More than a million birds living in a vast cave in the Malaysian state of Sarawak provide the raw material for one of the world's most expensive delicacies - birds' nest soup.

Fearless youths shimmy up 180-foot poles to dislodge nests from the roof of the cave, home of the swiftlets.The nests find their way to luxury restaurants where wealthy Chinese devour them in soup at celebrations or to ward off sickness.

Locals have collected the nests, made of feathers held together by bird saliva, for more than 1,000 years and some 50 licensed collectors work the dark cave using skills handed down from father to son.

They compete with an increasing number of illegal nest seekers, making their way to the cave along a wooden walkway through several miles of dense jungle.

Rosli bin Osman, a stocky 20-year-old from the nearby village of Sapopuk, said he had been collecting nests for four years.

His father had given up the job for the less testing occupation of gathering guano (ird and bat droppings) from the floor of the limestone cave.

Farmers buy large quantities of the pungent-smelling guano for use as fertilizer and to prevent plants from rotting.

But the cave, where a 37,000-year-old human skull has been found, is best known for the antics of the "tukang julok" (hose who dislodge the nests) and "tukang pungut" (eople who gather them from the floor of the cave).

While his brother Roy, 15, ascended a pole with ease, Osman said he daily gathered about 130 nests weighing a total of four pounds.

The collector climbs the pole and hauls up a bamboo stick with a torch on the end to dislodge the tiny nests. His assistant gathers them from the guano-strewn floor.

According to legend, locals started more than 1,000 years ago to bring the nests from the interior to the coast of Sarawak, in the northwest of the Asian island of Borneo.

Coastal Chinese immigrants exchanged the nests for pots and jewelry. Archaeologists have found Chinese pottery dating from the year 700 in the cave.

Niah is estimated to house about 1.5 million swiftlets, which eat some 11 tons of insects a day.

Swiftlets are the only birds truly adapted to cave life. Under their tongues are special saliva glands that produce "nest cement" with which they bind together the feathers and attach the nests to the cave wall.

The birds find their way in the dark by echo-location, which works in a similar way to radar.

But such details are of little concern to Osman and his colleagues, whose main priority is to sell the nests in a nearby town, Batu Niah.

There the nests are soaked in water overnight before the mainly Chinese buyers begin the painstaking task of separating the saliva, the main ingredient of the soup, from the feathers with tweezers.

Yong Set Moi, 18, said it took her four hours to remove the saliva from one nest. Her family's restaurant pays about $50 per pound of nests.

She has never eaten birds' nest soup. "I wouldn't touch it after seeing what it is made of," she said.

In the larger town of Miri, some 60 miles away, restaurant manager Edwin Siau charges $110 for a large bowl of the soup.

His chef soaks the hardened saliva for up to two days before cooking it in coconut milk, chicken or beef stock - or with rock sugar.

"The longer you cook the soup, the better. I like it to be simmered for four hours," he said over a bowl of the delicacy, which is reputed to cure fevers and coughs. Restaurants normally demand advance notice from a patron who wants the dish served.

Siau conceded that the soup was too expensive for all but the wealthy.

"Poor people can't afford it. Birds' nest soup is getting more and more expensive because supplies are not keeping pace with demand," he said.