It's a nose. A very long nose. It swings back and forth in our direction, combing the breeze for our scent like some animated Hoover nozzle. Finding nothing amiss, the owner continues her meandering path towards us. What now?
The long grass parts as her outlandish form emerges into full view. Fifteen metres, 10 metres, eight metres. Surely she has seen us. But the wind is in our favour and those stuck-on currants of eyes are fooling nobody. Now we can see her pickaxe front claws and metre-long witch's broom of a tail. And, best of all, her passenger: a mini-me clinging gamely to mum's back like some myopic clanger.
Six metres, four metres. We shift nervously. She stops. The wind changes. And she's off, turning tail and shuffling away down the hillside, that strange marking around her shoulders now a trailing scarf.
We breathe again. Giant anteater. The fourth of South America's Big Five – and definitely the weirdest yet. Grins all round: just one to go.
I'm not sold on this "Big Five" business, I admit. The term hails from colonial Africa, where the quintet in question (lion, leopard, elephant, rhino and buffalo), were supposedly the hunter's most dangerous adversaries and so topped his tick-list for trophies. Today it is really just a strap-line for the safari industry, and is roundly condemned in some quarters by conservationists. In any case, it is inappropriate in South America, where wildlife watching has traditionally involved a more general immersion in the continent's dizzying menagerie. Why not the Oddball Eight, say, or the Thrilling 37?
Yet inevitably, perhaps, five South American mammals have been saddled with "bigness": namely jaguar, tapir, maned wolf, giant anteater and giant river otter. Brazil, conveniently, is home to all five. Thus tracking them down seems as good a premise as any for charting a course around this immense country.
But back to where we started, our first stop: the Amazon. If ever there was a Big Five of habitats then this would surely top the list: there are more species of beetle here than there are life forms in the whole of Europe. It's also home to four of the Big Five. But finding these beasts in the world's biggest jungle is notoriously tricky. Admittedly we don't comb the whole 5.5 million square kilometres but opt, instead, for a few days at Cristalino Jungle Lodge.
This discreet forest hideaway, accessible only by river, is tucked into the heart of an estate the size of Greater London on the very southern fringe of the forest. In Amazonian terms it's a postage stamp. Yet it's stuffed with wildlife and as good a place as any to start.
And so we hit the trail. Each morning our guide Marcos leads us deep into the forest. We duck lianas, clamber over buttress roots and skirt columns of army ants, all the time peering up for movement in the canopy. It's hard work: an occasional crash or squawk betrays monkeys or macaws high above, but the green curtain gives little away.
At ground level, however, it's another story. Marcos points out exquisite bromeliads, electric blue morpho butterflies and the delicate clay funnels of cicada larvae. We gather around the trunk of a statuesque Brazil nut tree, where he retrieves a cricket ball-sized nut from the leaf litter. One swing of a machete reveals the seeds – the "nuts" we know from Christmas hampers – arranged like orange segments. They taste sweet and oily, like coconut.
There is no shortage of other giants: a fist-sized elephant beetle lumbers across the lodge terrace; a saucer-sized tarantula waves hairy pedipalps from its silk-lined burrow; and sheep-sized capybaras – at 50kg, the world's largest rodent – emerge from the river each night to graze the lodge lawns. We even come close to seeing the world's largest snake when we nervously investigate a fetid swamp where a monster anaconda has recently been spotted. I'm sure it sees us.
Then there are the birds: Cristalino's tally of more than 570 species is exceptional even by Amazon standards. And to make spotting them easier the lodge has built the world's highest canopy tower. Up here, swaying a nerve-jangling 52m above the forest floor, we watch scarlet macaws, channel-billed toucans and swallow-tailed kites commuting over the undulating treescape, while screaming pihas add their hidden shrieks to the chorus below.
