Republic of Congo: Odzala-Kokoua National Park is a glorious wilderness and home to critically-endangered western lowland gorillas

Stop. Be quiet. Listen to the voices of the jungle. It's not silent beneath the lush, perpetual blanket that smothers the Congo Basin. The hollows burbling like air sacs below its canopies aren't empty.

When the forest floor no longer crunches underfoot, when my breathing has slowed and my heartbeat has subsided and the chatter inside my head has abated, this is what I hear: an ear-splitting symphony discharged by the jungle's inhabitants.

Buzzing, warbling, droning, cackling, squawking, whistling, clicking, barking, howling. The sounds echo off the underside of the canopy, bounce off rubber-thick leaves, seep through impassable thickets. Underscoring this mangled refrain is a slow, persistent hiss. It slips through the forest like a fever.

From high above, I can see the fringes of this watershed spreading like a rash across west equatorial Africa. This is the world's second-largest rainforest (after the Amazon), a largely intact wilderness straddling six countries and draining its run-off into the distant Gulf of Guinea.

Below me is the most scarcely populated country south of the Sahara – the Republic of Congo, a former French colony frequently mistaken for its mightier and more menacing neighbour, the Democratic Republic of Congo (DRC).

Most of this country's scant populace has sunk southwards, settling in the metropolises of Brazzaville, Pointe-Noire and Dolisie, leaving the northerly reaches of rainforest largely unpeopled.

INTO THE HEART OF DARKNESS

The capital spreads out beneath me now in gentle waves, corrugated roofs glinting in the sunlight, banana groves embroidering the hillsides, crops plugging the earth's depressions. The Congo River snakes thick and ropey along Brazzaville's southern boundary; on the opposite bank, Kinshasa – capital of the DRC – is a mirage trembling in the haze.

Less than two hours later I'm descending into Odzala-Kokoua National Park, lodged like a beating heart inside this monumental greenbelt. The rainforest oozes from one horizon to the other; it is fragmented sporadically by twisting tributaries and luminous bais, or salt marshes, and pockets of moulted grassland.

Long tarnished in the eyes of outsiders by Joseph Conrad's Heart of Darkness and Herge's Tintin, Ebola outbreaks and that most unfortunate conflation with the neighbouring DRC, this otherwise glorious wilderness has remained largely unexplored by tourists.

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Odzala-Kokoua National Park was declared a Biosphere Reserve by UNESCO in 1977, and is home to one of the world's last strongholds of critically endangered western lowland gorillas. They coexist – inharmoniously, at times – with the Pygmy and Bantu people, whose villages are scattered around the park's yawning perimeter.

It's here that Spanish primatologist Dr Magda Bermejo and her husband German Illera began their pioneering research into these apes – slighter cousins of central-east Africa's mountain gorillas – two decades ago.

Interlopers in a region far from the meddling crowd, they discovered that the gorillas (along with other species) were prized as bush meat, and their numbers were rapidly dwindling. Then in the early 2000s a huge number of their population – about 5000 – died in two successive Ebola outbreaks.

Instead of abandoning their research project, Bermejo and Illera have remained at Odzala, encouraging local communities – caretakers of one of the world's most immaculate landscapes – to value gorillas not only for their critical role in the ecosystem but for their untapped tourism potential.

Their collective efforts have been boosted in recent years by new investors keen to see Odzala thrive. In 2010, park management was assumed by the Odzala Foundation, a partnership between the not-for-profit African Parks and the Congolese government.

Working closely with communities to counteract poaching and rehabilitate the habitat, their programs are already yielding benefits: multiplying wildlife populations, increasing tourism and the consequent flow of sustainable income to locals.

The lack of tourism infrastructure, meanwhile, was addressed by the Congo Conservation Company, an initiative of German businesswoman and philanthropist Sabine Plattner. Two new camps were constructed in the park, and an existing camp refurbished.

Communities were engaged through the benefactor's charitable organisation, Sabine Plattner Africa Charities (SPAC). Tourists started trickling in. Africa's lungs were expanding with the breath of new life.

