Deep in the jungle of eastern Borneo I found myself out of breath on the lip of a ravine. We'd been hacking through often dense, steamy rainforest for two days. This climb, about the 20th of the day, had been tiring. My journey to the top of this hill had begun with a series of hop-on-hop-off plane journeys from peninsular Malaysia to Sabah on Borneo, its easternmost state. Next, a 4x4 drive along rutted tracks carved between green oceans of palm oil trees. Then, we'd trekked on foot into barely touched virgin jungle one hour from the coast and camped overnight by a stream in the rainforest. That was three days' march ago. Now I had no bearings other than the ground immediately ahead and the backpack of the local guide-tracker in front.
Above me was a huge canopy of green punctured with occasional patches of blue where the sun and daylight penetrated. I was surrounded by tree trunks. The ground was covered by leaves, leeches, and a rapidly spreading pool of my sweat.
Ninety degrees Fahrenheit is hot with a breeze, but in a humid, occasionally fetid atmosphere it is sweltering. I'd been leaking sweat for 10 hours each day, fluid that was replaced by consuming vast quantities of water, sterilised each night over a campfire.
As I sucked in the humid air, I could hear distant thunderclaps, the prelude to the daily afternoon storm. Then I noticed the leader of our seven-strong group. He was staring intently ahead and motioning me to silence with a swat of his hand. There was something wild just over this tiny incline. I waved to alert the rest of our party, and we all fell silent. The only noise was the distant barking of a samber deer and the approaching storm.
All this sliding down through mud, crashing into branches, crossing rivers swollen by rain and cleaving a way through undergrowth had been about one thing: finding the elusive Sumatran rhino. With the best estimates putting the numbers of these creatures in the wild as low as 30, a glimpse – however fleeting – would be something special. It could also be important. Our trip was not entirely motivated by self-interest. It had been organised by SOS Rhino, a project organised by Sabah Wildlife Conservation and WWF, with the intention to survey and protect the species. So when our guide gestured for us to approach a large fallen tree, we did so with the stealth of assassins.
As I peered between the leaves I saw what had attracted his attention: seven big, hairy, wild boars. They were about 30 yards away digging around a mud wallow, the sort of jungle facility we'd been told was also favoured by elephant and rhino.
Not a rhino, then, but still a magnificent sight. In the jungle, to be seen is to be in danger – and if I was in any doubt of the boars' lack of conditioning to the presence of humans, then their panicked reaction on sensing intruders educated me. In an instant they bolted, screeching through the far undergrowth: seven low-slung prop forwards in an untidy scrum. Within seconds they were lost once more, deep in Tabin Wildlife Reserve.
The reserve is about 50 miles west of the eastern coastal town of Lahad Datu, itself a flight away from the state capital, Kota Kinabalu. It was made a protected zone in 1984. SOS Rhino's base camp is a small collection of old school buildings just outside the rainforest, with a 10-minute truck ride to their entry track.
Seventeen trackers work here, along with surveyors and visiting zoologists. It is from this base that SOS Rhino undertakes most of its work. Visits to villages and schools help to increase awareness of the rhino's plight. But I had volunteered for in-the-field work.
First and foremost is rhino protection. The local guides form Rhino Protection Unit patrols to prevent illegal poaching. Tourists like me can help with the surveying element, by studying the remaining habitat of the rhino, documenting sightings, dung or footprints. Anyone can volunteer and pay the US$1,200 (£632) for a week, provided they have a decent level of fitness.
On occasion I felt a little like a passenger (a situation not helped by limited English among the trackers and the need to keep moving). However my questions, when asked, were happily answered. And that is why they accommodate volunteers, both in small groups or singly. They need people to learn about their work and the dismal odds facing the rhino.
Of the five species of rhino left in the world, the Sumatran is the smallest – and the rarest. Last year scouts captured some grainy footage of a rhino which is now proudly displayed on the reserve's website. The reason for this scarcity is twofold: poaching and the destruction of primary forest, the rhino's habitat. Over the past half-century, logging and clearances to make room for palm-oil plantations have reduced the acreage of primary forest, with statistics from WWF showing that in the past 30 years more than 40 per cent of primary forest has been lost. Today, despite strict rules to stamp it out, illegal logging still threatens the rhino and other endangered species such as the pygmy elephant and the orang-utan.
