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Edible-nest Swiftlet

(Aerodramus fuciphagus, Thunberg 1812)

Anticlockwise from top:  Edible-nest Swiftlet in flight1  , perched on nest2 , harvested edible nest3 , prepared bird's nest soup4 .


Contents:

1. Introduction

    1.1 Description
    1.2 Identification
    1.3 Etymology

2. Range

3. Human interactions

    3.1 Bird's nest soup
    3.2 "Blood nests"
    3.3 House farming

4. Ecology and behaviour

    4.1 Feeding
    4.2 Reproduction
    4.3 Echolocation

5. Taxonomy and phylogenetics

  5.1 Species taxonomy
i 5.2 Phylogenetics of swiftlets
i 5.3 Subspecies taxonomy


1. Introduction

1.1 General information

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 rest5 . 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 1880s6 .

1.2 Identification

A medium sized swiftlet with glossy dark brown upperparts5 . 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

The genus Aerodramus stems from two Greek words: ἀερο, "aero" which means 'air', and δρόμος,"dromos" which means 'path'7 .

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

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)5 . 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)5

3. Human interactions

3.1 Bird's nest soup

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.)8 . Like many other Chinese delicacies, birds’ nest soup is not especially tasty, and relies on other culinary additions to appeal to the palate9 . 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 complexion10 . 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 nests11 12 (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 popular10 . 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 endangered13 14 . 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 unregulated9

3.2 "Blood nests"

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 blood9 . These nests are rarer and used to fetch up to five times the price of a regular nest10 . Instead, the red was due to nitrifying bacteria reacting to ammonia vapour from decaying guano (swiftlet and/or bat excrement)9 . 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 poisoning15 . 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 ban16 .

3.3 House farming

Two centuries ago, the Edible-nest Swiftlet nested solely on coastal habitats where caves were available, and there were no records of inland nesting colonies17 . 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 houses6 . 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 Malaysia17 . 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 again18 , leaving the depleted natural populations and habitats unrestored17 . 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, 201719 )


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

Swiftlet house farm in Thailand
(Photo: Alexander Heitkamp, 200720 )

4. Ecology and behaviour

4.1 Feeding

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 rest21 .

4.2 Reproduction

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 February22

  • 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 complete18 . Nests are re-used for subsequent nesting by the same pair in the future if not harvested22 . Here is a video of the nest building process:

  • 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

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 Aerodramus23 . This ability, however, is not diagnostic of the genus as the Pygmy Swiftlet (Collocalia troglodytes) has been proven to possess this ability too.

T4254-Aerodramusfuciphagus-snd-1.mp3
Sound recording of an Edible-nest Swiftlet's echolocating clicking calls. (Recorded by Lim Hong Yao, 2018)


5. Taxonomy

5.1 Original description

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)24 (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.

5.2 Phylogenetics of swiftlets

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). By the 1900s swiftlets were recognized as a separate taxon Collocalini and all its members were 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. (Figure 3) ( Cibois et. Al, 2018Päckert et. al, 2012Price et. Al, 2005Rheindt et. al, 2014)

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).

5.3 Species taxonomy

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 (Cibois et. Al, 2018Price et. Al, 2005Rheindt et. al, 2014). Even the most recent tree constructed using mitochondrial and nuclear DNA analysis depicts this (Figure 4) (Cibois et. al, 2018). The low genetic divergence between closely related taxa is likely due to occasional hybridisation events, which have been reported in Sabah (Lee, 1996), leading to genetic introgression in the form of mitochondrial DNA (mtDNA) sweeps (Rheindt & Edwards, 2011) that cause some individuals to appear closer to sister species than its own. 

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)5 :

  • 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 Swiiftlet complex.

AuthorSpecies

Subspecies

HBW25 & Stresemann (1931)

A. fuciphagusall 8 listed above
Clement's checklistA. 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. 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.

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 Malaysia17 . 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 overstated5 . Even if the morphological breaks separating the populations in different geographical ranges are real, in applying the Biological Species Concept, 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), 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. 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 examined17 .

