'Truly astounding': inside the Farallon Islands' battle against a plague of mice

With more than a thousand mice per acre, an ecosystem is under threat. But poison could make things even worse

The Farallon Islands of northern California are one of the world's great biodiversity hotspots. These stark granite outcrops, which sit 30 miles (48km) off the coast of San Francisco, are home to 300,000 breeding seabirds, five species of seals and sea lions, and a type of cricket found nowhere else in the world.

Scientists studying shark behavior or bird migration patterns flock here annually, but the islands have hosted other visitors for even longer: mice, tens of thousands of them.