IN WINTER AND early spring commuters on the fast train between Amsterdam and Vlissingen are sometimes confronted with the sight of emaciated and dying cattle, horses and deer, and the carcasses of earlier victims being picked over by scavengers. The railway line skirts the edges of the Oostvaardersplassen, 56 square kilometres of Dutch soil that constitute one of Europe’s most remarkable conservation efforts.

The Oostvaardersplassen is the world’s most visible example of Pleistocene rewilding, the idea of reintroducing the megafauna that man wiped out as he spread across the globe. The idea is more popular in theory than in practice. There is a rewilding park in Siberia, with Yakutian horses, wisent, wapitis and muskox, but hopes to reintroduce America’s megafauna have got no further than releasing some large Mexican tortoises in a ranch owned by Ted Turner, a media mogul.

The Oostvaardersplassen was reclaimed from the sea in the 1960s and intended for use as an industrial estate, but in the gloom of the 1970s it lay vacant. The idea of reintroducing Pleistocene fauna came from Frans Vera, a government scientist. He got hold of some Heck cattle, a German attempt, under the patronage of Hermann Göring, to recreate aurochs (strong, wild creatures untainted by domestication or foreign stock) by breeding primitive cattle from zoos. From Poland he imported Konik ponies, said to be descended from tarpans, the last of Europe’s wild horses. He shipped in red deer, which were among Europe’s original inhabitants.

The population of horses and deer exploded: at the peak there were 1,200 horses. With so much grazing, the trees died, and the area turned into grassland and marsh. To Mr Vera, that offered support for his theory that pre-human Europe was not covered in forests, as has been widely assumed, but was primarily grassland. Vast numbers of birds arrived, including 29 endangered species. Sea eagles started to breed in the Oostvaardersplassen in 2006, and have since spread beyond its borders.

As the herbivore populations grew, food supplies became thinner, and so did the animals. That was when the political problems started. Animal welfare is a big issue in the Netherlands: Partij voor der Dieren (Party for the Animals) holds two seats in the House of Representatives and one in the Senate. A video clip of a starving red deer calf shown on prime-time television did not help. “There was an uproar,” says Hans Breeveld, the park’s warden. “People were asking how this could happen in a civilised society.”

The Oostvaardersplassen has twice been investigated by government committees. It survived, but with its freedom constrained. These days its managers are required to undertake “early reactive culling”—a polite phrase for shooting animals before they starve to death. The political pressure has lessened, partly because starvation brought herbivore numbers down sharply, but plans to expand the reserve have been put on hold.

As a sight, the Oostvaardersplassen is extraordinary. In one of the world’s most densely populated regions, Amsterdam now has a wilderness beside it that looks like a bit of African savannah, with herds of grazing herbivores and flocks of birds wheeling above them. Its scientific value is limited by the absence of the large predators that in the Pleistocene era would have kept herbivore numbers down. They would help settle the debate about whether ancient Europe was grassy or forested.

They may not be absent for long. In July a dead wolf was found in the Netherlands for the first time since the 19th century. More will follow: thanks to legal protection from the EU and to growing land abandonment, wolves are spreading through western Europe. If they get to the Oostvaardersplassen, they should provide added interest for the commuters.