The river offers another perspective still. Each crescent sandbank erupts in butterfly confetti as our boat sweeps by. Far upstream we cut the engine and drift silently into a placid backwater. All is still but for the dancing light on the water – and an odd wheezing sound among the overhanging creepers. Paddling closer brings a crashing and flapping, followed by several large, prehistoric-looking birds lurching out across the water. These are hoatzins. They digest food in their throat and produce nestlings with claws on their wings. Not Big Five fodder, maybe, but another A-lister among Brazil's weird and wonderful.
The next day finds us 700km further south, bumping along a straight dirt road through a mosaic of grassland and swamp. Pink piuva trees and red termite mounds punctuate the flatness, while egrets and storks festoon the ditches.
This is the Pantanal – a vast wetland that western Brazil shares with Paraguay and Bolivia, and a world away from Cristalino's Amazonian tangle. Its open terrain and highly visible wildlife offer something more akin to an African safari. What's more, it's Big Five country. This is good news, as we are still not even on the score sheet.
Our road is the Transpantaneira Highway, originally built to cross the entire Pantanal (which is bigger than England) from north to south but grinding to a halt in 1976 on the banks of the Cuiaba River – about halfway down. You can understand why: 136 wooden bridges already knit together its 146km length. This is not the easiest place to build a road.
Today these bridges are a boon for wildlife watchers. We pull over on the rickety planks to watch capybara and marsh deer nibbling the greenery and countless yacaré caiman – the local crocodiles – cruising the waterways. Birds are everywhere: scarcely a fence post is without its heron or kingfisher.
Fence posts, it turns out, are integral to the character of the Pantanal, as this wildlife paradise is also cattle country. The tourist fazendas located at regular intervals along the road are working ranches that have diversified in search of the tourist dollar.
Our guide, Eduardo Falcao, is from local ranching stock himself and at each overnight stop friends or relatives emerge to greet him. These fazendas combine the charms of a traditional ranch with the tourist comforts of swimming pool and breakfast buffet. What's more, their grounds teem with wildlife, from the capybaras that wander the terrace to the hyacinth macaws – the world's biggest, and surely noisiest, parrot – cackling across the front lawns. Look away and you lose your breakfast to a cardinal, a cowbird or a kiskadee.
At the Pousada Rio Claro a cattle drive is passing through. Dust hangs over the beasts massing on the riverbank, and from behind a tree we watch the cowboys – and one cowgirl – urge the animals forward, their horses rearing among the mêleé. Horns toss and nostrils flare as 400 white brahmins thunder into the river; a heifer that strikes out for freedom is immediately lassoed and hauled back into the throng. Eduardo tells us how 12 drowned at this crossing last year. But today all emerge on the far bank, adorned with dripping trophies of water hyacinth.
It's an impressive sight. But we didn't come here for cows. The next few days see us combing the Pantanal's byways for its celebrated wildlife. Along forest trails we meet sleepy howler monkeys and inquisitive capuchins. From wooden viewing platforms we spot massive-hootered toco toucans and shy red brocket deer. And by night, Eduardo's spotlight picks out burrowing owls, crab-eating raccoons and even a shy ocelot mousing in a field.
Seeing the ocelot reminds us that a much larger spotted cat also prowls these parts. It's now 10 days into the trip, after all, and our Big Five list remains obstinately unticked. No problem, explains Eduardo, as we rumble on down the Transpantaneira. We're heading for jaguar country.
It is the jaguar that has planted the Pantanal on the tourist map. Sightings have become increasingly reliable here – helped by a recent let-up in persecution from ranchers who, understandably, have long resented the big cat's taste for cattle. Lucky visitors today might meet a jaguar almost anywhere – even swaggering down the Transpantaneira. But the Cuiaba River area is widely acknowledged to be Jaguar Central. With four nights booked at the Porto Jofre Hotel, a fishing lodge on its banks, our fingers are crossed.
