Bird's nest soup or yan wo is a traditional Chinese delicacy made from the nest of the swiftlet, a tropical bird which is found in many parts of Asia, including China and Thailand. The unique ingredient in this soup is believed to be an aphrodisiac which also increases longevity, and as a result, this dish is in high demand in some parts of China. The bird's nests used in the soup can be quite expensive, and the dish is typically served only at exclusive restaurants.
Swiftlets are birds in the family Apodidae. Several species within this family are able to use echolocation, which allows them to nest and breed in caves. These species produce a unique gummy saliva, which they use to build their nests; they lay down strands of saliva which harden when exposed to air, creating a solid nest. Harvesters enter the caves, retrieve the nests, clean them, and then offer them for sale.
To make bird's nest soup, the nest is simmered in chicken stock. The result is a broth with floating chunks of the nest; the chunks have a distinctive gelatinous texture when cooked which is not to the taste of all consumers. The soup is usually lightly seasoned, if at all, and some people actually find it rather bland. It is the exotic ingredient which makes the soup popular, rather than an amazing flavor, although it is high in some useful minerals like calcium and magnesium, making it at least nutritionally beneficial.
There are some serious ecological issues associated with bird's nest soup. Many companies which harvest nests engage in unscrupulous practices like harvesting nests too quickly for the birds to breed, and some have been accused of establishing private armies to protect particularly fruitful caves. Some companies also destroy nests from the wrong species of bird to encourage the growth of a colony which will produce usable nests, thereby putting other swiftlet species at risk. Overall populations of these birds have declined in Asia, possibly as a result of the growing market pressure for bird's nest soup.
Nests for making bird's nest soup can be obtained in Asian markets, where they are usually secured behind a counter due to their high cost. It is also possible to make the soup with vegetarian meat substitutes, some of which can very closely approximate the texture of swiftlet's nest, although they lack the perceived aphrodisiac benefits.