An unusual eradication program, which turns friends into traitors, has almost freed Kangaroo Island of its feral goat population.

The project uses what are called judas goats to betray the whereabouts of other wild goats on the island off the South Australian coast.

The unwitting traitors are shipped over from the mainland, sterilised, fitted with radio tracking collars and released.

Project officer Nick Markopoulos says the program exploits the animal's sociable nature.

"Generally the goat will have about a week's sulk and once it gets over its week of sitting down and just adjusting itself to the new environment it's been released into, it will go off ... and find friends," he said.

"The feral goats are quite happy to accept them into their mobs and they fit right in."

Mr Markopoulos says about 1,000 goats have already been removed and estimates there are about 100 left on the northern side of the island.

"It's probably one of the largest goat eradication attempts in the world in terms of area," he said.

Goats were originally brought to Australia's third-largest island by settlers almost two centuries ago, for their meat and milk.

Some residents, like fifth-generation farmer Jim Chapman, say the light-footed ferals have become part of the landscape and do not do much damage.

"I've loved the goats out here on Kangaroo Island. It's been part of my life growing up. I know these guys have come out here to do a job, but to be quite honest with you I'm not liking seeing the last goat go," Mr Chapman said.

But the Kangaroo Island Natural Resources Management Board, which is running the program, says the goats have a major impact on vegetation and threaten an endangered bird species.

"From their gut samples we've found that they eat over 70 plant species," said program manager Pip Masters.

"The one that we're most concerned about is the plant they eat the most which is the drooping sheoak."

"That's a very important food source on Kangaroo Island, because it's the sole food of the glossy black cockatoo."

The program has been going five years and has cost more than $500,000, with the money coming from the Invasive Animals Cooperative Research Centre and Federal and State Governments.

Mr Markopoulos says it is a worthwhile investment, as it has helped pinpoint the pests across farms, national parks and rugged coastlines.

"The last hunt we removed 40 animals and we only sighted four animals without judas goats, so if we were to hunt without these guys our efforts would be so much greater," he said.

Mr Markopoulos predicts the island's feral population will be eradicated in a year.

Once they have done their job, the judas animals will also be destroyed.