They're watching us, I'm sure of it. And laughing, too. Great chesty whoops and high-pitched hysterics echoing through the Velcro forest. My guide, Clint, calls it ‘pant-hooting' - a common method of communication. But then he would; he's a zoologist. My theory is that the chimps are simply enjoying a good joke.

I mean, look at it from their point of view: along come their long-lost cousins, showing off on ‘all-twos' - way up the evolutionary tree - then a few steps in the primeval forest and all they seem capable of is tripping over tree stumps, cursing horseflies and falling in streams. I'd laugh if I was a chimp.

Fortunately we humans have also evolved a sense of humour. After insect repellent, it's the most essential requirement for tracking our closest relatives through their Ugandan forest home. This is our third dawn trek in search of chimpanzees - and each time they've given us the slip. Our scout, Adolph, isn't surprised. He didn't dream of chimps last night. He says that until he does, we might as well have a lie-in.

It's a tempting thought. I'm staying at one of Uganda's most luxurious lodges - a rustic scattering of tented cabins, each with its own four-poster and dreamy mosquito net. Semliki Safari Lodge snuggles into its surroundings like a well-hidden bird's nest. From my bed I can gaze across lush, misty forest draped in ribbons across the tawny savannah of Semliki Valley Wildlife Reserve. Through another opening I can glimpse the dramatic escarpment of the Western Rift Valley, while far to the south, brooding in a purple haze, rise the Ruwenzoris, the fabled Mountains of the Moon.

Extending to the shores of Lake Albert in the north, the 500km2 reserve encompasses a rich tapestry of acacia-stubbled grassland, riverine forest, lake shore and rocky escarpment. Perhaps not surprisingly, Semliki boasts one of the most diverse avian faunas in East Africa. When the founders of Semliki Safari Lodge, Jonathan and Pamela Wright, first arrived here in 1992, poaching had taken a terrible toll on the region's wildlife. The situation was so dire that the reserve faced losing its protected status. However, since the lodge opened in 1997, the Wrights' conservation efforts have encouraged the return of lions, elephants and many other species. Such has been the success of this ‘modern-day Genesis' that numbers of Uganda kob alone have increased tenfold. Although chimpanzees were less affected by poaching, the Wrights have also initiated a research programme (in partnership with the University of Indiana Department of Anthropology) to investigate these elusive and endangered primates. So far, they have identified four different chimp communities in the forests of Semliki.

On our next dawn walk, the transition from savannah to forest is abrupt. One moment I am walking tall, wading through chest-high grass, the pepper-sweet tang of sun-baked Africa spicing my nostrils - the next, I am bent double beneath a pressing tangle of trees and vines; a twilight world of muted greens, intense and heady like steam from a rich stew.

I call this the Velcro forest because lianas lasso your limbs, hooked vines snag your clothes and even the smooth ones seem to bristle with biting ants. We follow a scant path, walking silently in single file. Every few minutes, Adolph pauses and tilts his head towards the forest canopy. He's listening for telltale sounds: the crackle of bark being stripped as the chimps search for insect grubs, the dull thud as one jumps from a tree to the forest floor… But all we can hear is the trill of cicadas and the incessant call of a red-eye dove. A little further on, Adolph sinks to his haunches. Using a twig, he probes the leaf litter, then lifts it to his nose. A smile streaks his sweat-beaded face and he nods knowingly. "Chimp shit," he whispers, proudly offering me the stick. Soon Adolph discovers the half-gnawed cherry-like fruits of a cola tree, as vivid as drops of fresh blood on the ochre patchwork of the forest floor. Some are still oozing. "Look, no ants yet," breathes Clint. "The chimps are close. They're on the move." Adolph points a clenched fist at a tangent to the path. "Mugiri?" Adolph nods. Mugiri is the name of the river flowing through the forest. To reach it we'll have to leave the path and thread ourselves through several hundred yards of unkempt undergrowth. "Don't step on sticks," Adolph urges in a half whisper-half hiss. Mid-limbo beneath a particularly challenging barbed vine, I grunt an apology. Moving about ‘off-path' is like pouring milk on Rice Krispies - you can't stop the snap, crackle and pop. I try walking in slow motion, easing my heel down and feeling the ‘give' of leaves and twigs as I transfer weight onto the ball of my foot. But compared to Adolph and Clint, I sound like an industrial twig-mulching machine.