Each day sees us out early in Eduardo's boat. There's an African Queen-style thrill to cruising between the jungled banks up the main channel. But the excitement – and wildlife – intensifies in the backwaters, where Eduardo cuts the engine to negotiate the weed-choked shallows by paddle. Sunbitterns pick warily along the shore, iguanas bask on overhanging branches and caimans are everywhere, their toothy snouts poking through the water hyacinth.
It is down one such channel that, on the first morning, a splash interrupts our meanderings. "Giant river otters," shouts Eduardo and swings the boat around. A head pops up, then another – and another. The animals eye us fearlessly, revealing whiskered muzzles, white bibs and ferocious canines. The world's largest otters, they can reach nearly two metres in length and are serious predators. Lobos del rio is the Spanish name: "river wolves".
For 20 minutes the otters – there are six in total – cavort around us, keeping up a refrain of chirrups, grunts and whistles. Our cameras can't keep pace as they bob up then roll under: one moment almost touchable, the next chomping on a fish 100 metres away. We're delighted: not only by the entertainment and rarity value, but also because they're the first of our Big Five.
The second comes unexpectedly as we are chugging back to camp in the midday heat. Four twitching ears turn out to be two Brazilian tapirs cooling off in the shallows. As we approach, their big, pig-like forms emerge from the water and walk up the bank on V C surprisingly delicate legs. The forest soon swallows them up – but not before we've clocked the stiff manes and mini-trunks that characterise South America's largest mammal.
Only one animal packs enough punch to consider a tapir fair game and we finally find the third member of our Big Five dozing on a riverbank. I catch my breath as the dappled shadows resolve through binoculars into the painted contours of a jaguar. He's a big male: all massive head and muscled shoulders, like a leopard on steroids. We cut the engine and drift closer. He seems untroubled by our presence – there's just a mildly irritated shift and twitch. But I feel a primal frisson when those implacable amber eyes bore into mine.
Eduardo remembers as a child hunting jaguars with his father. Today he's a conservation convert, and sets out to educate locals. "Always I tell Pantaneiros if they have one jaguar on their land to leave it alone," he explains. "If they kill it then others will come and eat their cattle." Besides, experience has shown Eduardo how tourism can trump ranching. "Binoculars," he grins, brandishing his own rather pricy pair, "are better than cowboys."
The sun is sinking by the time we turn towards camp. Eduardo swings into the current as the first fishing bats swoop and swerve across our bows. Behind us the river is dark and wild. South America's most powerful predator is surely safe here for a while yet.
Three down, two to go. But our prospects of completing the set are not looking good as our minibus crawls uphill into a pea-souper. We can hardly see the verge, let alone any passing wildlife.
It's two days later and we've left the Pantanal 1,000km to our west. This is now the Serra da Canastra National Park, perched on a plateau in Minas Gerais Province, where the Sao Francisco River is born as a trickling brook. Our guide, Regina Rebeiro, has explained how this rugged terrain is home to many specialised animals. How its high, rolling grasslands offer fabulous vistas over the surrounding plain. She never mentioned the mist.
I'm beginning to think we should give this up as a bad job. Return, perhaps, to our hotel in the quirky village of Sao Roque, whose residents must surely have developed Brazil's strongest thighs simply in order to walk the precipitously sloping cobbled streets.
But Regina's patience is rewarded as the mist begins to lift, and we soon spot the unmistakable outline of a giant anteater working a distant hillside. Number four in the bag. The park is thought to hold the world's densest population of this bizarre beast and we find half a dozen over the course of an hour – culminating in that memorable mother-and-baby close-up.
Just one left. And with the views now as panoramic as promised, we don't have long to wait. Regina spies something fox-red moving along the valley floor. Binoculars confirm that this is indeed a fox – but one apparently on stilts, and with a distinctly equine mane and tail. A maned wolf. We scramble from the vehicle just in time to see the strange, elegant animal disappear into the long grass. This animal – technically not a wolf but the world's tallest fox – is extremely rare. What's more, it's number five on our list. We've got the set.
