Marion Island, a speck of volcanic rock about 1,243 miles southeast of Cape Town, hardly looks like the setting for a horror story. Yet on this windy, treeless outpost, an invasion of house mice is turning a haven for seabirds into a crime scene.
Night after night, the rodents swarm across the nests of wandering albatrosses and other ocean-roaming birds, gnawing at eggs – and, more recently, at the birds themselves.
The attacks are easy to miss if you picture mice as timid scavengers. On Marion, milder winters have stretched their breeding season, ballooning their numbers.
With plants and insects picked clean, the rodents have discovered an easier, protein-rich target that can’t flee: birds that never evolved defenses against land predators.
Invasive mice wreaking havoc
House mice first arrived on Marion Island in the early 1800s, stowed away on sealing vessels. For most of the next century, they nibbled seeds and invertebrates.
Warming temperatures, though, gave them extra breeding cycles each year. The population boom pushed the mice to experiment, and birds – stationary, trusting, and plentiful – proved irresistible.
Visitors now report grisly scenes at dawn. Adult albatrosses sit tight on nests, unblinking, while scores of mice chew away at feathers, skin, and muscle.
Lacking any instinct to fight back, the birds endure the assault until sheer blood loss or infection finishes the job.
How mice can displace seabirds
Marion shelters roughly one-quarter of the world’s wandering albatrosses, legendary fliers whose wings can stretch 11 feet tip to tip. In all, 29 seabird species breed on the island, yet 19 now face local extinction.
Climate change adds another layer of trouble: warmer seas push fish farther south or deeper, forcing parent birds to travel longer for food and return to nests depleted.
Chicks miss meals; adults miss breeding windows. Extreme storms, whipped up by hotter oceans, wash away nest sites perched on exposed tussock slopes. Combined with the mouse attacks, these pressures make every breeding season a roll of the dice.
Kill the mice, save the seabirds
“These mice, for the first time last year, were found to be feeding on adult Wandering Albatrosses,” stated Anderson, who also serves as the CEO of BirdLife South Africa. His team’s camera traps record the slow-motion assaults in heartbreaking detail.
“Mice just climb onto them and slowly eat them until they succumb,” said Anderson. The sad, slow process of dying can take days for a bird. “We are losing hundreds of thousands of seabirds every year through the mice.”
Enter the Mouse-Free Marion Project, an operation every bit as ambitious as it sounds.
The blueprint involves loading helicopters with 600 tons of cereal pellets laced with rodenticide and spreading them across the island’s 15.5-mile length and 10.6-mile width.
Of the $29 million price tag, about a quarter is already in the bank.
“We have to get rid of every last mouse,” emphasized Anderson. “If there were a male and female remaining, they could breed and eventually get back to where we are now.”
Lessons from a previous fiasco
Conservationists have tried drastic fixes here before. In the 1940s, cats were introduced to curb the rodents; instead, the felines multiplied and devoured roughly 450,000 birds each year.
A massive trapping campaign finally removed the last cat in 1991, but the mice inherited an island free of natural enemies.
That cautionary tale hangs over today’s planning sessions. Project leaders stress that baiting must be swift and island-wide – no gaps, no second chances.
Precision GPS flight lines and winter timing, when most summer-nesting birds are offshore, aim to protect non-target wildlife.
Timing is everything
Winter 2027 is the chosen window, when food is scarce for mice yet most seabirds have migrated north. Helicopters, weather permitting, will crisscross Marion in overlapping swaths to rain down pellets.
Comparable missions on South Georgia and New Zealand’s Antipodes Islands wiped out rats and mice in recent years, showing the blueprint can work even in harsh sub-Antarctic weather.
Logisticians still face headaches: sudden katabatic winds, hidden lava domes, and thick coastal fog that can ground aircraft for days. Even so, a successful first pass is cheaper and kinder than chasing survivors for decades.
Seabirds, mice, and invasive species
The Marion saga isn’t an isolated oddity. Islands make up barely two percent of Earth’s land, yet they hold an outsize share of endangered species.
Invasive predators – rats, cats, pigs, and now even mice – have driven 75 percent of recorded bird, mammal, and reptile extinctions on islands worldwide.
Climate change intensifies that pressure, allowing hardy generalists to outcompete specialists already living on the edge.
Protecting seabird strongholds pays off far beyond the shoreline. Albatrosses and petrels fertilize oceans with guano rich in nitrogen and phosphorus, boosting plankton and fish that feed coastal communities.
Lose the birds, and marine food webs feel the pinch.
What happens next?
Funding gaps still loom, and the clock keeps ticking. Yet every dollar pledged brings the Mouse-Free Marion Project closer to takeoff.
If helicopters lift off in 2027 and every pellet lands where it should, Marion could echo with healthy albatross calls again within a decade. That would free the conservationists to tackle other invaded islands before more birds vanish.
For now, researchers keep watch through wind-lashed winters, counting nests and documenting each fresh wound.
The task is grim, but the payoff – restoring one of the world’s greatest seabird nurseries – would be well worth the sleepless nights.
Should the plan succeed, Marion Island might one day be known not for its tragedy, but for showing how persistence, good science, and a bit of grit can tip the balance back in favor of the wild.
This article by Eric Ralls was first published by Earth.com on 11 June 2025.
Wildlife in catastrophic decline
The 73% decline in vertebrate wildlife populations during the last 50 years (mammals, birds, amphibians, reptiles and fish), is primarily driven by human activities that threaten biodiversity.
Habitat Loss and Degradation – human activities like deforestation, urbanization, and agriculture have led to the destruction and fragmentation of natural habitats, reducing the space and resources available for wildlife.
Pollution – air, water, and soil pollution from industrial activities, agriculture, and other sources can harm wildlife directly or indirectly by affecting their habitats and food sources.
Climate Change – changing weather patterns, rising temperatures, and sea levels are disrupting ecosystems and impacting species’ ability to adapt and survive.
Overexploitation of Resources – unsustainable hunting, fishing, and logging practices can lead to the depletion of populations and the loss of biodiversity.
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