CNN's Arwa Damon reports on attempts to save the orangutans in Sumatra.
Sumatra, Indonesia (CNN) -- A loud crack echoes throughout the canopy as two young orangutans come tumbling down, grasping at branches along the way to break their fall. They recover and sheepishly scamper back up.
This is lesson one of jungle school here in the forests of central Sumatra, one of the few places where orangutans are being successfully rehabilitated into the wild.
"They have to learn that their whole environment is completely different from the cage," says Peter Pratje of the Frankfurt Zoological Society. "They have to learn that branches and small trees -- the size of bars in the cage -- don't carry them any longer. They bend and break."
"During the first phase of this jungle training, they are very often falling out of the trees because they use rotten branches."
... to continue reading & to view a slideshow of pictures taken at the refuge: Saving orangutans before extinction in Sumatra.