And so, it seems, a well-planned search – with a little bit of luck thrown in – can bag you South America's Big Five in a single trip to Brazil. But ours would have been a memorable wildlife trip even had none of the holy quinity deigned to show up. Whatever your agenda, if it's simply a ruse to explore Brazil's extraordinary wildlife riches, you won't be disappointed.
Brazil's Big Five
* Giant anteater
The world's largest species of anteater is classified as "vulnerable" by the International Union for Conservation of Nature and Natural Resources (IUCN). Males can grow to 7ft long, including 3ft of tail. Its main predators are jaguars and cougars which the anteater can fight or even kill by standing on its hind legs and using its claws. Its main habitat is the rainforest and grasslands of Central and South America. It can eat up to 30,000 ants or termites in a day.
* Giant river otter
The largest member of the mustelid (weasel) family is classed as "endangered" by the IUCN. Males can grow to be over 6ft long. The otters are often hunted for their pelt. They also face dangers from the loss of freshwater habitat in north-central South America.
Classified as "near threatened" by the IUCN, the jaguar is the world's third largest feline after the tiger and lion. It can be found from Mexico to Paraguay. Males can grow to 8ft long including a 2ft tail. The jaguar mainly hunts large mammals such as deer, and sometimes cattle, using its strength to haul its prey into trees out of danger. Unusually for a cat, it is at home in the water.
The Brazilian Tapir – a herbivore found near water in the Amazon rainforest and river basin – is the largest wild land animal in South America and is classified as "vulnerable" by the IUCN. Males can grow to be over 8ft long. Their main predators are jaguars. They are deceptively quick on land, and are excellent swimmers and divers.
* Maned wolf
The maned wolf is in fact a large fox and the largest canine in South America. It is classified by the IUCN as "near threatened". Mainly found in southern Brazil and northern Argentina it is unusual among its type as it does not form packs, instead hunting alone. It can be up to 1m tall and has been called a "red fox on stilts".
By Peter Harmer
Travel essentials: Brazil
* British Airways (0844 493 0787; britishairways.com ) and TAM Airlines (020-8897 0005; tamairlines.com ) fly direct from Heathrow to Sao Paulo. TAM offers multi-trip air passes to Alta Floresta (Cristalino), Cuiaba (northern Pantanal) and Belo Horizonte (Serra da Canastra).
* Similar tours, including transport, activities and guide, are available from Wildlife Trails (0844 686 5532; wildlifetrails.co.uk ) and other leading wildlife tour companies. Independent travellers can explore the northern Pantanal and Serra da Canastra using self-drive, but access to Cristalino is by the lodge's boat only.
* Regina Rebeiro ( email@example.com) is an English-speaking guide who organises wildlife tours in Brazil and South America.
* Cristalino Jungle Lodge, Alta Floresta, Mato Grosso (00 55 66 3521 1396; cristalinolodge.com.br ). Doubles start at US$340 (£227), full board with transfers from Alta Floresta and activities.
* Pousada Araras Eco Lodge, near Cuiaba, Pantanal, Mato Grosso (00 55 65 3682 2800; araraslodge.com.br ). Doubles start at US$572 (£381), full board with activities.
* Jaguar Ecological Reserve, Km110 Transpantaneira, Pantanal, Mato Grosso (00 55 65 3646 9679; jaguarreserve.com ). Doubles start at US$500 (£334), full board inc activities.
* Hotel Porto Jofre, Av Sao Sebastiao 357, Cidade Alta, Cuiaba, Mato Grosso (00 55 65 3637 1593; portojofre.com.br ).
* Hotel Chapadão Canastra, Sao Roque de Minas, Minas Gerais (00 55 37 3433 1267; canastra.com.br/hospedagem/chapadao ). Doubles start at £14, incl breakfast.
Brazilian Tourist Office: 020-7396 5551; braziltour.com