Rathlin Island off the north of Northern Ireland is now free from feral ferrets that were harming its native seabirds. Conservationists say this is the first time these nonnative animals, which were domesticated from polecats some 2,000 years ago, have been completely eradicated from any island.
Ferrets (Mustela furo) were introduced to Rathlin in the 1980s to control another invasive species, rabbits, which were considered agricultural pests. However, instead of targeting rabbits, the ferrets multiplied and feasted on seabirds, ground birds, and their eggs and chicks, said Erin McKeown, program manager of the Life Raft ferret-eradication project led by the Royal Society for the Protection of Birds Northern Ireland (RSPB NI).
Rathlin Island is home to more than 250,000 seabirds like puffins, razorbills, guillemots and Manx shearwaters.
“On Rathlin, there has been over 70% of decline in puffin population,” McKeown told Mongabay by phone. “There are loads of different reasons for this decline, but one of the big ones is overpredation by ferrets. For example, a feral ferret got into our puffin colony in 2017 and in a two-day period had killed over 26 mature puffin birds. These are a species that will lay one egg a year.”
In 2021, a five-year, 4.5-million-pound ($6.1 million) project, involving RSPB NI, government agencies, other charities and the local community, was launched to eradicate ferrets on Rathlin.
There were an estimated 93 ferrets on the island at the time; all have now been removed by trappers, McKeown said.
The project team also relied on a network of 110 cameras and thermal drones to search for ferrets. Woody, a detection dog, played a key role, sniffing out ferrets from their droppings.
After no signs of ferrets in two years, the island has been declared ferret-free. Still, the cameras and Woody continue to monitor Rathlin for the invasive mammals. “He is now still used to help us declare absence since he’s not detecting them on site,” McKeown said.
With ferrets removed, early signs suggest the seabirds are recovering. Puffin populations in 2025 were the highest in the last five years, and many shearwaters bred on Rathlin after 40 years, McKeown said. Last year, six male corncrakes (Crex crex), considered endangered in the U.K, were also recorded calling. Corncrakes are ground-nesting birds that have nearly disappeared from the region.
A ferret-free island will likely benefit the community as well, McKeown said. “We’ve heard anecdotally from the community that they can have livestock and chickens now that they couldn’t have had previously because they would’ve just been preyed on so easily by the ferrets.”
“Achieving a successful ferret eradication has never been done before anywhere in the world,” Elizabeth Bell, a technical expert from Aotearoa New Zealand-based Wildlife Management International, said in a statement. “The lessons learned here will benefit island restoration projects globally for decades to come.”
Ferrets are also considered invasive in New Zealand, where they’ve driven declines of several ground-nesting birds.
Banner image of a ferret by Alfredo Gutiérrez via Wikimedia Commons (CC BY-SA 4.0).
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