I make some lame remark along these lines. Mark frowns at me and a cloudy look comes into Don's face.

'Oh no,' says Don, 'I wasn't expecting an egg. Not an egg. Not here. Oh no, not at all.'

`Oh,' I say, `I 'thought when you picked up the potato...'

Mark says out of the corner of his mouth, `Don explained all this in the helicopter.'

'I couldn't hear anything in the helicopter.'

`You won't find eggs in a track and bowl system, you see,' says Don, patiently. 'It's just the courtship and mating area. I put the sweet potato there myself when I last came up here, last year. If there was a kakapo in the area it would have eaten the potato.' He picks it up again and hands it to me.

`There you see, not a mark on it. Not a nibble. And it would have trimmed and tidied its booming bowl. They are very meticulous birds. We don't know what has happened to the last one here. It may have been killed, possibly by a cat. We think they sometimes can come up this high. Fiordland is full of cats, which is bad news for the kakapo. Though probably not all cats would have a go at a kakapo. Some will have tried - and failed - to savage a kiwi and might therefore steer clear of kakapos. Others might have tried it, found they could get away with it and done it again. Kakapos are generally unused to defending themselves. They'll just freeze if they see a cat approach. Though they have powerful legs and claws they don't use them for defence. A kiwi, on the other hand, will kick hell out of a cat. Because kiwi fight each other. Put two in a cage together and there'll be a dead one in the morning.

`Or the kakapo may simply have died of old age. We don't know how long they live, though it seems that it might be a long time. Maybe as long as humans. Either way, the kakapo's not here any more, I think we can be quite sure of that. There are now no kakapos left in all of Fiordland.'

He takes the potato back from me, nevertheless, and with a last gesture of hopeless optimism puts it carefully back on the edge of the bowl.

Until relatively recently - in the evolutionary scale of things - the wildlife of New Zealand consisted of almost nothing but birds. Only birds could reach the place. The ancestors of many of the birds that are now natives of New Zealand originally flew there. There was also a couple of species of bats, which are mammals, but - and this is the point - there were no predators. No dogs, no cats, no ferrets or weasels, nothing that the birds needed to escape from particularly.

And flight, of course, is a means of escape. It's a survival mechanism, and one that the birds of New Zealand found they didn't especially need. Flying is hard work and consumes a lot of energy.

Not only that. There is also a trade off between flying and eating. The more you eat the harder it is to fly. So increasingly what happened was that instead of having just a light snack and then flying off, the birds would settle in for a rather larger meal and go for a waddle afterwards instead.

So when eventually European settlers arrived and brought cats and dogs and stoats and possums with them, a lot of New Zealand's flightless birds were suddenly waddling for their lives. The kiwis, the takahes - and the old night parrots, the kakapos.

Of these the kakapo is the strangest. Well, I suppose the penguin is a pretty peculiar kind of creature when you think about it, but it's quite a robust kind of peculiarness, and the bird is perfectly well adapted to the world in which it finds itself, in a way that the kakapo is not. The kakapo is a bird out of time. If you look one in its large, round, greeny-brown face, it has a look of serenely innocent incomprehension that makes you want to hug it and tell it that everything will be all right, though you know that it probably will not be.

It is an extremely fat bird. A good-sized adult will weigh about six or seven pounds, and its wings are just about good for waggling a bit if it thinks it's about to trip over something - but flying is completely out of the question. Sadly, however, it seems that not only has the kakapo forgotten how to fly, but it has also forgotten that it has forgotten how to fly. Apparently a seriously worried kakapo will sometimes run up a tree and jump out of it, whereupon it flies like a brick and lands in a graceless heap on the ground.

By and large, though, the kakapo has never learnt to worry. It's never had anything much to worry about.

Most birds, faced with a predator, will at least realise that something's up and make a bolt for safety, even if it means abandoning any eggs or chicks in its nest - but not the kakapo. Its reaction when confronted with a predator is that it simply doesn't know what the form is. It has no conception of the idea that anything could possibly want to hurt it, so it tends just to sit on its nest in a state of complete confusion and leaves the other animal to make the next move - which is usually a fairly swift and final one.

it's frustrating to think of the difference that language would make. The millennia crawl by pretty bloody slowly while natural selection sifts its way obliviously through generation after generation, favouring the odd aberrant kakapo that's a little twitchier than its contemporaries till the species as a whole finally gets the idea. It would all be cut short in a moment if one of them could say, 'When you see one of those things with whiskers and little bitey teeth, run like hell.' On the other hand, human beings, who are almost unique in having the ability to learn from the experience of others, are also remarkable for their apparent disinclination to do so.

The trouble is that this predator business has all happened rather suddenly in New Zealand, and by the time nature starts to select in favour of slightly more nervous and fleet-footed kakapos, there won't be any left at all, unless deliberate human intervention can protect them from what they can't deal with themselves. It would help if there were plenty of them being born, but this brings us on to more problems. The kakapo is a solitary creature: it doesn't like other animals. It doesn't even like the company of other kakapos. One conservation worker we met said he sometimes wondered if the mating call of the male didn't actively repel the female, which is the sort of biological absurdity you otherwise only find in discotheques. The ways in which it goes about mating are wonderfully bizarre, extraordinarily long drawn out and almost totally ineffective.

Here's what they do:

The male kakapo builds himself a track and bowl system, which is simply a roughly dug shallow depression in the earth, with one or two pathways leading through the undergrowth towards it. The only thing that distinguishes the tracks from those that would be made by any other animal blundering its way about is that the vegetation on either side of them is rather precisely clipped.

The kakapo is looking for good acoustics when he does this, so the track and bowl system will often be sited against a rock facing out across a valley, and when the mating season arrives he sits in his bowl and booms.

This is an extraordinary performance. He puffs out two enormous air sacs on either side of his chest, sinks his head down into them and starts to make what he feels are sexy grunting noises. These noises gradually descend in pitch, resonate in his two air sacs and reverberate through the night air, filling the valleys for miles around with the eerie sound of an immense heart beating in the night.

The booming noise is deep, very deep, just on. the threshold of what you can actually hear and what you can feel. This means that it carries for a very great distances, but that you can't tell where it's coming from. If you're familiar with certain types of stereo set-up, you'll know that you can get an additional speaker called a sub-woofer which carries only the bass frequencies and which you can, in theory, stick anywhere in the room, even behind the sofa. The principle is the same - you can't tell where the bass sound is coming from.