The noises emanating from Borneo's rainforest are thrilling, but to discover what's making them, you'll need a guide, says Sarah Shuckburgh.

In the early morning, the view from my verandah is magical. Mist hangs in the trees, forming a white veil from which only the tallest treetops emerge. Three sambar deer step daintily past a clump of teak trees near my chalet, leaning up to nibble the huge heart-shaped leaves. Nearby, a large bearded pig snuffles in the undergrowth. The sounds, too, are thrilling. Barking lizards grunt, a brown barbet makes a repetitive ‘tonk-tonk’ call, and cicadas, unlike our quiet European kinds, sound like dentists’ drills. From the jungle, gibbons whoop their ululating greetings. As the mist lifts, I spot a family of orang utans, swinging through the distant canopy. Further down, branches shake as other primates leap through the trees.

I am staying at the Borneo Rainforest Lodge in the middle of the largest surviving area of primary forest in Sabah. Today, palm-oil plantations cover most of north Borneo, and lorries laden with hardwood trundle in convoys from other remnants of jungle. But the Sabah government has decreed a 30-year ban on logging from 2008, and in the Danum Valley, 175 square miles of lowland rainforest have been designated a protected reserve. The field centre here is one of the leading tropical rainforest research stations in South East Asia, and the nearby lodge is an eco-friendly guesthouse with 23 stilted huts built of local wood and stones from the Danum riverbed.

Equipped with leech socks (one-size-fits-all canvas bags worn inside trainers) I set off on sodden jungle trails with Donny, the chief naturalist guide. Towering trees, 400 years old, are surrounded by slender buttresses which create cave-like antechambers. Huge fallen trunks are covered in fungi and glistening spiders’ webs. The ground is a dense mass of fallen leaves and branches. It’s hot, and with humidity often at 100%, nothing evaporates. Flies, desperate for salt, land on my sweating body.

A giant millipede curls up into a ball in alarm as we approach, but I find it hard to spot forest wildlife. Donny sees clues everywhere. He points to an orang-utan nest of folded branches in a treetop. A pile of fruit seeds and scats under another tree show where the orang-utan had breakfast. These holes in the ground were made by foraging wild boar; this flattened circle of earth, cleared of leaves, is the mating area of a silvery-grey argus pheasant; and that tangle of bent llianas was trampled by an elephant.

Donny explains the medicinal uses of each tree - one secretes resin that is used in HIV medicines, another produces poisonous sap which kills fish if it is sprinkled on the river, and the sap from a third tree prevents malaria – Donny drinks an infusion of this every month.

At the riverbank, we watch a cavorting family of long-tailed macaques on the far bank. They swing on llianas and push each other into the brown sunlit river from the spindly branches of a fruit-tree. At my feet, an agamid lizard, like a twelve-inch dinosaur, stalks nonchalantly by.

All day, leeches, blind but cunning, sense our approach, and groping from leaf tips, clamp themselves to our legs, arms, necks and backs as we pass. Only our shins and ankles are safe, inside the canvas socks. Donny has the answer – he strokes the leech to confuse it and as it loosens its grip, sharply flicks it away. My leeches aren’t easily confused, so Donny obligingly flicks them for me.

We follow a narrow path to a waterfall which thunders into a circular pool of muddy grey-green, forming a natural jacuzzi. The canopy almost blocks out the sky, but a small blue gap admits a shaft of sunshine. A kingfisher skims over the patch of sunlit water. This is a perfect place to cool off.

Donny tells me that he comes from the Orang Sungai tribe – the ‘river people’ - whose traditional lands included the area where the lodge now stands. Danum was the name of a brave tribal king, a warrior who set off into the forest and was gone for so long that one of Donny’s ancestors was elected king to replace him. When Danum came back, unexpectedly safe and sound, he deferred to the new king. In honour of his bravery and his modesty, Donny’s ancestor named the river and surrounding area after him.

After the Second World War, when the British took over from the Borneo Company, tribal people were encouraged to give up their nomadic life of hunting, gathering, and growing rice on temporary fields. Donny’s family started work on tobacco plantations, and converted to Anglicanism. Donny’s Christian name was chosen by the Australian missionary who baptised him.

After our dip, we clamber up roughly-cut steps to a rock-shelf overlooking the horseshoe curve of the river and the lodge. Here, members of Donny’s tribe traditionally brought their dead; from this vantage point the spirits could watch over their descendants. Burying a body underground was seen as a final punishment, reserved for the most evil and criminal. I spot scattered bones in small caves and crevices, and the remains of several ironwood coffins. There are also fragments of Chinese pottery – precious tribal heirlooms acquired as long ago as the 16th century through barter with oriental traders, in exchange for hornbill beaks, edible birds’ nests, elephant tusks, rhinoceros horn and monkey gallstones, which are used to this day in Chinese medicine.

Donny explains that tribal animist beliefs are easily reconciled with Christianity. Jesus, too, was buried in a cave, and cliff-tops are nearer to heaven. He tells me that most tribal people today retain their animist beliefs even if they call themselves Christian.

Donny’s grandfather was a famous orang tahu – a sage – whose magical powers could cause crop failure and even death by the point of a finger. Donny’s earliest memory is of his grandfather, Nenek. Donny, aged four, wanted a coconut and started chopping at a palm tree with a machete. Nenek saw, and told him to wait on the verandah with his eyes shut. Donny peeped through his fingers and saw Nenek point at the palm. Instantly, several coconuts fell to the ground.

Donny’s grandfather was greatly in demand to kill members of rival tribes such as the bloodthirsty Keniah Dayaks – formidable hunter-gatherers who could survive for a year alone in the jungle. The spirits inhabiting Nenek’s body prevented him from dying, and it was only when he renounced magic at the age of 107 that he finally passed away. The old man had warned his grandchildren not to follow him into black magic, but to study at school and forget tribal hostilities. As he wished, today young Dayak and Orang Sungai naturalists work alongside each other at the reserve, and Donny has married a girl from another tribe.

We climb steps to a suspension bridge of slippery ironwood struts and metal cables - a bouncy, wobbling cakewalk 100 feet up, but a brilliant place for spotting a red-legged monkey guzzling fruit in a treetop, a vivid scarlet-breasted minivet, and a noisy rhino hornbill. Emergent trees poke from a mesmerising sea of green.

Only thirty rangers are employed to patrol the Danum Valley’s 175 square miles – an impossible task. Local poachers are knowledgeable and resourceful, and seem undeterred by the threat of 20-year prison sentences or the lure of £300 rewards. But elephants are just as clever – they have learned to keep in groups of at least five, and to stay safe near the lodge.

Night falls suddenly and at 7 o’clock Donny takes me on a night drive. Following the beam of his torch, I peer through binoculars (which, oddly, work perfectly in the dark) at a spotted owl feeding its young on a branch, two rabbit-sized mouse deer, a snake curled on a fern, an elegant red flying squirrel gliding from a high branch, and a rarely sighted western tarsier. Donny turns his torch off, and we sit, listening to the cacophony of weird rainforest noises and the thundering river Danum. The stars are hidden by looming rain-clouds, and apart from the intermittent flicker of fireflies, the night in one of the world’s most remote wildernesses is utterly, intensely, unimaginably black.

First published by the Telegraph
©SarahShuckburgh