Mice were accidentally introduced to Marion Island, most probably by sealers in the early 19th century, and have had a devastating impact on the ecology of the island. A warmer and drier climate over the last 30 years has contributed to an increase in the densities of mice on the island each summer, causing a shortage of invertebrates, upon which the mice had been surviving in the winter months. This shortage of food has driven mice to find alternative food sources. As on other oceanic islands, the mice found many of the seabirds had no defence against their attacks and were literally “sitting ducks”. The scale and frequency of attacks has been increasing since they were first observed in the early 2000s and have escalated dramatically in the last few years. Without immediate action, Marion Island’s seabirds face local extinction. Left unchecked, the mice are predicted to cause the local extinction of 19 of the 28 species of breeding seabirds currently found on the island, some within the next 30 years.
In an ambitious undertaking, the Mouse-Free Marion Project aims to remove the introduced House Mice which are endangering the long-term survival of the seabirds and other native species of South Africa’s sub-Antarctic Marion Island.
In the southern hemisphere winter helicopters brought by sea across the ‘Roaring Forties’ from South Africa will spread rodenticide bait from underslung bait buckets in overlapping swathes across the entire island – the only method that has so far proven successful in eradicating rodents from large islands. At 30 000 hectares, Marion will be substantially larger than all previous rodent eradication efforts undertaken on islands in a single operation.