Figure 6: Maximum Parsimony tree created using cyt-b haplotypes from Edible-nest Swiftlet samples by Cranbrook et. al (2013)17 . Numbers at nodes are the Neighbour Joining/Maximum Parsimony bootstrap values (tree topology was identical for both methods). 

References: 

Footnotes
Ref Notes
1 Photo by Lim Hong Yao (2017)
2 Photo by Lim Hong Yao (2018)
3 Photo by Ediblebirdsnest (2016) on Wikimedia Commons, accessed from https://commons.wikimedia.org/wiki/File:Edible-birds-nest-bowl-shape.png
4 Photo by Crue (2010) on Blogger, accessed from http://ichikichikehem.blogspot.com/2010/01/thai-hatyai-bird-nest-soup-7ps.html
5 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 b c d e f ]
6 Lim, C. and Cranbrook, G. (2002). Swiftlets of Borneo. Natural History Publications (Borneo). [ a b ]
7 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].
8 Lau, A. and Melville, D. (1994). International trade in swiftlet nests with special reference to Hong Kong. Cambridge, U.K.: Traffic International.
9 Thorburn, C. (2015). The Edible Nest Swiftlet Industry in Southeast Asia: Capitalism Meets Commensalism. Human Ecology, 43(1), pp.179-184. [ a b c d ]
10 Marcone, M. (2005). Characterization of the edible bird’s nest the “Caviar of the East”. Food Research International, 38(10), pp.1125-1134. [ a b c ]
11 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.
12 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.
13 Lau, A. and Melville, D. (1994). International trade in swiftlet nests with special reference to Hong Kong. Cambridge, U.K.: Traffic International.
14 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.
15 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].
16 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].
17 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 [ a b c d e f ]
18 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. [ a b ]
19 Photo by Jaden Hair (2017) on Steamy Kitchen, accessed from https://steamykitchen.com/44260-chinese-birds-nest-soup-recipe.html.
20 Photo by Alexander S. Heitkamp (2007) on Wikimedia Commons, accessed from https://commons.wikimedia.org/wiki/File:Nestinghouse_003.jpg
21 Lourie, S. and Tompkins, D. (2008). The diets of Malaysian swiftlets. Ibis, 142(4), pp.596-602.
22 Langham, N. (2008). Breeding biology of the edible-nest swiftlet Aerodramus fuciphagus. Ibis, 122(4), pp.447-461. [ a b ]
23 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.
24 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
25 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).

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

Lau, A. and Melville, D. (1994)

Edible-nest Swiftlet

(Aerodramus fuciphagus, Thunberg 1812)

Anticlockwise from top:  Edible-nest Swiftlet in flight26  , perched on nest27 , harvested edible nest28 , prepared bird's nest soup29 .


Contents:

1. Introduction

    1.1 Description
    1.2 Identification
    1.3 Etymology

2. Range

3. Human interactions

    3.1 Bird's nest soup
    3.2 "Blood nests"
    3.3 House farming

4. Ecology and behaviour

    4.1 Feeding
    4.2 Reproduction
    4.3 Echolocation

5. Taxonomy and phylogenetics

  5.1 Species taxonomy
i 5.2 Phylogenetics of swiftlets
i 5.3 Subspecies taxonomy


1. Introduction

1.1 General information

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 rest30 . 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 1880s31 .

1.2 Identification

A medium sized swiftlet with glossy dark brown upperparts32 . 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

The genus Aerodramus stems from two Greek words: ἀερο, "aero" which means 'air', and δρόμος,"dromos" which means 'path'33 .

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

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)30 . 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)30

3. Human interactions

3.1 Bird's nest soup

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.)34 . Like many other Chinese delicacies, birds’ nest soup is not especially tasty, and relies on other culinary additions to appeal to the palate35 . 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 complexion36 . 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 nests37 38 (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 popular36 . 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 endangered39 40 . 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 unregulated35

3.2 "Blood nests"

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 blood35 . These nests are rarer and used to fetch up to five times the price of a regular nest36 . Instead, the red was due to nitrifying bacteria reacting to ammonia vapour from decaying guano (swiftlet and/or bat excrement)35 . 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 poisoning41 . 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 ban42 .

