1998, Bird watching in Spain

A nightingale burst into song only a few feet away in the bushes but we could not see it. Then a small grey bird appeared on a branch as if it was trying to steal the spotlight. Its own song did not have quite the operatic range of its neighbour, but at least we could see it. "That's a Cetti's warbler. In Spain we call it a bastard nightingale," said Josep del Hoyo.

A light breeze was rustling the rushes in the Emporda Marshes Natural Park. Marsh harriers flew overhead and a solitary small-toed eagle found its predatory glide disturbed briefly by a flock of seagulls which had scrambled to meet the enemy.

"They're yellow-footed herring gulls," said del Hoyo, explaining this small distinction from their more common pink-footed brethren. "That's what I like about birds - their diversity. A humming bird could fly through the eye socket of an ostrich."

Del Hoyo should know. What began as a hobby at the age of 19, developed first into a passion and then to a vocation as he decided to attempt a venture that other ornithologists had said was impossible - documenting and describing every species of bird known to man in a published work.

"I thought he was mad and told him so," said Jordi Sargatal, director of the reserve and del Hoyo's closest friend and collaborator. It was 1982 when del Hoyo first mentioned the idea. Five years later, on a bird watching trip to the Netherlands, Sargatal was still telling him he was mad but he said: "Let's give it a try." It made all the difference. "I needed someone to share my belief," said del Hoyo.

Without providing the full picture, beyond that of "bird book publishing", they also sought financial backing from fellow bird enthusiast and entrepreneur, Ramon Mascorta. Finally they recruited a third editor, Andrew Elliot, football fan, classicist and linguist, whose talents were vital to the book's production in English.

Lynx Edicions, the company established to produce the Handbook of The Birds of The World , has published four volumes so far. By the time the 12th and final volume is issued in 2008, del Hoyo will have devoted more than 25 years and most of his working life to this one venture. From the very first volume, the book attracted critical praise for its quality and attention to detail.

Much of the research is carried out at the world's two greatest bird collections - the Natural History Museum's collection in Tring and at the American Museum of Natural History in New York, which each house more than a million specimens. But, if necessary, researchers will go to collections anywhere in the world to examine a single specimen. This happened in a museum in Lima. "It took them three days to find it," said del Hoyo.

Another problem is the discovery of new species as the work continues. When the Udzungwa Forest Partridge, a previously unrecorded species, was found in Tanzania in 1994, Volume II, which included partridges, was well into production for publication the same year. But if you turn to the partridge section you find the bird is where it should be, drawn on the same plate as the others, described in detail and photographed. "I think our readers were impressed by that," said del Hoyo.

As new species emerge, there is a real possibility that others may be extinct by the time the volumes are complete. The kakapo, a flightless New Zealand parrot, was caught on the evolutionary hop by the arrival of people and the rats they brought with them. Today there may be about 50 or 60 kakapo left in groups that have been transferred to islands free from predators.

The handbook will describe between 9,000 and 10,000 species, using the most traditional form of classification. There are newer forms, including some that have adopted DNA testing to describe families, but the editors have chosen to use the system most familiar to ornithologists the world over.

Del Hoyo, 43, developed his bird - watching skills when practising as a GP in a Spanish village. Later he became involved in medical publishing and compiled a health encyclopedia. The experience would come in handy with the handbook. But there were some things for which he could not prepare.

"I collected together all the bird books I could find. We now have 5,000-6,000. I thought we would have about 90 per cent of the information we would need from these sources, but much of the information was not of the quality we were seeking. So we have scoured private collections and zoos because we wanted to see live birds, not just specimens in museums.

The success of the first and subsequent volumes has led to a steadily increasing number of contributors. The 300 photographs in each volume are selected from about 27,000 possible contributions. The handbook is no longer an ornithological reference but the ornithological reference.

Now del Hoyo wants to repeat the success with mammals. "It will be a separate venture for which we will seek separate funding, but we know the format now and how to go about it.

"I feel very grateful to birds because they have given me the chance to travel the world doing the things that I enjoy," says del Hoyo, whose personal philosophy has been inspired by a quote from Pablo Neruda, the Chilian poet and Nobel prize winner: "Bird by bird I knew the world."

He also points out that the handbook could not have waited. "I believe we are living in a window of history probably no broader than 100 years because the travel opportunities and the technology exists to carry out this undertaking. In 50-100 years, many of the species are likely to have disappeared."

© Financial Times