Smithsonian.com

Esculent Swallow and Nest by John Latham, 1831/Wikipedia

Up there on the weirdest-things-you-can-eat list has to be bird’s nest soup. It would be weird enough just to eat your standard twiggy-grassy robin’s nest, but this predominantly Chinese delicacy is made almost entirely from the goopy spit of a southeast Asian bird called a swiftlet (check out a couple of close-up nest photos over at EatingAsia). The birds glue their nests hundreds of feet high on sheer cave walls. When cooked, they yield a slick, nearly flavorless broth that’s prized for such medicinal chestnuts as increased longevity and, you guessed it, libido.

Unfortunately, swiftlets are not an invasive species we can proudly devour. To the contrary, growing demand from a prosperous China is compromising the birds’ ability to continue, uh, spitting out the nests. It doesn’t help that the sticky nests are the devil to clean, so collectors take the nests before they’ve been used to raise any young swiftlets. And in a weird double-twist, an unlikely solution—farming the nests—has increased supply and at the same time endangered some wild populations.

The monetary incentive is tremendous: swiftlet nests can sell for more than $1,200 per pound and fuel a multi-million dollar trade that can rival the fishing returns of poor regions. One Web site offers an 8-ounce “family pack” for about $600 (five percent discount on orders over $1,000).

In traditional harvesting, extremely daring men scale teetering bamboo poles to reach the nests, then scrape them from the cave walls. If you’ve ever shinnied up a flagpole with a basket and stick slung over your back and then performed your favorite yoga poses at the top, you may have some idea how dangerous this is. (Rock climbers tend to be fascinated; one has even made a documentary.)

A low-tech alternative—constructing artificial caves to farm the nests—has proved both successful and popular in Indonesia, where multistory buildings are erected in the middle of towns (sometimes even with a shop or apartment on the ground floor). The upper stories feature generous entrance holes, swiftlet songs play at the entrance to set a welcoming mood, and owners can add insect attractants and a swiftlet-pleasing scent, as chronicled in the World of Swiftlet Farming blog.

The set-up appeals to enough swiftlets that Indonesian production of the nests is booming (up to 280 tons, valued at more than $800 million, according to a 2004 source). Unfortunately, the high prices encourage wild-nest collectors to redouble their efforts. The toll is felt most keenly on islands, where nest farming is limited and so is the ability of swiftlets to recover from raids. In a 2001 study in India’s Andaman and Nicobar Islands, swiftlet populations had declined 83% in 10 years.

Overharvesting was a clear cause, with declines recorded in 366 of 385 known nesting caves. Of 6,031 nests surveyed, only two had been left alone long enough for swiftlet chicks to have hatched. Harvesting was so devastating that the authors urged the islands’ governments to encourage nest farming as the swiftlets’ only chance for survival. (Though nest farming still involves destroying nests, the damage is counterbalanced by the increased nesting opportunities provided by the farms. Farmers typically allow late-nesting swiftlets to raise young, and even captively raise swiftlets in the nests of other birds to keep numbers up.)

National parks in India, Thailand, and other countries typically ban wild nest harvesting. But restrictions have yet to be enacted on a comprehensive, international scale – partly because farming has been so successful and global numbers are fairly high. Swiftlets are not listed as endangered by CITES or the International Union for the Conservation of Nature.

I’m fascinated by the good-news bad-news saga of farming. Since its inception 10,000 years ago, farming has been our solution to the difficulty and unpredictability of securing animal food. By all accounts it’s been a huge success, but never a complete one. Disappearing swiftlets are just another curve ball in a world tainted by the likes of mad cow disease, brucellosis, and avian flu. Farmed salmon, anyone?