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These albatrosses are plagued by mice

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This article was originally hakai magazine, Online publication on science and society in coastal ecosystems.Read more articles like this

Steffen Oppel remembers his first close encounter with a Tristan albatross. It was a balmy day on Gough Island, a small British overseas territory in the South Atlantic Ocean halfway between South Africa and Argentina. He thought it strange that the birds were waddling and running down the little hill. That is, until one of his birds spread his big wings and caught the wind. “They have very large wingspans and are very adapted to flight,” he says.

Oppel, a conservation scientist at the Royal Society for the Conservation of Birds, visited Gough in 2018 and was part of a team seeking to protect the Tristan albatross and 21 other seabird species that live and breed there. .

200 years ago, mice landed with seal hunters. As the mouse population exploded, it exceeded the seed and insect supplies. Some even started eating seabird chicks. Some have even started attacking adult birds— creatures hundreds of times larger.

Last year, conservationists put out a bid to finally eliminate the invaders. They used helicopters to drop poisoned rat bait all over the island. However, their goal of annihilating Gough’s rats failed. A live rat was found soon after.

“We were all completely devastated,” says Oppel. Cameras her traps and other detection equipment, which researchers have set up, show that the mice have repopulated and spread across the island.

Through a series of dramas, conservationists have been surprised that albatross breeding populations have not suffered so badly despite rat attacks. Estimates show that the nesting Tristan Albatross population on Gough Island has remained stable since 2004, at approximately 1,500 pairs per year.

But its stability is shown by Oppel and his colleagues in new research, is an illusion. In their paper, scientists show that Gough’s Tristan albatross is suffering a mysterious decline. That instability was not represented in the data because of the way ecologists estimate population numbers by counting birds perched on nests.

Oppel and his colleagues, using a complex demographic model that takes into account birds where about 70 to 75% of the Tristan albatross population is always at sea, found that the total population of this bird actually declined from 9,795. I think I did. Between 2004 and 2021 the number of birds increased to 7,752. It’s the rat’s fault.

According to Oppel, mice are eating up the albatrosses’ ability to recruit new members to their breeding populations. The number of breeding pairs remains relatively stable, but the birds age and new chicks do not survive to adulthood. “Not enough young birds are coming,” says Oppel.

This makes the future of Gough’s albatross even more dire. It also raises the stakes on what comes next.

Although it wasn’t possible to completely wipe out the island’s rats, the eradication attempt gave the birds some respite, says Oppel. Attacks on seabirds will not resume anytime soon unless the numbers increase rapidly and the rats again exhaust their favorite prey. After all, he says, it’s desperation that causes small mammals to start gnawing on giant birds armed with formidable beaks.

“At least, we put a timeframe on Gough’s seabirds,” he says.

Andrea Angel is BirdLife South Africa’s Albatross Task Force Manager. During his 2003-2004 visit to Gough, Angel, along with his colleague Ross his Wanless, captured the first video evidence of mice attacking Tristan his albatross chicks. . Although she is not involved in the rat eradication project, Angel supports it.

Like Oppel, Angel believes the efforts have dramatically reduced the rat population. It has brought birds, and the island’s unique plant and insect life, rest.

This is evidenced by the successful breeding of Gough’s other seabirds this year, she says. For example, McGillivray’s prions and gray petrels had their highest breeding success rate this year since record-keeping began for her in 2014. This is a drastic change, says Angel. In 2004, she and her colleagues searched the island for gray petrel nests. They found only one chick.

It is too early to tell whether the numbers of young albatrosses reared by Tristan’s albatross are also increasing. But so far, conservationists have yet to see evidence that albatross chicks have been attacked by rats. It’s a silver lining, says Oppel, and eradicating mice could lead to reproductive success in birds.

After last year’s failure, the team is now trying to figure out how to increase the chances of success in future eradication attempts.The process could take years, Oppel said. First, we need to understand what went wrong and why some mice didn’t eat.

“Something needs to change. You can’t go out there and repeat the same thing and hope for better results.”

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