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 29 bird 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.
A warming and drying climate on Marion Island has contributed to an increase in the densities of mice on the island with each passing summer. Mouse impacts are striking when researchers compare Marion Island with its mouse-free neighbour, Prince Edward Island, where seabirds, insects and plants are abundant and thriving. Declining insect populations have driven mice to find alternative food sources, which now include the eggs, chicks and increasingly the adults of many of the island’s globally important seabirds. Of the 29 species of birds breeding on the island, 19 are at extreme risk to mouse predation. Almost all these species are the wide-ranging, long-lived and slow-breeding petrels and albatrosses that are key predators in the vast Southern Ocean. About one quarter of the world’s population of Wandering Albatross breeds on Marion Island and is increasingly vulnerable to this threat; several of the other species preyed on by mice are red-listed as Endangered or Vulnerable.
Albatrosses and petrels evolved at least 50 million years ago. They specialise in eating food at sea, not picking up mice – they never feed when on land. Ever since they began to breed on islands, this group of seabirds has bred in locations where they have not had to contend with mammal predators, or, indeed, predators of any kind other than birds. Because behaviours develop where they are needed to help survival, and are usually lost when not needed, albatrosses and petrels no longer respond as their ancestors might have done to attacks from an unlikely threat such as a mouse. This is common for species that breed on islands, which are known to be mostly defenceless to recently-introduced predators.
Helicopters guided by Global Positioning Systems (GPS) and flown by highly-skilled pilots will spread bait pellets from underslung bait buckets over the whole island in two separate applications. The bait contains brodifacoum, an anticoagulant toxin commonly found in rodenticides available for domestic and commercial rodent control. The amount of bait spread will be determined by the mouse densities in different areas of the island. The operation will happen in the southern hemisphere winter (April to September), to reduce impacts on non-target species such as skuas, gulls, and giant petrels. This is also the period when the mice are at the lowest point in their annual population cycle and many of their natural food sources are scarcer, motivating them to seek out and eat bait.
We are using a best-practice approach, with methods that have been tried, tested and proven successful in hundreds of similar operations worldwide. Our intended approach is based on the culmination of more than 40 years of development, research, and implementation. A comprehensive assessment of alternative approaches to solving the problems caused by House Mice on Marion Island has been undertaken but none of the alternatives are considered suitable to use for an eradication of this scale, where every individual mouse needs to be removed. If there are any surviving mice or even one pregnant female, the population will recover so rapidly that the island’s ecology and wildlife will not benefit in the long-term from the eradication. All alternatives that were considered were rejected due to likely outcomes that did not meet the projects goals, including unacceptable risks of failure; risks to native and threatened species; lack of long-term benefits to native species; an imbalance in the extent of animal suffering involved; or impracticality.
The duration of the baiting operation is weather-dependent and will be influenced by the number of helicopters used. Helicopter spreading of bait will take approximately six months on the island. We will be working in winter when mice are at their hungriest and to reduce risks to non-target species which means shorter daylight hours for helicopter flying. 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. Certain areas will be hand-baited, e.g. base station, field huts, lava tunnels, etc. This phase will be followed by a follow-up monitoring phase two years after the eradication operation (a Success Check), to determine that we have eradicated all the mice.
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.
Most mice will die in their burrows, where they will decay within a few weeks.
We have thoroughly considered the impacts on other species. This included convening a panel of independent experts to review the impacts of the eradication operation on non-target species. As seabirds and seals eat fish and squid, they are unlikely to consume bait. There may be minor short-term impacts on populations of scavenging bird species. Similar projects elsewhere have experienced rapid recovery of affected species after rodents were removed. Importantly, the eradication operation will occur in winter when most seabirds have left the island. In similar projects on over 700 islands around the world, no non-target species has been found to be extirpated (become locally extinct) – and seabirds and other indigenous wildlife have recovered dramatically after the predators have been removed. Invertebrates are not affected by the toxin.
The rodenticide bait that we will be using, brodifacoum, is highly insoluble in water and binds strongly to soil. The baiting operation won’t impact soil, ground water, or vegetation. The toxin degrades with time and exposure to its constituent components (carbon dioxide and water): the half-life of brodifacoum in soil varies from 12-25 weeks, depending on soil type and conditions, so there is no long-term contamination of soils. Small amounts of bait entering the ocean will be quickly broken up by wave action and dispersed, due to the highly dynamic nature of the coastal zone.
In the last decade, over 90% 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.
Introduced predators kill seabirds and disturb the ecological balance of the island. For example, in 1949, five cats were taken to Marion Island to control the mice in and around the Weather Station. By the 1970s, these five cats had increased to over 2,000 individuals, that were killing approximately 450,000 seabirds each year. It took a sustained 15-year programme to finally eradicate the cats (by 1991). It is evident that if predators like cats or owls were introduced, they would target seabirds over mice. Further, we want to eradicate the mice, and introducing predators has never yet eradicated an invasive species from an island – they tend to cause more problems than they solve, by switching to other prey, as witnessed by the previous introduction of cats to Marion Island.
