I have been walking for hours, trekking through the rainy highlands of Santa Cruz in search of a giant. I am on one of the biggest islands in the Galapagos, the archipelago known for its strange species: marine iguanas, the northern hemisphere’s only penguins – and the world’s largest tortoises. It is these lumbering giants I am looking for.

The Galapagos are home to 10 types of giant tortoises . Lacking natural predators, they regularly grow to 400 kilograms and can live for a century. But despite their size they are …