A deratting and mouse eradication team has just returned from the French Southern and Antarctic Lands after five months of operations. While we wait to be sure that the birds are free of these introduced predators, let’s take a look back at the implementation of this mission, the great success of South Georgia and the Mouse-Free Marion project.
On the island of Amsterdam, the cliffs of Entrecasteaux rise 700 meters above the Indian Ocean. Thousands of albatrosses and penguins nest on 350 hectares of land. These are remarkable colonies in the eyes of Unesco, the NGO Bird Life International, the European Union and the nature reserve of the French Southern and Antarctic Lands (TAAF)… but also to the taste of unintentionally introduced animals.
Since the first human presence in the 18th century, rats, mice and cats have populated the 58 km² island. They have gained considerable ground, much to the chagrin of nature conservationists, birds and the island’s native vegetation. Mice nibble phylicas – the only native shrub. Rats can spread other pests such as avian cholera. “We very strongly suspect that they are circulating it among rockhopper penguin and Indian yellow-nosed albatross chicks. They injure the birds by biting and could also attack the eggs,” explains Jérémy Tornos, eco-epidemiologist at the Centre d’Écologie Fonctionnelle et Évolutive in Montpellier.
The island’s rodents are responsible for the collapse of Indian yellow-nosed albatross populations, which are also suffering from other setbacks (fishing, climate change). To loosen this slowly-closing noose, the TAAF territorial authority has just completed an operation to eradicate cats, mice and rats, which began in early April. It ended in early September, with the helicopter being ferried back to the French overseas department called La Réunion aboard the Marion Dufresne II. The aircraft was essential for spreading granules of Brodifacoum, an anti-coagulant against rodents – banned in France and the European Union, except for missions of this type.
A test of patience
No living rodents were detected in the first two weeks following the end of the eradication attempt, according to the Mouse-Free Marion project website (a similar program under study on the southern South African island of Marion). A few survivors would be enough to recolonize the former volcano, as was the case with the mice on Gough Island (South Atlantic) in 2021. It will take 2 years to declare the island rodent-free – a test of patience – following the example of the successful 2018 experiment in South Georgia (an island in the Southern Ocean, close to South America).
This British land is 60 times larger than Amsterdam, made up of “a high mountain for the most part”, describes Mark Belchier, Director of Environment and Fisheries for the South Georgia and South Sandwich Islands Government. “The rats weren’t going above the vegetation line. In a way, we were lucky, because the glaciers and mountains delineate several perimeters, preventing them from spreading completely.” The rats were isolated in sectors, which could be treated one after the other. “We were pressed for time because the glaciers are retreating, but we were able to work for three summer seasons.” In Amsterdam, the TAAF took action during this austral winter, doubling the spraying of the product, one in June and one in July.
“One of the principles of this kind of initiative is to be overengineering in order to maximize your chances of success, even when faced with the most degraded scenarios,” explains Anton Wolfaardt of the Mouse-Free Marion project, which aims to eradicate mice from the island with the South African Department of Forestry, Fisheries and the Environment and the NGO Bird Life.
On land and in the air
As the Amsterdam cliffs are steep and difficult to access, the TAAF used a tank that can direct the emission of poison pellets when flying over the cliffs of Entrecasteaux. “In South Georgia, helicopters covered all the baiting areas. The New Zealand pilots were very good at this, recording their tracks and the quantities of granules sprayed on GPS, which was very precise,” explains Mark Belchier. “On the steeper slopes, we worked on foot and by hand.” A method used on former whaling stations, whose architecture – even when decomposed – provides refuge for rodents. In Amsterdam, the inhabited Martin-de-Viviès scientific base received special attention to control the spread of the poison.
Heavy rain can wash away granules and compromise operations. Flights depend on the state of the sky. In South Georgia, pilots flew in summer, avoiding katabatic winds. In Amsterdam, milder weather means that we can fly in winter, when rodents are looking for food close to the coast and “reproduce less”, explains Jérémy Tornos.
Most birds are at sea in winter. Those that stay put, like skuas, risk ingesting a few pellets. These scavenging birds may also eat dead mice and suffer the consequences. So, is it beneficial to eradicate rodents?
Collateral damage
To answer this question, Anton Wolfaardt set up a commission of ecotoxicologists and experts. “It confirmed that, in view of the damage caused by the mice on Marion Island, the ecological benefits far outweigh the costs,” he explains. “What’s more, in the vast majority of cases, contaminated rodents retreat to their burrows, where they are less accessible. Removing the threat posed by mice will then benefit all species.”
Mice are opportunistic omnivores, which means they can adapt. In Marion, before attacking birds, they reduced the size of native invertebrate populations by 90%. Now that the climate is warming up, they are more numerous and have discovered seabirds. “They’re naïve and did evolve without defense mechanisms against predatory mammals,” remarks Anton Wolfaardt. “We have a real crisis on Marion because the mice have totally undermine the ecosystem integrity.” They warm all around the birds and munch on their flesh, both chicks and adults.
One of the risks in Amsterdam is that the operation will be a success for the rats and a failure for the mice.
A unique case providing inspiration
Let’s get back to the risks to skuas. “It was necessary to clarify the regulatory framework because it is difficult to apply the principle of selectivity in the case of aerial spraying, unlike shooting,” explains Florian Aumond, lecturer in international law at the University of Poitiers. “The Prefect therefore asked the Ministry of the Environment’s Directorate General for Risk Prevention to clarify its powers on this point. The flights were then authorized by prefectoral decree.”
To justify his decision, the Prefect of the TAAF drew on the advice of the Ethics Committee and the Scientific Committee for the Polar Environment, which includes Anne Choquet, a lecturer and researcher in law of the sea, international law and law of the poles: “The use of invasive products must take into account the cascade of impacts on species and the ecosystem, and is based on knowledge acquired over the long term. And the Amsterdam experience will be very useful for other territories.”
Amsterdam is being closely monitored by the Mouse-Free Marion project, whose initiators are still seeking funding. These operations are costly. The TAAF have raised over 2 million euros at national and European level, and from the private sector. The island is smaller than Marion, and part of the logistics are included in current operations. Thirty million US dollars will be needed for Anton Wolfaardt. “We’ve raised a quarter of the funds needed, so we’re a long way off, but we’re convinced that financing solutions for projects like this do exist,” he explains. “We can’t afford to scale back the project; we need to be able to cover worst-case scenarios to ensure the mission’s success.”
A gap soon to be filled
The result is the return of birds that were previously endangered or banned from the territory. In South Georgia, the famous rescue of the pipit – the island’s only passerine – is a case in point. “The ducks and prions are doing much better, and we haven’t been able to track the return of the burrow-nesting birds, but we have every reason to believe that they have benefited greatly,” explains Mark Belchier. 90 kilometers south of Amsterdam, the Saint-Paul crater was freed of rats in the late 1990s. “It worked very well: all the petrel populations returned from the 2000s onwards”, explains Jérémy Tornos.
“Vessels cruising in South Georgia waters, even those that stay offshore, have to be inspected to make sure they’re not carrying small stowaway rodents. Dogs go through the holds in the Falkland Islands to detect them”, explains Mark Belchier, since everything could be turned upside down – again – if the rats returned.
Camille Lin, Polar Journal AG
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