Wild horses

The endangered species of Retuerta horse is being given a second chance of survival thanks to a special breeding project. One of the oldest horse breeds in Europe, the Retuerta closely resembles the race of ancient Iberian horse that populated the region around the Spain-Portugal border.

Only 150 Retuerta remain in the world - most of them are in a national park in southern Spain. Disease or disaster in this area could wipe out the entire species, experts warn.

Rewilding Europe, a non-governmental organization that seeks to protect biodiversity and replenish natural spaces in Europe, has arranged for 50 Retuerta to be introduced to the Campanarios de Azaba Biological Reserve in western Spain.

Wild continent

"It's a wild horse - so it's in its DNA to roam free in the wild," said Diego Benito, a forestry engineer who lives and works at the reserve. "Our idea is to just let them manage the ecosystem themselves."

Benito admits though that since it's an endangered species, rangers will intervene to help the horses survive. "If one of them gets ill, we could call the veterinarian," he said. "In the future, we'll treat them like wild horses - but for now, they could use a little care," he added.

Reintroducing horses at Campanarios is just one of six pilot projects taking place across the continent sponsored by Rewilding Europe. Programs to reintroduce European bison, red deer, beavers, brown bears and white-tailed eagles are happening in Romania, Poland, Slovakia and Croatia, as well as in Spain.

"In Europe, we live in a shadowland - in a dim and flattened relic of what there once was, and of what there could be again," writes George Monbiot, an environmental expert. His recent book is entitled "Feral: Searching for enchantment on the frontiers of rewilding."

"We've lost most of the big predators in Europe," Monbiot says. Europe has also lost all its large herbivores.

"Huge elephant-sized rhinos used to live in Eastern Europe," Monbiot says, adding that middle-sized herbivores are gone, as well. "But this can be changed, and I think there's a very exciting future for rewilding here."

Spain's changing landscape

Spain is particularly suited to rewilding. The last Ice Age drove many native European species southward onto the Iberian Peninsula, so Spain retained high biodiversity and low human population density.

As the Industrial Revolution was drawing rural populations to big cities in northern Europe 300 years ago, Spain remained a relatively poor, agrarian society. The country saw massive migration to cities after the Spanish Civil War in the late 1930s, and now again during Europe's debt crisis. As Spaniards abandon rural life for jobs in the city, the land they've left behind is returning to a primordial state unseen for thousands of years.

Previously heavily grazed by domesticated animals, underbrush in the countryside now grows unchecked and is fueling wildfires that are growing in number and size in recent years.

In the last 4 decades, the bush has increased by more than 4 million hectares, says Benigno Varillas, president of Rewilding Spain, which works with Rewilding Europe. "That's nearly 10 percent of the country converted to bushland," he said. Big herbivores like horses trample and graze the bush, Varillas explained.

But "people have taken their horses and cows away. So this reintroduction of wild horses is very important," he said.