Massacre on Marion Island | Polarjournal
It looks harmless, but the house mice on Marion Island are a threat to the island’s seabirds and need to be controlled. (Photo: Stefan Schoombie / Mouse-Free Marion)

Please note that some of the images in this article may be shocking.

On Marion Island, a small sub-Antarctic island in the Indian Ocean, millions of seabirds breed. There are 28 species in total. The island was discovered by chance on March 4, 1663 by the Dutch navigator Barend Barendszoon Lam. South Africa has maintained the permanent research and weather station on the north-east coast since 1948.

What sounds so peaceful is deceptive. Introduced house mice have been a plague for decades. In the meantime, mice are already threatening 19 bird species with extinction. Attacks on adult wandering albatrosses have already been observed and documented.

600 tons of poisoned bait are to be distributed all over the island to combat the plague of mice. The funding target for the launch of the operation is 25 million US dollars, but this has not yet been fully secured. The project is due to start in winter 2026.

Scalped! A house mouse eats the head of a defenseless wandering albatross chick on Marion Island at night. (Photo: Stefan Schoombie / Mouse-Free Marion)

“Zombie mice”, as they are called by conservationists, are non-native mice that adapt to environments into which humans have inadvertently introduced them.

The mice were most likely introduced by seal hunters at the beginning of the 18th century and it wasn’t long before they took over.

William Phelps, a seal hunter who spent time on Marion from 1818 to 1820, wrote: “The whole island was infested with common house mice, which had been brought in from a sailing vessel, probably with the supplies of the crew.”

In 1949, five domestic cats were brought to Marion Island to combat a plague of mice in the station. However, the cats multiplied rapidly and by 1977 there were already around 3,400 cats living on the island, feeding on petrels instead of mice, threatening to wipe out the birds on the island.

A “cat eradication program” was launched, which reduced the number of cats to around 600 in 1982. The remaining cats were killed by hunting at night. The project was successful and in 1991 only eight cats were caught within twelve months. It is assumed that there are no more cats on Marion Island today.

However, the mouse population increased sharply again as a result. In the 20 years that followed, the number of mice on Marion Island increased by around 430%. A 2015 study found that mice killed one in ten albatross chicks. Mark D. Anderson, CEO of BirdLife South Africa , says: “Not only has the situation escalated, one of our concerns is that the mice are now starting to feed on adult wandering albatross.”

The mice “nibble” mercilessly on the chicks all night long. If they survive, they will spend the day exhausted and in pain, trying to recover until the mice attack again the next night.

The mice also scalp” the older chicks, as videos recorded for the first time in 2009 showed. They attack the crown of the head while the bird tries to protect itself.

Not a pretty sight. A house mouse feeds at night on the exposed scalp of a wandering albatross chick on Marion Island. (Photo: Stefan Schoombie / Mouse-Free Marion)

Presumably due to drought and food shortages, the mice changed their behavior. The urgency to do something about it has grown, but the process of conducting feasibility studies to eradicate the invaders, complying with regulations and trying to raise the funds for a massive extermination operation has been slow.

The high stakes justify the arduous progress, says Anderson: “The result is binary: either we succeed or we fail. A remaining pregnant mouse is a failure. If two mice of different sexes remain, this is also a failure. We must therefore do everything in our power to ensure that we are successful.

“After all, this is a project costing almost 25 million US dollars. And if we are unsuccessful, it will be a long time before we can repeat the work, perhaps even decades.”

Mark D. Anderson, CEO of BirdLife South Africa insists, however, that the deadly attack on the rodents will take place soon. (Photo: BirdLife-South Africa)

Difficult task

Successful eradication campaigns were carried out on rabbits, rats, reindeer and mice on Macquarie Island in the Pacific Ocean, on rats on the Shiants in the Hebrides and on St. Agnes and Gugh in the Isles of Scilly.

The largest project against rodents took place on South Georgia in the Atlantic Ocean, which was declared rodent-free in 2018. Also on South Georgia, reindeer introduced by Carl Anton Larsen in 1911 were removed by Norwegian hunters in 2013. At that time, there were 6,000 reindeer. The reindeer campaign was successfully completed back in 2014.

“Of course there is a chance that eradication will fail. But there is also a good chance that it will succeed. It’s a much less complicated environment (in terms of habitat complexity) than Gough Island, where the eradication attempt failed.”

Prof. Peter Ryan, one of the project’s scientific advisors, emphasizes that “the need for action has increased.” A reduction in chick production will wipe out the populations, but over a very long period of time. But if you kill adults, it will go much faster.

“The first attacks on wandering albatrosses were recorded in 2002, but were very sporadic. The first attacks on Russian albatrosses took place in 2009. Large-scale attacks on Russian albatrosses were also recorded in 2014-15, and since then there has been no stopping their advance.”

Right between the eyes. A gray-headed albatross chick was seriously wounded by house mice at night. (Photo: Kim Stefens / Mouse-Free Marion)

Mark D. Anderson: “Logistically, Marion Island presents some challenges. For starters, it’s 30,000 acres, plus there’s no harbor, so everything has to be brought to the island by helicopter from the ship. Unloading the equipment, helicopters and team will take around 10 to 20 days, depending on weather conditions. The helicopters will be flying in quite difficult conditions, especially in strong winds. We will be using six helicopters to distribute almost 600 tons of bait across the island.”

The eradication campaign is being led by New Zealander Keith Springer, who has extensive experience in rodent eradication. The project is led by Dr. Anton Wolfaardt, who has more than 20 years of experience in the Antarctic and sub-Antarctic.

Springer says the Department of Fisheries, Forestry and Environment’s polar research vessel SA Agulhas II will be used to supply the scientific bases on the Gough and Marion Islands and in Antarctica.

The bait used consists of a cereal matrix with an anticoagulant rodenticide poison, brodifacoum. Anderson says the work is done in winter, when the mice are hungriest and not pregnant.

“They take the bait that is on the surface into their underground burrows and hide it there, or eat it. Most mice die in the burrows within three to four days.”

The success of the operation, which will be carried out in 2026, can only be known two years after the end of the operation and after sniffer dogs and cameras have completely searched the island. However, failure could be signaled earlier if mice were discovered again in the meantime.

Frederik Paulsen, a pharmaceutical entrepreneur, is one of the largest individual donors with an amount of 1.5 million US dollars. He is also Director of the NPC Board of the Mouse-Free Marion Project. (Photo: Heiner Kubny)

Financing not yet secured

There is still something standing in the way of getting rid of the mice: money. The funding target is to raise 25 million US dollars, but “we are still about 19 million US dollars short,” says Anderson.

“We are pulling out all the stops. The South African government has already pledged 3.5 million US dollars, with the likelihood of more to come”.

When asked about the criticism that this operation is about playing God, Anderson says: “Unfortunately, in this situation you essentially have to play God because the problem won’t solve itself.”

Heiner Kubny, PolarJournal

Website: https://mousefreemarion.org/

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