IN THE CITY OF TREES

The road to Ngaga Camp from Odzala's Mboko airstrip is a river of mud. It was freshly graded last week, guide Alon Cassidy tells me, and subsequent rains have turned it to slop. He machetes branches off a tree, jacks up the Landcruiser, wedges the logs beneath its tyres.

"The Congo Basin is not the place to find rocks," he says, beating the branches into place. "It's been colonised and re-colonised with detritus. Its nutrients are poor due to run-off and leaching – the first three feet of soil are rich, the rest isn't."

The forest arcs above us like a wave, spills into the road, swamps us oppressively. It's hard to believe this city of trees has been constructed on such weak foundations. We've passed through a swatch of savannah on our way here, waited for a forest buffalo to remove its wallowing bulk from rainwater pooled in the dirt road, observed a dung beetle burying its load, seen the shadows of moustached monkeys darting through the trees.

Now the forest is still except for that inexorable hissing and the cacophonous zinging of bees. They congregate on our skin, lapping up sweat summoned by the equatorial humidity. If gorilla eyes are watching us from behind dreadlocked vines, we'd never know it. Cassidy revs the motor, drops the clutch. The wheels spin, grip and – yes – propel us through the morass.

ON THE GORILLA TRAIL

Ngaga Camp is a scattering of huts tucked treehouse-like into dense forest in the Ndzehi concession near the village of Mbomo, just beyond the park's south-west boundary. It occupies the overlapping home ranges of several groups of gorillas; among them are those habituated by Bermejo and Illera: Jupiter and Neptuno, named for their respective silverback alphas.

Early next morning, we follow tracker Zepherin Okoko as he tunnels deep into the forest. Up a steep rise we go, down into a gully, across a translucent stream, over logs impregnated with white fungi quivering like fluff, past regiments of Matabele ants returning from battle, the bodies of termites held aloft in their jaws. There's no other visible sign of life here save the silhouette of a tiny sunbird; yet the forest moans at our every move.

Okoko stops abruptly, jabs his hand at the sky. He's detected Jupiter's group feeding nearby. We pull masks over our mouths (gorillas are highly susceptible to human-borne respiratory diseases) and fly nets over our faces to deter the stingless sweat bees enticed by gorilla-scent and the beads of perspiration pebbling our faces.

Through oceans of marantaceae we wade, their leaves whining against our incursion. We skirt impassable undergrowth, duck beneath vines and inhale the gorilla-scent that is unmistakably primal. And then, suddenly, there it is, manifesting before us like a phantom: a juvenile gorilla lazing in the crook of a tree, stuffing leaves in his mouth, looking directly at me.

My heart thunders against my ribs; my breath condenses clammy inside the flynet; the forest's melody evaporates into the airless gloom. A pool of green light cocoons the gorilla like an aura, distilling this moment into a hallucinatory dream.

An hour later, when our allotted time is over and we've retreated downhill from the group – now swelled to several individuals who swing from trees and discard bitten fruit as their leader, Jupiter, lords over them from the upper canopy – Okoko smiles at my elation.

"Every day I go out to see the gorillas, and when tourists come in I work a little bit harder to find them," Alon translates from Okoko's French. "If the visitors don't have a good sighting, I feel a bit bad about it. We aren't really that OK with it, if the sighting's not great."

THEY ARE NOT ALONE

Gorillas aren't the only charming residents of this biosphere. They cohabit with spotted hyena and chimpanzees, sitatunga and bongo, forest elephants and 1000 species of bird.

To better view some of these creatures, we must cross back over the park's boundary, travel through the buffer zone in which villagers are still permitted to plant their crops, and burrow through the rainforest until we reach the Lekoli River.

The clamour and murk of the jungle dissolves out on the water; my senses are clarified here, the shadows rinsed off with sunlight. I catch the warble of an African grey parrot as we float downriver in our kayaks, smell the pungent, trailing sprigs of the rauvolfia caffra tree, hear the alarmed trumpeting of a forest elephant as it beholds us from the depths ahead.

