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It is not every day that you get a telephone call asking you to come and collect a dead sheep. Yet that is what happened when I returned from a morning spent watching griffon vultures in their nests.

We jumped in the car and drove through the forest to an abandoned farmhouse where we found the sheep lying in a field. Franjo took out a knife and began to chop up the carcass. We bundled the remains into the car and drove to a remote hilltop where we left the body out for the vultures. It was all in a day's work at the Caput Insulae eco-centre in Croatia.

There are many reasons not to spend your holiday as a volunteer at Caput Insulae, in an old schoolhouse outside the clifftop village of Beli on the Adriatic island of Cres. The dormitory accommodation is spartan. The food will probably remind you of school dinners. The work is hard and backbreaking at times. And you might have to handle a dead sheep.

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But if that doesn't put you off, think of the rewards. Staying almost free in one of the wildest, most beautiful regions of Europe. The view of the sea from your window. And, just possibly, the chance to do your bit by helping to preserve one of its most mysterious and vulnerable creatures.

The centre was founded in 1993 by Dr Goran Susic, a scientist from Zagreb who was moved by the plight of the Eurasian griffon vulture. These birds, with a wing span of almost three metres, were once found all over Croatia but are now confined to a handful of islands in Kvarner Bay.

Only about 100 pairs survive, most on Cres. Pollution, threats from tourist boats, the decline of sheep farming and poisonous traps laid by farmers to catch foxes are among the causes of their decline. In addition, hunters have introduced wild boar and deer to the island, upsetting the ecosystem.

The eco-centre has a museum where visitors can learn about the vulture, and a sanctuary where vultures are nursed back to health after being poisoned or falling into the sea while learning to fly. It also monitors the behaviour and migration patterns of the vultures, tags chicks in their nests for identification and puts out food at “vulture restaurants” in the hills. Much of this work is carried out by volunteers.

I joined a team of volunteers for a week. Lucie, from France, was looking for a cheap holiday working with wildlife. Rich was an American who wanted to do something useful for a few days. Sonia was a French ornithologist who was staying for three months, while Wolfi, from Austria, was in his eighth year as a volunteer.We were led by Franjo, who grew up on Cres and developed a deep love for the vultures.

No two days as a volunteer are the same. You might find yourself cooking lunch, showing visitors around the exhibition, feeding the donkey, shearing sheep or helping Bernardo, the handyman, repair stone walls or carry back hay from the fields.

My favourite days were those which simply involved observing the vultures. We set up camp under a wild olive tree on the edge of the cliffs, training our telescope on the nests across the water. Hours passed in silent meditation as we waited for something to happen. Then a buzzard would circle gracefully overhead, or a griffon would return to the nest with food.

Every detail was minutely recorded for what it might reveal. Most days, we worked until lunch and the afternoon was free for exploring. I loved wandering around Beli, an eagle's nest of a village with a permanent population of 29 that bursts into life each summer as the Italian tourists arrive at their holiday cottages and a campsite is set up on the beach.

This was also the time when I would walk the network of eco-trails through the Tramuntana forest, stumbling across derelict farmsteads and abandoned villages, prehistoric temples and Roman bridges, wildflower meadows and secret ponds teeming with dragonflies and frogs.

And labyrinths. Goran Susic believes that labyrinths can help us to connect with the spirit of nature. He has spent the past few years building stone labyrinths along the trails. “Take off your shoes, leave your watch and mobile phone behind, enter the labyrinth slowly and listen to the silence,” he says.

It is difficult to know what this has to do with griffon vultures, but then Goran is no ordinary ecologist. His books are sprinkled with references to masmalic, the mischievous fairies said to inhabit these woods. Goran's vision is not just saving the vultures, but the entire biodiversity of Cres, which for him means archaeology, folklore, poetry and religion as well as butterflies, flowers and birds.

One evening, I climbed the hill to Lada's labyrinth, named after the Croatian goddess of beauty. It was raining when I arrived, but by the time I reached the centre of the labyrinth the sun was shining and a rainbow appeared in the sky. All I could hear was birdsong and the peck-peck-peck of a woodpecker. It was as close as I have come to a mystical experience.

In one week on Cres I may not have done anything to prevent the griffons from becoming extinct. But in that moment, I understood the beauty of this place and why we need people like Goran Susic to preserve it.

Need to know

Croatia Airlines (020-8563 0022, www.croatiaairlines.hr) has weekly flights from Heathrow to Rijeka and Gatwick to Pula until the end of October, from £123 return. Ryanair (www.ryanair.com) flies three times a week in summer from Stansted to Pula.

The eco-centre can be reached by a short drive from Rijeka or Pula followed by a ferry crossing to Cres (www.jadrolinija.hr). Volunteers arriving by public transport will be met at the bus station or ferry port.

Caput Insulae eco-centre (00 385 51 840525, www.supovi.hr) is open from March to October. Volunteers pay £80 for one week in low season and £120 from June to September. Food is £5 per day.

Croatian National Tourist Office (020-8563 7979, www.croatia.hr).

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