subspecies range, Edible-nest Swiftlets observed in Singapore should be A. f. germani which extends into the Malay Peninsula, but specimens collected appeared identical to the nominate race A. f. fuciphagus, likely because colonies in Malaysia and Singapore are of the house farmed variety (see House Farming below), which is suspected to be of Javan origin (ssp. fuciphagus). To complicate matters, their feeding ranges are likely overlapping.

Several authors believe that this species should be split into two or three. Table 1 on the below presents a summary of the 3 different treatments.

Table 1: Summary of the authors' different species treatments of the Edible-nest Swiftlet complex.

AuthorSpecies

Subspecies

HBW

Footnote Macro

Chantler, P. & Boesman, P. (2018). Edible-nest Swiftlet (Aerodramus fuciphagus). In: del Hoyo, J., Elliott, A., Sargatal, J., Christie, D.A. & de Juana, E. (eds.). Handbook of the Birds of the World Alive. Lynx Edicions, Barcelona. (retrieved from https://www.hbw.com/node/55287 on 29 November 2018).

& Stresemann (1931)

Footnote Macro

Stresemann, E. (1931). Notes on the systematics and distribution of some swiftlets (Collocalia) of Malaysia and adjacent subregions. Bulletin of the Raffles Museum, 6, pp.83–101.

A. fuciphagusall 8 listed above

Clement's checklist

Footnote Macro

Clements, J. F., T. S. Schulenberg, M. J. Iliff, D. Roberson, T. A. Fredericks, B. L. Sullivan, and C. L. Wood. 2018. The eBird/Clements checklist of birds of the world: v2018. Downloaded from http://www.birds.cornell.edu/clementschecklist/download/ 

A. germani

germani, amechanus

A. fuciphagus

fuciphagus, vestitus, inexpectatus, perplexus, dammermani, micans

Cranbrook et al. (2013)

A. fuciphagus

fuciphagus, vestitus, dammermani, micans

A. inexpectatus

inexpectatus, germani, perplexus

A. amechanusamechanus

The Clement's checklist treatment appears to be based on morphology and original descriptions of the subspecies, but does not appear to explicitly explain the treatment in any publication or platform. Despite this, many authors have adopted this treatment.

 Stresemann (1931) postulated that populations with a paler rump from A. f. germani and those of a darker rump from A. f. vestitus and germani formed a transition zone over Peninsula Malaysia where intergrades of rump colour can be observed

Footnote Macro

Stresemann, E. (1931). Notes on the systematics and distribution of some swiftlets (Collocalia) of Malaysia and adjacent subregions. Bulletin of the Raffles Museum, 6, pp.83–101.

. Thus, it was proposed that the populations were interbreeding, and thus the taxa were regarded as subspecies of A. fuciphagus. Medway (1966) also arrived at a similar conclusion

Footnote Macro

Medway, L. (1966). Field characters as a guide to the specific relations of swiftlets. Proceedings of the Linnean Society of London, 177, pp.151–172.

.

Cranbrook et. al (2013) on the other hand, re-examined the specimens used in Stresemann (1931) and postulated that there was not a cline in morphology, but rather an overlap of feeding range in Peninsula Malaysia

Footnote Macro

Cranbrook, E., Goh, W. L., Lim, C. K., and Rahman, M. A. (2013). The species of white-nest swiftlets (Apodidae, Collocaliini) of Malaysia and the origins of house-farm birds: morphometric and genetic evidence. Forktail, 29, pp. 107–119

. It was observed that the specimens could be grouped into two main groups: grey-rumped and brown rumped (Figure 5). Given that the rump colour was maintained as a character amongst these two groups with no gradation, it was concluded that these two should be grouped into two species, while amechanus was considered an endemic given its unusual glossy colouration and variable rump band. Grey-rumped swiftlets were grouped under A. inexpectatus while brown-rumped swiftlets remained as A. fuciphagus. Mitochondrial DNA analysis was also conducted in the study with both Maximum Parsimony and Neighbour Joining methods using cyt-b haplotypes but the nodes were all poorly supported and the tree appeared inconclusive regarding the phylogenetic relationships between populations (Figure 6).

