I know you are not supposed to click your own Google AdSense ads, but recently there were two ads for purveyors of bird’s nest soup, and I had to go see what that was all about. I knew that bird’s nest soup is made from the nests of various Asian species of swifts. Not mud or straw or grasses, but the bird’s saliva. This seems revolting to me, but it prompted me to look into the natural history of these birds.
The swifts in question are in the genus Aerodramus (formerly Collocalia), and the nests of five species are typically harvested.
The most highly valued are the nests from the Edible-nest Swiftlet (A. fuciphaga). Their 15-gram nests are comprised of nearly entirely of inspissated saliva strands, and are marketed by color: white (75% of the market, shown here), red, or golden. The various colors are theoretically due to differences in diet, humidity, temperature, and ammonia level in the nesting area (which depends on the amount of feces the birds produce).
The Glossy Swiftlet (A. esculenta) makes nests that are mostly conifer needles and grasses, glued together with saliva, which makes up less than 15% of the nest mass. The nest of the Black-nest Swiftlet (A. maxima) also has little saliva, and the rest is usually feathers (this is getting more unappetizing as we go along). Nests of Mossy-nest Swiftlet (A. vanikorensis) and Himalayan Swiftlet (A. brevirostris) are also sometimes used.
Swiftlet nests have been used as food in Asia for centuries, and like many rare and unusual animal products, it was (and is) presumed that they have numerous special medicinal (and, of course, aphrodisiac) qualities. Analyses of the nests, comprised of inorganic ash, protein, and carbohydrates, reveal no such beneficial properties. They don’t even have much taste. For the table, nests are soaked, cleaned, shredded, cleaned, rinsed, then cooked, with or without sweeteners and other ingredients, into a gelantinous soup or stew.
Not surprisingly, perhaps, there have been alarming declines in species of exploited Aerodramus swiftlets due to overharvesting over the last several decades. For much of history, systems were in place, often reinforced not only by law but by ethnic and cultural customs and mores, which established sustainable harvest. Continually rising prices (to astronomical sums), spurred by the rapidly growing affluent consumer sector in China, has seen a breakdown in these systems. Nest collectors cannot even be bothered to wait until the young have left the nests to strip them from the walls. Increased rarity drives prices even higher.
To overcome the shortage, swiftlet nests are now being “farmed.” House or barn-like shelters are erected to attract swiftlets. Some are near natural colonies, others are existing structures that already have nesting swiftlets. In structures housing Glossy Swiftlets, the more valuable Edible-nest Swiftlets are encouraged to nest by placing their eggs in Glossy Swiftlet nests. The cross-fostered youngsters return to the structure to nest in subsequent years.
Yet swiftlet farming is not practiced or practical across the whole geographic range of the swiftlets. These structures cannot replace the vast cave complexes in which the swiftlets historically nest. Plundering of these caves not only depletes swiftlet populations, but threatens other cave organisms. Nest poachers also vandalize geological formations in the caves, litter the trails, and the nest revenue often goes to buy drugs in some localities.
China’s growing economy means more people can afford exotic foods, traditionally valued for their purported healthful properties. I respect the rich cultural history of many Asian countries, a history which includes numerous folk remedies and aphrodisiacs. But I hope that increased prosperity also brings with it a sophistication that allows an understanding of medical science, and a respect for the natural world that prohibits the exploitation of dwindling rare animals.