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Massacre at Marion: mouse eradication project gathers pace

Yves Vanderhaeghen interviews the team spearheading an operation to rid Marion Island of mice which are annihilating seabirds and other life.

  • Marion Island is home to millions of seabirds from 28 species
  • Mice are putting 19 species at risk of extinction
  • Mice are now attacking adult Wandering Albatross, imperilling the bird’s survival on Marion
  • 600 tonnes of poison bait to be distributed across the island
  • Funding target to launch the operation is US$25 million

A “zombie apocalypse” has been playing itself out on Marion Island for over a decade as flesh-eating mice massacre vulnerable seabirds, having already laid waste to invertebrates and otherwise tenacious vegetation.

The urgency to do something about it has been growing, but the process of conducting feasibility studies on island rodent eradication, meeting regulations and trying to raise the funds for a massive extermination operation has been a slow one.

Mark D. Anderson, the CEO of BirdLife South Africa, which has been spearheading the Mouse-Free Marion rodent eradication project in conjunction with the South African Department of Forestry, Fisheries and the Environment, is adamant, however, that a terminal blitz on the rodents will take place soon. The high stakes justify the painstaking progress, because, says Anderson, “the outcome is binary: either we succeed, or we fail. A pregnant mouse remaining is failure. Two mice of opposite sexes remaining is failure. So, we’ve got to do everything in our power to make sure we’re successful. It is after all an almost half-a-billion-rand project. And if we’re not successful, how long will it be before the work is undertaken again? Decades perhaps.”

Anderson and Mavuso Msimang, the Chair of the Mouse-Free Marion Non-Profit Company, gave a presentation on the crisis on Marion Island at the annual Oppenheimer Research Conference, which this year took place from October 4-6 in Midrand, Gauteng. The title of the presentation was “Saving Marion Island’s seabirds – the world’s most important bird conservation project”.

An isolated volcanic outcrop about 2 000 km from Cape Town in the Southern Indian Ocean, Marion Island, together with its sister Prince Edward Island, was declared a Special Nature Reserve in 1995 and falls under South Africa’s stewardship. South Africa established a research station on Marion in 1948.

Marion is a perfect breeding ground for seabirds, although between the relentless winds associated with the Roaring Forties and icy temperatures, it is hostile to terrestrial animals and plants. However, its 30 000-hectare surface (roughly 30 000 rugby fields) teems with birdlife. Ornithologists estimate that the island is home to millions of seabirds from 28 species, including penguins, giant petrels, diving petrels, storm petrels, terns and prions. But it is also called “Albatross Central”, as it is the breeding ground for about a quarter of the world’s Wandering Albatrosses, as well as the Grey-headed Albatross, the Sooty Albatross and the Light-mantled Albatross.

Marion is not an impregnable fortress, however, and researchers have found that it is now home to 46 alien species, of which 29 are invasive. One of these, and the only mammal among them, is the house mouse, Mus musculus. The mice most probably jumped ship from seal-hunting brigs in the early 1800s, about 150 years after the island was first sighted by the Dutch East India Company in 1663.

It didn’t take them long to take over. William Phelps, a sealer who spent time on Marion from 1818-1820, wrote that “… the whole island was infested with common house-mice, which had … been introduced from some sailing vessel, probably with the stores of the gang; and they had multiplied until their name was legion.  They thickly populated the beaches, and inhabited the caves; they burrowed with the birds in the banks, and were found among the snows of the mountains”.

It is not clear how anything survived this invasion, but it is thought that an equilibrium of sorts was maintained until, Anderson reckons, climate change enabled the mice “to breed more regularly over a longer period and have bigger litter sizes”. Not to mention the cats which, introduced in 1948 to kill off the mice at the research base, bred so furiously that they in turn were “hunted, trapped, and had a virus let loose on them” until by 1991 there were none left. Apart from mice, they were also killing half a million seabirds a year.

Conservationists then had to look at what could be done about the mice. Successful eradication operations have been carried out on rabbits, rats and mice on Macquarie Island in the Pacific Ocean, rats on the Shiants in the Hebrides, and St Agnes and Gugh in the Isles of Scilly. The biggest project was on South Georgia island in the Atlantic Ocean, which in 2018 was declared free of rodents.

