Marion Island’s wandering albatrosses can’t protect themselves from an invasive mouse population that’s eating the birds alive, but conservationists say a rodenticide ‘bomb’ could save them. Invasive mice are eating albatrosses alive on a remote Indian Ocean island, so conservationists have come up with an explosive solution: ‘mouse bombing’.
Mice have been wreaking havoc on Marion Island, between South Africa and Antarctica, for decades. Humans accidentally introduced mice in the 19th century, and the rodents have since taken a liking to wandering albatrosses (Diomedea exulans) and other endangered seabirds.
The Mouse-Free Marion Project, a joint venture between the South African government and BirdLife South Africa, is seeking to raise $29 million to drop 660 tonnes (600 metric tons) of rodenticide pellets on the island in the winter of 2027, AFP news agency reported on Saturday (August 24).
The project plans to send a squadron of helicopters to drop pellets. By striking in winter, when the mice are at their hungriest, conservationists hope to wipe out the entire mouse population of up to 1 million.
“We need to get rid of every last mouse,” Mark Anderson, director general of BirdLife South Africa, told AFP news agency. “If there was a male and a female left, they could breed and eventually return to where we are now.”
House mice (Mus musculus) first arrived on Marion Island on seal ships. They began their reign of terror, devouring the island’s invertebrates and eating seabird eggs. By 2003, the mice were eating seabird chicks alive, and now, a decade later, the mice have learned that they can attack adults, too.
Researchers discovered the carcasses of eight adult wandering albatrosses in April 2023. The birds had deep wounds on their elbows, consistent with mouse attacks, and likely died of secondary infection or starvation. Since then, further reports of adult seabird deaths suggest that mouse attacks are becoming more common.
“The mice just climb on them and slowly eat them until they die,” Anderson said. “We lose hundreds of thousands of seabirds every year to mice.”
Mice have been attacking wandering albatross chicks on Marion Island since 2003. The Mouse-Free Marion Project
Albatrosses are defenseless against mice because they did not evolve with land predators. They spend most of their lives at sea, and nesting sites like Marion Island are so isolated that mice and other non-marine mammals couldn’t reach them until humans arrived. Because the birds evolved to live in an environment where they didn’t encounter any land predators, they have no mechanisms to protect themselves.
A previous attempt to control Marion Island’s invasive mouse population using cats backfired horribly. Researchers took five cats to the island’s weather station in 1948, but the cats’ offspring went feral and began preying on seabirds as well as mice.
Feral cats multiplied and spread across the island until they were killing about 455,000 birds a year in the 1970s. Researchers successfully eradicated the cats in 1991.
The rodenticide at the heart of the new eradication strategy, by contrast, only needs to kill mice, as it has no effect on Marion Island’s native invertebrates or the seabirds that typically feed at sea.
Adult albatrosses on a remote island are being attacked and eaten by an aggressive invasive species – mice.
Invasive mice have been wreaking havoc on the ecosystem of Marion Island, located roughly halfway between South Africa and Antarctica, for decades, eating native invertebrates and the chicks of the many seabirds that nest there. But the latest discovery is the first time they have been documented attacking adult albatrosses on the island.
At 115 square miles (298 square kilometers), Marion Island is about half the size of Chicago but is home to an impressive array of wildlife, including king penguins, elephant seals, and seabirds such as wandering albatrosses (Diomedea exulans), one of the world’s largest flying birds. No non-marine mammals lived on the island until the 19th century, when house mice (Mus musculus) were introduced there by human ships.
Since then, mice have decimated many of the invertebrates and plant species that live there. But in recent decades, the local mouse population has increased dramatically, likely due to warmer, drier weather due to climate change.
Wandering albatrosses have a 10-foot (3-meter) wingspan, making them significantly larger than mice, but they have evolved to live on islands with no mammalian predators and have no defense mechanisms against invasive rodents, Anton Wolfaardt, a seabird researcher with the Mouse-Free Marion Project, told Live Science. The project is an initiative of the South African government and the nonprofit BirdLife South Africa.
Mice have recently been observed attacking adult albatrosses in other seabird habitats, including Tristan albatrosses (Diomedea dabbenena) on Gough Island in the South Atlantic and Laysan albatrosses (Phoebastria immutabilis) on Midway Atoll in the Pacific Ocean. It’s a worrying trend for this critically endangered group of birds—of the world’s 22 albatross species, nine are listed as endangered or critically endangered.
But this isn’t an isolated case of invasive species control — the U.S. Fish and Wildlife Service has released a final proposal to kill about 450,000 invasive barred owls in the Northwest in an attempt to save two native species.
U.S. wildlife officials plan to kill nearly half a million “invasive” American owls over three decades, new documents confirm. Experts say the cull is necessary to protect two native owl species that are under threat from the invaders. But animal rights activists have denounced the plan as cruel and unnecessary.
Barred owls (Strix varia) are large owls native to eastern North America. In the early 20th century, these owls began moving west of the Mississippi River following “human-induced modifications” to the Great Plains and northern boreal forests, according to the U.S. Fish and Wildlife Service (FWS). As a result, the owls have gained a foothold in Washington, Oregon, and California, where they are considered an invasive species.
The arrival of barred owls to the Northwest has negatively impacted two native owl species — northern spotted owls (Strix occidentalis caurina) and California spotted owls (Strix occidentalis occidentalis) — which are both much smaller than the invaders and are being outcompeted for food and territory. Both native species have also suffered from extreme logging over the past few decades, which has significantly reduced their range, according to the University of California, Santa Clara.
Barred owls have also begun mating with spotted owls, creating hybrids that could potentially reduce the spotted owl gene pool.
The northern spotted owl population has declined dramatically over the past few decades, and the species is now outnumbered by barred owls throughout much of its range. The species is currently listed as threatened under the Endangered Species Act (ESA), meaning the FWS is required to help protect the species. The FWS has also proposed adding California spotted owls to the ESA list as their numbers begin to decline as well.
On July 3, the FWS released its final Barred Owl Management Strategy after completing a public comment process. Documents show the agency intends to remove about 450,000 barred owls, including barred-spotted owl hybrids, over 30 years. The plan could be formally approved by the end of this year.
That may seem like a lot of owls. However, the cull would remove less than 1% of the projected U.S. barred owl population over the proposed time period, resulting in fewer casualties than other, more aggressive management options proposed by the FWS, which would have killed nearly twice as many birds. The cull would also be limited to about half of the areas where the ranges of barred and spotted owls overlap.
Officials hope the approach will help restore northern spotted owl populations and stop barred owls from spreading south, protecting California spotted owls. However, the plan would also allow barred owls to remain in the Northwest.
“This is not about one owl versus another,” Kessina Lee, a state ranger for the FWS in Oregon, said in a statement.
The shooting will be limited to licensed hunters, and the public will not be allowed to shoot barred owls. The FWS report also notes that lead ammunition will not be used in the shooting due to its environmental impact.
Not everyone is happy with the FWS plan, however. In March 2024, when a draft of the new management strategy was released, a group of at least 75 wildlife and animal rights groups wrote an open letter condemning the plan, calling it “colossally reckless” and “doomed to fail.”
Critics say the barred owls are being punished for human actions that have allowed them to expand their range. They also point out that owls are notoriously difficult to hunt, which can lead to cases of mistaken identity where the wrong owl and other forest animals are killed. As a result, these groups are proposing a non-lethal approach to control. However, they have not specified what that alternative approach would be.
However, FWS officials say culling is the best solution for all species.