Gunung Leuser, in northern Sumatra, is one of the biggest national parks in the world. Its steep, rainforested valleys and hills are home to gibbons, monkeys, elephants and some of Indonesia’s last tigers and rhinoceroses. I would be happy with any of those sightings, but I was trekking into these remote hills specifically because I wanted to visit the orang-utan, the ‘old man of the forest,’ in his jungle home.

Logging, poaching and a growing human population have reduced Indonesia’s orang-utan numbers to a dangerously low level and only about 7000 are now believed to survive in Sumatra. Most live in the highland jungles of the far north and over recent years guerrilla warfare in Aceh has further depleted their numbers. Unfortunately, baby orang-utans make attractive pets and mothers are often killed so the orphan can be adopted by people who find its child-like grief and subsequent affection for the foster parents alluring … until it grows up.

Conservationists believe that in 50 years there will be fewer than 250 Sumatran orang-utans left in the wild and, since this is not a viable gene-base for a healthy population, total extinction will be just around the corner. For the moment, Gunung Leuser is still probably the best place to see this most enchanting of apes in the wild.

A steady drizzle was coming down as we climbed away from the river that runs through Bukit Lawang village. The track was slippery and tangled with roots, and my guide, Adit, warned me that we had a long way to go before we could set up camp in the jungle. Still, he was confident the weather would not hinder us and that within the next three days he would be able to lead me to wild orang-utans.

As we struggled, slipping and sliding, up the slope, a troop of gibbons began to follow us. They swung gracefully through the canopy as if to show us how easy it could have been if we ‘higher primates’ had never turned our backs on the trees. Then, as we crested the hill, a pair of hornbills flew past with their mighty wings making chugging noises like steam-locomotives. These sightings, adding to the simple thrill of being back in the jungle, made the day’s trek pass quickly.

But the rainforest continued to live up to its name and by the time we had eaten our evening meal of fried rice, we’d been driven under the cover of the large plastic sheet that served as our tent. I was woken the next morning by a family of macaques that were intent on getting at our breakfast before we did and, as I pulled on my damp clothes, a big monitor lizard slithered out of the jungle to flick his tongue around our campfire.

These visits seemed like good omens and we had only walked for half an hour away from our camp when Adit suddenly stopped and crouched down. He pointed into the trees, doing his best to show me my first wild orang-utan. You would imagine that a large, bright orange ape would be easy to see among a sea of greenery, but during several sightings in the next few days I would realise just how secretive and elusive these animals can be. Finally I spotted what Adit was pointing at – not one, but two orang-utans.

The orang-utan is the only ape that is almost entirely solitary, but we had been lucky enough to find a mother with a young baby. It was amazing how silently these creatures were able to move. Their combined weight would have been about the same as a seven-year-old child’s, but the mother could judge exactly how much weight the thinnest branches could take and was able to swing herself and her baby almost soundlessly between one tree and the next.

Adit estimated that the mother might be as old as 35 and the baby would not yet be two. We worked our way slowly closer and neither animal seemed to be disturbed by our presence. In fact, the pair ignored us completely, at one point swinging within a couple of metres of the spot where I crouched with my camera.

I would see other wild orang-utans during the next few days but the peaceful hour that we spent, sat in the drizzle, watching this mother and her baby stands out in my memory as one of the most unforgettable wildlife experiences I’ve ever had.

How to get there

Tragically, a massive flash flood hit Bukit Lawang in November 2003 and wiped out almost the entire town along with more than 200 of the inhabitants. The national park is open again to visitors and Bukit Lawang’s tourism industry is slowly getting back on its feet. You can visit orang-utans during feeding times at the orang-utan rehabilitation centre at the edge of the town or organise a more extensive expedition in search of wild apes deeper in the park. The nearest international airport is Medan.