Flecks of sunlight spatter the leaves as we approach the Mugiri River. It's more of a shallow stream the colour of lightly-brewed tea than a full-bodied torrent. So, without stopping, we wade straight in. "Watch out for hornets," Clint says. "About this long." He spreads a forefinger and thumb. "They go for your neck." "Anything else I should be aware of?" "Only the Nile terrapins - nasty nippers." Adolph has reached the far bank and is squatting down again. This time, even I recognise what he has found - three grooves slotted in the powder-white sand of the riverbank: the perfect knuckle print of a chimpanzee.

A droplet of sweat dances at the tip of my nose, tickling, teasing. But I daren't make a sudden movement to wipe it off. Like a blunt needle through stubborn cotton, I ease myself back into the forest. After less than a dozen paces, Adolph freezes. Behind me I hear Clint's voice, barely nudging the still, humid air: "If it's a buffalo, keep calm. Look around; find a tree to climb if it charges." I nod slowly, my eyes flicking through tears of sweat from one tree to the next. Every one is either thinner than my wrist or sprouts its lowest branch ten yards above my head. I want to point this out to Clint, but my voice is held hostage by fear and expectation.

I can hear footsteps now - a rhythmic patter on dead, brittle leaves. Whatever it is, it's moving towards us - fast. I focus on a minute gap in the meshwork of vegetation. Something dark passes behind it. Surely too small for a chimp, though? I glance at Adolph. It's as I feared. The tension has already slipped from his body. He rocks back on his haunches and turns to me, mouthing an unmistakable word: "guineafowl".

Once again the chimps have run circles around us. Even as the guineafowl emerge into a clearing ahead of us, we hear a brief, distant outburst of pant-hooting. "You're right, I think they are laughing at us," says Clint. He shakes his head, Adolph shrugs and I slap a horsefly. Back at Semliki Safari Lodge, we console ourselves with a sumptuous meal of tilapia, fresh from Lake Albert, wrapped in banana leaves and steamed in their own juices. We could always try our luck at a spot of fishing," Clint suggests.

It's an hour's drive to a small fishing village on the lake's southern shore. A crowd gathers to watch Clint reverse the Land Cruiser and its heavily laden boat trailer to the water's edge. In a few minutes our aluminium skiff is afloat. Clint fires the outboard engine and we nose through rafts of floating hyacinth. Reaching clearer water, he eases the throttle forwards and the boat lifts eagerly in response, cleaving an arrowhead across the glassy surface of the lake. After the Velcro forest, Lake Albert is vast and uncluttered, the horizon merely a faint blur between water and sky. Revelling in the freedom of space, Clint seems optimistic. "The record is 320lbs," he tells me, as we unravel viciously hooked lines from the stern. "That's a serious Nile perch!" I haven't the heart to tell him that I was nine when I last went fishing and all I caught was a lily pad. It's strange how history can repeat itself, though. After two hours trawling across Lake Albert, my rod suddenly bows alarmingly; Clint leaps to my aid and together we reel in the ‘big one'. It takes a full ten minutes before we realise that a large clump of hyacinth is following the boat.

The next day, back in the forest, the chimp trail has turned cold and Clint is worried. He says they often go quiet and withdrawn when one has died. Crouching on damp leaf litter, we sift the sounds of the forest for clues of the chimps' whereabouts. A rustle of leaves momentarily lifts our heads and our hopes. But it's a troop of black-and-white colobus monkeys performing leaps of faith high in the canopy. Once I hear a distant hooting cry, but Adolph has heard this one before - an eastern grey plantain eater, a bird whose chimp-like call has led him on many a fruitless search.