3.3 House farming

Two centuries ago, the Edible-nest Swiftlet nested solely on coastal habitats where caves were available, and there were no records of inland nesting colonies43 . 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 houses31 . 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 Malaysia43 . 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 again44 , leaving the depleted natural populations and habitats unrestored43 . 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, 201745 )


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

Swiftlet house farm in Thailand
(Photo: Alexander Heitkamp, 200746 )

4. Ecology and behaviour

4.1 Feeding

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 rest47 .

4.2 Reproduction

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 February48

  • 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 complete44 . Nests are re-used for subsequent nesting by the same pair in the future if not harvested48 . Here is a video of the nest building process:

  • 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

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



49



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


T4254-Aerodramusfuciphagus-snd-1.mp3
Sound recording of an Edible-nest Swiftlet's echolocating clicking calls. (Recorded by Lim Hong Yao, 2018)


5. Taxonomy

5.1 Original description

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 Kungl. Svenska vetenskapsakademiens handlingar (Remarks about the Swallows that build jelly-like, edible Nests) (1812) (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.

5.2 Phylogenetics of swiftlets

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). By the 1900s swiftlets were recognized as a separate taxon Collocalini and all its members were 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. (Figure 3) ( Cibois et. Al, 2018Päckert et. al, 2012Price et. Al, 2005Rheindt et. al, 2014)

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).

5.3 Species taxonomy

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 (Cibois et. Al, 2018Price et. Al, 2005Rheindt et. al, 2014). Even the most recent tree constructed using mitochondrial and nuclear DNA analysis depicts this (Figure 4) (Cibois et. al, 2018). The low genetic divergence between closely related taxa is likely due to occasional hybridisation events, which have been reported in Sabah (Lee, 1996), leading to genetic introgression in the form of mitochondrial DNA (mtDNA) sweeps (Rheindt & Edwards, 2011) that cause some individuals to appear closer to sister species than its own. 

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)32 :

  • 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 Swiiftlet complex.

AuthorSpecies

Subspecies

HBW50 ]]>& Stresemann (1931)

A. fuciphagusall 8 listed above
Clement's checklistA. 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. 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.

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 Malaysia43 . 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. Even if the morphological breaks separating the populations in different geographical ranges are real, in applying the Biological Species Concept, 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), 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. 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 examined43 .

Figure 6: Maximum Parsimony tree created using cyt-b haplotypes from Edible-nest Swiftlet samples by Cranbrook et. al (2013)43 . Numbers at nodes are the Neighbour Joining/Maximum Parsimony bootstrap values (tree topology was identical for both methods). 

References: 

