Orangutans hit the ground walking

Red apes leave the trees when nobody’s watching

MATERNAL LEAVE  A video camera in a forest on the island of Borneo caught an adult female orangutan in action as she moved along the ground carrying an infant.

© Andrew Hearn, Joanna Ross

Logging has orangutans on the run in Borneo. But an unappreciated tendency to go to the forest floor and scoot short distances while upright or on all fours gives red apes a chance to survive in patchy, partially destroyed forests, researchers report February 13 in Scientific Reports.

More than 1,400 unobtrusive video cameras recorded 641 instances of orangutan ground travel between June 2006 and March 2013. Orangutans left the trees as frequently in dense forests as in areas hit hard by logging, indicating that this is Bornean orangutans natural behavior, says a team led by veterinarian Marc Ancrenaz of HUTAN/Kinabatangan Orangutan Conservation Program in Sabah, Malaysia.

Ground travel enables orangutans to forage for shoots, termites and other food, Ancrenaz says. Unfortunately, it also makes the apes more vulnerable to hunters and humanborne infections.

Adult males engaged in the most ground travel. Females — alone, holding babies or accompanied by youngsters — accounted for 115 cases of walking on the forest floor.

Orangutans, listed as endangered, have been spotted walking upright across tree branches on the island of Sumatra (SN: 8/4/07, p. 72), but are rarely observed trekking on the ground. Human observers make the apes reluctant to descend from their leafy homes, the scientists suspect.

Editor’s Note: This story was updated February 17, 2014, to correct the number of cameras the researchers used.

Bruce Bower has written about the behavioral sciences for Science News since 1984. He writes about psychology, anthropology, archaeology and mental health issues.

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