Aurelia, a female waldrapp ibis who turns four this spring, has had a tough year. In September, somewhere south of the Austrian Alps, she lost her two offspring and her mate while migrating south. It was a major blow to one of Europe's most precarious bird species and to the team of researchers trying to increase their numbers.

Then, last month, she left a bird sanctuary on the Tuscan coast in central Italy along with a male bird, Medea, embarking on the arduous 930km return journey that, if followed properly, would take them north-east over Italy's Apennines, along the Adriatic coast, up and over the Venice lagoon and then steadily north-north-east into Austria. At the end of the line, the two would be able to breed again. For a tense week, the whereabouts of the birds were unknown until last Monday, when Dr Johannes Fritz, an Austrian biologist specialising in animal behaviour and head of the waldrapp research team, received a phone call from an excited bird enthusiast who came within two metres of Aurelia, solo, in a valley in the Austrian Alps, about 30km off course. She was lost in the same spot as last year, about 140km southeast of the final destination, Scharnstein, Austria - so Dr Fritz's team collected her and drove her the rest of the way. She is now safely at the breeding ground; unfortunately, there is still no sign of Medea, her intended mate.

If they are to survive, the waldrapp ibises, also known as northern bald ibises, need more human assistance than the average bird. The northern bald ibis is one of the rarest bird species on the planet. In the wild there remains just one large colony, of about 350 birds, on the Moroccan coast; less than a dozen more are scattered in a small community in Syria. They are on the World Conservation Union's "red list" of threatened species. As Fritz says, any combination of factors - a nasty virus, an unscrupulous resort developer, a sudden depletion of fresh water or food supplies - would mean instant extinction in the wild. The birds disappeared from southern Europe about 400 years ago, hunted out of existence by the locals, who developed an appetite for these poky flyers. Aurelia and Medea are two of a small number of hand-reared ibises that Fritz's team is attempting to reintroduce to their former habitat.

To be sure, the birds have not evolved well. If they don't take flight in the first autumn of their life, they usually settle into a sedentary existence. And even the mobile ones are far from fleet. When they are motivated to take flight, they need almost ideal conditions to get anywhere. A stiff tail wind is best; a headwind is a deal-breaker. Generations of poor self-motivation and even poorer stamina (their top speed is 35 kph, and during migration the young require ample recuperative days off) seem to have robbed the birds of one crucial instinct: an innate sense of direction. They still have a powerful migratory instinct; they just cannot be counted on to find their way. "Early attempts to study their southerly migratory patterns were a disaster," says Fritz. "We had reports of them showing up in the Netherlands, Poland. One made it as far as St Petersburg."

The birds seem completely at home on the ground, loitering in one spot, pecking at the occasional grub. Their jet black plumage, growing spiky and unkempt on top, gives them a distinctly punky, adolescent appearance. Convincing them to take flight appears to be a major challenge; even the most devoted conservationist would be tested by the northern ibis' slacker disposition. Not surprisingly, while this species is dying out in the wild, it is thriving in zoos around Europe. "In general, zookeepers have more of a problem getting rid of them than they do in obtaining them," says Fritz.

Key to the reintroduction in Europe is teaching a dozen or so young ibises to follow the near-1,000km route that their ancestors may have taken centuries ago, south from the Alps to Orbetello on the Tuscan coast. The idea is to program into each generation a migratory route, plus a place to breed, which they can then pass on to the next generation. If they don't learn to migrate safely, they will never reach the breeding area and reproduce.

Aurelia and Medea were retracing a route they learned in summer 2004. At the time, they had help. They flew south alongside Microlight aircrafts navigated by Fritz and his team. It was one of the first successful human-assisted migrations covering such a vast distance. This spring is the third time Aurelia has completed the northerly journey unaided. Well, almost.

Fritz and his team fly at roughly the same altitude and at the same deliberate pace as the birds to guide them along the chosen course, which last year started at Burghausen on the German-Austria border. The odd sight of a small flock of northern ibises trailing behind Microlights is now visible from some of the Adriatic's beach resorts in late August and early September; last year the migration included a low-level fly-over of the Lido during the Venice film festival.

The migration is supposed to take about three and a half weeks; last year it took closer to seven. The majority of the class of 2007 was unfit for the journey. Fritz started with 17 young ibises, all born last spring at the waldrapp team's sanctuary in Austria. Just five completed the journey. The others had to be driven to Tuscany.

Another casualty was one of the aircraft. During the journey, Fritz's Microlight caught a tricky wind and crash-landed in a field outside Arezzo just after the birds had completed one of the most arduous parts of the journey. While Fritz tended to his Microlight, he watched in dismay as the birds, showing an uncharacteristic burst of energy, broke free of their human handlers and flew back over the mountains they had just crossed, to settle close to where they had started. The 300km day exhausted them; the team collected the birds in their van the next day and drove them back across the mountains to resume the final leg, after another day off.

Despite the delays, a cost overrun of a few thousand euros, the wrecked Microlight, and the fact that the majority of the ibises watched the migratory route from the back of a van, the waldrapp team regards last year's migration as an undisputed success. It is, they point out, how Aurelia learned the route.

Last week, three more ibises started their northerly migration journey from Orbetello. This time, the birds are equipped with GPS anklets to track their progress. "It's a much better start," Fritz deadpans.