Orkney Native Wildlife Project to eradicate stoats from the islands has recorded an increase in the number of Orkney voles and Hen Harriers.

According to a new report by ONWP, in 2025, Orkney vole activity in spring was the highest since 2019, when the Orkney Native Wildlife Project began regular surveys, and autumn activity was also high. In addition, the number of confirmed hen harrier breeding attempts was the highest it has been in more than a decade, and the number of short-eared owls recorded during the breeding season remained high, having recovered from low levels reported in 2019-20.

Matt Marsh, Monitoring Officer for the Orkney Native Wildlife Project, said:

“It’s fantastic to see the continued positive impact that removing stoats from Orkney is having on our native wildlife. 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. 

“We’re also very excited about what these studies can tell us about their relationship with the island’s vole population. 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. 

“It’s great to see the hard work of the project team and volunteers, and the strong levels of support from local communities, are starting to turn the tide for these vulnerable species. Ongoing monitoring is critical to understanding and addressing current and future threats to Orkney’s native wildlife.” 

Orkney voles are surveyed by looking for signs such as droppings and grass clippings (which are left behind from feeding). In spring 2025, the number of signs spotted were the highest recorded in any year since annual surveys began in 2019. Across 22 sites surveyed in Mainland Orkney and the Linked Isles, vole signs were found in one-third of the small survey squares searched (358 out of 1082).

The increase in the Orkney vole population the report says has had a knock on effect to the wildlife that would feed upon them, such as Hen Harriers, and Short Eared Owls.

In 2025, monitoring by the Orkney Raptor Study Group included 201 Mainland sites checked for hen harrier occupancy, with breeding proven at 74 sites – the highest number since 2012. Sadly, this did not result in record breeding success due to wet weather at a critical time resulting in high chick mortality. Despite this, it is thought nearly 60 chicks still successfully fledged in 2025 from monitored nests – a not insignificant number given the total hen harrier breeding population in 2023 in the UK/Scotland was 653/529 territorial pairs. 

For short-eared owls, which are notoriously hard to survey, birds were confirmed at 55 locations on islands with stoats during the breeding season, with proven breeding at 16 and nests found at six places by the ORSG. The results show a continuation of the increase in breeding site occupancy for short-eared owls since 2019, when the project began removing stoats. 

More intensive monitoring of Orkney voles has been happening since 2019 as part of the ONWP’s activities. An analysis of hen harrier breeding data between 2019 and 2025 has shown a close link between the improved numbers, and the recovery of Orkney vole populations. Vole abundance in the spring surveys was positively correlated with hen harrier presence in the breeding season, and particularly strongly correlated with breeding attempts. Furthermore, nest success rates were associated with autumn vole abundance. 

Graeme Walker, a long-time volunteer with the project, said:

“I’ve taken part in the vole monitoring survey every year since 2019, and every year, we’ve seen their numbers increase.

“It’s been great to see the positive impact that removing stoats has had on the voles I have been surveying. It’s fantastic that this iconic species is coming back so strong – and in turn, they’ll be helping Orkney’s native birds of prey to thrive as well.” 

Taken together, these results support the findings of a 2015 study on the anticipated effect of the arrival of stoats on Orkney’s native wildlife which predicted that, without intervention, stoats would have a devastating impact on Orkney’s native wildlife particularly voles, hen harriers and short-eared owls.  

Given Orkney is home to a sizeable proportion of the UK’s hen harrier population, these results have UK-wide significance for one of our rarest birds of prey. 

They also suggest that without the actions of the Orkney Native Wildlife Project and the support of so many people across Orkney, the county’s natural heritage would be in trouble. Lots of factors influence population trends in voles and birds of prey including weather, but these are encouraging signs that the efforts that have removed more than 8,500 stoats are helping these vulnerable species. 

Speaking on behalf of the project, Sarah Sankey, commented:

“Year after year, the results from efforts to monitor trends in native wildlife are showing us the positive impact removing stoats from Orkney is having. 

“Invasive non-native species are a significant threat to island wildlife and removing them is essential to giving Orkney’s native wildlife their best chance for the future, as well as sustaining the parts of our economy that relies on it.

“These results show the difference our efforts are making, and everyone involved in the progress so far should be really proud. But we can’t rest yet, we need to all come together to finish the job as soon as possible to not put what we’ve achieved so far at risk”.

All the monitoring data was collected thanks to volunteers from the local community, the ORSG and local staff. Additionally, members of the public report sightings of short-eared owls to ONWP. These are collated each year for potential future analysis. In 2025, 51 records were submitted, providing valuable additional information on short-eared owl distribution in Orkney on top of the breeding data collected by the ORSG. 

This shows how essential volunteers are for the understanding what is happening to native wildlife.

Anyone interested in joining the survey efforts this year should visit: Surveyor (Not on a Reserve) (Orkney Local Nature Conservation Sites) | RSPB Volunteering

The ONWP is funded by partners including The National Lottery Heritage Fund, EU Life, and the Scottish Government’s Nature Restoration Fund, managed by NatureScot. The project is the largest of its kind in an inhabited landscape, and the first to be attempted in the Northern Hemisphere.