In the 20 years up to 2018, the number of mice on Marion increased by about 430%. As a result, says Anderson, “the frequency of mice attacks is increasing very significantly. It’s exponential, and it’s related to the fact that the invertebrates on which the mice used to prey have been decimated, so the mice are feeding off the seabirds and their eggs as an alternative food source” to replace their diet of weevils, moths and seeds”.

In a 2015 study, mice were found to be killing one in 10 albatross chicks. Not only has this escalated, says Anderson, but “one of our concerns is that the mice are now starting to feed on adult Wandering Albatrosses as well. The loss of chicks obviously has a big impact, but once you start killing adult birds of breeding maturity, then the impact on populations increases. And this is a more recent phenomenon.”

These deaths are not a clinical process. The mice “nibble” mercilessly on chicks through the night, which if they survive will spend the day exhausted, in pain, trying to recover until the mice attack again the next night. The mice will also “scalp” the older chicks, as videos first taken in 2009 showed, attacking the crown of the head as the bird attempts to protect itself. Attacks on adult birds are aimed at the rump and wings, eventually felling them so that a feeding frenzy is launched at the stomach and the bird is eviscerated. “It’s an absolutely gruesome death,” says Anderson. Wildlife photographer Tom Peschak described the horror in a 2019 National Geographic podcast: “All of a sudden in this landscape of black and green and grey there is this red that pops out at you … and you’re just going, ‘Well, what is that?’ You come around this boulder and you are literally looking at a bird that has been scalped. The entire back of its head and the entire neck has been eaten away.” He added “I’ve watched every single season of The Walking Dead and this is rougher than any one of those episodes.”

Little wonder that ecologist Otto Whitehead dubbed this a “zombie apocalypse”, which is putting 19 of the 28 seabird species breeding on Marion Island at risk of extinction if nothing is done. He notes that “one only needs to look at Gough Island to see how bad things can get in terms of impact on the survival of albatross chicks. Marion is not there yet, but it is heading that way and the eradication is crucial to preventing things from getting out of hand. There is a chance that the eradication will fail, of course. But there is also a good chance that it’ll succeed. It’s a much less complicated environment (in terms of habitat complexity) than Gough Island, where the eradication attempt failed.”

Professor Peter Ryan, one of the project’s scientific advisors, stresses that “the need to act has been ramped up this year. Reducing chick production will wipe out populations, but over a very long time. But killing adults, it will go a lot quicker. This year we suddenly had seven adult deaths, in an area that wasn’t being monitored closely, so we don’t know how many attacks there were to result in seven deaths. That is a game changer. The first Wanderer attacks were recorded in 2002, but they were very sporadic. The first attacks on Sootys were in 2009, and then in 2014-15 we had the big outbreaks of attacks on the Light-mantleds and Sootys. And it’s taken off since then.”

Ryan cautions that while attention is on the damage to birdlife, “the impact on invertebrates has been even more devastating, and this has been clear for 20 to 30 years, but people don’t care about invertebrates so it’s hard to muster a lot of support.”

Of those that are hardest hit, he says are endemic weevils, and the flightless moth. There are two species of flightless moth on Prince Edward, and only one on Marion, he says, “so we suspect that probably Marion has lost one entirely already due to mice. You really struggle to find a flightless moth on the island now. It’s desperate what the mice have done to the invertebrates; they’re just strip-mining the island of them.”

Ben Dilley injured Grey Headed Albatross
Grey-headed albatross injured by mice on Marion Island. Picture: Ben Dilley, Mouse Free Marion

What is to be done?

It’s clear that a few mousetraps won’t suffice. Eradication is seen as the only solution, and the process to achieve this started in 2015, says Anderson, when a feasibility study was commissioned, “but it’s only in the last three years that things have really started moving”.

It will be a massive task.

“The mice are found across the island, and this would be the largest island by a large margin from which mice have been eradicated in a single attempt if we’re successful.

