Thousands of bird "motels" have opened across Malaysia to lure the swiftlets whose nests are harvested to make bird's nest soup, a costly delicacy in Chinese cuisine.
But as the business booms and flocks of swiftlets -- who make the nests out of their saliva -- descend on towns and villages, the noisy, messy practice has triggered a wave of protest.
In the heart of the coastal town of Klang, southwest of the capital Kuala Lumpur, the owner of the Goldcourse Hotel has converted part of the multi-storey building into a swiftlet "motel".
To entice the swiflets to build their nests in their concrete home -- and not their natural cave habitat -- from sun-up to sun-down a soundtrack of shrill bird noises including mating calls is blasted from speakers.
Nearby, other entrepreneurs have opened competing ventures by turning four-storey shophouses into bird havens, and the cacophony and shower of bird droppings is alienating those living and working nearby.
"The sound is so loud and irritating, and the bird droppings can be harmful to our health," said local resident Abdul Hamid Abdullah as he watched the swiflets dart in and out of the buildings.
"These birds build their nests in caves. That is where they should be," the 46-year-old told AFP.
Malaysia's swiftlet industry began in the 1980s but gained momentum after the 1997 Asian financial crisis when entrepreneurs converted the interiors of abandoned properties into bird motels.
Fans of the gelatinous soup, which is popular in China, Hong Kong and Taiwan, say it can stave off ageing, boost sex drive, prevent lung disease and enhance the complexion.
A kilogram (2.2 pounds) of the small, cup-shaped nests can fetch 4,000 ringgit (1,130 dollars), and the combination of big profits and a lack of legislation has seen countless swiftlet "farms" established illegally in populated areas.
Kenneth Khoo, from the Small and Medium Industries Association in northern Penang, told AFP that the global trade in raw bird's nests was estimated at 20 billion ringgit (5.7 billion dollars).
"Swiftlet farming in Malaysia is a sunrise industry. Demand far exceeds supply as more wealthy Chinese emerge," he said, adding that bird's nest soup remains a status-booster on business menus in China, Hong Kong and Taiwan.
Khoo said Indonesia controls up to 70 percent of the business in the region, sourcing its bird's nests from both caves and farms, while the other two main producers are Thailand and Malaysia.
He estimated that there are at least 35,000 swiftlet farms in Malaysia, only about 4,500 with legal permits, in a business worth 800 million to 1.2 billion ringgit.
But as the industry expands along the east and west coasts of peninsular Malaysia, opposition to the swiflet farms is growing louder and environmentalists are demanding a complete ban.
There are also allegations of cruelty as some "farmers" reputedly destroy chicks and fertilised eggs in order to harvest the nests at times when prices are high.
Conservation group Friends of the Earth has condemned the trade and called on the government to close down the proliferating swiftlet farms.
"This rather impetuous booming industry has led to complaints from the public due to the nuisance, health hazards and the number of bird hotels coming up," said Mohamad Idris, president of the group's Malaysian branch.
"Collectors may not wait long enough for the young to fledge, often throwing the chicks onto the ground or leaving them to die after taking the nests," he said.
"In view of the problems faced by many in the farming of swiftlets and from the welfare point of view of the birds, we would like to call for a ban on all farming of swiftlets."