It sounds like a horror story. But for birds on Gough Island, the nightmare is real. Invasive mice, with no natural predators, have evolved to grow fifty percent larger than the average house mouse and to rely on a sinister food source.
They gather at night, forming groups of up to nine and descending upon chicks in the nest, eating them alive. Now, a study published in Ibis Journal has revealed that the scale of this devastation is far greater than we ever thought, resulting in that at least two million fewer chicks a year than there would be had the mice never arrived.
If the 19th century seal hunters who accidentally introduced the mice knew how harmful these rodents would become, they might have been more careful about where they docked their ships.
“We knew there were large numbers of chicks and eggs being eaten each year but the actual number being taken by the mice is just staggering,” says Dr Alex Bond, one of the lead authors. “The seabirds of Gough Island desperately need our help.”
Gough Island (part of the Tristan da Cunha Island group, a UK overseas territory in the South Atlantic) is a seabird haven worth protecting. Considered one of the most important sites for seabirds in the world, this remote, uninhabited island hosts over ten million birds from 24 species, some of them found nowhere else.
Albatrosses are among the most imperilled residents. These enormous and long-lived voyagers mate for life and lay only one egg a year. Tragically, many of them now return from a fishing trip to find the year’s only offspring dead in the nest.
For the Tristan Albatross Diomedea dabbenena, a Critically Endangered species whose chicks are particularly vulnerable because their parents leave them alone for several days in winter, this problem is especially dire.
Although these chicks can weight up to 10 kg, the open wounds inflicted by mice over a series of nights often kill them. They do not know how to defend themselves, as they have not evolved the instincts to respond to this new threat.
Now, there are only 2,000 Tristan Albatross pairs left in the world – 99% of them living on Gough Island. Without action, the species is likely to go extinct.
“We usually think of rats as problem rodents on islands but this shows that house mice can have catastrophic impacts all on their own,” says Anthony Caravaggi, lead author and researcher at University College Cork and Queen’s University Belfast. “If we don’t remove the mice from the island then we’re going to lose several unique species and an important island for breeding seabirds.”
Fortunately, help is at hand in the form of one of the most ambitious mouse eradication projects ever attempted, which will benefit six Globally Threatened species at once, finally allowing populations to recover.
Our UK Partner the RSPB has teamed up with Tristan da Cunha government, with help from across the world*, to develop The Gough Island Restoration Programme, set to begin in 2020.
It’s not going to be easy. The island is remote, with rough terrain and often extreme weather. Highly experienced helicopter pilots will perform a series of complex aerial manoeuvres to drop bait across the island.
In hard-to-reach areas, hikers will spread the bait on foot to ensure that every mouse on the island is targeted. But it’ll be worth it – and previous successes like the recent rat eradication on South Georgia Island prove it can be done. The task is so monumental that it has taken years of planning just to get to this stage – but by 2020, it will finally be ready to roll out.
“We have a unique opportunity to save Gough Island and the species that make their home there,” says Ian Lavarello, Chief Islander of Tristan da Cunha. “If we do nothing, we will eventually lose this amazing South Atlantic seabird mega-colony and its contribution to the world’s oceans will cease. With dedication and rigorous planning, success is possible. Monumental programmes such as this are not without their challenges but the rewards for global conservation are great.”
You can help ensure this project’s success. Go to goughisland.com to read more about the project and make a donation.
This article was first published by BirdLife International on 22 Oct 2018.