Smaller than its savannah cousin, yet at the same acute risk of poaching, the elephant flaps its ears, raises its trunk and emits another infuriated proclamation. Then it wades ashore and slips into the forest's protective embrace.

We ease our kayaks into a tributary diverging from the Lekoli River towards Lango Bai and step into the knee-high inlet. It feels dangerous, submerging my feet in a Congolese waterway; yet this is one of the few places in Africa where streams and marshes can be explored on foot, for the only crocodiles here are harmless dwarf species, and irate hippopotami aren't likely to be awaiting us in the channels (they generally confine themselves to deeper waters).

The sky is a purple-gold mosaic with storm clouds and dying sunrays as we approach the bai. Animals walk for hours to sip from this mineral-rich font, Cassidy says. Water buffaloes throng it like barflies, greedily slurping its waters.

Birds suck its goodness from the mud. Elephants dig holes in the swamp bed, dispersing deposits with a blast from their trunks and imbibing the nourishing beverage. On busy days, guests can observe this unruly feast from the deck at Lango Camp, which projects discreetly from a fringing forest and is elevated to allow elephants to pass beneath it on their way to the party.

BEYOND THE QUAGMIRE

The elephants are bickering out on the bai before dawn next morning. They've resolved their differences and vanished into the forest by the time African Parks eco-monitor Dieudonne Bocka leads me out into the clearing. Few people have a more intimate relationship with this wilderness than he, for he's lived in it – and off it – his whole life.

Before Odzala was turned over to conservation, the forests were used by villagers as a source of food and minerals; Bocka's parents and grandparents would extract salts from Lango Bai. But for the past 22 years the forest has provided his livelihood in a new and more sustainable way, as he shares his knowledge with the conservationists trying to preserve it.

At the far end of the bai, African green pigeons are swooping for mud like a squadron of jets, the air thunderous with their comings and goings. We pass from the bai into an adjacent thicket; unlike the towering foliage of Ngaga, the trees here are stunted, their canopy impervious to sunlight, the floor scant with undergrowth. The forest closes over us like a coffin.

We crunch along its tunnels, crossing carpets of mauve wenge petals, passing an assassin bug camouflaged in its victim's liquefied carcass, stepping over fallen caloncoba fruit, its spiny carapace peeled with ease by dexterous monkey fingers. We loop through crackling savannah punctuated with termite mounds and come finally to the edge of a swamp whose shallows are an abstract swirl of elephant tracks.

Wading into the muddied depths, we drag our boots over unseen debris. Water inches towards our waists. Walls of vegetation surge beside us. Bocka moves slowly, alert to the voices of the jungle. Gradually the depths slope into shallows, and we arise unharmed from the quagmire.

No-one has seen us but the water monitor sunning itself on a rock, the jumping spider springing from a leaf, the flycatcher chirruping its sweet call. By tomorrow our footprints will be gone, erased by the creatures wading in behind us, colonised and re-colonised by their inexorable tracks until our own are nothing but a rumour.

FIVE OTHER NEW WAYS TO ENGAGE WITH WILDLIFE

CHIMPANZEES IN TANZANIA

Primatologist Jane Goodall launched her seminal research into chimpanzees at Gombe Stream National Park in 1960s. Today, visitors can track habituated groups at Gombe and downstream at Mahale Mountain National Park on the shores of Lake Tanganyika. See janegoodall.org; tanzaniatourism.go.tz

SHOEBILLS IN ZAMBIA

Bangweulu Wetlands is home to one of the most globally-important populations of endangered shoebills. Community guards protect their nests as part of the Shoebill Nest Protection Plan, thus preventing the theft of eggs and chicks for the illegal wildlife trade. See africanparks.org; zambiatourism.com

PANGOLINS IN THE CENTRAL AFRICAN REPUBLIC

The world's most illegally traded animal, pangolins are researched and rehabilitated at Sangha Lodge near Dzanga-Sangha Special Reserve. Though wild sightings are rare, visitors might spot these mostly nocturnal mammals on night walks through the forest. See sanghalodge.com

