Top predators like wolves can shape entire ecosystems (Image: Joel Sartore/National Geographic Creative)

Top animals shape ecosystems, so some conservationists want to unleash big beasts like elephants and lions to restore the countryside

THE sky is purple and the wind is fierce on top of the cliff. David Burney has to shout as he explains what we’re looking at. Below us is the Makauwahi Cave, which contains the remains of plants and animals going back thousands of years. It is revealing what the Hawaiian island of Kauai was like before people arrived. Here you can find the bones of moa-nalo, the giant flightless ducks that once ruled Hawaii.

The moa-nalo were giant flightless ducks that once ruled the Hawaiian islands

For millions of years, these plant-eating fowl roamed the islands, taking their pick of the lush vegetation. There were no large predators to threaten them. Then came the Polynesians. They probably started feasting on the plump, defenceless birds as soon as they had jumped out of their canoes. “It was an instant luau” – a feast – says Burney.

The ducks were soon wiped out, and the onslaught was only just beginning. European settlers introduced rabbits and goats to Hawaii, and the defences that native plants had evolved against the ducks’ thick beaks were little use against sharp teeth. Today, many of the original plant species of Kauai are extinct, replaced by invasive weeds. “For years, I documented extinction,” says Burney, who has spent much of the past two decades unearthing fossils here with his wife Lida Pigott Burney. “I felt like the county coroner.”

Then, a few years ago, the Burneys …