Parenting also played an intriguing role in other parts of the programme. For example, the conservationists used artificial incubation and egg adoption to make the most of the eggs laid by the captive birds, and grow a population big enough to replenish the wild community.

In the wild, bearded vultures lay two eggs in the winter months, but end up raising only one chick, Tavares from the Vulture Conservation Foundation explains. That’s because in the days after the chicks hatch, the stronger one kills the weaker one, a strategy known as evolutionary cainism. It is thought to have evolved to give the surviving chick the best chance of making it through the harsh Alpine winter and spring.

In captivity, the vulture pairs also lay two eggs. But to save the second chick, the conservationists then take one of the eggs, hatch it in an incubator, and slip the chick into the nest of a pair that has accidentally smashed its own egg, or whose chick has died. The pair then usually adopts and raises the chick.

Today, the bearded vulture is the most threatened vulture in Europe, with only 309 breeding pairs spread across the Alps, the Pyrenees and some islands. But in the Alps, the population is now considered to be self-sustaining. “We have reached the point where we are nearing the end of this [reintroduction] project, because it has been very successful,” Tavares says. The birds that are now released are not needed to boost the wild population’s numbers, but are selected for genetic diversity, to widen its gene pool, he says.

More like this:
• The Dutch rewilding project that took a dark turn
• The lost birds making a comeback in the Galapagos Islands
• The undersea mountains where sharks rule

Terraube points out that there are however new threats to vultures. One is the reappearance of poisoned bait, thought to be aimed at the growing wolf population in Europe, but which can kill birds such as griffon and bearded vultures when they feed on the bait. Collisions with power lines and wind turbines are another threat, says Terraube. (Read the BBC’s story on making wind farms safer for birds.)

As for Balthazar, the elderly vulture from the first generation of returners: he is currently being cared for in one of the conservation centres, Tavares says, as he was too weak to be left in the wild. Tavares hopes that the Alpine revival will be replicated by reintroduction projects in other parts of Europe. “It has worked,” he says, adding that in his view, “It’s one of the most successful wildlife comeback stories of our times.”

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