The first-ever analysis of long-term orangutan population trends revealed a worrying decline, they said.
An international team of researchers used a combination of helicopter and ground surveys, interviews with local communities, and modelling techniques to draw a picture of change over the past ten years.
Previous counts have largely relied on estimations based on ground and aerial surveys of orangutan nests. Some suggested that Bornean orangutan numbers were in fact increasing.
The new findings, the team said in a statement, are "a wake-up call for the orangutan conservation community and the Indonesian and Malaysian governments who have committed to saving the species."
Every year, some $30-40 million (26-35 million euros) is spent in the region to halt wildlife decline.
"The study shows that these funds are not effectively spent," said the team.
The biggest threat to orangutans, one of only two great ape species found in Asia today, are habitat loss due to farming and climate change, and their killing for food or in conflict with humans.
Some 2,500 orangutans are killed in Borneo every year, the researchers said.
The findings were published in the journal Scientific Reports. The study provides no raw population numbers, but an estimate of individuals per 100 square kilometres (39 square miles) of forest—down from about 15 in the period 1997-2002 to about 10 in 2009-2015.
One step from extinction
"The species (is) estimated to have declined at an alarming rate of 25 percent over the past 10 years," the researchers concluded.
Right now, 10,000 orangutans live in areas earmarked for oil palm production, said study co-author Erik Meijaard of the University of Queensland.
"If these areas are converted to oil palm plantations without changes in current practices, most of these 10,000 individuals will be destroyed and the steep population decline is likely to continue," he said.
"The study's worrying outcomes suggest that we need to fundamentally rethink orangutan conservation strategies."
Orangutans need a solid network of protected forests that are properly managed.
Current efforts focus on rescues and rehabilitation, said Meijaard, "but that only addresses the symptoms and not the underlying problem."
Last year, the International Union for the Conservation of Nature declared the Bornean orangutan as "critically endangered"—one step away from extinction.
Borneo is the third-largest island in the world, administerd by Malaysia, Brunei and Indonesia.
Source: Phys.org | 7 July 2017