Descent of the Orangutan

Orangutans might be the king of the swingers, but primatologists in Borneo have found that the great apes spend a surprising amount of time walking on the ground. The research, published in the American Journal of Primatology found that it is common for orangutans to come down from the trees to forage or to travel, a discovery which may have implications for conservation efforts.

An expedition led by Brent Loken from Simon Fraser University and Dr. Stephanie Spehar from the University of Wisconsin Oshkosh, travelled to the East Kalimantan region of Borneo. The region's Wehea Forest is a known biodiversity hotspot for primates, including the Bornean orangutan subspecies, Pongo pygmaeus morio, the least studied of orangutan subspecies.

"Orangutans are elusive and one reason why recorded evidence of orangutans on the ground is so rare is that the presence of observers inhibits this behaviour," said Loken. "However, with camera traps we are offered a behind the scenes glimpse at orangutan behaviour."

The team positioned ground-based cameras across a 38-square-kilometre region of the forest and succeeded in capturing the first evidence of orangutans regularly coming down from the trees.

The amount of time orangutans spent on the forest floor was found to be comparable to the ground-dwelling pig-tailed macaque, Macaca nemestrina, which is equally abundant in Wehea Forest. Over 8-months orangutans were photographed 110 times, while the macaques were photographed 113 times.

The reason orangutans come down from the trees remains a mystery. However, while the absence of large predators may make it safer to walk on the forest floor, a more pressing influence is the rapid and unprecedented loss of Borneo's orangutan habitat.