Footnotes
Ref Notes
26 Photo by Lim Hong Yao (2017)
27 Photo by Lim Hong Yao (2018)
28 Photo by Ediblebirdsnest (2016) on Wikimedia Commons, accessed from https://commons.wikimedia.org/wiki/File:Edible-birds-nest-bowl-shape.png
29 Photo by Crue (2010) on Blogger, accessed from http://ichikichikehem.blogspot.com/2010/01/thai-hatyai-bird-nest-soup-7ps.html
30 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 b c ]
31 Lim, C. and Cranbrook, G. (2002). Swiftlets of Borneo. Natural History Publications (Borneo). [ a b ]
32 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 b ]
33 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].
34 Lau, A. and Melville, D. (1994). International trade in swiftlet nests with special reference to Hong Kong. Cambridge, U.K.: Traffic International.
35 Thorburn, C. (2015). The Edible Nest Swiftlet Industry in Southeast Asia: Capitalism Meets Commensalism. Human Ecology, 43(1), pp.179-184. [ a b c d ]
36 Marcone, M. (2005). Characterization of the edible bird’s nest the “Caviar of the East”. Food Research International, 38(10), pp.1125-1134. [ a b c ]
37 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.
38 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.
39 Lau, A. and Melville, D. (1994). International trade in swiftlet nests with special reference to Hong Kong. Cambridge, U.K.: Traffic International.
40 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.
41 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].
42 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].
43 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 [ a b c d e f ]
44 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. [ a b ]
45 Photo by Jaden Hair (2017) on Steamy Kitchen, accessed from https://steamykitchen.com/44260-chinese-birds-nest-soup-recipe.html.
46 Photo by Alexander S. Heitkamp (2007) on Wikimedia Commons, accessed from https://commons.wikimedia.org/wiki/File:Nestinghouse_003.jpg
47 Lourie, S. and Tompkins, D. (2008). The diets of Malaysian swiftlets. Ibis, 142(4), pp.596-602.
48 Langham, N. (2008). Breeding biology of the edible-nest swiftlet Aerodramus fuciphagus. Ibis, 122(4), pp.447-461. [ a b ]
49 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.
50

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).

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).

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Organise to make it interesting, maybe biology first etc, but type/taxo portion important for module and show off knowledge, apply concepts. Try to differentiate your species page from existing ones out there, think about target audience.
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Thorburn, C. (2015). The Edible Nest Swiftlet Industry in Southeast Asia: Capitalism Meets Commensalism. Human Ecology, 43(1), pp.179-184.

Lau, A. and Melville, D. (1994)

Edible-nest Swiftlet

(Aerodramus fuciphagus, Thunberg 1812)

Anticlockwise from top:  Edible-nest Swiftlet in flight51  , perched on nest52 , harvested edible nest53 , prepared bird's nest soup54 .


Contents:

1. Introduction

    1.1 Description
    1.2 Identification
    1.3 Etymology

2. Range

3. Human interactions

    3.1 Bird's nest soup
    3.2 "Blood nests"
    3.3 House farming

4. Ecology and behaviour

    4.1 Feeding
    4.2 Reproduction
    4.3 Echolocation

5. Taxonomy and phylogenetics

  5.1 Species taxonomy
i 5.2 Phylogenetics of swiftlets
i 5.3 Subspecies taxonomy


1. Introduction

1.1 General information

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 rest55 . 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 1880s56 .

1.2 Identification

A medium sized swiftlet with glossy dark brown upperparts55 . 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

The genus Aerodramus stems from two Greek words: ἀερο, "aero" which means 'air', and δρόμος,"dromos" which means 'path'57 .

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

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)55 . 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)58

3. Human interactions

3.1 Bird's nest soup

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.)59 . Like many other Chinese delicacies, birds’ nest soup is not especially tasty, and relies on other culinary additions to appeal to the palate60 . 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 complexion61 . 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 nests62 63 (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 popular61 . 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 endangered64 65 . 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 unregulated60

3.2 "Blood nests"

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 blood60 . These nests are rarer and used to fetch up to five times the price of a regular nest61 . Instead, the red was due to nitrifying bacteria reacting to ammonia vapour from decaying guano (swiftlet and/or bat excrement)60 . 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 poisoning66 . 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 ban67 .

3.3 House farming

Two centuries ago, the Edible-nest Swiftlet nested solely on coastal habitats where caves were available, and there were no records of inland nesting colonies68 . 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 houses56 . 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 Malaysia68 . 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 again69 , leaving the depleted natural populations and habitats unrestored68 . 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, 201770 )


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

Swiftlet house farm in Thailand
(Photo: Alexander Heitkamp, 200771 )

4. Ecology and behaviour

4.1 Feeding

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 rest72 .

