Anticlockwise from top: in flight, Edible-nest Swiftlet perched on nest, harvested edible nest, prepared bird's nest soup.
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). 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.
Figure 1: Range map of the Edible-nest Swiftlet, adapted from HBW (2018)
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.
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. (Nigel Langham 1979).
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. This ability, however, is not diagnostic of the genus as the Pygmy Swiftlet (Collocalia troglodytes) has been proven to possess this ability too.
Sound recording of an Edible-nest Swiftlet's echolocating clicking calls. (Recorded by Lim Hong Yao, 2018)
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" (1812) (Figure 2), which, with help of Google Translate, roughly states that
Figure 2: Scans of the original swedish description of H. fuciphagus in Kungl. Svenska vetenskapsakademiens handlingar by Thunberg (1812), obtained from Biodiversity Heritage Library.
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, 2018; Päckert et. al, 2012; Price et. Al, 2005; Rheindt 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).
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, 2018; Price et. Al, 2005; Rheindt 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:
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 right presents a summary of the 3 different treatments.
The Clement's checklist treatment appears to be based on morphology and original descriptions of the subspecies, as well as ranges, but does not appear to explicitly explain the treatment in any publication or platform.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 Malaysia. As such, A. germani and A. inexpectatus were suggested as separate species. Mitochondrial DNA analysis was conducted but only revealed significant differences between house farmed swiftlets and A. f. vestitus, while the parsimony tree constructed using neighbour joining techniques revealed poor support on the nodes and appeared inconclusive regarding the phylogenetic relationships between populations (Figure 3). Previous cytochrome-b mitochondrial DNA work by Lee et. al (1996) also failed to reveal any conclusive results (Figure 4). 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 very effective as a taxonomic indicator for Edible-nest Swiftlets, and genomic methods may be a better alternative to resolve these relationships. While morphological breaks separating the populations in different geographical ranges may exist, 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) postulated that the house farmed swiftlets could be a hybrid population of A. f. fuciphagus and A. f. inexpectatus or A. f. 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 on this page and by several other authors. Future genomic research with Next Generation Sequencing can be conducted to help reveal the phylogenetic relationship of these taxa more conclusively.In 1931, Stresemann postulated that populations with a paler rump from A. f. germani and those of a darker rump from A. f. vestitus and fuciphagus 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 Aerodramus fuciphagus. Medway (1966) also arrived at a similar conclusion.
*critique on methods of analysis in fig 3 and 4*
*How different species concepts would treat this*
|HBW & Stresemann (1931)||A. fuciphagus||all 8 listed above|
|Clement's checklist||A. germani|
|Cranbrook et al. (2013)||A. fuciphagus|