CHARLIE Bird gets down on his haunches and sticks his head inside his tent for a preentry inspection. Startled, he suddenly swears and exclaims that "something big got in." He calls one of the guides for assistance.

"Can you pick him up?"

"No."

"Would he sting you?"

"Yes."

"Oh, this is real. This isn't fun.

Bollocks."

The tent, a fancy name for a mosquito net suspended off some branches, is eventually cleared of invaders and Charlie settles in to try and catch some shut-eye in an area where anacondas are known to sleep, while all through the night various detritus from the forest ceiling and who knows what else disturb the thin sheet separating him from the outside and very unknown world. Welcome to the jungle Charlie.

Not that he has anyone other than himself to blame. It was Bird's idea to trace the 6,500km journey of the Amazon from its source, 5,500m above sea level at Mount Mismi in the Peruvian Andes, down to where it meets the Atlantic ocean in Brazil, right on the equator. Even given his 20 years travelling the world as a news reporter for RTE, this is an epic journey through one of the least explored areas on the planet, and at various points during the documentary you can see Bird pondering if he's bitten off more than he can chew.

"I'm an ordinary type of outdoors person, but not to these extremes, " explains Bird. "I'd do a bit of hill walking and the like, but I hadn't done any mountain climbing or anything as extreme as this." Even the starting point for the journey proved to be a challenge. The source of the Amazon is located on a peak higher than any in Europe, and while it can be trekked to, at that height the air becomes so thin it's difficult to breathe.

"Getting used to the altitude is the hard part. I suffered really bad altitude sickness. I did panic a bit and when we got to the last 100 yards, I said I just can't f***ing go on. It's hard to explain altitude sickness, it clears up quickly when you come back down but at the time my head was pounding and my heart was racing and I felt so ill, I just wanted to lie down and curl up. It got down to minus 15 when we were camping on the mountain during the night and I found myself doubting the wisdom of the project at that stage." But find the source they did. Where the Amazon reaches the ocean the river mouth is 270km wide, but the starting point is just a small glacial stream, little more than a trickle out from the rocks. From small acorns and all that.

And so it was with this project.

Having done an episode of Wild Trials with the Crossing the Line production team Bird joined up with them again for his South American expedition, specifically the sister-brother partnership of director Kim and cameraman Ross Bartley. There's a slightly masochistic pleasure to the programme as the harsh conditions fray some of Bird's edges and he freely admits at one point that were the option available to him he would jump on the first plane and be gone home. Backpacker culture is so strong in Ireland that travellers are well accustomed to relaying their stories of far-off climates, editing their tales to accentuate the positives and either completely ignoring the low-points or sweetening them with the sugar of hindsight. But few people venture into the harshness of the Amazon jungle, and Bird has a camera in his face constantly to record the various lows. It's to his and the production team's credit that these moments of tetchiness are left in alongside the highs.

At the river's first navigable point, Pongo de Mainique, Bird starts to travel downstream in what is little more than a canoe. A set of rapids that guard the Amazon basin give some fraught moments before they are officially in the largest rainforest on earth.

After that, Bird is entirely in the hands of his local guides and it was an uncomfortable experience for someone who prefers to be in control.

"I was scared. Well, apprehensive, " admits Bird. "Because people keep telling you about scorpions and snakes and bugs that bite and this and that. We were in the jungle. Our guides were native people who've lived there all their lives, members of the Cocama tribe, a hundred years ago they wouldn't have had clothes on, and they were brilliant people to be with but we were totally dependent on them."

More at home in the rainforest was cameraman Ross Bartley, having worked there previously, and his loving eye is evident in the stunning scenery and wildlife he captures, which would sit easily beside the best of the BBC's nature films.

"I loved the jungle, I could have spent ages there. In Peru we had time to go trekking in the jungle and go down small tributaries on boats and the like. It was so atmospheric and the sounds were so incredible, it's just such an alien world for us."

It's an alien world that's fast disappearing, and no journey through the region could be undertaken without becoming aware of this.

The rate of deforestation is accelerating, where previously the loggers moved in first, followed by cattle ranchers and finally soya farmers, the influx of large corporations intent on exporting soya to China means that these middle stages are now even being skipped. A flight over the area in a small plane rammed this point home to Bartley.

"Nothing could have prepared us for the scale of the devastation, it was mind-boggling, as far as you could see to the horizon. And because of the season the soya had only grown a few centimetres off the ground so you go straight from having a 40-foot high canopy to just bare earth." This soil is quickly dried out to useless dust, a staggering transformation for one of the richest ecological areas on the planet.

The further Bird and his crew travel the closer they get to civilisation, including the wonderfully anachronistic Manaos, a modern city of two million people that looks like it was built elsewhere and then dropped in the middle of the jungle, where the suburbs are rainforest but they have an ornate opera house. And as the river meanders it widens out to become like a highway, with traffic levels that befit the description. "At some points it's 10 and 15km wide and you feel like you're in the ocean because you can't even see the banks, " says Bird. "In one way you could spend a whole series doing the Amazon and not do it justice, but we just took one glimpse, one journey. We're not pretending that we're telling you the life of the Amazon or the whole history of it, but it gives a great flavour to it."

And despite the trials of bizarre food, numbing colds, oppressive heat and medicine poured, rather worryingly, directly from a newlysevered branch, the highs easily outweighed the lows and simply whetted Bird's appetite for more.

"I loved the experience and would love to do something like this again if the programme is a success.

Crossing the Line have expertise in working in both the North and South Pole. I'm interested in Greenland and have half a notion of doing a trek to the South Pole, but I want to walk before I leap. I'd like to build on this experience."

'Charlie Bird Explores . . . The Amazon' airs on Thursday, 4 January, RTE 1, 21.30