The mice on a warming island breed uncontrollably and eat seabirds. An eradication is planned

By | March 16, 2024

CAPE TOWN, South Africa (AP) — Mice accidentally introduced to a remote island near Antarctica 200 years ago are breeding out of control because of climate change, eating seabirds and causing havoc in a special nature reserve with “ unique biodiversity”. ”

Now conservationists are planning a mass eradication using helicopters and hundreds of tons of rodent poison, to be dropped over every part of Marion Island’s 180 square miles to ensure success.

If even one pregnant mouse survives, their prolific reproductive potential means it may all be for naught.

The Mouse-Free Marion project – large-scale pest control – is seen as crucial to the ecology of the uninhabited South African territory and the wider Southern Ocean. If successful, it would be the largest eradication of its kind.

The island is home to globally significant populations of nearly thirty bird species and a rare, undisturbed habitat for wandering albatrosses – with their 3-meter wingspan – and many others.

Undisturbed, that is, until stowaway house mice arrived on sealers’ ships in the early 19th century, introducing the island’s first mammalian predators.

The past decades have been the most significant for the damage caused by the mice, says Dr. Anton Wolfaardt, Mouse Free Marion project manager. He said their numbers have increased dramatically, mainly due to rising temperatures caused by climate change, turning a cold, windy island into a warmer, drier and more hospitable home.

“They are probably one of the most successful animals in the world. They came to all kinds of places,” Wolfaardt said. But now on Marion Island, “their breeding season has been extended, and this has resulted in a dramatic increase in mouse density.”

Mice don’t need encouragement. They can reproduce from around 60 days of age and females can have four or five litters per year, each with seven or eight babies.

Rough estimates indicate that there are more than a million mice on Marion Island. They feed on invertebrates and increasingly on seabirds – both chicks in their nests and adults.

A single mouse feeds on a bird several times its size. Conservationists snapped a photo of one perched on the bloodied head of a wandering albatross chick.

The phenomenon of mice eating seabirds has only been observed on a handful of islands in the world.

The size and frequency of mice preying on seabirds on Marion has increased alarmingly, Wolfaardt said, after the first reports of it in 2003. He said the birds have not developed the defense mechanisms to protect themselves from these unknown predators and often sit there while mice nibble them away. Sometimes several mice swarm over a bird.

Conservationists estimate that if nothing is done, 19 species of seabirds will disappear from the island within 50 to 100 years, he said.

“This incredibly important island as a seabird refuge has a very uncertain future due to the impact of mice,” Wolfaardt said.

The eradication project is a single shot at success, without an iota of room for error. The rapidly growing mouse and rat populations have been problematic for other islands. South Georgia, in the South Atlantic Ocean, was declared rodent-free in 2018 after an eradication, but that was a multi-year project; the one about Marion could be the biggest intervention.

Wolfaardt said four to six helicopters will likely be used to drop up to 550 tons of rodenticide bait over the island. Pilots are given exact flight lines and Wolfaardt’s team can track the drop using GPS maps.

The bait is designed not to damage the island’s bottom or water sources. It should not harm seabirds, which feed at sea, and will not have a negative impact on the environment, Wolfaardt said. Some animals will be affected on an individual level, but those species will recover.

“There’s no perfect solution for this kind of thing,” he said. “There’s nothing that just zaps mice and nothing else.”

The eradication project is a partnership between BirdLife South Africa and the national Department of Forestry, Fisheries and Environment, which has designated Marion Island as a Special Nature Reserve with the highest level of environmental protection. It has a weather and research station, but is otherwise uninhabited and committed to conservation.

The department said the eradication of mice was “essential if the island’s unique biodiversity is to be preserved.”

Wolfaardt said the amount of planning required means a likely start date in 2027. The project also needs to raise around $25 million – part of which is funded by the South African government – ​​and receive final approval from authorities.

Scientists have tried to control Marion’s mice in the past.

They were already a pest to researchers in the 1940s, so five domestic cats were introduced. In the 1970s there were about 2,000 feral cats on the island, killing half a million seabirds every year. The cats were eliminated by introducing a cat flu virus and tracking down any survivors.

Islands are critical to conservation efforts, but vulnerable. The Island Conservation organization says they are “extinction epicenters” and that 75% of all extinct species lived on islands. About 95% of these were bird species.

“This is truly an ecological restoration project,” Wolfaardt said. “It’s one of those rare conservation opportunities where you solve a conservation threat once and for all.”


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