The Dutch primatologist, Marc van Roosmalen, had his first sighting of the new monkey in 1996 when a local fisherman brought the tiny animal to his house in Manaus. Recognising it immediately as a new species, Roosmalen set off in search of the monkey's home.

All he knew was that the monkey had come aboard a boat somewhere along the 3,000 kilometre-long Madeira river in the west of the Amazon basin. Everywhere he went he showed people a snapshot of the monkey.

It was an eventful trip. People sometimes showed him the 'wrong' monkey, and on four occasions these 'wrong' monkeys proved also to be new species.

He also discovered a new tapir and a new jaguar. Roosmalen decided that the region had more primates in it than anywhere else in the world.

Finally Roosmalen tracked down the family of his original monkey. The monkeys live on a tiny patch of land in a region 300 kilometres south of Manaus.

They're being fed three times a day by a local fisherman. But the region is already under threat.

The Madeira river is being widened so it can be used to transport soyabeans for export. And, with the improved access, loggers are already moving in.