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The field glitters in the early morning sun, catching a thousand dew flecked spiderwebs. Cows graze at the south end of the field, their hooves leaving pools in the damp soil. In their shadows, midges dance, while the long black bodies of St Mark’s flies rise from the grassy tussocks. It is one of those rare, still days in Orkney, and it is deathly quiet. Other than the whir of an insect passing close to your head, the air is dull with silence. Then, you hear it. From a patch of irises in the north end of the field, a ‘whaup, whaup’ rings out. You know what you think it is, but how can it be? No one has heard a Curlew in Orkney for almost 40 years.

Thankfully, this has not yet come to pass. It is hard to imagine an Orkney without Curlews, but it is a real possibility. Stoats were first reported in Orkney in 2010 and have a proven track record of driving ground-nesting birds to extinction. Introduced to New Zealand in the late 1800s, Stoats contributed to the disappearance of the Mātuhituhi, Laughing Owl, and South Island Kokako. All within 100 years. Older residents of New Zealand’s South Island still recall the Kokako’s mournful call from their childhood. While some believe they have heard it since it was declared extinct, evidence for its survival is inconclusive.

Orkney’s internationally important wildlife

The Orkney Native Wildlife Project (ONWP) was set up to prevent a similar tragedy from befalling Orkney. These islands have long been a haven for birds which are struggling to adapt to the pace of change across the UK. Despite being less than 1% of the UK landmass, Orkney is home to 20% of its Hen Harriers, 11% of its breeding seabirds, and around one in ten Curlews. Orkney is also home to Lapwings, Oystercatchers, and the Orkney Vole, a subspecies found nowhere else in the world! These voles are a crucial part of the food web, supporting stable populations of Hen Harriers and Short-eared Owls.

A low-lying and treeless landscape on the East Atlantic Flyway, Orkney is also a vital waypoint for migratory birds. This abundance of permanent and transitory wildlife is not only important in itself, but provides a major boost to the local economy. Tourists who engage in nature-related activities spend around £25 million in Orkney every year. In 2019, Orkney’s farmers received £2.35 million in Agri-Environment Climate Scheme Payments, 9% of all Scottish payments, despite being just 1.3% of its land area. These payments hinge on the presence of species like Hen Harrier and Curlew in high enough numbers to be considered viable populations.

The impact of stoats

All of this is threatened by invasive Stoats. In parts of the UK where the ‘whaup’ of a Curlew has become an unfamiliar sound, similar payment schemes have been withdrawn. Stoats are extremely skilful predators, with a big appetite and a rapid rate of reproduction. Capable of taking prey ten times their own size, Stoats have to eat a third of their own bodyweight every day, just to survive. If the same was true for an adult human, it would mean eating 41 fish suppers a night. Because of this, they have a tendency to kill more prey than they can eat, often caching the excess carcasses for later. Female Stoats are almost always pregnant, and can delay giving birth until they have found suitable territory. When they do, they give birth to anywhere between six to 12 kits.

These characteristics make Stoats extremely dangerous for wildlife which has not evolved to cope with mammalian predators. Just one Stoat cache in Orkney was found to contain the carcasses of over 100 Orkney Voles, while Curlew numbers have declined since they arrived. Stoats have been seen rolling eggs away from Oystercatcher nests, and raiding seabird colonies. Because of the abundance of prey and the absence of natural predators, the Stoat population was able to explode, colonising the whole of the Orkney Mainland and Linked South Isles in less than a decade.

The Orkney Native Wildlife Project

Watch this video about the Orkney Native Wildlife Project and check out this podcast from RSPB Scotland.

To date, the ONWP has removed more than 5,000 Stoats from Orkney, lifting the pressure on native wildlife, and preventing them from colonising any of the Stoat-free islands. This is a huge achievement, given the speed at which invasive Stoats are known to have spread across Orkney and New Zealand. As the biggest invasive predator eradication of an inhabited island, anywhere in the world, this has required a colossal effort, involving professional trappers, volunteers, and the support of over 900 landowners. Since 2019, there have been tentative signs of recovery among Curlews on the Orkney Mainland, and in 2022, 83% of Oystercatcher nests escaped predation. The project has decisively turned the tide on invasive Stoats in Orkney, but it has also encountered challenges.

Yet although Stoats have already done damage to Orkney’s native wildlife, the ONWP was set up to prevent the kind of destruction which invasive predators have caused elsewhere in the world. To this end, the project began trapping in 2019, deploying a network of some 7,623 active trap boxes. Most of these contain two lethal humane DOC-200 traps. The project also established a biosecurity programme, using Europe’s first Stoat detection dogs to find out which of the Orkney Islands had Stoats, and which did not. Stoats can swim up to 3.5km in the ocean, and islands within swimming range now have their own trap networks to keep them Stoat free.

Challenges, foreseen and unforeseen

The ONWP was always an extremely ambitious project, full of world firsts. With funding available for five years, the original timeframe for the eradication was shorter than many international equivalents. In New Zealand, most predator eradications aim for completion by 2050. However, because of the comparative recency of the arrival of Stoats in Orkney, and the imperative to act before they colonised more islands, it was decided that the project should work as quickly as possible.

Whereas most comparative eradications use massive poison drops to significantly reduce (technical term ‘knock-down’) the population, the ONWP could not. This is because the poison would not only be eaten by Stoats. It would therefore spread through the food chain, poisoning Hen Harriers, and Short-eared Owls, via their prey. Orkney’s Otters would also be at risk. For all these reasons and more, poison was neither a desirable nor legal option. In general, the scale of the task and the methods available made for a pioneering project.

