Thousands of screaming seabirds wheel through the air above and below me as I lean over the railings of a viewing platform halfway down a cliff. The chocolate backs of guillemots are packed so closely on the sheer rock face before me that they seem part of it. Higher up, on precarious ledges, they jostle with fulmars, kittiwakes and puffins, guarding their chicks and waiting for food from their mates.
It鈥檚 a wonderful sight, and one that draws in plenty of tourists. But it is not just the birds 鈥� much as I love them 鈥� that have prompted my trip to Rathlin Island in Northern Ireland. It is another animal that is really responsible for me being here, one that tends to evoke quite different feelings in the human psyche: the rat.
Rats are a huge threat to the seabirds on Rathlin, and the same is true on many islands across the world, where they, and other invasive predators like stoats and cats, eat eggs and chicks. There is now a growing movement for humans to step in and save the birds by killing all the rats. Predator eradication is difficult, but it is 鈥渙ne of the most powerful conservation interventions possible鈥�, says conservation biologist at the University of Auckland in New Zealand.
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Now, the strategy is being applied to Rathlin, one of the largest and most populated islands on which it has been attempted. Success isn鈥檛 guaranteed, but it is going well so far, thanks to a campaign involving lethal traps, poison, thermal drones and even a sniffer dog. I have come here to investigate what happens when you try to rid an island of rats, and where the idea goes next.
Rats have a long history of wiping out island birds, with their pawprints all over one of the world鈥檚 most famous extinctions, that of the dodo. This unfortunate bird disappeared within, having been hunted by the settlers and their menagerie of pigs, dogs, cats 鈥� and stowaway rats.
Whenever rodents arrive on an island with ground-nesting birds that haven鈥檛 evolved any defences, they can cause an apocalypse. It is extremely difficult to stop rats from reaching any island that has boat traffic, as they stow away in transported goods, especially animal feed, and can even swim to new islands less than a kilometre away.
Their impact is notorious in New Zealand, whose fauna evolved in geographical isolation for 80 million years, with no rat-like predators 鈥� indeed, no native land mammals at all, other than bats. Since humans arrived, the country has suffered sequential invasions of three rat species across its 600-odd islands. The first was in the 13th century, as , bringing along Pacific rats.
A few centuries later, these were outcompeted by the larger black and brown rats that hitched rides with European sailors. By the 1960s, conservationists were watching in horror as rodents reached New Zealand鈥檚 small outer islands, which until then had been sanctuaries for multiple bird, bat and other native species experiencing precipitous declines on the country鈥檚 two main landmasses.
One teacher, Alistair McDonald, took matters into his own hands. In 1960, he was touring Maria Island, a 150-metre-long island off the country鈥檚 north coast, when he noticed hundreds of small, delicate-looking seabirds, white-faced storm petrels, floating dead in the water. Rats had finally reached the island.
McDonald turned saving the birds into a school project, encouraging children to fundraise for poisoned rat bait and taking them on hunting expeditions with his dog. Some children even used the more direct method of whacking rats over the head, McDonald told . A park ranger visiting Maria a few years later confirmed the rats were all gone.
McDonald鈥檚 school project was one of the first island rodent eradications in the world. Since then, conservationists elsewhere have followed his lead and attempted to eliminate rats and mice from many hundreds of other islands, including those in Australasia, Europe and North America, as well as tropical islands with their unique ecosystems.
So far, there have been efforts to eradicate rodents on nearly 1000 islands around the world, with a 90 per cent success rate for rats and 75 per cent for mice (albeit with some reinvasions). Over the years, the techniques have become much more sophisticated. 鈥淲e started in the 1960s with people crawling around on hands and knees throwing poison everywhere,鈥� says Russell. 鈥淣ow we use helicopters, sowing the poison aerially. We have gone from islands that were tens of hectares to hundreds of hectares to thousands of hectares.鈥�
Conservationists had been discussing predator eradication on Rathlin Island for more than 20 years. Reports and feasibility studies were partly led by聽, a New Zealander who is a global leader in the field and who was drawn聽to Rathlin as the home to Northern Ireland鈥檚 largest seabird colony. At about 14 square kilometres, Rathlin isn鈥檛 the largest island to undergo predator eradication, but it is the largest one that is fully inhabited.
