In the inky-black dark ness of the rainforest night, we stand, a ankle-deep in water. With only head torches to guide us, we scan the riverbanks for signs of life. One eye means spider, two eyes means frog, we’re told, as we dodge low-hanging branches and navigate slippery rocks. Tree frogs reveal themselves, including a strange white one with translucent skin and tiny frog lets the size of fingernails. A giant river toad, native to Borneo, perches on a rock, showing off its craggy, wart-covered skin. Tonight we’re looking for amphibians, but somewhere out them lurks a not her creature, the real object of our fascination.

It’s the first evening on the Red Ape Trail, an extended, multi-day trek taking us through prime orangutan terrain in Borneo’s remote Batang Ai region. It has already taken an adventure to get to this point — a five-hour, 170-mile drive from the cosmopolitan city of Kuching, past ever-more dense jungle and terraces dotted with pepper and rice plantations to a jetty on the shores of the vast Batang Ai reservoir. Then, a bracing two-hour journey up river by longboat — the traditional wooden vessel favoured by Borneo’s indigenous Iban tribe — to reach Nanga Sumpa lodge on the upper reaches of the Delok River. After a night spent acclimatising to jungle life, a three-hour hike has taken us even deeper into the forest to reach Mawang Camp, our home for the next few days.

The Red Ape Trail was created in 2000 by Borneo Adventure, a local tour operator, founded by Philip Yong and Robert Basuik in 1987. The pair came in search of an experience that would offer travellers the chance to glimpse Borneo’s prized wildlife, while learning something of the region’s dominant Iban tribe. They settled on Nanga Sumpa, a traditional, timber longhouse in which the locals lived communally. A trail network has since been developed from the longhouse into the surrounding forest. The Red Ape Trail is the most challenging of these, taking walkers out into the jungle to camp out over multiple nights, in the hope of glimpsing wild orangutans. It originally started as an epic, 10-day challenge, but has since been reduced to a more manageable five- day trek — wise, in a country with humidity levels that can rise to up to 80%.

At camp after our frog hunt, we sit playing cards with our Iban guides, drinking potent tuak rice wine. As well astwo guides, Bayang and Sobeng, we’re accompanied by a team of Iban men, who lavish us with spicy Malaysian curries and fried jungle ferns. The biggest character is Ronny, who speaks great English, having worked on the oil and gas rigs in Bintulu further north. With a big smile and prominent tribal tattoos, he sports a football shirt with his name on it — a modern token in an otherwise traditional life. Among the tourists are two young engineers from England and a French couple in their mid-50s. With anticipation high, we try to bed down for the night, donning long sleeves and trousers to keep the insects at bay, before clambering under mosquito nets to sleep on simple roll-out mattresses. But the jungle has other ideas. As the sound of cicadas chimes out, howls and cries join in to disrupt the silence of night. I listen to the hypnotic chorus, eyes wide open.

EMPTY NESTERS – Life at Mawang Camp is simple, and over the next few days, we settle into the easy rhythm of waking early to bathe in the river, before feasting on a breakfast of eggs, toast and banana fritters. Morning treks are followed by lunch at camp, and afternoon hikes, carried out when the weather is cooler and the orangutans are busy building their nests in the trees for the coming night. We spot many of these sturdy nests crafted from folded back branches, and can tell if they’re old or new from whether the leaves are brown or green. The technological skills needed to create them are often cited as evidence of the primates’ innate intelligence.

But the significance of the nests goes beyond this. When logging companies recently started rounding in on the prized timber of the region’s Dipterocarp forest, a team spearheaded by Robert Basuik set out to protect the area. Together with the Forestry Department of Sarawak, the World Conservation Society and the local Iban, they carried out surveys, counting nests to prove this was a crucial orangutan habitat. Their efforts resulted in the creation of the 34,000-acre Sungai Menyang conservation area, between the reservoir and the upper Delok River. It was a vital move, especially as Batang Ai is now the last remaining viable orangutan habitat in the state of Sarawak.

It was good news, too, for the rest of the forest’s residents, which includes 200 species of bird, from yellow-eared spider hunters to red-crowned barbers, as well as bearded pigs, horned deer, civets and reticulated pythons — though I’m in no rush to meet these. Instead, I spy fruit bats hanging from a riverside cave, tarantula nests, pigtailed macaques and several of the eight different species of hornbill that reside in Batang Ai. The walking, though, is the real highlight, taking us through glassine rivers, silent valleys and dense jungle. Indeed, to call it the Red Ape Trail is something of a misnomer, as any evidence of a clearly marked trail seems entirely absent at times. Instead, our Iban guides use their knowledge of the jungle to forge a way through, hacking down six-foot ferns and persistent palms with long machetes to create a path where previously there was none. At other times, we use tree roots and bamboo shoots to clamber up and down steep slopes. With the humidity high, it makes for sweaty going and demands a certain level of fitness from the walker. But regular breaks, peppered with tales of the forest and the Iban’s customs, make it a fascinating adventure.

Each night, as evening falls, we return to camp, muscles aching and heads filled with the day’s exploits. We sit at long wooden benches, staring out at the mist rising over the river, listening to the jungle start up its nightly song. With candles flickering on the tables, dinner arrives and we fill our hungry bellies, before retiring for the night. With all this excitement, it seems to matter little that the orangutans remain elusive. We spy evidence of their existence everywhere, from nests and discarded fruit on the forest floor, to ripped palm shoots, which the animals tear apart to reach the hearts. The Red Ape Trail is over, but the adventure is not yet finished. After a night back at Nanga Sumpa, with a trip to swim in the refreshing waters of Enseluai waterfall, we board a longboat once again for the journey back.

The going is smoother this time and calmer than the way in — there’s no need for the Iban to use their long wooden poles to push us up river, or get out to push when the boat drags along the river’s floor. Suddenly, the calm is broken by a rustle in the trees. Our guides have spotted an orangutan, a female with at least one, possibly two, infants in tow. From the boats, we sit and watch as the apes move from tree to tree, a tiny face at one point clearly visible, staring back at us inquisitively. Of course, they would be here: basking beside the cool, shaded waters of this mighty waterway, that has helped shape this landscape for centuries. While we toiled and tired on the Red Ape Trail, all this time, they were sitting beside the Batang Ai, hiding in plain sight.