“Everything about Rushenya is big: his head, his arms, his feet, and especially his bum.” Augustine Muhangi doesn’t stand on ceremony as he gives a running commentary about the 250kg silverback gorilla we’re tracking. In turn, Rushenya waddles away, affording us a perfect view of that colossal backside.

Unlike most mountain gorillas met by tourists in western Uganda’s Bwindi Impenetrable National Park, Rushenya hasn’t encountered many humans. His group, Bikingi, roams the Rushaga area in Bwindi’s southern sector, and is only semi-habituated – used to trackers and rangers but not to strangers or tourists.

The ultimate gorilla experience in Uganda Show all 10 1 /10 The ultimate gorilla experience in Uganda The ultimate gorilla experience in Uganda A toddler in the more socialised Mubare group Will Whitford The ultimate gorilla experience in Uganda A shy female from Rushenya's group Will Whitford The ultimate gorilla experience in Uganda The Ivy Trail, en route to the gorillas Will Whitford The ultimate gorilla experience in Uganda Augustine Muhangi and trackers connect samples from gorilla beds Will Whitford The ultimate gorilla experience in Uganda Geoffrey Twinomuhangi works with the trackers to find the gorillas Will Whitford The ultimate gorilla experience in Uganda Forget the gorillas, the views aren't bad either Will Whitford The ultimate gorilla experience in Uganda Sue Watt with Kanyonyi in the more socialised group Will Whitford The ultimate gorilla experience in Uganda Big Daddy Rushenya Will Whitford The ultimate gorilla experience in Uganda Rushenya shows the crew his assets Will Whitford The ultimate gorilla experience in Uganda One of the Mubare gorillas freshening up Will Whitford

Although the 400 or so gorillas in this dense 321sq km forest are all essentially wild, some are wilder than others. The last family I was tracking – the Mubare family in the park’s northern sector – were completely unperturbed by our group of eight’s presence. Kanyonyi, the silverback, had almost brushed against my thighs as he ambled past; others were completely relaxed as they munched on stalks, played in trees and chilled out on cushions of ferns.

But being in the Bikingi’s presence has a definite edge.

Gorilla encounters here in Bwindi have traditionally been limited to one hour: magical yet fleeting. They’re costly, too, at $600 (£480) a head – though the fees are ploughed back into conservation in this park that’s home to half the world’s critically endangered mountain gorillas.

But last year, the park introduced something a little different.

“Normally, trackers find the gorillas before the visitors arrive, so the groups can go straight to them, have their hour with them, and go away,” says Pontius Ezuma, Bwindi’s conservation manager. “We wanted to offer something more enriching – to show what tracking actually means. Things like gorilla behaviour, what nests look like, finding their trail.”

The new visit, run by Uganda Wildlife Authority in Rushaga, the southern area of the park, is a four-hour “gorilla habituation experience”. Groups are limited to just four guests, and permits cost $1,500 each.

A shy female in Rushenya's group (Will Whitford)

You don’t necessarily get more time with the gorillas themselves; instead, you join trackers right from the start and find the families with them. Depending on how quickly you find them, however, it's possible to get two, or even three hours with them. As well as providing you with the experience of a lifetime, the visit helps the gorillas too, allowing animals like Rushenya to get used to human presence.

We’d already walked for three hours along the Ivy Trail to reach the south, starting at Buhoma, where we’d spent the night, and passing through fairytale rainforest with giant ferns, vibrant birdsong and monkeys swinging in the shadows. Our bed for the night was Nkuringo, the nearest village for Rushaga with two lodges: Nkuringo Bwindi Gorilla Lodge, a welcoming home-from-home perched on Nteko Ridge, and the high-end, community-owned Clouds Mountain Gorilla Lodge, overlooking the Virunga Volcanoes.

At 7am the next day, we set off with Augustine (our guide), porters and tracker to where they left the Bikingi group the night before. It's only when we reach that point that the four-hour clock starts ticking, starting with a crash course in tracking. Discarded leaves, stems stripped of foliage, bent vegetation and knuckle prints in the mud are tell-tale signs of the gorillas’ trail, Augustine explains. But it’s the acrid stench of urine that finally reveals their nests.

Gorillas build new nests every night, we learn, leaving a mine of information for trackers. Augustine and his team don facemasks and latex gloves to examine “mattresses” of leaves and branches perched on top of shrubs. Rushenya’s bed is easily identified by its vast size and silver hairs; a small turd next to a larger pile reveals the nest of a mother and baby. Diligently recording everything on data sheets, the team collect samples for analysis. Then it’s straight on with the search.

Checking the gorilla nests for clues (Will Whitford)

It takes around three years to habituate gorillas. Over 18 months of daily visits, the Bikingi group have become accustomed to their trackers, but are still wary, particularly with new people. “Remember they might charge,” says Geoffrey Twinomuhangi from UWA. “Copy their movements. Crouch down. If they eat grass, pretend to eat grass. But don’t beat your chest: that’s their sign of supremacy. Whatever you do, don’t run.”

Suddenly there’s Rushenya, munching stalks in a clearing about 12m away. The trackers cough softly – the sound of contentment in gorilla language. “Speak to him,” Augustine whispers. “Let him know you’re a friend.” Nervously, I try a quiet, guttural rumble that tickles my throat. When he responds, grunting deeply, I feel shivers down my spine.

Rushenya and his family – four females, three toddlers and a three-week old baby – are constantly on the move, and both the purpose and the challenge of habituation is to stay with them and keep in their vision no matter what. We hurtle after them, battling through tangled jungle, crawling through bushes and scurrying up and down near-vertical slopes of loose earth, wet leaves and slippery vegetation. Gradually, we narrow our distance until we’re a mere seven metres apart. Big Daddy Rushenya eats incessantly; youngsters play tag in the trees, laughing and smiling; mums keep a watchful eye on them and on us.

Suddenly, a female carrying her three-week old baby tumbles down the slope, landing between the silverback and me. Rushenya swings into action, running towards us, almost shouting a reverberating “uh uh” noise. Thankfully, we remember our briefing. We avert our eyes and crouched submissively. He freezes in front of us, all 40-odd stone of him, sussing out the situation... and then slowly moves on. It felt like forever but must only have been seconds. “He was just warning us, protecting the baby,” Augustine reassures us.

Whether you have one hour or four with these majestic, vulnerable creatures, it will never be enough, and all too soon our time is up. As is Rushenya’s – as we turn to leave, he’s already heading deep into the forest. For Augustine and his crew, tomorrow is another day.

Rushenya heads off into the sunset (Will Whitford)

Travel Essentials

Getting there

Steppes Travel (www.steppestravel.co.uk; 01285 601050) offer a 7 day trip from £5,695 per person based on two people sharing in low season. This includes one normal gorilla permit and one gorilla habituation permit, Nkuringo Walking Safaris’ Ivy Trail trek, international flights via Nairobi with Kenya Airways, internal flights, transfers, two nights at Volcanoes Safaris Bwindi Lodge (www.volcanoessafaris.com), two nights at Clouds Mountain Gorilla Lodge (www.wildplacesafrica.com), and one night in Entebbe on a full board basis.

Staying there

Nkuringo Bwindi Gorilla Lodge (www.mountaingorillalodge.com) has doubles from $250, full board.

More information