Erik Meijaard, and colleagues from the Nature Conservancy, World Wildlife Fund and 18 other private organizations, found that the primates were illegally slaughtered to protect crops from being raided as well as for their meat.
Indonesia is home to about 90 percent of the world’s wild orangutan population, and was once covered by lush rain forests.
But widespread deforestation during the past 50 years has resulted in most of the remaining 50,000 to 60,000 apes living in a scattered patchwork of forests.
This has increasingly forced them into conflict with the expanding human population.
The survey of nearly 7,000 Borneo residents between April 2008 and September 2009 found that 73 percent know killing the orangutans was illegal.
But Ashley Leiman, director of the Orangutan Foundation in London, points out that the Indonesian government rarely prosecutes or punishes perpetrators.
The country’s forest ministry spokesman Ahmad Fauzi Masyhud disputed the results of the study, which he described as “bombastic.”
But Meijaard challenged officials to face the facts. “We used robust scientific methods to assess the social dimensions of orangutan conservation," he said. "Unless we assume that most of the survey respondents lied, we have to accept the hunting issue as an uncomfortable truth that needs to be addressed if we want to save the orangutan.”