Bornean Orangutans Coming Down From The Trees
February 14, 2014

Orangutans Are Coming Down From Trees More Often

Lee Rannals for - Your Universe Online

According to a new study published in the journal Scientific Reports, orangutans spend more time on the ground than previously thought.

Orangutans have always been seen as tree dwellers, but the latest study from researchers at the University of Leicester says these apes are coming down from their castles more often than scientists knew.

The researchers performed a large-scale analysis of orangutan groundings by using camera-trapping data from 16 sites across Borneo. In all, there were 641 independent orangutan records taken at 1,409 camera trap stations over 159,152 trap days.

"We've known for some time that orangutans use the ground to travel and search for food, but the influence of anthropogenic disturbances in driving this behavior has been unclear. This is crucial to understand in this age of rampant forest loss and fragmentation, which is slicing up the orangutan’s jungle home,” Dr Mark Harrison, based in the Department of Geography at the University of Leicester and Managing Director of the Orangutan Tropical Peatland Project (OuTrop), said in a statement.

He said they found that although the degree of forest disturbance and canopy gap size influenced these sightings, orangutans were recorded on the ground as often in heavily degraded habitats as in primary forests.

"All age-sex classes were recorded on the ground, but flanged males - those with distinctive cheek pads and throat pouches – travel on the ground more. This suggests that terrestrial locomotion is a greater part of the Bornean orangutan’s natural behavioral repertoire than previously understood and is only modified by habitat disturbance,” Harrison said. "The capacity of orangutans to come down from the trees may increase their ability to cope with at least smaller-scale forest fragmentation, and to cross moderately open spaces in mosaic landscapes, although the extent of this versatility remains to be investigated."

The team said more than 70 percent of orangutans occur in fragmented multiple-use and human-modified forests because they have lost their original ecological characteristics. They added that these apes are spending more time on the ground due to this, which has both pros and cons.

"Increased terrestriality is expected to increase predation risk, interactions with and persecution by humans, and exposure to novel diseases. Unlike in Sumatra, where tigers are present, predation is less of a concern in Borneo, although infants might be at risk from bearded pigs and clouded leopards,” Harrison said. “In recent history, their biggest predator has been man, who is actually more likely to pick orangutans off in the trees: orangutans make a lot of noise and so are very obvious in the trees, whereas they can move with almost no noise and so more easily get away on the ground.”

The scientists said terrestrial behavior could facilitate movement and dispersal, especially in degraded or fragmented landscapes as a result of natural or man-made processes.

"Ultimately, a better understanding of what drives orangutan terrestriality, how this influences their dispersal, movement and survival in a human-modified landscapes is important for designing effective management strategies for conservation of this endangered species in Borneo,” Harrison concluded.

Image 2 (below): An adult male wades through the flooded Sabangau peat-swamp forest. Credit: © OuTrop-WildCRU (Orangutan Tropical Peatland Project/Wildlife Conservation Research Unit, University of Oxford)