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The regional demise of a non-native invasive species: the decline of grey squirrels in Ireland

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Abstract

Following the introduction of the grey squirrel (Sciurus carolinensis) to Ireland in 1911, the species quickly established and spread to cover the eastern half of Ireland. Historically, the River Shannon has delineated the western boundary of its distribution in Ireland, however the factors limiting the spread of the species westwards were unclear. The aims of this study were to assess the current squirrel distribution in the area directly bordering the River Shannon, and to identify habitat types and landscape characteristics that could be facilitating or impeding the spread of grey squirrels in Ireland. The current distribution was established through hair tube and live trapping surveys and through sightings from a citizen science survey. Grey squirrels are absent or in very low numbers in much of the study area. In some areas, red squirrels have reappeared where they previously had been displaced by the grey squirrel. Discriminant function analysis was used to identify significant differences in habitat types and landscape characteristics between a region with high grey squirrel occurrence records and a region where they are now rare. Several landscape attributes were found to be significantly different, including the presence of pine marten, water bodies, peatland and coniferous forests. The area in which grey squirrels have disappeared overlaps with the core pine marten population range, and in a landscape that is more fragmented than the areas in which grey squirrel are continuing to be invasive. The demise of the grey squirrel in Ireland is more widespread than previously believed.

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Acknowledgements

Margaret Flaherty was funded by Department of Agriculture, Food and the Marine of the Irish Government under the National Development Plan 2007–2013. We would like to thank Michael Carey, Emily Goldstein and Emma Sheehy for contributing to the sightings data; woodland owners and managers in particular Coillte and National Parks & Wildlife Service (Department of Culture, Heritage and the Gaeltacht) for access to woodlands and facilitating trapping studies; citizen scientists for contributing to the survey as well as the National Biodiversity Data Centre, the Centre for Environmental Data and Records, the National and Regional Game Councils, the Forest Service (Northern Ireland), technical staff and students at NUI Galway for assistance with field work.

Funding

This study was funded by the Department of Agriculture, Food and the Marine of the Irish Government (Grant No. 10/RD/WIGS/NUIG/719).

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  1. Zoology, Ryan Institute, School of Natural Sciences, National University of Ireland Galway, Galway, Ireland

    Margaret Flaherty & Colin Lawton

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  1. Margaret Flaherty
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  2. Colin Lawton
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Correspondence to Margaret Flaherty.

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Flaherty, M., Lawton, C. The regional demise of a non-native invasive species: the decline of grey squirrels in Ireland. Biol Invasions 21, 2401–2416 (2019). https://doi.org/10.1007/s10530-019-01987-x

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