4. Ecology and behaviour
Edible-nest Swiftlets are aerial insectivores that catch arthropods on the wing. Diet analyses have been conducted by examining regurgitated food boluses; hymenoptera, diptera and ephemeroptera made up majority of the food items, while arachnida, coleoptera and hemiptera made up most of the rest.
Breeding has been observed to take place year-round but peak in October and February. (Nigel Langham 1979).
- 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. (Kang et al 1991). Nests are re-used for subsequent clutches in the future if not harvested. (Nigel Langham 1979).
- 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 (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)
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" (1812) (Figure 2), which, with help of Google Translate, roughly states that
- he collected a specimen that appeared similar to Hirundoesculenta, 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 black and 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.
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 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. (Cibois et. al 2018 and others)
Several studies have attempted to resolve the phylogenetic relationships of the Edible-nest Swiftlet, but success has been rather limited as it does not show up as a monophyletic clade on the tree; results often show that one or more individuals of A. fuciphagus are more closely related to the sister species A. salangana (Mossy-nest Swiftlet) than other A. fuciphagus (Cibois et. Al, 2018; Price et. Al, 2005; Rheindt et. al, 2014). The most recent tree constructed using mitochondrial and nuclear DNA analysis is shown on the right (Figure 2) (Cibois et. al, 2018).
*add info on methods of analysis in Cibois here*
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 sweeps (Rheindt & Edwards, 2011) that cause some individuals to appear closer to sister species than its own. It is evident that mitochondrial DNA is not very effective as a taxonomic indicator in the case of the Aerodramus swiftlets, and genomic methods may be a better alternative to resolve these relationships.
5.3 Subspecies taxonomy
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.
Subsequently, Cranbrook et. al (2013) re-examined the specimens for the subspecies 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 and this treatment is currently adopted by several authors. 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). 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.
*critique on methods of analysis in fig 3 and 4*
*How different species concepts would treat this*
Figure 2: Scans of the original swedish description of H. fuciphagus in Kungl. Svenska vetenskapsakademiens handlingar by Thunberg (1812), obtained from Biodiversity Heritage Library.
Figure 2: Phylogenetic tree of Aerodramus swiftlets obtained using nuclear and mitochondrial DNA analysis. Adapted from Cibois et. al (2018).
Figure 3: Phylogenetic tree of Edible-nest Swiftlets from different populations using mitochondrial DNA and neighbour-joining methods. Adapted from Cranbrook et. al (2013).
Figure 4: Phylogenetic tree of swiftlets using mitochondrial DNA. Adapted from Lee et. al (1996).