A million mice are eating seabirds alive on a remote island. Conservationists have a plan

Warning: This story contains distressing images.

Conservationists are hatching a plan to kill up to one million mice on the remote South Africa island of Marion, over fears that the invasive rodents could wipe out the seabirds that live there.

"They're essentially eating them alive," said Anton Wolfaardt, a conservation scientist in Cape Town and manager of the Mouse-Free Marion project (MFM). "[The birds] just sit there while swarms of mice often will kind of nibble away at them."

The project aims to drop bait laced with rodent poison all over the island, in a bid to eradicate every single mouse. Wolfaardt said the stakes of not intervening are high.

"[We] predict that the majority of the seabirds on Marion Island, including the wandering albatross, will become locally extinct in the next 30 to 100 years if the mice are not removed," he told The Current's Matt Galloway.

Marion is a windswept volcanic island in the Indian Ocean, about 2,000 kilometres southeast of Cape Town. The island is designated as a special nature reserve, with Wolfaardt describing it as a "haven" for the albatrosses, petrels, penguins and seals that hunt on the subantarctic waves but come ashore to breed and moult.

Mice first hitched a ride to Marion on seal-hunting boats about 200 years ago, but in recent decades their population has ballooned up to a million rodents at high season. Wolfaardt said that spike is driven by climate change; warmer and drier conditions extended the mice's breeding window. 

The mice have learned to attack where a bird's plumage is thinnest, usually at the head, to more easily reach the soft tissue. Photographs taken on Marion show birds with bloodied wounds on their heads and necks, sometimes with mice nibbling away at the live bird, in behaviour that scientists have called scalping. 

Wolfaardt explained that the island's birds have not developed defence strategies for these relatively new predators, and younger chicks can't yet fly away.

"Eventually the birds become so fatigued that they will eventually die, or will die due to some kind of bacterial infection," he said. 

The Marion project will involve a fleet of helicopters dropping poison along precise, overlapping routes across the island. This approach has worked in eradication programs on smaller islands, but Wolfaardt said "the size and the topographic complexity" of Marion presents unique challenges.

That complexity means the plan likely won't be ready to go until 2027. Wolfaardt said the team is studying extensive data and making contingency plans around variables like the weather — but noted there is zero margin for error.

"[We need] to make sure that every single square inch of the island … has the rodenticide bait distributed across it, so that we ensure that every mouse … consumes a lethal dose," he said. 

The birds would get temporary respite if most but not all of the mice are eradicated, he noted. But that could be short-lived: mice can have four or five litters a year, with six to eight babies per litter.