Yes, rodents 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 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.
Current estimates and exchange rates place the total budget at approximately R600 million. Government (the Department of Forestry, Fisheries and the Environment: the DFFE) is providing a financial contribution and in-kind support with crucial ship support, helicopter fuel, and accommodation on the island. The balance of the costs is being sourced from the private sector, with BirdLife South Africa (BLSA) spearheading these fundraising initiatives both in South Africa and abroad. Financial institutions are exploring investment possibilities that yield returns for conservation, such as Nature Performance Bonds and other similar instruments. Various foundations have supported the Mouse-Free Marion (MFM) Project, as well as international organisations such as the United Nations Environment Programme. The project’s supporters are shown here. Crowd-funding such as the Sponsor-a-Hectare programme, and Given Gain, have also provided valuable support.
The Mouse-Free Marion Non-Profit Company. This is a special purpose project set up solely to implement the eradication, and is a formal partnership between BirdLife South Africa (BLSA), and the South African Department of Forestry, Fisheries and the Environment (DFFE), under a Memorandum of Understanding. For free exchange of knowledge and expertise, many less formal but well-cemented technical and financial collaborations with universities, other research units, island conservation organisations, and financial institutions add great capacity to the Mouse-Free Marion Project.
A team of experienced and trained staff will stay on the island for 12 months, starting two years after the eradication operation. They will monitor intensively for the presence of mice using methods that have been proven effective on other islands. These include attractant devices such as tracking tunnels (baited with peanut butter and oats, with ink pads to ensure that mice leave detectable footprints as they run through the tunnel), tasty chew sticks and wax tags that are regularly inspected for mouse toothmarks, as well as trail cameras close to the base, which provides shelter and food that appeal to mice. Presence of mice will be checked for by specialised and highly-trained rodent detection dogs. These dogs are trained to exacting standards before being deployed to the island, and will range over the island with their handlers, checking for mouse scent and signs.
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.
If mice survive the aerial baiting in different locations across the island, it is unlikely that remedial actions can be taken. This is because mice are difficult to detect at low densities, but have a high reproductive capacity. This means that by the time mouse presence is evident, their numbers and distribution will be too advanced to attempt a retrospective eradication without mounting a full island-wide response, which will not be feasible financially or logistically. A response kit will be maintained on the island and will include bait. This can be used locally if mice are subsequently detected around the base buildings or field huts.
Prevention of mouse reinvasion – or any other non-native species – is called biosecurity, and will focus on all the people, vessels, aircraft and cargo visiting Marion Island (as well as Prince Edward Island). As the Management Authority for Marion Island, it is the DFFE’s responsibility to implement strict biosecurity protocols, and to ensure the full cooperation and compliance of all people visiting the island. Preventing incursions of mice – or any other stowaways – that can potentially reach the island via the ship in cargo, luggage, and equipment requires thorough and regular inspections. The ship’s mooring lines and gangways are fitted with rodent guards to ensure that rodents can’t climb onto the ship from the pier. Ongoing stringent rodent control measures are required in the warehouses and piers near where the S.A. Agulhas II docks, and suppliers providing materials for Marion Island also need to follow rigorous biosecurity protocols.
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.
The significant budget required to implement the project means that fundraising is an ongoing challenge for the MFM project team. The authorisations required to use toxic bait in this Special Nature Reserve, and to fly helicopters over the whole island, are complex. The remoteness and size of island pose logistical challenges, as does the prevailing poor weather conditions in the sub-Antarctic winter. Perceived environmental and human health risks related to use of the poison bait must be managed sensitively and carefully.
The Prince Edward Islands group (comprising Marion and Prince Edward) was declared a Special Nature Reserve in 1995 due to its extremely high biodiversity significance. It is the only such reserve in South Africa. Invasive alien species, such as the house mice on Marion Island, are widely acknowledged to be one of the most significant threats to the world’s biodiversity. South Africa is signatory to the United Nations Convention on Biological Diversity, which obliges us to eradicate invasive alien species, and is one of the 13 countries (Argentina, Australia, Brazil, Chilé, Ecuador, France, New Zealand, Norway, Peru, South Africa, Spain, the United Kingdom and Uruguay) that are Parties to the multilateral Agreement on the Conservation of Albatrosses and Petrels. It is our national and global responsibility to protect this unique part of South Africa and its inhabitants. Nineteen of the 29 species of birds on the island could face local extirpation if mice are not eradicated.
Raise awareness of island restoration projects among your family, friends, colleagues and acquaintances; connect MFM Project team members with individuals whom you think might be willing to donate or able to help in any way. Donate any amount pr sponsor a hectare through this webpage. Keep an eye on the “Vacancies” page of our website, and apply to join the MFM Project if a position comes up for which you have the necessary skills.
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