Orkney’s Wildlife Thrives as Stoat Eradication Efforts Show Remarkable Success
Orkney’s unique native wildlife is experiencing a significant resurgence, with recent reports highlighting a dramatic increase in the activity of the endemic Orkney vole and a corresponding boost for one of the UK’s most endangered birds of prey, the hen harrier. These positive developments are directly attributed to the ongoing project aimed at eradicating invasive stoats from the islands.
A comprehensive monitoring report released recently reveals that Orkney vole activity in the spring of 2025 reached its highest point since 2019, the same year that a dedicated initiative to protect the islands’ precious native fauna from the predatory stoats was launched. This surge in vole populations is a critical indicator of ecosystem health, as these small mammals form a cornerstone of the local food web.
The success isn’t limited to the voles. The report also indicates that the number of breeding attempts by hen harriers, a species that relies heavily on voles as a primary food source, has also hit its highest mark since the project’s inception in 2019. Furthermore, numbers of breeding short-eared owls, another predator dependent on voles, were notably high when compared to figures from six years ago. Conservationists have lauded these outcomes, describing them as “fantastic” and a clear demonstration of the positive impact of removing the invasive stoats, which posed a severe threat to Orkney’s vulnerable native wildlife.
Stoats, while native to mainland Britain, are not indigenous to Orkney. Their introduction to the islands was first documented in 2010. Conservation experts had long warned that without intervention, these non-native predators could decimate populations of native species, particularly the Orkney vole, which is found nowhere else on the planet. Disturbingly, evidence of the stoats’ impact has been stark, with stoat food stores discovered containing as many as 100 Orkney voles.
A Monumental Eradication Effort
Since 2019, the Orkney Native Wildlife Project has been engaged in an ambitious operation to remove stoats from the islands. This large-scale undertaking has seen the humane removal of over 8,500 stoats using carefully designed lethal traps. The project team proudly states that this represents the largest stoat eradication effort ever conducted on an inhabited landscape globally.
The latest monitoring report provides concrete evidence of the project’s effectiveness. Surveys, which involve identifying signs of vole presence such as droppings and gnawed grass, showed that Orkney vole activity in the spring of 2025 was the highest recorded since the systematic surveying began in 2019. Across 22 surveyed sites spanning Mainland Orkney and the interconnected South Isles – areas known to have stoat populations – signs of voles were detected in a significant portion of the surveyed squares. Out of 1,082 small survey squares examined, vole activity was noted in 358. The monitoring also indicated high vole activity during the autumn months, further reinforcing the positive trend.
A Boon for Birds of Prey
The benefits of the stoat removal have extended significantly to Orkney’s avian population, particularly the hen harrier. These birds, classified as one of the UK’s rarest birds of prey, have a substantial breeding presence on the islands. In 2025, volunteers from the Orkney Raptor Study Group (ORSG) documented hen harriers breeding in 74 locations across islands affected by stoats. This makes it the most successful year for hen harriers on Orkney since 2012.
Despite the encouraging breeding numbers, the project faced a setback due to adverse weather conditions during a crucial period for chick development. Wet weather led to higher-than-usual chick mortality. Nevertheless, it is estimated that nearly 60 chicks successfully fledged from the monitored nests, a vital contribution to the overall UK hen harrier breeding population, which comprises approximately 650 pairs.
Short-eared owls, another species that can be challenging to survey, also showed positive signs. During the 2025 breeding season, these owls were confirmed at 55 sites on islands with stoats. Of these, 16 sites were confirmed breeding locations, with nests discovered at an additional six sites. The conservation team noted a consistent increase in breeding sites for short-eared owls since the stoat removal project commenced in 2019.
The strong correlation between healthy vole populations and successful breeding attempts by both hen harriers and short-eared owls is a well-established ecological principle. These birds rely on the Orkney vole as a crucial food source for themselves and their young, making the increase in vole numbers a direct driver of improved breeding success for these raptors.
A Collaborative Conservation Triumph
The stoat eradication initiative is a collaborative effort spearheaded by the Orkney Native Wildlife Project, a partnership involving RSPB Scotland, NatureScot, and Orkney Islands Council. Beyond protecting voles and birds of prey, the project also aims to safeguard other vulnerable species, such as curlews, a ground-nesting bird with a nationally significant population found in Orkney. The project employs advanced techniques, including the use of detection dogs to pinpoint stoat presence and robust biosecurity measures to prevent the invasive mammals from spreading to stoat-free Orkney islands.
Matt Marsh, monitoring officer for the Orkney Native Wildlife Project, expressed his enthusiasm for the project’s outcomes. “It’s fantastic to see the continued positive impact that removing stoats from Orkney is having on our native wildlife,” he stated. “Hen harriers are one of the most fascinating species we monitor, as well as being one of the rarest birds of prey in the UK, so it’s excellent to see that their numbers are increasing.” He added, “Orkney voles are found nowhere else in the world and are the species that is probably most threatened by the arrival of stoats, so to see historically high rates of vole activity is very encouraging.”
Anne McCall, director of RSPB Scotland, highlighted the broader implications of the project. “The Orkney Native Wildlife Project is showing that we can halt and reverse species declines if we take action to address the threats wildlife is facing,” she commented. “Invasive non-native predators are a significant threat to much of the iconic wildlife found on Scotland’s islands.” She concluded, “There are many factors that influence survival. However, to give species like the Orkney vole their best chance, removing invasive non-native species like stoats from islands is essential.”
This success in Orkney follows a series of triumphs for island invasive species eradication projects across the UK. Most recently, conservationists announced the successful removal of feral ferrets from Rathlin Island off the coast of Northern Ireland, a feat that has protected thousands of breeding seabirds and other rare avian species.
