Indonesia: The twilight screaming

New Guinea, the final frontier, where a man will eat another's brains and great cassowaries stalk the jungle deeps

Even now, decent maps of Irian Jaya, the Indonesian half of the large island of New Guinea, just north of Australia - the other half is the independent Papua New Guinea - show areas the size of London without any relief data: just pristine jungle and tangled alluvial mangrove swamps that have never borne the imprint of a shoe.

For travellers seeking to relive the days of Livingstone and Cook, Irian Jaya is the final frontier in an ever-shrinking world. In 1996, emissaries from two unheard-of tribes speaking unknown languages emerged from the jungles of the south to inspect the new way of life that had impinged upon their world. One tribe began its first tentative steps on what will undoubtedly be a terrifying familiarisation process: the other slipped back into the jungle and has not been heard of since. Missionaries in the interior still state categorically that there are areas - only days from their own stations - where headhunting and ceremonial cannibalism are still practised, and where Westerners have never, and probably should never, venture.

Which is not to say that a slightly intrepid backpacker cannot explore parts of Irian Jaya today in safety. My trip into the rain forest began in the southern town of Merauke, a dusty mess of wire mesh- fronted stores and parched red savannah, more like an Outback sheep station in Oz than an Indonesian military post. From here, an eight-seater plane flew me over some of the most inhospitable wildernesses left in the world. I flew for an hour looking down on nothing but lightly undulating oceans of jungle through which cut vast, meandering brown rivers - and saw not a glimmer of life.

Once I landed, however, it was a completely different story. A few hours from the grass air strip in a dugout canoe, and nervous crocodiles were ducking beneath the surface at our approach, as streaks of colour in the forest told of fabulous birds, and reptiles dangled from mossy boughs. Before us in the river, a skinny periscope with a beak popped out of the water to survey us, before a body and then wings emerged from beneath the surface; then the "snake-necked bird" rose from the water with ponderous sweeps of its vast wings.

I was pushing up river to visit the Korowai peoples, a remote band of clans who live in treehouses some 20 metres up in the forest canopy and who, in some places, remain cannibals. The most practical river transport is a motorised canoe, but on my own I couldn't afford the fuel prices, and the freak droughts that had struck parts of New Guinea meant that many rivers were impassable to engined boats. So I was stuck with paddle power - even though it meant a five-day trip and sleeping rough in the jungle - just to get to the village closest to the Korowai.

However exciting a trip into the jungle of the Asmat region may sound, it should not be undertaken lightly. It bears no resemblance to travel in any other part of Indonesia. There is no tourist infrastructure; transport is dangerous and expensive; and, unless you sell off a kidney for finance, you will see nothing at all. All the best-laid plans could disintegrate, leaving your planned year's tour stuck up the Siretsj river without a paddle.

As I journeyed upstream with my crew of muscular Irianese paddlers at late dusk, one of the most incredible natural noises I have ever heard soared above the wall of trees lining the river. A high-pitched scream surged past me along the riverbank in a Mexican wave, before haring back again like an ethereal police siren. In fact this unearthly noise is made by hundreds of thousands of male cicadas in the trees - timed to the nearest minute to coincide with the fall of dusk.

But while the cicadas were providing the joy, some of their less decorative cousins were contriving to make this one of the most uncomfortable places I had ever visited. In the mangrove swamps, I slopped on an insect repellent that (honestly) melted plastic; slept under a mosquito net fully clothed; took the anti-malarial drug Lariam (so strong it gave me paranoid hallucinations), and was still, it appeared, main course for a million blood-sucking midges. At the same time leeches and ticks hung off me like soggy earrings, and bugs the size of dachshunds haunted the inside of my sleeping bag.

Putting these minor anxieties aside, I decided to concentrate on the meaning of the name Asmat. The most probable theory is "tree people", from the connection of the word Os (tree) and amot (man).

In fact the Asmat's affinity with the trees and the jungle is absolute: many inland tribes live their entire lives in the treetops. Trees are even seen as representing people, with the roots as feet and the fruit the human head. Just as a tree must lose its fruit in order to germinate a new tree, so Asmat warriors must take the heads of their enemies to ensure new life is born.

