Frequently Asked Questions

Marion Island is a globally important breeding site for surface-nesting and burrowing seabirds and other wildlife, supporting, for example, a quarter of the world’s Wandering Albatrosses. Introduced House Mice are eating the island into a state of ecological crisis. 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 have been surviving in the winter months. This shortage of food has driven mice to prey on many of the island’s seabirds, which have no defence against their attacks. The scale and frequency of mouse attacks on seabirds has been increasing since they were first observed in the early 2000s. Left unchecked on Marion Island, the mice are predicted to cause the local extinction of 19 of the 28 seabird species that breed on the island and continue to impoverish the entire ecosystem of this remarkable and important sub-Antarctic island.

We don’t know exactly – presumably either in materials landed ashore to support sealing operations, or from an early shipwreck. The first record of mice on Marion Island is from an early sealer’s log written in 1818.

  • Wandering Albatross Diomedea exulans
  • Grey-headed Albatross Thalassarche chrysostoma
  • Sooty Albatross Phoebetria fusca
  • Light-mantled Albatross Phoebetria palpebrata
  • Northern Giant Petrel Macronectes halli
  • Grey Petrel Procellaria cinerea
  • Great-winged Petrel Pterodroma macroptera

These are the species for which mouse predation has been observed and recorded. There are many other species which are not actively monitored, and seabird scientists working at Marion Island predict that 18 of the 28 species breeding on the island face a real risk of local extinction in the next 30-100 years if mice are not eradicated.

Albatrosses and most petrels only breed in habitats that lack terrestrial mammal predators. Because they have never experienced mammal predation before, they haven’t evolved appropriate responses to being attacked by fast-moving, numerous, nocturnal predators.

The mice will be killed via the use of a rodenticide bait containing the second-generation anticoagulant brodifacoum. Cereal bait pellets laced with brodifacoum will be spread over the entire island from bait buckets slung beneath helicopters. The bucket is linked to a GPS unit, which records exactly which parts of the island have been treated, to ensure that bait is distributed across the entire island. This is the only method that has proven successful in eradicating rodents from large oceanic islands.

The duration of the baiting operation is weather-dependent and will be influenced by the number of helicopters used. The plan is to treat the entire island once, wait 10-14 days, and then bait it again, to maximise the chances of delivering bait to every mouse territory. Each bait treatment will take about 8-10 days of good weather, but with frequent bad weather on Marion Island, the total operational window is 4-5 months. Certain areas will be hand-baited, e.g. base station, field huts, lava tunnels, etc.

The feasibility study, undertaken by John Parkes, was completed in 2015 (Click Here) and the first drafts of the Project Plan and Operational Plan were completed in 2018. Due to the complexity of these projects and the need to ensure that the eradication is done properly, the planning can take about a decade.

This depends on the temperature and the amount of rain, but it can last for weeks or even months under certain conditions. As the bait weathers, the bait and the active ingredient in it are broken down into inert components and are bound in the soil. The active ingredient (toxin) is not soluble in water.

Most mice will die in their burrows, where they will decay within a few weeks.

Seabirds primarily eat fish and squid so will not be interested in the bait. The same applies to the seal populations on the island. We expect a relatively minor short-term impact on some scavenging bird species; however, similar projects elsewhere have experienced rapid recovery of affected species after the impacts of mice are removed. Because most mice die underground in their burrows, they therefore won’t be available to scavenging birds. Moreover, the baiting operation will take place in winter when many of the scavenging birds are away from the island.

Invertebrates are not impacted by anticoagulant toxins, although individual birds that eat invertebrates may be at risk.

In the last decade, about 80% of attempts to eradicate mice from islands have been successful. We can’t ever be 100% certain, but experts who have been involved in successful operations on other sub-Antarctic and cool temperate islands are confident that we also have a high chance of success on Marion Island. The operation is being carefully planned and peer-reviewed to minimise the risk of failure.

Yes, mice have been eradicated from more than 700 islands worldwide. Marion Island will be the largest island attempted to date where mice are the only introduced mammal. South Georgia is much larger, but mice only occurred at low densities in two distinct rat-free areas. At Australia’s Macquarie Island (12,800 ha), three species (rabbits, rats and mice) were successfully eradicated in 2014, so even though that island is smaller than Marion Island, it was a very complex operation. While only targeting one species is an advantage, Marion Island is much larger and has higher topography than Macquarie Island and these, together with the shape of the island, present significant challenges. Eradicating a species from a sub-Antarctic island is ambitious and challenging; however, with careful and detailed planning, involving experienced personnel and with appropriate resources, it can be a significant and durable conservation achievement.

Post-eradication monitoring will be done using a variety of passive detection devices, including camera traps, and most likely rodent detection dogs, to determine whether the MFM Project was successful. It will probably be two years after the implementation of the project before we can conclusively say that all mice on the island have been removed.

Marion Island has strict biosecurity measures in force, limiting the amounts and types of materials that can be taken ashore. Only ships that are certified rodent-free before leaving port can visit the island, and there is no dock where ships can tie up, so the risk of a rodent sneaking ashore are very small. Ongoing efforts will ensure that strict biosecurity standards are maintained.

The Mouse-Free Marion (MFM) Project is a partnership between the Republic of South Africa’s Department of Forestry, Fisheries and the Environment (DFFE) and BirdLife South Africa, which established the Mouse-Free Marion Non-Profit Company in 2020 to help facilitate the implementation of the project. With the help of partners around the world, such as the FitzPatrick Institute of African Ornithology (University of Cape Town), the Royal Society for the Protection of Birds (UK), the South Georgia Heritage Trust, the New Zealand Department of Conservation’s Island Eradication Advisory Group, and BirdLife International, the project has made significant progress. BirdLife South Africa and DFFE are supporting the project financially as well providing staff support for the effort. The Republic of South Africa and BirdLife South Africa are grateful for the extraordinary effort that will be needed to make this project possible.

Definitely. Removing the House Mice will be a positive step for biodiversity and ecosystem functioning on Marion Island. By restoring hydrological functioning, nutrient cycling, plant and invertebrate communities, the Mouse-Free Marion Project will act as an ecosystem-based adaptation measure against climate change. With close to one million mice present on the island currently, their burrows, nests and tunnels allow aeration of the substrate and result in drying out of the mires and bogs; mice also prey heavily on endemic invertebrates, plant seeds and soil organisms. When combined with climate change, the impacts of House Mice are accelerating habitat degradation and changing the flow of nutrients and fresh water to the marine environment. Removing the predation threat that mice pose to many of the island’s seabirds will help increase the resilience of these species against future climate change impacts.

Yes. The Mouse-Free Marion Non-Profit Company is a registered Public Benefit Organisation (No. 930071579) in South Africa and authorised to issue Section 18A tax certificates (for South African tax payers) where applicable. Please email info@mousefreemarion.org if you require a certificate. Please note that these might take up to three months to be issued.

Mouse-Free Marion has fiscal sponsors in several countries which can issue tax certificates for supporters in other countries. For more information, contact tarryn.havemann@mousefreemarion.org