4.2 Reproduction

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 February73

  • 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 complete69 . Nests are re-used for subsequent nesting by the same pair in the future if not harvested73 . Here is a video of the nest building process:

  • 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

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



74



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


T4254-Aerodramusfuciphagus-snd-1.mp3
Sound recording of an Edible-nest Swiftlet's echolocating clicking calls. (Recorded by Lim Hong Yao, 2018)


5. Taxonomy

5.1 Original description

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 Kungl. Svenska vetenskapsakademiens handlingar (Remarks about the Swallows that build jelly-like, edible Nests) (1812) (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.

5.2 Phylogenetics of swiftlets

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). By the 1900s swiftlets were recognized as a separate taxon Collocalini and all its members were 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. (Figure 3) ( Cibois et. Al, 2018Päckert et. al, 2012Price et. Al, 2005Rheindt et. al, 2014)

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).

5.3 Species taxonomy

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 (Cibois et. Al, 2018Price et. Al, 2005Rheindt et. al, 2014). Even the most recent tree constructed using mitochondrial and nuclear DNA analysis depicts this (Figure 4) (Cibois et. al, 2018). The low genetic divergence between closely related taxa is likely due to occasional hybridisation events, which have been reported in Sabah (Lee, 1996), leading to genetic introgression in the form of mitochondrial DNA (mtDNA) sweeps (Rheindt & Edwards, 2011) that cause some individuals to appear closer to sister species than its own. 

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)55 :

  • 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 Swiiftlet complex.

AuthorSpecies

Subspecies

HBW & Stresemann (1931)A. fuciphagusall 8 listed above
Clement's checklistA. 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. 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.

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 Malaysia68 . 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. Even if the morphological breaks separating the populations in different geographical ranges are real, in applying the Biological Species Concept, 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), 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. 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 examined68 .

Figure 6: Maximum Parsimony tree created using cyt-b haplotypes from Edible-nest Swiftlet samples by Cranbrook et. al (2013)68 . Numbers at nodes are the Neighbour Joining/Maximum Parsimony bootstrap values (tree topology was identical for both methods). 

References: 

Footnotes
Ref Notes
51 Photo by Lim Hong Yao (2017)
52 Photo by Lim Hong Yao (2018)
53 Photo by Ediblebirdsnest (2016) on Wikimedia Commons, accessed from https://commons.wikimedia.org/wiki/File:Edible-birds-nest-bowl-shape.png
54 Photo by Crue (2010) on Blogger, accessed from http://ichikichikehem.blogspot.com/2010/01/thai-hatyai-bird-nest-soup-7ps.html
55 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 b c d ]
56 Lim, C. and Cranbrook, G. (2002). Swiftlets of Borneo. Natural History Publications (Borneo). [ a b ]
57 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].
58 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).
59 Lau, A. and Melville, D. (1994). International trade in swiftlet nests with special reference to Hong Kong. Cambridge, U.K.: Traffic International.
60 Thorburn, C. (2015). The Edible Nest Swiftlet Industry in Southeast Asia: Capitalism Meets Commensalism. Human Ecology, 43(1), pp.179-184. [ a b c d ]
61 Marcone, M. (2005). Characterization of the edible bird’s nest the “Caviar of the East”. Food Research International, 38(10), pp.1125-1134. [ a b c ]
62 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.
63 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.
64 Lau, A. and Melville, D. (1994). International trade in swiftlet nests with special reference to Hong Kong. Cambridge, U.K.: Traffic International.
65 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.
66 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].
67 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].
68 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 [ a b c d e f ]
69 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. [ a b ]
70 Photo by Jaden Hair (2017) on Steamy Kitchen, accessed from https://steamykitchen.com/44260-chinese-birds-nest-soup-recipe.html.
71 Photo by Alexander S. Heitkamp (2007) on Wikimedia Commons, accessed from https://commons.wikimedia.org/wiki/File:Nestinghouse_003.jpg
72 Lourie, S. and Tompkins, D. (2008). The diets of Malaysian swiftlets. Ibis, 142(4), pp.596-602.
73 Langham, N. (2008). Breeding biology of the edible-nest swiftlet Aerodramus fuciphagus. Ibis, 122(4), pp.447-461. [ a b ]
74 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.

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