Then, like most of the world, the Coronavirus pandemic brought life in Orkney to a standstill. The restrictions stopped the project from trapping for the entire 2020 breeding season, allowing Stoat numbers to rebound to pre-eradication levels. This effectively undid the previous year of trapping, as reducing the number of predators, of course, allows prey numbers to rebound. This abundancy of prey can create a predator boom if you do not trap during the breeding and dispersal season. In the case of Orkney, recovering Voles were an easy banquet for uncontrolled young Stoats. This is why it is so important to apply continuous pressure to the Stoat population until the eradication is complete. In real terms, the project had to begin over once trapping could resume.

When trapping restarted, the unusual behaviour of invasive Stoats in Orkney became increasingly apparent. In their native habitat, Stoats are generally shy and elusive creatures. In Orkney, they exhibit unusually bold behaviour, which is likely due to the lack of predators, and the abundance of prey. Stoats have been found denning beneath kitchen floorboards, living in the attics of holiday homes, and caching kills in residential gardens. What is more, Stoats in some parts of Orkney appear to den in greater density than in their native range. The interplay between people and nature is part of what makes Orkney so special, but there is no denying that it has posed unique challenges for a Stoat eradication project.

The solution

The project has had to adapt to overcome these challenges. The original plan was for the static trap network to reduce (‘knock down’) the number of stoats by 90%. Then, in the second phase of the eradication (technically called ‘mop up’), the remaining 10% would be found and removed using the detection dogs and public sightings to identify the location of remaining Stoats, followed up with ‘response traps’ to remove them. Due to the factors touched upon above, the project has had to move forward with this active method of trapping earlier in order to reach ‘mop-up’. Because of how labour-intensive response trapping is, this would not have been possible at the start of the eradication, when there were still lots of stoats everywhere.

However, with more than 5,000 Stoats removed, the project has been responding to detection dog searches and public sightings across the East Mainland and Linked Isles since March 2023. Response trapping has proved extremely effective at driving the first (‘knock-down’) phase forward. While the 10% threshold has not yet been reached, all the evidence suggests that this method is the way to get there. With more detection dogs and trappers, the aim is to be searching with dogs and responding with traps across the whole of the Orkney Mainland from January 2024.

The project is applying for funding to extend

Developing, trialling, and hiring for this new approach all takes time, however. While the data shows that response trapping is a genuine solution, it also shows that the eradication will not be complete by the end of 2024. With four years of data collected, the project is in a far better position to model how long the eradication will take. Based on this, the ONWP is applying for funding to extend the eradication by three years, followed by two years of monitoring. Response trapping across the whole eradication zone is expected to propel the project into ‘mop-up’ within 12 months from the start of the extension. The next two years will be spent in ‘mop-up’, using now tried and tested methods to remove every last Stoat from Orkney.

The following two years of monitoring is international best practice for any eradication. This was originally included in NatureScot’s legacy plan for the project. However, given the current economic climate, it is sensible to include it in the funding application for the project’s extension. This will guarantee that the eradication will be completed to the highest possible standard. Based on eradications elsewhere in the world, if a Stoat is found during this period, it is highly likely to be within the first year. Therefore, 12 months of contingency is being built into the project plans and funding applications, for just such a scenario.

Put simply, the ONWP is seeking funding to finish the job of removing invasive non-native Stoats from Orkney. Securing funding for a project as big and ambitious as this is always a complicated jigsaw. The project is in dialogue with its partners and funders like RSPB Scotland, NatureScot, EU Life, and the National Heritage Lottery Fund, about the extension and reallocation of current funding. Other funding options are also being explored. While there are limits to what can be said during the funding application process, the project is committed to being as open as possible about it. Community support is the backbone of the ONWP, and it is for this reason that the project is announcing the need for extension before it has confirmed further funding. Updates will be provided at every major milestone of the application process.

Stoat free Orkney

This decision has not been taken lightly, and transitioning to a predator control programme with continued biosecurity measures on the Stoat free islands was considered. Controlling Stoats means trying to keep their numbers down, without aiming to remove them all. The cost of this would be in the region of £1.5 million a year, forever, with a low chance of success. The cost of finishing the eradication averages a similar amount per year but for just five year, followed by a far smaller amount each year for biosecurity.

This means within six years a control and biosecurity programme would cost 15 times more per year than the eradication and subsequent biosecurity to prevent re-invasion. The ONWP is the only viable way of protecting Orkney’s native wildlife from invasive Stoats. Giving up, when we know eradication is achievable, would mean accepting the presence of a destructive invasive predator in the islands. On top of a warming climate and changes in the land, this is an added pressure which many species may prove unable to withstand.

In a global biosecurity crisis, it is of paramount importance that Orkney continues to function as a haven for struggling wildlife. Invasive species are responsible for 40% of extinctions in the past 400 years. 60% of these extinctions have taken place on islands. Whirling Lapwings, the ‘whaup’ of a Curlew, the silhouette of a Hen Harrier, a cloud of strident Terns; these things are as much a part of Orkney’s unique landscape as the Standing Stones of Brodgar. It is unthinkable that they could vanish. Undoubtably, New Zealand’s South Islanders once thought the same about the South Island Kokako. Yet within 100 years of Stoats arriving, it was gone.

Such a fate is far from inevitable for Orkney. Eradicating Stoats is possible, using a methodology which is now proven to work. While it will take longer than hoped, giving up with so much already achieved would be a betrayal of Orkney’s wildlife, and the huge number of local people who have supported the project by volunteering, reporting sightings, and granting access to their land. This is an opportunity to turn the tide on the single biggest cause of island extinctions in modern history. Together, we can protect Orkney’s native wildlife now, and for future generations.

Thanks for reading! To stay up to date with the latest news from the Orkney Native Wildlife Project follow us on Facebook, subscribe to the blog, and, if you’re local to Orkney, pick up a copy of the Orcadian on the last week of every month.

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