In Cape Town, South Africa, a pressing environmental issue has emerged on a secluded island near Antarctica. Two centuries ago, house mice were inadvertently brought to Marion Island, and now, due to climate change, their population is skyrocketing. These rodents are wreaking havoc on the island’s seabirds, posing a significant threat to its “unique biodiversity” within a vital nature reserve.
Conservationists have devised a bold plan to tackle this crisis. They intend to carry out a large-scale extermination by deploying helicopters to distribute hundreds of tons of rodent poison across Marion Island’s 115 square miles. The operation’s success hinges on leaving no mouse behind, as even a single surviving pregnant mouse could render the entire effort futile.
The initiative, known as the Mouse-Free Marion project, aims to protect the ecology of this uninhabited South African territory and the broader Southern Ocean. If successful, it would mark the largest eradication effort of its kind.
Marion Island serves as a crucial sanctuary for nearly 30 bird species, including the wandering albatross, known for its impressive 10-foot wingspan. However, the introduction of house mice by seal hunter ships in the early 1800s has introduced mammal predators to the island for the first time.
According to Dr. Anton Wolfaardt, the project manager, the damage caused by mice has escalated significantly in recent decades. Climate change has led to warmer and drier conditions on the island, providing an ideal environment for mice to thrive. Their extended breeding season has resulted in a dramatic increase in mouse population density.
Mice are remarkably efficient breeders, capable of reproducing from about 60 days old, with females producing several litters a year. It’s estimated that over a million mice now inhabit Marion Island, preying on invertebrates and increasingly on seabirds, including both chicks and adults.
The situation has become so dire that conservationists have documented mice attacking birds several times their size. This unusual predatory behavior has been observed on only a few of the world’s islands, but it has become alarmingly common on Marion Island since the first reports in 2003. The seabirds, lacking defense mechanisms against these unfamiliar predators, are often helpless against the mice.
If no action is taken, experts estimate that 19 seabird species could vanish from the island within 50 to 100 years. The eradication project represents a critical, one-time opportunity to address this issue, with no margin for error. Similar rodent population challenges have been faced by other islands, but Marion’s eradication could become the most significant single intervention to date.
The plan involves using four to six helicopters to distribute up to 550 tons of specially designed rodenticide bait across the island. This bait is intended to minimize environmental impact, not affecting the soil, water sources, or seabirds that feed at sea. While some individual animals may be affected, the overall species populations are expected to recover.
This eradication effort is a collaboration between BirdLife South Africa and the national Department of Forestry, Fisheries, and the Environment. Marion Island has been designated as a special nature reserve, offering the highest level of environmental protection. The project, requiring extensive planning, is slated for a potential start in 2027 and needs to secure around $25 million in funding, with some support already provided by the South African government.
Efforts to control the mouse population on Marion Island have a historical precedent. In the 1940s, domestic cats were introduced to combat the mice, leading to an explosion in the feral cat population and significant seabird losses. The cats were eventually eradicated through disease introduction and hunting.
Islands play a crucial role in conservation but are exceptionally vulnerable to extinction events. The Island Conservation organization highlights that islands are hotspots for extinction, with 75% of known extinct species originating from islands, the majority being bird species. The Mouse-Free Marion project represents a rare opportunity to address a significant conservation threat once and for all, aiming to restore the ecological balance of this unique island.