Humans drove orangutans to leave trees for ground

Our male ancestors inspired orangutans to get down from the trees and spend more time on the ground to help them cope better with the forest degradation challenges, finds a study.

"We have known for some time that orangutans use the ground to travel and search for food, but the influence of human disturbances in driving this behaviour has been unclear till date," explained Mark Harrison from department of geography at University of Leicester in the UK.

This is crucial to understand rampant forest loss and fragmentation which is slicing up the orangutan's jungle home, he added.

The research is based on a large-scale analysis of orangutan terrestriality using comprehensive camera-trapping data from 16 sites across Borneo - the largest island of Asia.

In total, there were 641 independent orangutan records taken at 1,409 camera trap stations over 159,152 trap days.

"We found that although the degree of forest disturbance and canopy gap size influenced terrestriality, orangutans were recorded on the ground as often in heavily-degraded habitats as in primary forests," added Harrison.

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 of the Bornean orangutans is only modified by habitat disturbance.

"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," said Harrison.

Orangutans make a lot of noise and so are very obvious in the trees whereas they can move with almost no noise and so get away more easily on the ground.

The scientists report that terrestrial behaviour therefore could also facilitate movement and dispersal, especially in degraded or fragmented landscapes as a result of natural or man-made processes.

This is important to design effective management strategies for conservation of this endangered species in Borneo, said the study published in the journal Scientific Reports.