Orkney removes 8,500 invasive stoats as native vole and hen harrier numbers recover

What is the background?

Stoats are not native to Orkney and were first recorded on the islands in 2010, where they have no natural predator and prey heavily on ground-nesting birds and the endemic Orkney vole. Invasive species removal Scotland projects like this one target species that threaten island ecosystems with no evolved defences against them.

What happened?

The Orkney Native Wildlife Project has removed more than 8,500 stoats from the islands using humane lethal traps that comply with the UK’s Spring Trap Approval Order. As of March 20, 2026, the project had 8,813 trap boxes deployed across Orkney, most containing two DOC-200 spring traps each.

The 2025 monitoring report found Orkney vole activity in spring at the highest level recorded since regular surveys began, with autumn activity also high. Across 22 survey sites on Mainland Orkney and the interconnected South Isles, vole signs were found in 358 of 1,082 survey squares searched.

How did it happen?

Volunteers from the Orkney Raptor Study Group confirmed hen harriers breeding in 74 locations across islands with stoats in 2025 — the highest number of breeding locations since 2012. Wet weather during a critical period reduced chick survival that year, but researchers estimate nearly 60 chicks still fledged from monitored nests.

Analysis of hen harrier breeding data from 2019 to 2025 found a close link between falling stoat numbers and the recovery in Orkney vole populations, which are a key food source for the harriers and other native raptors.

Why does it matter?

Removing an invasive predator with no natural checks on Orkney allows two separate parts of the food chain to recover at once: the vole population directly, and the birds of prey that depend on voles as food. The seven-year link between stoat removal and hen harrier breeding success gives conservationists a rare, clearly measured example of island predator eradication working as intended.

The scale of the trapping effort — over 8,800 trap boxes across the islands — shows the project has moved well beyond a pilot, into sustained, islands-wide management.

What were the key results?

• More than 8,500 invasive stoats removed from Orkney to date
• 8,813 trap boxes deployed across the islands as of March 20, 2026
• Orkney vole spring activity at its highest level since regular surveys began
• Vole signs found in 358 of 1,082 survey squares across 22 sites in 2025
• Hen harriers bred in 74 locations in 2025, the highest count since 2012
• Nearly 60 hen harrier chicks estimated to have fledged in 2025 despite poor weather
• Seven years of breeding data (2019–2025) show a direct link between stoat removal and vole recovery

What happens next?

The Orkney Native Wildlife Project will continue expanding and maintaining its trap network to keep stoat numbers suppressed long-term.

Researchers plan to keep tracking hen harrier breeding success against future stoat and vole survey data. Visitors keen to watch the recovery from a distance often bring a wildlife trail camera* or a pair of birdwatching binoculars to record activity without disturbing nesting birds.

The project said it will publish updated 2026 vole and raptor survey results once the next breeding season concludes.

Conservation groups elsewhere in the UK are watching Orkney’s results as a model for island-based invasive predator eradication.