When seal hunters landed on Marion Island in the early 19th century, they accidentally brought unwanted guests with them: house mice.
Now, decades later, the descendants of those stowaway creatures are wreaking havoc on the sub-Antarctic island’s unique wildlife. After devouring invertebrates and plants, the carnivorous mice have moved on to bigger targets—chiefly, the eggs, chicks and even adults of seabirds that nest on the island, which is part of South Africa. Their methods are brutal: The mice slowly eat the defenseless birds alive by nibbling away at their skin.
Situated some 1,370 miles southeast of Cape Town, this island is uninhabited by humans—but it’s home to millions of breeding seabirds, including four types of penguins and a quarter of the planet’s total wandering albatrosses. But without intervention, scientists worry the mice might drive some of these birds to local extinction: They estimate that 19 out of 28 seabird species on Marion Island will disappear within the next 30 years, reports the Telegraph’s Ben Farmer. Climate change appears to be making the problem worse, with warmer winters allowing more of the mice to survive and reproduce.
To rid the island of the pests, conservationists intend to launch an ambitious eradication project that they say will be the world’s largest effort of its kind. The initiative, called Mouse-Free Marion, will transport helicopters by boat from South Africa across the Southern Ocean. From there, pilots will fly back and forth across the 74,000-acre island and drop rodenticide-laced bait pellets from buckets on the underside of the helicopters. The project’s team members will also distribute bait by hand to some hard-to-reach places, including the island’s widespread lava tunnels and caves.
The plan, which was initially slated to be carried out in 2020 but has been delayed until 2025, is a partnership between South Africa’s Department of Forestry, Fisheries and the Environment and BirdLife South Africa, a nonprofit conservation organization. Prince Edward, the new Duke of Edinburgh, has signed on to help drum up support for the campaign, reports Jane Flanagan for the London Times.
Similar efforts on other islands have had mixed success. South Georgia, a British territory in the south Atlantic Ocean, is now mouse- and rat-free after helicopters dropped about 330 tons of poison onto the island over several years starting in 2011. Seabird populations have also made a comeback on Lundy, an island off the coast of England, after rats were wiped out there from 2002 to 2004. On the south Atlantic’s Gough Island, however, extensive mouse eradication efforts have produced disappointing results so far, as Jonah Fisher reported for BBC News in 2021. Despite conservationists’ best efforts, it’s challenging to kill off every single mouse or rat on an island, and even just a handful of survivors can doom the project.
And with this new effort on Marion Island, a lot could go wrong. Helicopter pilots will have to navigate the island’s extreme winds and bad weather. Conservationists will also have to contend with any collateral damage of the poison drop, such as scavenger birds, like the lesser sheathbill, feasting on the poisoned mice, per National Geographic. In the past, conservationists have said they’ll address that issue by temporarily capturing the island’s lesser sheathbills, but that’s an expensive and labor-intensive proposition.
If the Marion Island project does manage to be successful, it will “secure the ecological integrity” of the island by restoring its ecosystem and allowing its birds to flourish, says Mark D. Anderson, CEO of BirdLife South Africa, to the Guardian’s Patrick Barkham.