This is a serious obstacle, as it rules out using helicopters for bait distribution because the poison could be eaten by livestock, pets and possibly even children. 鈥淧eople don鈥檛 like poison dropping out of the sky,鈥� says Russell. Instead, the poisoned bait has to go in containers that only rats or smaller creatures can access, which must be placed by hand, massively increasing the work involved.
An added complication was Rathlin鈥檚 feral ferret problem. Though there were fewer ferrets than rats, they are lethal predators. In 2017, one ferret managed to reach the cliff-side breeding area I visited, killing 27 puffins over two days.
Despite these difficulties, the idea of eradicating both rats and ferrets on Rathlin gained ground, promoted by conservationists, organisations such as the Royal Society for the Protection of Birds (RSPB) Northern Ireland and some islanders themselves.
The campaigners had to convince farmers and other residents to allow strangers onto their land to distribute lethal traps. But there would be clear benefits. If bird numbers recovered as expected, it would attract more birdwatchers and bring in more tourism, the island鈥檚 main source of income. Plus, ferrets and rats are agricultural pests, eating the food of livestock and attacking poultry. After numerous community meetings, several residents joined the campaign as employees or volunteers, and the eradication started in 2023.
The first job was to tackle the ferrets. This was done by placing 450 traps around the island, with non-lethal ones used near homes to ensure no pet cats were killed by mistake. In the end, 98 ferrets were killed.
Two years need to have passed since the last sighting for any eradication to be considered certain and, this March, the RSPB proudly announced success 鈥� having carried out the first eradication of feral ferrets on an inhabited island in the world.
The rats, however, were a far bigger problem.
With an estimated 10,000 living on Rathlin, it was a mammoth undertaking, requiring 7000 bait stations, designed so nothing larger than a rat could get in and eat the poison. These were placed at 50-metre intervals all over the island. Permission was needed from nearly every resident, as some bait stations had to go in barns, outhouses and even homes.
The farmland and residential areas weren鈥檛 the only problematic locations. Much of the shoreline is surrounded by steep cliffs, requiring professional climbers to abseil halfway down and dangle bait stations further down on long wires. 鈥淚t鈥檚 about getting to every last place to make sure that you鈥檝e got total coverage,鈥� says Glenn Slade, project scientist for the RSPB. 鈥淚f you leave just one pregnant female rat, you鈥檝e potentially got recolonisation.鈥�
The rat poisoning began in September 2024. Slade estimates that most of the rats were killed within the first month. 鈥淭he vast majority of the decline happens in a short space of time, and then you spend a very long time chasing down those last ones,鈥� he says. That final hunt involved innovative methods like bringing in thermal drones and a specially trained sniffer dog, both of which were used to find any remaining rats.
As far as we know, the last rat was killed in June 2025. So, if all goes well, the campaign could be declared a success by next summer. 鈥淚 don鈥檛 want to jinx it, but, so far, we鈥檝e been successful,鈥� says Slade.
While the intensive part of the campaign is over, several Rathlin residents and volunteers have switched to the monitoring phase, with monthly checks of bait stations and camera traps to ensure no rats remain. They have added extra bait stations and cameras in the harbour area to spot any rats that arrive on boats. If any do, a new localised poisoning campaign would swing into action.
Charlie Bosanquet, a resident who is one of the harbour monitors, says the campaign works only with the islanders鈥� enthusiastic participation. She helped teach residents to spot signs of rats, giving out laminated sheets with pictures of scat from rats, mice and rabbits, as well as 3D-printed models of rat gnaw marks. The giveaway is that rats have two large front incisors, which leave distinctive grooves. Any resident who notices a rat knows to alert the RSPB.
Life after rats
The residents I speak to enthuse about the benefits of becoming a rat-free island. On my visit, I notice chickens strutting boldly around the lanes and fields, an unusual sight for a Londoner like me. Since rat numbers started falling, some non-farming residents began keeping chickens and ducks, says Marina McMullan, chair of the residents鈥� group, the Rathlin Development and Community Association.
