Although primarily tree-dwellers, the great apes have been captures in camera trap images spending a surprising amount of time walking on the ground, the researchers report in the American Journal of Primatology.
"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 behavior," said study leader Brent Loken of Simon Fraser University in British Columbia. "However, with camera traps we are offered a behind the scenes glimpse at orangutan behavior."
Camera traps in a 15-square-mile area succeeded in capturing the first evidence of orangutans regularly coming down from the trees, the researchers said.
A rapid and unprecedented loss of Borneo's orangutan habitat may be driving the changes in behavior, they said.
"Borneo is a network of timber plantations, agro-forestry areas and mines, with patches of natural forest," said Loken. "The transformation of the landscape could be forcing orangutans to change their habitat and their behavior."
Despite that they are still dependent on natural forests for their long-term survival, researchers said.
"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," Stephanie Spehar from the University of Wisconsin Oshkosh said.
"Even in forest plantation landscapes they rely heavily on patches of natural forest for food resources and nesting sites."