I'm fortunate to have travelled widely: to have held and tasted the rich damp air of Brazil's tropical forests in my mouth and lungs; to have caught my breath on the very edge of a Himalayan gorge, balanced for a moment between the sky and the earth; to have felt small and immaterial and utterly relaxed amongst the red stones and the emptiness of the South African karoo. Very fortunate: travelling brings experiences, and experiences can change your life.

At Saemangeum though, on Korea's west coast, things weren't going so well, and I didn't feel fortunate at all. I was hungry and I was tired. The sun was in my eyes. A strong breeze was tugging hard at my camera. And the birds we'd come to see were a distant, indistinct dark line, an abstract, a smudged layer between the indistinct grey of the mud and the indistinct haze of a burnt-out sky. Somewhere out there, I'd been promised, were birds I'd grown up wanting to see: amongst the Great Knots and the Godwits, the Dunlins and the Curlews, were both Spoon-billed Sandpipers and Nordmann's Greenshanks. And right now, "out there" was a very long way off.

I'd travelled a long way for this, to film for a video we were making to promote Korea and the importance of its wetlands. I'd been to wetlands - diamond points of light scattered on blue water, ullulating reedbeds and clouds of swallows, willowherb and glistening demoiselles, the scent of peaty soils and and natural decay - but this wasn't like that at all: it was barren, it was almost colourless, it was muddy. It smelt of dessicated sea-grass. I was sitting on a sea-wall waiting for the spring's highest tide at the single most important staging site for migrant shorebirds in the whole of the Yellow Sea, but the sun was in my eyes, the breeze was tugging hard, I was hungry, and, in truth, I was feeling miserable.

Listening to my brother Nial, as he listed the data, told the story of his coming here for the first time and seeing just staggering numbers of birds, I couldn't feel what he evidently did. Try as I might, the mud just would not resolve itself into a complex eco-system. I could see the trails left by an almost infinite weight of crabs and shellfish, see the round, small puddles formed by rising polycheate worms, but what I wanted to see was a Spoon-billed Sandpiper, to film its spatulate, ridiculous bill, to get close to an almost mythical bird I'd missed in Hong Kong and couldn't find at Thailand's Samut Sakhon salt-pans, had heard Nial talk about so many times: and I wanted it very badly indeed.

As the incoming tide spilt across the mud, as the indistinct line of birds began to separate into identifiable flocks and groups, as his stories turned to the sea-wall being built this very minute across the mouth of this massive estuary, of the men and the politics, of the failure of environmental groups to work together, I found myself getting more frantic - if I missed it this time, when would I get another chance? How would our video look without a Spoon-billed Sandpiper? How could I come all this way….

Nial had been staring hard through his scope while I'd been focussing on how bad things were going to be if I missed this most-important bird again, when I realised that the tide was now pouring across the mud in front of us - surging unnaturally through the narrowing neck of the sea-wall and the land it was stretching out towards - and pushing literally thousands of birds towards the embankment we were sat on. Groups and groups of Great Knot landed and rose again seconds later as the water soaked into mud that had been dry just moments before, and the air was filling with the clipped calls of Black-tailed Godwits and Common Greenshanks. Just behind the smaller, shorter-legged shorebirds, Far Eastern Curlews waded through the bursts of sunlight and shallow waves, probing with improbably long bills beneath the water.

From across this now vast expanse of sea, wisps of smoke were transforming into lines of Dunlin, driven by the rising water off mud-flats now submerged, from somewhere "out there" too distant for us to have even seen from where we were sat. Thousands upon thousands of birds, all heading towards our patch of mud, one of the last to be washed over, heading towards the point where my brother had first come some five years ago and been staggered by the richness of Saemangeum, heading towards the point that literally since the last Ice Age, tired, hungry, birds had been finding food and shelter as they battled north towards the Arctic summer or south towards the flats or beaches of south Asia and Australia….

I was suddenly struck that this, this was what I needed to be filming: these epic lines of birds that seemed at that moment to be carrying the essence of wilderness in their bodies, this convergence of ancient cycles and the modern world Nial and I belonged to, the seemingly desolate mud-flats being filled to the brim with life. They'd arrived at this point in front of me on their way to gravelled river banks in northern Russia, to taiga and tundra, to a sun that would hardly set for months; and some, increasingly, to a summer spent endlessly searching for one another amongst clouds of mosquitoes as fewer and fewer individuals are spread ever thinner across the massive land they once populated….

When Nial suddenly called, "Spoon-billed Sandpipers", I was already filming, trying hard to capture a "feeling", a passion that I'd not felt for an age. Finding them was hard as they were jostled and shoved by larger birds all competing for the same, dwindling dry patches of slightly higher ground - but then, there they were: smaller than I'd expected, rare, declining, incredible, from so far away, going to places I couldn't pronounce, fragile, beautiful, so much relief, right there…

…and then they were gone, as with a final push the sea claimed the last of the dry land and in a blur of wings and shapes the entire huge flock, Spoon-billed Sandpipers, Great Knots, Godwits, Greenshanks, some 20 or more species, lifted up into a blinding sky and flew inland to find somewhere safe to roost. I've never felt so privileged in my life.

I am fortunate indeed to have travelled. But…I've tasted the air in forests that are no longer there, I've hung in the crystalline sky above a gorge that now has traffic killing it, walked in fields that are now housing estates…and I've sat and watched the arctic north sweeping over a mud-flat in Korea that very soon will be dead. I wrote this because I was asked, "Why Korea?". In a very short time the sea-gates at Saemangeum will close, as they have in so many other sites across China, Korea, and Japan. We will have interfered yet again in a world we seem hell-bent on destroying. I will become one of the last people on Earth to have seen a party of Spoon-billed Sandpipers feeding amongst 40,000 Great Knots. And to know that and then do nothing is simply not good enough…not good enough, at all.

This article also appears on the Surfbirds website.