Borneo Orangutans Drop from the Trees: New Behavior in the Face of Deforestation

First Posted: Jul 29, 2013 12:54 PM EDT

Orangutans are the king of swingers, travelling between branches with their long arms. Using large leaves as umbrellas and nesting in leafy branches above the rainforest floor, it's not surprising that these creatures spend so much time in the canopy. Now, scientists have made an unusual finding. It turns out that these apes are coming down from their trees to forage and travel, possibly adapting to a changing environment.

These apes have some of the longest arms in the world. A male's span can measure seven feet or more from fingertip to fingertip; that's much longer than his standing height of about five feet. In fact, when an orangutan fully stands up, their hands nearly touch the ground. This reach makes them adept at grabbing and reaching for branches as they travel through the forest.

Studying these creatures, though, is difficult. The apes are elusive, which means that researchers had to employ camera traps in order to capture the orangutans on film. Because this species is endangered, it's important for scientists to understand their behavioral patterns.

In this case, the researchers placed ground-based cameras across a large region of forest in Borneo. With these cameras, they managed to capture the first evidence of orangutans regularly coming down from the trees. In fact, the amount of time these apes spent on the forest floor was comparable to the time spent by the ground-dwelling pig-tailed macaque.

So why do orangutans come down from trees? Scientists still aren't sure. However, the absence of large predators may make it safer for the apes to walk on the forest floor. Another reason could be the rapid and unprecedented loss of Borneo's orangutan habitat.

"Borneo is a network of timber plantations, agro-forestry areas and mines, with patches of natural forest," said Brent Loken of Simon Fraser University in a news release. "The transformation of the landscape could be forcing orangutans to change their habitat and their behavior."

The findings show that orangutans could be adapting to their changing environment, learning how to cope with less trees and instead taking to the forest floor. That said, it doesn't mean that these apes can just walk into new territory if their habitat is destroyed.

"While we're learning that orangutans may be more behaviorally flexible than we thought and that some populations may frequently come to the ground to travel, they still need forests to survive," said Stephanie Spehar of the University of Wisconsin Oshkosh in a news release. "Even in forest plantation landscapes they rely heavily on patches of natural forest for food resources and nesting sites."

The findings are published in the American Journal of Primatology.

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