At dusk, we drive to the edge of the savannah where it dips into the corridor of riverine forest. In silence, we continue our vigil. Chimpanzees are creatures of habit. Each evening, around 7pm, they build sleeping nests and usually call loudly to each other as they settle down - a kind of ape version of The Waltons. But we hear nothing more than the steady staccato beat of insects and birds. Shadows rake the escarpment, shrinking into valleys and fissures as the sun nuzzles the horizon. "What time do you leave tomorrow?" Clint asks. "Not until after breakfast - plenty of time for one last dawn walk." I try to sound optimistic, but the simple truth is that without some kind of clue, we don't stand a chance of finding the chimps. "Let's give it another ten minutes," says Clint. They call in less than two: a riot of pant-hoots shattering the peaceful climax of sunset. It takes a second for Adolph to judge their position. "I don't believe it!" says Clint, jerking the Land Cruiser into gear. "We must have walked straight past them earlier." "How much daylight do we have?" I ask as we career along a dirt road towards the nearest forest access point. "About half an hour." The engine has barely died before we leap from the vehicle and march into the forest. I hear the ratchet click of metal on metal as Adolph checks the safety catch on his rifle. Then the chimps call again, a series of deep hoots rising to a screaming crescendo. Adolph takes another bearing. We're running now, fording streams in a single stride, a slick of sweat across our backs and faces. Then Adolph whistles softly, clenches his fist and points to our right. We slow to a brisk walk, bats flickering around our heads in the murky slide towards night. "We're so close!" Clint whispers. "If only they'd call again, we could pinpoint where they're nesting." But the forest has fallen silent. We have no choice but to turn back. Tomorrow will be our best chance yet. It will also be my last.

Dawn in the Velcro forest is heralded by the usual cacophony of honking hornbills, croaking colobus and barking baboons. But there is no sound of the chimps. We sit and wait. Twitching in its death throes, a praying mantis is edging towards me, carried aloft on a grisly tide of safari ants. I begin to accept defeat - the chimps have eluded us. But then Adolph tenses and I see the familiar fist signal. He's seen something - a branch moving? We walk a few paces off the trail, then simultaneously freeze and sink to our haunches like balloons deflating. "There!" Clint's voice is a hoarse whisper. I follow his stare, but my brain is scrambled by the riot of plant life. I can see movement, but nothing more specific. "Where?" I hiss back. "They're climbing out of that tree." Clint sounds desperate - eyes bulging, chin straining forwards, he's willing me to spot them. "Yes!" I breathe. "I can see one!" A hairy shoulder; hands and feet clasped around a trunk - at least four chimps are shinning down the tree. I can hear the soft thud as each one jumps the last few feet to the ground. Briefly, a face appears around the trunk, eyes staring as intently as mine. It's the merest glimpse, but I know the image is already embedded in my memory. In seconds they've vanished, moving silently like smoke in the forest. Clint breathes a ragged sigh and Adolph is smiling. "Last night I dreamed of chimps," he whispers.

Fact File
Checklist Language: Officially English.
Time: GMT+2
Int. Dialling Code: +256
Money: Ugandan Shilling, currently 3179 shillings to the UK £. Prices are often quoted in US$. Credit cards are rarely accepted outside the major towns.
Visas: Obtainable overseas or on arrival at Entebbe International Airport; cost US$30.
When to go Uganda's equatorial climate is characterised by warm days of around 24-28oC and cool nights. The rainy seasons occur April to May and October to December, with the wettest month being November.
Getting there British Airways (www.ba.com) flies direct between London and Entebbe three times weekly. Indirect flights are available from Emirates (www.emirates.com), EgyptAir (www.egyptair.com) and Kenya Airways (www.kenya-airways.com). Expect to pay from £400 return. There are several companies in the UK and Africa who can tailor a package, including international flights, internal transport, accommodation and safaris. See the advertisers index on page 111 for details.

Getting around The Uganda Safari Company (www.safariuganda.com) can customise any Ugandan itinerary. A typical 12-day safari costs US$3575 (based on two people travelling), including ground transport, guides, accommodation, meals, gorilla permits and activities. Highlights include Lake Mburu National Park, gorilla watching in Bwindi Impenetrable Forest, game drives and boat trips in Queen Elizabeth National Park, chimpanzee tracking in Semliki Valley Wildlife Reserve and boat trips at Murchison Falls.
Where to stay Full-board accommodation at Semliki Safari Lodge costs US$260 per double per night.
Health A certificate of yellow fever immunisation is required for entry to Uganda. A course of malaria prophylactics should also be taken before, during and after your visit.
Find out more www.visituganda.com Uganda (Bradt, 1998) Uganda Handbook (Footprint, 2002)