It's a tiny organ that, the superstition goes, holds the secrets of the future. When smoked and inhaled, the brain of a vulture is said to confer the gift of premonition. To put it bluntly, most users hope to sneak a look at next week's national lottery numbers.

Such is the demand for vulture brains to use in muti – traditional medicine – that wildlife experts fear the birds could be driven to extinction within two or three decades. They also warn that hunting could intensify as gamblers seek an advantage when betting on the football World Cup in South Africa.

Vultures' acute vision, and ability to find prey, has kindled a belief that they possess clairvoyant powers. Their brains are dried and rolled into a cigarette or inhaled as vapours in the hope they will bring a vision of the future - including lottery numbers and sports results.

Andre Botha, manager of the birds of prey working group at the Endangered Wildlife Trust in South Africa, said: "People believe it's foresight and this finds fertile ground in people's imagination. If it worked for the lottery, everyone would use it and we'd have a lot of millionaires walking around today.

"There is a lot of betting in South Africa. So we may see an increase connected to gambling around the 2010 World Cup."

A 2007 study found that 160 vultures are sold a year for muti in eastern South Africa, with the total across the region thought to be much higher. About 1,000 are killed every year in Tanzania alone.

The birds are shot, trapped or poisoned by hunters. One tactic is to poison an animal so the vultures that feed on the carcass themselves fall victim. "You can have 300 or 400 converge on a poisoned carcass and all be wiped out," Botha added. Brains and other body parts are then sold at street markets or shops in Johannesburg and other cities.

Steve McKean, a researcher at the conservation body Ezemvelo KZN Wildlife, was quoted by South Africa's Star newspaper: "Traditional use as it is currently happening is likely to render vultures extinct in southern Africa on its own within 20 to 30 years."

Seven of the nine species of vulture are rated endangered. Botha said there was demand for the bearded vulture in Eastern Cape province. Traditional healers prefer that the bird be captured alive as the head needs to be removed while it is still living so that "the brain does not flow down into the spinal cord" and the muti loses its potency.