Enemy's brains pass on the powers of their owner to the consumer and an ancestor's decorated skull is a protective talisman. Headhunting was, and in some remote places still is, an integral part of Asmat life, and, though some tribes may wait several years between raids, a crop of enemy deaths is essential for the Asmat to maintain their equilibrium with their ancestors' and the environment's spirits. In 1961 when Michael Clark Rockefeller went missing in the Asmat jungles, it was thought that he had fallen foul of this same ideology - lightly sauteed so that the white tribes' power could be ingested by Asmat warriors.

In a dark communal longhouse, wreathed in smoke to deter the mozzies, I sat watching groups of naked artists carving extraordinary sculptures of tangled limbs and cavorting figures by firelight. My guide was an Indonesian- speaking Asmat, with the physique of a prize-fighter and a carved nautilus shell pushed through his nose to give him the intimidating appearance of a wild boar: it worked. He carried the decorated skull of a legendary ancestor around with him, which he used as a pillow to ward off evil spirits. Personally I prefer duckdown.

I tried to understand his explanations of the days of headhunting and the sexual flamboyance of some of their ritual events, many of which still survive today. In rites-of-passage festivals, boys are inseminated by all of the village elders before they are considered to be men. Headhunting raids are followed by huge feasts, where orgies and wife-swapping are de rigueur. Then - after a head-hunter has smashed his enemy's dead skull with an axe to spoon out and eat the brains - the killer sucks on the corpse's penis. Both of these processes are believed to transport the power and spirit of the dead man into the person who consumes him.

In the contemporary world, such traditional rituals sit surprisingly comfortably with adopted Christian practices (consuming the "body of Christ" at communion, for example). Communities that may have lost contact with missionaries have simply incorporated Christian rites into their own beliefs. Just as eating sago grubs is sometimes substituted for eating an enemy's brains (which resemble the puffy, wrinkled white larvae), taking the eucharist is easily accepted as a "symbolic" ingestion of God's spirit.

Paddling back down the muddy river, and a flash of green iridescent feathers passed in a bouncing flight mere metres from our canoe. My guide got wildly excited and scrabbled around for his spear, rocking the flimsy dugout and threatening to plunge us all into the mud. "Bird of paradise," he told me, but it was already gone. I never got to see the legendary cassowary [up to 5ft tall and a relative of the emu] either, at least not in the wild. These huge flightless birds - one of the largest creatures in New Guinea - have ugly, electric blue heads, turkey throats and claws that can tear a man to pieces.

Another of the most extraordinary sights of the riverside is one of the least often seen, as it only occurs at night when most jungle paddlers are safely tucked up under leaking tarpaulins. Drifting along in the pitch black, it can suddenly seem that the banks have been lined with Christmas trees, draped with dense curtains of blinking fairy lights. They cast dramatic flickering shadows over the tangles of the forest canopy, like the bridge scene in Apocalypse Now. It is only when you get up really close that the cause of the glow - so powerful you can read a map or a book by it - becomes clear: billions of fireflies are lighting up the jungle.

Traveller's Guide

Getting there: The main gateways to Irian Jaya are Jakarta and Bali. The only flights from the UK to Jakarta are twice-weekly on British Airways from Heathrow, but this ends in October. To Denpaser, Bali's main airport, Indonesia's Garuda International has three flights a week from Gatwick. Outside peak season, expect to pay about pounds 500 return through a discount agent.

There are several entry points to Irian Jaya: for visiting the south the best is Timika.

Getting around: Travellers need a surat jalan or travel permit, available in major cities for a small fee. The haze from fires that has covered some parts of Indonesia should not affect visitors to Irian Jaya.

Where to stay: Accommodation ranges from hotel rooms for a dollar or so a night, to an unexpected five-star Sheraton in Timika (00 62-90l-39 4949, e-mail: Sheraton-reservation@ fmi.com)

Further information: The author is also co-author of the brand new Rough Guide to Indonesia (pounds 15.99); for browsing try www.roughguides.com/travel