Native pine marten recovery reverses decline of the red squirrel by suppressing grey squirrel populations – Dr Emma Sheehy


Red Squirrel on a Branch of a Tree, Ireland

Invasive species contribute greatly to the loss of biodiversity and cause extensive economic damage worldwide. The grey squirrel was introduced from North America to Britain and Ireland in the early 20th century. Given their size and other biological advantages, their success in the ecosystem has had detrimental consequences for native red squirrel populations. It has been found in the UK that the damage caused by grey squirrels bark-stripping costs the government millions annually and is prohibitive to the planting of many native tree species. This increase of the grey squirrel population has adversely impacted biodiversity and the economy in Britain and Ireland, and native red squirrels are now a near-threatened species.

Although in decline globally, historically persecuted native predator populations are recovering in Europe in response to large-scale conservation initiatives. Dr Emma Sheehy’s MSCA COFUND ELEVATE project (2014-2017), was hosted by South East Technological University (formerly Waterford Institute of Technology) and the University of Aberdeen. The project investigated how the recovery of a native predator, the European pine marten, influences native red and non-native grey squirrels populations in Britain. The project combined spatial capture–recapture techniques to estimate pine marten density, and squirrel site-occupancy data.

Dr Sheehy found that the impact of exposure to predation is highly asymmetrical, with grey squirrel occupancy very negatively affected by exposure to pine martens. In contrast, exposure to pine marten predation was found to have an indirect positive effect on red squirrel populations. The study concluded that pine marten predation thus reverses the well-documented outcome of resource and disease mediated competition between red and grey squirrels, and that native predator recovery can provide biotic resistance to invasive non-native prey species.

The findings of Dr Sheehy’s study have implications for a range of diverse stakeholders, including the forestry sector (state and private), government agencies responsible for wildlife and the environment in Ireland, the UK and Europe, conservation NGOS (for example, those focused on red squirrel conservation, such as SSRS in Scotland, Red Squirrel Survival Trust & UK Squirrel Accord), as well as shooting estates and the gamekeeping community. Globally, evidence that the restoration of native predators can suppress invasive species and restore balance is of interest at both academic and policy levels. Similarly, the extensive coverage of the project in popular media is evidence of the engagement of members of the public with conservation interests.



There has been considerable media interest in Dr Sheehy’s research, both during and after the fellowship. She discussed her findings on television, including on BBC News, BBC2 Winterwatch—Unsprung, Scottish TV News, and The One Show, as well as on the radio, including on BBC’s ‘Inside Science’ and ‘Out of Doors’. She wrote numerous blogs on her research, such as for The Conversation and The Ecologist, and her work received coverage in national and international news media, including The Irish Times. Her results were also disseminated in more traditional academic fora like the Proceedings of the Royal Society B and in Global Change Biology.

Dr Sheehy’s professional advice was sought by NatureScot (formerly SNH) and Forestry and Land Scotland (formerly FCS and FCE), and one of the project’s most significant outcomes was a Policy Brief on her findings. The project’s outcomes were also disseminated through numerous outreach events such as the launch of the North-East Scotland Biodiversity Champions Project, the Annual Forestry Show, and the Pine Marten Strategy for England and Wales Group Meeting, Malvern, where she was invited as a speaker. The impact of this project is still ongoing, demonstrated by a recent publication in The Financial Times in 2023 which highlighted the significance of the outcomes of Dr Sheehy’s research.


The Elevate funding was instrumental in launching my post-doctoral career as a zoologist. It was well funded over three years which is better than average in terms of project length for a post doc, in a sector that is notoriously difficult to gain footing in. It was also long enough for me to realise that academia was not a route that I wanted to continue, however, the experience has stood me very well in my subsequent applied conservation career.

European Pine Marten hunting in the woods. Martes martes.
Dr Emma Sheehy

Dr Emma Sheehy

Dr Emma Sheehy began her zoology career as a “mature student” at NUI Galway (now University of Galway) at age 26. She then went on to do an IRC funded PhD there on the role of the pine marten in Irish squirrel population dynamics, and then moved to Scotland on a small Forestry Commission Scotland start-up grant, based at the University of Aberdeen, to carry on research into the relationship between the three species in the UK. At that point, she was awarded a prestigious MSCA COFUND ELEVATE fellowship, which was instrumental in enabling the continuation of the research. Towards the end of the fellowship, she became ill with ME/CFS, which meant that at the completion of the fellowship, she was unable to continue working in academia. In 2022, after several years of recovery, she began working for the Scottish Wildlife Trust’s Saving Scotland’s Red Squirrels project as Conservation Officer in the Northeast of Scotland, leading the eradication of an island population of grey squirrels from Aberdeen City. In 2023, she was promoted to Eradication scientific Lead, Northeast Scotland.

The ELEVATE MSCA COFUND programme, which ran between 2013 and 2018 under the FP7 COFUND programme, was an International Career Development Fellowship that gave the opportunity to researchers to spend two years at an international host organisation in any country outside of Ireland, followed by a one-year return phase at a host higher education institution.  This fellowship allowed experienced researchers to establish new, and strengthen existing research networks, and to work with leading experts in their respective fields. There were 45 projects funded across all academic disciplines under the ELEVATE programme. The fellowships represent an investment of €13.5 million.  

This project received funded through the European Union’s Seventh Framework Programme, under Grant Agreement no. 291760

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