“Logistically Marion Island presents some challenges. It is 30 000 hectares for starters, so that’s big. Then, there is no port, so everything has to be taken from the ship to the island by helicopter. It will take about 10-20 days to offload the gear, the helicopters and the team, depending on the weather conditions. You’re flying helicopters in pretty difficult flying conditions, with strong winds in particular. We’ll use six helicopters, which will spread almost 600 tonnes of bait over literally every square metre of the island.”

The eradication operation is being run by New Zealander Keith Springer, who has had extensive experience in rodent eradication. The project is managed by Dr Anton Wolfaardt, who has more than 20 years’ experience working in the Antarctic and sub-Antarctic.

Springer says that the Department of Fisheries, Forestry and the Environment’s polar research vessel S.A. Agulhas II, which is used to resupply the scientific bases at Gough and Marion Islands and in Antarctica, will deploy the eradication team and pick them up again. South African helicopter companies will shortly be invited to tender for the project implementation.

Springer points out that the bait is not just dumped by the helicopters, as a water-bomber might do on a fire. “We use a bucket slung beneath the helicopter to disperse the bait. Below a hopper which holds the bait is a motor-driven spinner. The bait falls down into the spinner and is flung out in a 360o pattern. We expect that each bucket will be able to deposit a swath of bait about 80 metres wide. We fly in parallel flight lines across the whole island distributing bait, and then do it again, from a slightly different angle. The objective is to get a bait pellet in every potential mouse territory on the island. This is where some of the pilot skills come in – it’s not easy to stick absolutely on a plotted line shown on your instruments, without deviating more than a couple of metres either side of the line, and do that all day.”

This can only happen, says Anderson, if the weather co-operates. “The team will be on the island for the better part of five months, and they will wait for two weather windows. We’ll have top meteorologists watching the weather, and when there’s a week to 10-day weather window they’ll be ready to roll. They’ll fly the helicopters during that period. Then they’ll do a second bait drop during a subsequent weather window a few weeks or even months later. “

The bait used comprises a cereal matrix, with an anticoagulant rodenticide poison, Brodifacoum, in it. Anderson says the work will be done in winter, when the mice are at their hungriest and when they’re not breeding. “They’ll take the bait, which is on the surface, into their underground burrows and cache it, or consume it. The majority die underground, within three to four days.” As for collateral damage, Anderson says there will inevitably be some. But, “the important thing is that this is a once-off intervention. If you think about managing the Kruger Park, for example, that is for ever, literally. Here, we go in, we do it well, with biosecurity in place post eradication: Job Done! There’s almost no conservation work where you say you’re going to move in and be able to say problem solved. That’s nice.”

The success of the operation, which will be undertaken in 2026, could only be known two years after the baiting is completed, and after sniffer dogs and cameras have fully swept the island. But failure could be signalled earlier if any mice are detected in the meantime.

There is still something standing in the way of getting rid of the mice: money.

The funding target is to raise US$25 million (R469 234 100), but “we’re still about $19 million short”, says Anderson. “We’re pulling out all the stops. The South African government has committed R60 million, with the likelihood of more,” and one of the biggest individual donors is pharmaceutical magnate Frederik Paulsen, who has donated US$1,5 million. He is also a director of the Mouse-Free Marion Project NPC Board.

Asked about criticism that this operation would be a case of playing God, Anderson says that “unfortunately in this situation one has to essentially be playing God, because the problem is not going to resolve itself. It may be resolved when every last seabird is gone, and the mice have got nothing else to feed on, and we can’t wait till then.

“But nobody likes killing. I agonise over the things we need to do. Whether it’s removing Himalayan Tahrs from Table Mountain, or dealing with House Crows in Cape Town and Durban, but we’ve got to think of what the long-term benefits are, as custodians of biodiversity on the planet. The mice don’t belong there. They need to go.”

They need to go because, says Mavuso Msimang, “it is imperative that protected areas serve their purpose in providing safe spaces for the species that call them home.”


Main image credit: Ben Dilley, Mouse Free Marion

This story was first published in the Daily Maverick on 27 September 2023.

Yves Vanderhaeghen writes for Jive Media Africa, science communication partner to Oppenheimer Generations Research and Conservation.


Yves Vanderhaeghen

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