Richard Lewis is a man who has worked out a foolproof way of getting snappy answers to his questions.

He drives his Landrover (well, not actually his Landrover, but the Landrover of anyone foolhardy enough to lend him one) with what can only be described as pizzazz along Mauritian roads that were built with something less than pizzazz in mind. The roads are often narrow and windy, and where they are tarmacked, the Tarmac tends to finish with an abrupt six-inch drop at the edge. Richard drives along these with a pizzazz that borders dangerously on élan, and when he asks you a question he turns and looks at you and doesn't look back at the road again until you've answered. Mortal terror is not the best state of mind in which to try and frame intelligent answers, but you have to try.

We had managed OK with `How was the flight? (`Fine!') and 'How was the meal? (`Fine!') and 'Feeling jet-lagged? (°We're fine!'), but then we got to what he clearly regarded as being the crunch, so to speak

`Why are you coming all the way to Mauritius to look for some crappy old fruitbat? The Landrover veered frighteningly.

One of the first things you need to know about Richard Lewis, indeed the thing you need to know about him, is that he's an ornithologist. Once you know that, everything else more or less falls into place.

'I just couldn't figure it out,' he protested, twisted half round in his seat to harangue us. `You're going to Rodrigues? To look for a fruitbat? It's not even particularly rare.'

`Well, it's all relative,' protested Mark. 'It may not be particularly rare by Mauritian standards, but it is the rarest fruitbat in the...'

`Why don't you stay here on Mauritius for heaven's sake?'

`Well...'

`What do you know about Mauritius? Anything?'

`Well,' I said, `I know that... er, there's a lorry coming...'

`Never mind about that. I'll take care of the lorries. What do you know about Mauritius?

`I know that it was originally colonised by the Dutch, and when they left it was taken over by the French who lost it to Britain after the Napoleonic Wars. So it's an ex-British colony, part of the Commonwealth. The inhabitants speak French or Creole. The law is basically English and you're, er, supposed to drive on the left...'

`All right, you've read the guide book. But do you know about the birds here? Don't you know about the pink pigeon? The echo parakeet? Don't you know about the Mauritius kestrel?'

'Yes, but...'

`Then why are you going off to the stupid island of Rodrigues to look for some ridiculous fruitbat? We've got a bunch of them here at the captive breeding centre if you really want to see one. Common as muck, stupid things. You'd be much better off staying here and seeing some real stuff. Jesus!'

He had suddenly caught an inadvertent glimpse of the road ahead of us and had to yank hard on the steering wheel to avoid an oncoming truck.

Tell you what,' he said, turning round again. `How long have you got? Two weeks??

'Yes,' said Mark hurriedly.

`And you were planning to spend two days here and then fly to Rodrigues to spend, what, ten days, searching for the world's rarest fruitbat?'

`Yes.'

'OK. Here's what you do instead. You stay here for ten days, and then go off to Rodrigues for two days. Right?

`Will we find it in two days?'

Yes.'

`How do you know??

'Because I'll tell you exactly where to find it. Take you ten minutes. Take a couple of photos, go home.'

Oh.

'So you're staying here, right??

'Er...'

We were swaying erratically along, more or less in the middle of the road. Another truck hove into sight ahead of us, frantically flashing its lights. Richard was still looking round at us.

`Agreed?' he insisted. `You'll stay?'

'Yes! Yes! We'll stay!'

`Right. Good. I should think so too. You'll get to meet Carl then as well. He's brilliant, but completely mad. Jesus!'

The brilliant but completely, mad. Carl Jones is a tall Welshman in his late thirties, and there are those who say of him that his sheer perverse bloody-mindedness is the major thing that stands in the way of the almost total destruction of the ecology of Mauritius . It was Carl that Mark had contacted to make the arrangements for our trip, and it had been quite apparent from the first moment that we set foot on Mauritius that he was a man to contend with. When we told the immigration official at the airport that we would be staying `with someone called Carl Jones at somewhere called Black River ,' it had produced the unexpected and unnerving response of hysterical laughter, and also a friendly pat on the back.

When Carl met us at Richard's house, he greeted us with a scowl, leant in the doorframe, and growled, 'I hate media people.' Then he noticed our tape recorder and suddenly grinned impishly.

`Oh! Is that on? he asked.

`Not at the moment.'

`Turn it on, quick, turn it on!'

We turned it on.

`I really hate media people!' he boomed at it. `Did you get that? Do you think it'll come out all right?'

He peered at the recorder to make sure the tape really was running.

`You know I once did an interview for Woman's Hour on the radio,' he said, shaking his head in wonderment at the folly of a malign and silly world. `I hate media people, they take up all my time and don't pay me very much - but anyway... the interviewer said to me that he was sick of boring scientists and could I tell him about my work but be sure to mention women and babies. So I told him that I preferred women field assistants to men, that we reared lots of baby birds, and that women were better at looking after baby birds because they were more sensitive and all that. And it went out!'

This rendered him speechless with laughter and he tottered helplessly out of the room and was not seen again for hours.

'That was Carl,' said Richard. `He's great. He's really brilliant. Honestly. Don't worry about him being a complete sod.'

We quickly discovered that we had fallen in with a bunch of passionately obsessed people. The first obsession for Carl and for Richard was birds. They loved them with an extraordinary fervour, and had devoted their entire adult lives to working in the field, often in awful conditions and on horribly low budgets, to save rare birds, and the environments they live in, from extinction. Richard had trained in the Philippines , working to save the Philippines monkey-eating eagle, a wildly improbable looking piece of flying hardware that you would more readily expect to see coming in to land on an aircraft carrier than nesting in a tree. From there he had, in 1985, come to Mauritius , where the entire ecology of an island formerly famous for its abundant beauty is in desperate trouble.

They work with a manic energy that is disconcerting for a while until you begin to appreciate the enormity of the problems facing them, and the speed with which those problems are escalating. Ecologically speaking, Mauritius is a war zone and Carl, Richard and others - including Wendy Strahm, an equally obsessed botanist - are like surgeons working just behind the front line. They are immensely kind people, often exhausted by the demands that their caring makes on them. Their impatience often erupts into a kind of wild black humour because, faced with so much that is absolutely critical, they can't afford the time for anything that is merely very, very urgent.

The focus of their work is Carl's captive breeding centre in the village of Black River , and Richard took us along to see it the next day.