All those I speak to on the island seem delighted with the campaign apart from one thing: it has led to a surge in rabbits, after the loss of ferrets, their only predators. As I take an evening walk, bunnies certainly bob up and down charmingly through long summer grass, but the next day, I hear how they ravage gardens and farmers鈥� fields.
I am shown a community allotment near the quay, where a whole row of sunflowers has just been beheaded. Similar destruction has been wrought on the strawberries, peas and herbs. As a keen allotmenteer myself, I feel the pain of this loss.
Then again, this outcome wasn鈥檛 wholly unexpected, seeing as the first ferrets were brought to Rathlin by residents in the 1980s specifically to control rabbits. When they got loose and started breeding, it must have felt like the song about the old lady who swallowed a fly.
I ask the RSPB what plans there are for the rabbits. For now, all a spokesperson will say is that their numbers are being monitored. Some of the islanders, however, mutter about taking matters into their own hands.
The rabbits may not seem like a big deal. Farmers elsewhere use various methods to keep their numbers down, including shooting them and gassing their warrens. But they show how, if one species disappears, the effects on an ecosystem鈥檚 complex web can be multiple and not always welcome.
When rats are eradicated, there is often a surge in mice, which are usually outcompeted by rats. 鈥淢y prediction is that mice populations will explode now that the rats are gone,鈥� says at California State University in Sacramento, who researches the impacts of invasive species.
Mice are also an agricultural pest and sometimes eat seabird eggs and chicks. On other islands where rats have been eradicated, the surge in mice has been for some other species, like lizards.
When one Rathlin resident wonders aloud to me whether the next step could be eradicating mice, it starts to sound like a game of Whac-A-Mole. Mouse-eradication campaigns are possible, but they are generally harder because the animals are smaller than rats and have even faster breeding cycles.
In the short term, though, there is already an uptick in some seabirds, with about 1700 puffins recorded in 2025 by the RSPB, compared with 1200 in each of the previous two years. There have also been the first signs in decades of breeding by Manx shearwaters and storm petrels.
Zooming out, the global picture of rat eradication projects suggests they can have broader benefits than initially expected. On tropical islands, for example, restoring seabirds to their former numbers is and its fish, as the birds deposit nutrient-rich droppings. After rat eradication on two Indian Ocean islands in the mid-2000s, seabird numbers steadily rose, and nutrient levels in the surrounding water were 13-fold higher than around similar islands that remained rat-infested.
Just how far could the eradication of introduced predators go? New Zealand is home to Predator Free 2050, a campaign launched by the government in 2016 to rid the entire country of its most harmful invasive predators by the middle of the century. While it first covered rats, possums and stoats, it later expanded to include ferrets, weasels and feral cats. 鈥淣ew Zealand鈥檚 ecosystem needs to remove these invasive predators for us to be able to have our seabirds, our land birds and our lizards and frogs back, and our massively cool invertebrates,鈥� says Bell, who advises on aspects of the campaign.
But many conservationists think this goal is both . For one thing, it would take huge resources 鈥� requiring an estimated NZ$1 billion (US$570 million) a year, more than 0.5 per cent of the country鈥檚 GDP 鈥� that haven鈥檛 yet been made available. And these funds would be better spent in other ways, like protecting islands that are already free of predators, says Linklater, who.
Although it may be unrealistic to eradicate the six invasive predators from the whole of New Zealand, the country has achieved stunning conservation successes through smaller-scale projects on many of its islands, including creating island聽sanctuaries for birds such as the kakapo, a large, waddling, frankly adorable parrot, and even the iconic kiwi.
Elsewhere in the world, work continues to suppress and eradicate invasive predators, including on both inhabited and uninhabited islands in the Scottish Orkneys and Hebrides.
With so many threats to wildlife from complex global problems like climate change and habitat loss, it is wonderful to work in a field that can count real successes, says Bell. 鈥淭he recovery of these islands has been mind-blowing in a lot of places,鈥� she says. 鈥淧lant recovery, bird recovery, invertebrates, reptiles 鈥� it鈥檚 magic.鈥�
