Asian Scientist (Jul. 30, 2013) – 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.
The discovery was made after a team of researchers 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 behavior,” said Brent Loken, a leader of the expedition. “However, with camera traps we are offered a behind the scenes glimpse at orangutan behavior.”
The team positioned ground-based cameras across a 38-square-kilometer 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 eight months, the 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.
“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.”
The study shows how orangutans can adapt to their changing landscape; however, this does not suggest they can just walk to new territory if their habitat is destroyed.
The orangutan subspecies P. p. morio may be adapted to life in more resource scarce forests, having evolved larger jaws which allow them to consume more tree bark and less fruit but they are still dependent on natural forests for their long term survival.
“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 Dr. Stephanie Spehar, a leader of the team. “Even in forest plantation landscapes they rely heavily on patches of natural forest for food resources and nesting sites.”
Because 78 percent of wild orangutans live outside of protected areas, it is critical that all of Borneo’s remaining forests are either protected or sustainably managed.
“We do not know how long this may take, but protecting Wehea Forest and Borneo’s remaining forests is vital to the long term survival of the orangutans,” concluded Loken.
The article can be found at: Loken et al. (2013) Terrestriality In The Bornean Orangutan (Pongo Pygmaeus Morio) And Implications For Their Ecology And Conservation.
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Source: Wiley; Photo: Daniel Kleeman/Flickr.
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