Thousands of swiftlets swarm about in the cathedral-like Gomantong cave on Borneo. The damp air is suffused with chitter and the ammoniacal smell from the mounds of guano littering the floor. The swiftlets, cousins to swallows and house swifts, shoot in and out of small, cup-shaped nests they’ve built along the walls. A flashlight illuminates one of the colonies and a man standing on a ladder suspended from ropes thirty meters up in the air, swings into position. He starts picking the nests, one by one, filling up a large sack. It’s harvesting season of one of the world’s most highly priced food products, known as “Asia’s caviar.”

Edible bird’s nests are craved across the Chinese world for their supposed medicinal properties. Consumers dissolve the nests, which are made purely out of swiftlet saliva, and use them in soups and desserts or drink the solution as a tonic. In tandem with the rapid expansion of the Chinese middle class, the industry has mushroomed to an estimated value of $4 billion. However, the increased demand has not led to a windfall for the harvesters risking their lives in caves across Southeast Asia.