Conservationists have called on the Indonesian authorities to take urgent action to save the orangutan after a report warned that the endangered great apes were being hunted at a rate that could bring them to the brink of extinction.

Erik Meijaard, who led a team carrying out the first attempt to assess the scale of the problem in Kalimantan, the Indonesian part of Borneo, said the results showed that between 750 and 1,800 orangutans were killed as a result of hunting and deforestation in the 12 months to April 2008.

The numbers, which were higher than expected, indicated that most orangutan populations in Kalimantan could be in serious danger "within the foreseeable future", said Meijaard, of the Jakarta-based People and Nature Consulting International. "At that rate… you're talking about 10-15 years until pretty much all orangutans [in Kalimantan] are gone."

Home to 90% of the world's orangutans, Indonesia also has one of the highest rates of deforestation – a phenomenon driven by a combination of illegal logging, palm oil plantations and gold mining. Loss of habitat is the main reason behind the steep decline in both the Bornean orangutan (Pongo pygmaeus) and its critically endangered Sumatran counterpart (Pongo abelii). The Sumatran orangutan population is believed to be less than 7,000 and has featured on the World's 25 Most Endangered Primates list since its inception in 2000. In Borneo, an estimated 54,000 orangutans survive, half the number of 25 years ago.

Habitat loss is compounded by hunting, which, though anecdotally well known as a cause of orangutan decline, has been a neglected issue. While much of the killing documented by Meijaard and his researchers appears to have been motivated by opportunism, with villagers hunting for food, a significant proportion could be related to habitat loss. "There is conflict-related hunting where you've got plantations going in. You've got people expanding their fields and gardens and infringing on orangutan habitat, so they are being squeezed into smaller and smaller pockets of forest and automatically come into contact with people more frequently," Meijaard said.

"If you find an orangutan sitting in your garden or eating the fruit from your fruit tree or pulling up your oil palm, the logical reaction is either to scare it off or to kill it. That's what people do."

To tackle the fall in orangutan populations, the Indonesian authorities had to crack down on those responsible for habitat degradation so that the Bornean forests were "better managed", according to Meijaard. Equally important was the need to curb the hunting of orangutans by raising awareness of their endangered status – and enforcing the law when such hunting was found, he said.

"So far in the entire history of orangutan conservation, I think only two people in Indonesia have ended up in jail because of illegal activities related to orangutans," Meijaard said.

Only days after his survey was published last week, two Indonesian plantation workers were arrested on suspicion of killing at least 20 orangutans and proboscis monkeys. Police said the men admitted chasing the primates with dogs before shooting, stabbing or hacking them to death, but claimed they were offered money for every kill by the owners of palm oil plantations keen to reduce crop raiding. If found guilty, the workers face up to five years in prison.

Ashley Leiman, of the London-based Orangutan Foundation, agreed that better law enforcement must be the priority in the fight to save the species. "There should be more awareness, there should be more education and definitely… more enforcement," she said, accusing the Indonesian authorities of a "very lax" approach. Leiman believed the current laws were almost impossible to implement. "You almost have to find people in the very act of doing it," she said.

A spokesman for the Indonesian forestry ministry has described the report's findings as "bombastic" and said he doubted they were true.

But the hunting issue should not distract from the primary threat of forest degradation, which was the root cause of conflict-related hunting, said Leiman. "When you take the combination of both, the problem is totally compounded. But it goes back to the original problem [of habitat loss]," she said, adding that the Indonesian government needed to create more protected areas if forest loss continued at the present rate.

Scaremongering was counterproductive, she said. "I don't believe orangutans will be extinct. I think as a species they will survive. They may only survive in protected areas, and probably in smaller numbers than now, but I don't think the 'cry wolf' [approach] is going to help."