It has a large, wide, downturned bill of yellow and green, which gives it a slightly glum and melancholic look, small, round eyes like diamonds, and three ridiculously little plumes sticking out of its tail. One of the first Englishmen to see this large dove said that 'for shape and rareness it might antagonise the Phoenix of Arabia'.

None of us will ever see this bird, though, because, sadly, the last one was clubbed to death by Dutch colonists in about 1680.

The giant tortoises were eaten to extinction because the early sailors regarded them much as we regard canned food. They just picked them off the beach and put them on their ships as ballast, and then, if they felt hungry they'd go down to the hold, pull one up, kill it and eat it.

But the large, gentle dove - the dodo - was just clubbed to death for the sport of it. And that is what Mauritius is most famous for: the extinction of the dodo.

There had been extinctions before, but this was a particularly remarkable animal, and it only lived in the naturally limited area of the island of Mauritius . There were, very clearly and obviously, no more of them. And since only dodos could make a new dodo, there never would be any more of them ever again. The facts were very clearly and starkly delineated for us by the boundaries of the island.

Up until that point it hadn't really clicked with man that an animal could just cease to exist. It was as if we hadn't realised that if we kill something, it simply won't be there any more. Ever. As a result of the extinction of the dodo we are sadder and wiser.

We finally made it to Rodrigues, a small island dependency of Mauritius, to look for the world's rarest fruitbat, but first of all we went to look at something that Wendy Strahm was very keen for us to see - so much so that she rearranged her regular Rodrigues-visiting schedule to take us there herself.

By the side of a hot and dusty road there was a single small bushy tree that looked as if it had been put in a concentration camp.

The plant was a kind of wild coffee called Ramus mania, and it had been believed to be totally extinct. Then, in 1981, a teacher from Mauritius called Raymond Aquis was teaching at a school in Rodrigues and gave his class pictures of about ten plants that were thought to be extinct on Mauritius .

One of the children put up his hand and said, 'Please, sir, we've got this growing in our back garden.'

At first it was hard to believe, but they took a branch of it and sent it to Kew where it was identified. It was wild coffee.

The plant was standing by the side of the road, right by the traffic and in considerable danger because any plant in Rodrigues is considered fair game for firewood. So they put a fence round it to stop it being cut down.

Immediately they did this, however, people started thinking, 'Aha, this is a special plant,' and they climbed over the fence and started to take off little branches and leaves and pieces of bark. Because the tree was obviously special, everybody wanted a piece of it and started to ascribe remarkable properties to it - it would cure hangovers and gonorrhoea. Since not much goes on in Rodrigues other than home entertainments it quickly became a very sought-after plant, and it was rapidly being killed by having bits cut off it.

The first fence was soon rendered useless and a barbed wire fence was put around that. Then another barbed wire fence had to be put around the first barbed wire fence, and then a third barbed wire fence had to be put around the second till the whole compound covered a half acre. Then a guard was installed to watch the plant as well.

With cuttings from this one plant Kew Gardens is currently trying to root and cultivate two new plants, in the hope that it might then be possible to reintroduce them into the wild. Until they succeed, this single plant standing within its barbed wire barricades will be the only representative of its species on earth, and it will continue to need protecting from everyone who is prepared to kill it in order to have a small piece. It's easy to think that as a result of the extinction of the dodo we are now sadder and wiser, but there's a lot of evidence to suggest that we are merely sadder and better informed.

At dusk that day we stood by the side of another road, where we had been told we would have a good view, and watched as the world's rarest fruitbats left their roost in the forest and flapped across the darkening sky to make their nightly forage among the fruit trees.

The bats are doing just fine. There are hundreds of them.

I have a terrible feeling that we are in trouble.

There's a story I heard when I was young which bothered me because I couldn't understand it. It was many years before I discovered it to be the story of the Sybilline books. By that time all the details of the story had rewritten themselves in my mind, but the essentials were still the same. After a year of exploring some of the endangered environments of the world I think I finally understand it.

It concerns an ancient city - it doesn't matter where it was or what it was called - it was a thriving, prosperous city set in the middle of a large plain. One summer, while the people of the city were busy thriving and prospering away, a strange old beggar woman arrived at the gates carrying twelve large books, which she offered to sell to them. She said that the books contained all the knowledge and all the wisdom of the world, and that she would let the city have all twelve of them in return for a single sack of gold.

The people of the city thought this was a very funny idea. They said she obviously had no conception of the value of gold and that probably the best thing was for her to go away again.

This she agreed to do, but first, she said, she was going to destroy half of the books in front of them. She built a small bonfire, burnt six of the books of all knowledge and all wisdom in the sight of the people of the city and then went on her way.

Winter came and went, a hard winter, but the city just about managed to flourish through it and then, the following summer the old woman was back.

'Oh, you again,' said the people of the city. 'How's the knowledge and wisdom going??

'Six books,' she said, `just six left. Half of all the knowledge and wisdom in the world. Once again I am offering to sell them to you.'

'Oh yes?' sniggered the people of the city.

`Only the price has changed.'

`Not surprised.'

`Two sacks of gold.'

'What?

'Two sacks of gold for the six remaining books of knowledge and wisdom. Take it or leave it.'

'It seems to us,' said the people of the city, `that you can't be very wise or knowledgeable yourself or you would realise that you can't just go around quadrupling an already outrageous price in a buyer's market. If that's the sort of knowledge and wisdom you're peddling then, frankly, you can keep it at any price.'

'Do you want them or not?'

No.

`very well. I will trouble you for a little firewood.'

She built another bonfire, and burnt three of the remaining books in front of them and then set off back across the plain.

That night one or two curious people from the city sneaked out and sifted through the embers to see if they could salvage the odd page or two, but the fire had burnt very thoroughly and the old woman had raked the ashes. There was nothing.