THEY move with ease. In the shade of the jungle, a round-bellied orangutan glides towards the ground. Her long limbs give her a gangly appearance, but the flaming strands of her hair are beautiful. Mina is a notoriously bad-tempered ape, who has scratched and bitten dozens of locals on the Indonesian island of Sumatra. But humans harm orangutans far more than orangutans harm humans.
Estimating the number of orangutans is difficult. Researchers have to extrapolate from the number of nests observed. (The apes build new ones to sleep in each night.) A new study published in Current Biology finds that the number of orangutans on Borneo, an island divided between Indonesia and Malaysia, declined by some 148,000 between 1999 and 2015, leaving fewer than 100,000. Within the next 30 years, another 45,000 could disappear. The decline has been steepest, naturally, in areas where the jungle has been razed to plant palm-oil trees. But it is areas that are still forested that account for most of the fall in the orangutan population. This suggests that hunting and crueller activities—carcasses have been found maimed and riddled with airgun pellets—are also taking a bloody toll, says one of the study’s authors, Maria Voigt of the Max Planck Institute, a research organisation in Germany.
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People have long since supplanted other creatures as the greatest threat to orangutans. The tigers which sometimes kill Sumatran orangutans (there are no tigers in Borneo) have become even rarer than the apes. The jungle guides strumming guitars at a bar in the Sumatran village of Bukit Lawang know of just one peer who has seen a tiger in the wild. More than half of the island’s forest cover has disappeared since the 1980s.
Local officials still push for more palm-oil plantations, mines and roads. But tourism in Sumatra’s Gunung-Leuser National Park shows the value of leaving the jungle, and its inhabitants, alone. A night and two days of climbing and crawling in search of orangutans can cost a visitor around $100. Those leading tours receive a hefty chunk of this and are therefore well-paid by local standards, says Dodi Perangin Angin, who runs a trekking company which employs 13 guides. Tourism is far better for the local economy than palm oil, he reckons.
Eco-tourism can benefit orangutans, too, if controlled. But tourists often get too close to the animals, risking the transmission of disease, or leave rubbish in the forest, says Serge Wich of Liverpool John Moores University. In 2016 he was part of a team which found that there were more than 14,000 apes on the island, far more than the 6,600 or so previously thought. In spite of the revision, this is a minuscule number given the island’s vast size (it is bigger than Japan or Germany). And unless local officials begin to grasp the potential of tourism, their numbers are likely to dwindle even more.