The wolves of Yellowstone

I spent three cold mornings in Yellowstone's Lamar Valley before I saw a wolf, after two days of driving to get there. Our guide, a former park ranger called Rick, set up a telescope by the road at dawn. When a grey shape finally trotted across the snow, a dozen grown adults went completely silent. Rick just smiled. 'Thirty years ago, you couldn't have seen this,' he said.

Wolves had been missing from the park for about seventy years when fourteen of them were brought in from Canada in 1995. Hunters and government programmes had wiped them out in the early twentieth century. Bringing them back was controversial. Ranchers feared for their cattle and doubted the wolves would stay inside the park. In the end the plan went ahead, and more wolves followed a year later.

Over breakfast in a diner, Rick told us the famous version of what happened next. He has told it hundreds of times, and he still enjoys it. Without predators, the elk had spent their days grazing along the rivers, eating young willow and aspen trees. Once the wolves were back, the elk kept on the move. Trees began to recover, songbirds returned and beavers built new dams. A short video claiming the wolves even changed the shape of rivers has been watched tens of millions of times.

Then he poured cold water on it. 'It's a great story, but it's too neat. Nature is messier than that,' he said. Scientists still argue about whether the wolves deserve all the credit. Bears also hunt young elk, people hunt them outside the park, and a run of dry years hit elk numbers too. In some places the trees have come back strongly, while in others you'd hardly notice a change.

What nobody disputes is that removing the wolves had effects no one predicted, and that bringing them back couldn't simply turn back the clock. On my last morning, we watched a pack feeding on an elk while ravens waited their turn. Rick pointed out an eagle sitting further off. 'Everyone's eating today,' he said. I went home with a lot of blurry photos of distant grey dots, and I wouldn't swap them for anything.