However, upon examining the plates, it is apparent that rump colouration can vary significantly within a subspecies; A. inexpectatus germani of plate 3A (Figure 5) clearly shows an individual with a brown rump instead of a whitish rump as described for germani and shown in plate 1A. This raises concerns about using rump colour as a diagnostic trait to treat the species complex (HBW also mentions that the white on the rump is often overstated

Footnote Macro

Chantler, P. & Boesman, P. (2018). Edible-nest Swiftlet (Aerodramus fuciphagus). In: del Hoyo, J., Elliott, A., Sargatal, J., Christie, D.A. & de Juana, E. (eds.). Handbook of the Birds of the World Alive. Lynx Edicions, Barcelona. (retrieved from https://www.hbw.com/node/55287 on 29 November 2018).

. Even if the morphological breaks separating the populations in different geographical ranges are real, in applying the Biological Species Concept

Footnote Macro

Wheeler, Quentin D., and Rudolf Meier, editors. Species Concepts and Phylogenetic Theory: A Debate. Columbia University Press, 2000. JSTOR, www.jstor.org/stable/10.7312/whee10142.

, there is insufficient evidence to establish reproductive isolation given that the colonies breed in allopatry. Additionally, Cranbrook et. al (2013) suggested that the house farmed swiftlets could be a hybrid population of fuciphagus and inexpectatus, or fuciphagus and germani, indicating that these taxa may not withstand the test of sympatry when brought together in nest houses. Therefore, A. fuciphagus is currently treated as a single species (encompassing all 8 subspecies) on this page and by several other authors.

In considering the Phylogenetic species concept sensu Wheeler & Platnick (2000)

Footnote Macro

Wheeler, Quentin D., and Rudolf Meier, editors. Species Concepts and Phylogenetic Theory: A Debate. Columbia University Press, 2000. JSTOR, www.jstor.org/stable/10.7312/whee10142.

, most of these subspecies are likely to be elevated to the rank of species given that the different populations appear to have a unique set of character states in terms of size and plumage differences. However, more work needs to be done as well to adequately sample the different populations to establish the existence of these different character states.

Future taxonomic work is required to concretely establish the relationships between these taxa, both in terms of confirming morphological differences as well as investigating molecular evidence. Goh et. al (2018) recently investigated more house farmed Edible-nest Swiftlets from Peninsula Malaysia and found that they appeared to be closest to A. f. vestitus rather than A. f. fuciphagus (which was first to be recorded in the Malay Peninsula), but the node was not very well supported (bootstrap = 78) and no conclusive statements about their origin could be made

Footnote Macro

Goh, W.L., Siew, W.S., Davies, S.E.W., Ball, S. Ball., Khoo, G., Lim, C.K., Rahman, M. A., and Cranbrook, E. (2018). Genetic diversity among white-nest swiftlets of the genus Aerodramus (Aves: Apodidae: Collocaliini) of house-farms in Malaysia. Raffles Bulletin of Zoology, 66, pp.350–360

. Given the many unsuccessful attempts with mtDNA thus far, it is likely that mtDNA is unsuitable as a marker for intraspecific studies as it is only maternally inherited. Coupled with the issues of mtDNA sweeps, it is evident that mtDNA is not an effective  taxonomic indicator for the Edible-nest Swiftlets, and adopting genomic methods using Next Generation Sequencing is likely the way forward to unravel the true relationships between these populations.


Figure 5: Photo plates by Cranbrook et. al (2013) depicting the grey-rumped and brown rumped Edible-nest Swiftlet specimens examined

Footnote Macro

Cranbrook, E., Goh, W. L., Lim, C. K., and Rahman, M. A. (2013). The species of white-nest swiftlets (Apodidae, Collocaliini) of Malaysia and the origins of house-farm birds: morphometric and genetic evidence. Forktail, 29, pp. 107–119

.


Figure 6: Maximum Parsimony tree created using cyt-b haplotypes from Edible-nest Swiftlet samples by Cranbrook et. al (2013)

Footnote Macro

Cranbrook, E., Goh, W. L., Lim, C. K., and Rahman, M. A. (2013). The species of white-nest swiftlets (Apodidae, Collocaliini) of Malaysia and the origins of house-farm birds: morphometric and genetic evidence. Forktail, 29, pp. 107–119

. Numbers at nodes are the Neighbour Joining/Maximum Parsimony bootstrap values (tree topology was identical for both methods). 

References: 

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