I can't tell you how weird this feels. Because I might have seen an extinct bird. Imagine that: a bird I saw on a jaunt a dozen years ago: and gone. As in never to be seen again. As in a cul-de-sac of evolution. As in a measurable diminishment of the biodiversity of the planet.

I was there, in Morocco, peering through my bins at this neat and stylish wader, as it picked its way fastidiously through a pretty field of cresses in fetching pastel shades. It was a rare bird then: it is now unquestionably Europe's rarest. It might be so rare it has gone altogether: and so they have organised an expedition to find the slender-billed curlew.

It doesn't feel right. I really don't feel happy about the possibility that I have seen a bird that is now extinct. Well, it is not right that any one should, but since it's me that saw it, on a brief but rather dazzling trip, the whole thing has become oddly personal. I feel almost guilty: as if I shouldn't have seen it, as if my viewing of it somehow contributed to its downfall.

There have been no confirmed records of this bird since 1999. If it has gone, it will be the first extinction of a European bird since the Canary Islands oystercatcher went in 1981. Everything about the slender-billed curlew is strange and difficult: it really is a bird of mystery. For a start, no one has ever managed to find out where it breeds. You can't begin to protect nesting sites if you don't know where the nests are. It's probably somewhere in Siberia: well, that doesn't narrow the field much,

The slender-billed curlew is similar to the curlew that lives here, but is altogether daintier, and with a much funkier lifestyle. It is one of those perplexing birds that migrates sideways, instead of up and down. It breeds on its mysterious Siberian fastness and winters in North Africa and the Middle East, crossing Central and Eastern Europe on the way.

It was actually pretty abundant in the 19th century, but has declined catastrophically, and no one knows why. It has always lived in mystery and obscurity, and it might already have died out in the same way. That singleton, in the marshes of Morocco, was one of the last slender-billed curlews ever seen. I don't feel privileged: I feel really rather horrible. Birding is a celebration of life: I don't feel happy celebrating death though binoculars.

Last-chance search

Birdlife, the RSPB and other partners are launching what looks a lot like a last-chance search for the slender-billed curlew. It is not hopeless: it is far from unknown for birds to turn up after a long absence: and after all, if you try and work out how many serious birding expeditions have been operated in Iraq and Iran in recent years, you will understand that there could be viable numbers still hanging about.

The bird is also quite difficult to identify: hard to tell from a non-slender-billed curlew if they are not standing side by side. The bird also has a taste for remote places: you're not going to bump into one on the way to the supermarket.

The first step is to find out if the slender-billed curlew still exists: and after that, to try to make sure it doesn't stop existing. If the birds can be found, the next priority is to try to find their breeding grounds, and discover whether there is a problem there. Radio-tracking devices are now light enough to be carried by a slender-billed curlew without discomfort: it is possible that the key to the mystery and the answer to the bird's survival is already in our hands.

But it may be already gone: another strand in the web of diversity snapped, subtly weakening the structure on which we all depend. There is a cartoon by Charles Addams in which the Ark is sailing away from a mountain top on which two sad unicorns stand, gazing forlornly at the vanishing vessel. I feel as if I have made a guest appearance in that cartoon.

Look, it's a miracle

The wild world is a place of infinite generosity and it will always reward and even console and comfort those who have acquired the knack of looking. I was leaving a wild and remote riverside Suffolk pub as the sun vanished, and the air was in an instant filled with brent geese.

These are small black geese picked out with flashes of white, and when they are on their wintering grounds they love to be together. And so, like a sublime conjuring trick, a thousand or so brent geese appeared, became solid, took to the air and filled it with their honking chatter: a sudden and majestic demonstration of the extraordinary possibilities of life.

I had guests, up from London, and they were entranced, never seen anything like it. But then people tend to see stuff when they are out with me, because I look, and, at least to an extent, I know what I'm looking at. I can produce miracles in between lunch and tea.

Times Recommends

• Treat Africans as part of the human jigsaw
• Too bitter a pill for me to swallow
• This Bill is a panic measure in a tarnished age