Much of the rainforest that is left is in isolated pockets, reducing the chances of rhinos breeding. There has been some recent success in this area: a set of baby rhino prints was found in a mud wallow last year. It was to this area that we set off the next morning.
"Rhinos are creatures of habit," explained Fadzilawati Hamdan, the project co-ordinator, "and they tend to stay in an area for a month and then move on. We have to keep checking all the wallows, though, searching for rubbing signs on trees where they scrape the mud off after a wallow, or footprints for our records. This wallow is special because it is where there was a baby. We know that the mother uses it."
When we reached the wallow there was indeed an adult rhino print preserved in the wet mud, each toe perfectly visible. It was documented, discussed, and finally catalogued as being made about two months previously. Despite the age of the print, it was heralded as good news. As Hamdan said: "At least we know a rhino was here two months ago – no guessing."
Other wild animals provided compensation for the absence of the star event; the manual dexterity of gibbons swinging high in the trees proved a particularly graceful show. And there is a satisfying feeling to living rough in a jungle.
For three nights I camped next to a river that was harvested for dinner upstream (small fish and snails primarily) and washed-in downstream. Collecting wild ferns and mangoes from the forest floor appealed to my hunter-gatherer instinct. The only concern was the nightly battle with millions of horrific fire ants. These arrive not long after dark, and there's no avoiding them.
Once the scouts make contact, they send for the rest, and millions follow, devouring whatever is in their path. Their bite is excruciating. The only defence is a path of fire and hot ash from the campfire: you have to make them pursue a different path. On my final night in the jungle I fought non-stop for more than four hours.
Some surveys last for 10 days, but we left the jungle on the fourth morning – with a mixture of regret and joy. A hot shower and cold beer beckoned, as did the tameness of normal life. While the scouts returned to their base camp to collate the information and schedule their next survey, I booked in to Tabin Wildlife Lodge for a couple of days' rest. The lodge sits on a river and attracts many wild animals. But without the thrill of jungle living, the adrenalin of the physical activity involved, and the focus of seeking out our rhino, everything felt a bit less exciting. Although hot water and air conditioning provided comfort, I began to feel a bit flabby and indulgent.
Yet the jungle has a habit of coming up with surprises. Danger lurks in the trees and beneath the mulch on the ground. I followed a guide around a corner near Lipad waterfall, which boasts a wonderful natural pool ideal for swimming. He suddenly jumped back into me shouting, "No! No! Snake!"
About six feet ahead of us – and so well hidden at the side of the trail that it took me many seconds to spot it – was a king cobra, head raised poised to strike. One more step from the guide would have put us in range – and the cobra's venom is often lethal. It was beautiful: 8ft long, dark and thick-bodied, menacing but elegant. It was also slightly more visible than the rhinos had been. A certain kind of luck, after all.
Volunteers can register with SOS Rhino (00 60 88 388 405; www.sosrhino.org). A one-week programme in the Tabin Wildlife Reserve costs US$1,200 (£632) per person, including a processing fee, transfers from Lahad Datu, full board accommodation and volunteering activities. Flights are not included. Lahad Datu can be reached from Kota Kinabalu, which is served from Heathrow by Malaysia Airlines (0870 607 9090; www.malaysiaairlines.com) via Kuala Lumpur and Royal Brunei Airlines (020-7584 6660; www.bruneiair.com) via Bandar Seri Begawan. Connections to Lahad Datu are available with MASWings (00 603 7843 3000; www.maswings.com.my).
To reduce the impact on the environment, you can buy an "offset" through Abta's Reduce my Footprint initiative (020-7637 2444; www.reducemyfootprint.travel).
Tabin Wildlife Lodge, Sabah, Borneo, Malaysia ( www.tabinwildlife.com.my) also offers a seven-night rhino survey expedition package for $1,249 (£657) full board. Alternatively, a two-night stay costs $311 (£164) per person, full board and including guided nature activities. Daily tours of the reserve cost $70 (£37) including transfers and lunch.
Tourism Malaysia: 020-7930 7932; www.tourism.gov.my