MOUNTAIN GORILLAS IN RWANDA

After surviving Rwanda's genocide, these critically endangered primates are helping restore the country's tourism industry. While the recent doubling in trekking permit fees – from $US750 to $US1500 a trek – has reportedly affected visitor numbers, it has also increased community and conservation revenue while retaining low-impact tourism. See visitrwanda.com

MARINE LIFE IN THE SEYCHELLES

Isolation has helped the remote Seychelles Outer Islands retain their diverse biome and pristine conditions. Blue Safari offers conservation facilities where guests can learn about projects such as turtle tracking, surveys and beach clean-ups. See bluesafari.com

FIVE TRENDS IN WILDLIFE CONSERVATION

TAKING SANCTUARY

Collaboration between African Parks, governments and communities has led to the development of sanctuaries in countries such as Chad, Benin and the Central African Republic – and the consequent restoration of habitats degraded by poaching, hunting and human encroachment. See africanparks.org

SIGNING UP

Signatories to United for Wildlife's (UFW) Buckingham Palace Declaration commit to helping shut down lucrative trafficking routes and removing systemic vulnerabilities that encourage their exploitation. See unitedforwildlife.org

GOING DIGITAL

Change Wildlife Consumers is co-opting digital and social media platforms (Google, eBay, Facebook, Instagram) to help stamp out online wildlife trafficking by removing adverts for trafficked animals and training staff to analyse and flag offending posts.

RELOCATION, RELOCATION, RELOCATION

Groups such as Rhinos without Borders continue to relocate rhinos, elephants and even giraffes to habitats that have been depleted of them or – in the case of black rhinos – establish breeding herds away from poaching hotspots. See rhinoswithoutborders.com

TRAFFIC CONTROL

Conservation groups are partnering through organisations such as TRAFFIC to reduce demand for trafficked wildlife through awareness campaigns and the development of toolkits with which to influence consumer behaviour. See traffic.org.au

TRIP NOTES

Catherine Marshall was a guest of The Classic Safari Company.

MORE

traveller.com.au/republic-of-congo

africanparks.org/the-parks/odzala-kokoua

VISIT

Visas can be obtained on arrival in the Republic of Congo at a cost of $US50. Visa applications must be accompanied by a letter of invitation, which is issued by the tour operator. The Federal Government's Department of Foreign Affairs (DFAT) doesn't currently issue travel advice for the Republic of Congo.

HEALTH

Yellow fever vaccinations must be current; in order to comply with gorilla trekking requirements visitors must also supply a doctor's letter confirming they are in good health and that their vaccinations for communicable diseases are up to date. The Republic of Congo has not experienced an Ebola outbreak since 2003. However, there has been a recent outbreak in eastern Democratic Republic of Congo. The affected area lies about 1500 kilometres from Odzala and the park is therefore not considered to be at risk. However, travellers should check for updates on potential Ebola outbreaks with their travel doctor and tour operator.

FLY

Etihad flies to Abu Dhabi twice daily from Sydney and Melbourne, and once daily from Brisbane and Perth. See etihad.com Onward connections to Brazzaville (with stopovers) are available with codeshare partner Kenya Airways. See kenya-airways.com/au

STAY

The Classic Safari Company's Odzala Discovery Package starts from about $US8720 a person twin share and includes a seven-night circuit between the three Odzala Discovery Camps, return schedule charter flights from Brazzaville to Odzala-Kokoua National Park and daily guided activities, including two gorilla-trekking permits. A new itinerary combines safaris in Odzala and Dzanga-Sangha Special Reserve in the Central African Republic, with transfers by charter flight and boat. Children aged 15 years and older are welcome; full adult rates apply. See classicsafaricompany.com.au or call 1300 130 218.

See also: The peaceful Congo's colourful capital

See also: From unspeakable horrors in the 90s, this is now Africa's safest country