Range map of the Edible-nest Swiftlet, adapted from HBW (2018).
8 current subspecies are recognized as shown below (with range and comparative descriptions):
- A. f. amechanus (Oberholser, 1912) – Anambas Is, off SE Peninsular Malaysia.
- 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 (E to Sumbawa), and Tanahjampea.
- 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
Several authors believe that this species should be split into two. In that treatment, ssp amechanus and germani are named Germain’s Swiftlet, while the rest of the subspecies retain the name of Edible-nest Swiftlet. However, taxonomical evidence for splitting the species has been unconvincing to many, and this species page will treat the group as a single species under the Biological Species Concept (see Taxonomy section).
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, but specimens collected appeared identical to the nominate race, 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 not known and may overlap.
3. 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.
Natural populations of the swiftlets nest in caves, such as the Niah and Gomantong caves in Borneo, and on the Andaman and Nicobar Islands in the Bay of Bengal. However, due to the practice of farming swiftlets in nest houses (see below), the Edible-nest swiftlets have adopted nesting in man-made buildings as early as the 1880s. (Lim & Cranbrook 2002).
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.