Ecosystems, introduced species, and climate change.

The Mouse-Free Marion project

[Didn’t want to post this yesterday as some might have thought it an April Fool.]

Mice were introduced to Marion Island, a remote island between South Africa and Antarctica (Figure 1), 200 years ago. The house mice arrived on seal-hunter ships in the early 1800s, introducing the island’s first mammal predators. However, due to the warming climate their numbers are now said to be out of control, and they are eating young seabirds and causing major harm in a special nature reserve with ‘unique biodiversity.’ Climate change has turned a cold, windswept island into a warmer, drier, more hospitable home for the rodents.

Conservationists are now planning a mass extermination using helicopters and hundreds of tons of rodent poison, which needs to be dropped over Marion Island’s 297 km² to ensure success. They say that even if one pregnant mouse survives, their prolific breeding ability means it may have all been for nothing.

Estimates indicate there are more than a million mice on Marion Island. They are feeding on invertebrates and, increasingly, on seabirds - both chicks in their nests and adults. A single mouse will feed on a bird several times its size.

Figure 1. Location of Marion Island

The Mouse-Free Marion project is seen as critical for the ecology of the largely uninhabited South African territory and the Southern Ocean. It would be the largest eradication of its kind if it succeeds. The island is home to globally significant populations of nearly 30 bird species and provides a rare undisturbed habitat for wandering albatrosses.

The amount of planning and finance needed ($25 million) means that a likely start date is not until 2027.

Figure 2. Marion Island, part of the Prince Edward Islands, a South African territory in the southern Indian Ocean near Antarctica.

[Photo: Anton Wolfaardt / AP file]

Burgeoning mice and rat populations have been problematic for other islands too. South Georgia, in the southern Atlantic, was declared rodent-free in 2018 after such an eradication, but that was a multi-year project. The one on Marion could be the biggest single intervention. It is thought that up to six helicopters will be used to drop up to 550 tons of rodenticide bait across the island. Conservationists will be able to track the drop using GPS mapping. The bait has been designed to not affect the soil or the island’s water sources. It should not harm the seabirds, who feed out at sea, nor have negative impacts for the environment.

This is not the first-time scientists have tried to control the mice of Marion. They were previously a pest for researchers in the 1940s, so five domestic cats were introduced. But, by the 1970s, there were around 2,000 feral cats on the island, killing half a million seabirds per year. The cats were eliminated by introducing a feline flu virus and hunting down survivors.