Swiftlets are birds from the four genera Aerodramus, Collocalia, Hydrochous and Schoutedenapus, which form the tribe Collocaliini within the swift family Apodidae. The group contains around thirty species mostly confined to southern Asia, south Pacific islands, and northeastern Australia, all within the tropical and subtropical regions. They are in many respects typical members of the Apodidae, having narrow wings for fast flight, with a wide gape and small reduced beak surrounded by bristles for catching insects in flight. What distinguishes many but not all species from other swifts and indeed almost all other birds is their ability to use a simple but effective form of echolocation to navigate in total darkness through the chasms and shafts of the caves where they roost at night and breed.
The nests of some species are built entirely from solidified threads of their saliva, which are edible and thus collected for human consumption as the famous Chinese delicacy, the bird's nest soup.
Description and ecology
The swift family remains one of the more complicated groups of birds in taxonomic research, but the swiftlet tribe is a rather well-defined group. Its internal systematics is confusing; the plumage is usually dull, with shades of black, brown, and gray; from their outward appearance, most species are very similar. Swiftlets have four toes, except the Papuan swiftlet which lacks the hallux (back toe). Their legs are very short, preventing the birds from perching, but allowing them to cling to vertical surfaces. Flight is mainly gliding due to very long primary feathers and small breast muscles. The larger Aerodramus swiftlets weigh about 14 grams and are 10 cm long.
Swiftlets are insectivores; hymenopterans and dipterans being the most abundant prey. It is also believed to strengthen the lungs and prevent coughs, improve the constitution and prolong life. The nutritional value of 100 g of dry nest includes 49.9 g of water-soluble protein (including amido nitrogen, monoamine nitrogen, non-amino nitrogen, arginine, humin, histidine, lysine and cysteine), 30.6 g carbohydrate (glycoprotein and mucin), 4.9 g iron, 2.5 g inorganic salt (including potassium, sodium, calcium, magnesium, sulfur, phosphorus, silica and other trace elements), and 1.4 g fiber (Dictionary of Traditional Chinese Medicine, The History of Chinese Medicine and the Nutrition Table).
The energy contained in 100 g of swiftlet nest is 345 kcal. The nests are often served simmered in chicken broth.
Authentic bird's-nest soup is quite popular throughout Asia. It is also extremely expensive; many western restaurants serve a less expensive version consisting of soup with noodles shaped to resemble a bird's nest.
Cave ecology
Guano from both the swiftlets and the many bats that inhabit the caves supports a huge array of specialized animals that feed on the dung. There are yet other creatures that have evolved to feed on these dung eaters as well as on the bats and the swiftlets themselves, including snakes that can climb the sheer walls to snatch a passing meal and huge carnivorous crickets that prey on chicks and bat pups. This cave fauna ecosystem is self-sustaining, the only link with the outside being the birds and the bats that bring the nutrients into the caves in the first place.
The Philippine municipality of El Nido in Palawan, known for its limestone cliffs and pristine beaches, is home to a thriving bird's-nest market. The name El Nido is the Spanish term for literally "The Nest". Many locals still practice manual climbing of the limestone caves to gather swiftlet nests.
Species
The Papuan swiftlet is apparently closer to the waterfall swift than to the other Aerodramus species and probably best placed in a separate genus,
Further reading
- Camfield, Alaine (2004) Apodidae. Animal Diversity Web (online). Accessed August 24, 2006.
- Gausset, Quentin (2004): Chronicle of a Foreseeable Tragedy: Birds' Nests Management in the Niah Caves (Sarawak). Human Ecology 32(4): 487–506. (HTML abstract)