Research by Emma Sheehy and Colin Lawton of NUI Galway suggests that the recovery of the pine marten population in certain parts of Ireland has caused a significant decline in the number of non-native grey squirrels. This has allowed the native red squirrel to return to woodlands from which it had been driven out by the grey squirrel. The grey squirrel was introduced to Ireland in the early 20th century and soon displaced the red squirrel, through a combination of competition for food and disease. Adult grey squirrels are twice the size of red squirrels and, although they have a very similar life cycle and biology to the red squirrel, have a broader diet.
The squirrel/pine marten relationship was explored more rigorously in Scotland by Emma Sheehy and a team from the University of Aberdeen. They found that grey squirrel occupancy decreased with increased abundance of pine martens, whereas red squirrel occupancy was positively related to pine marten abundance. The findings suggest that red squirrels can coexist with pine martens but grey squirrels cannot, though grey squirrels still occurred in areas where there was low pine marten density (newly colonised areas).
What is not yet understood is the mechanism underpinning grey squirrel decline in the presence of pine martens; whether it is direct predation, increased stress from exposure to pine martens (pine martens creating a ‘landscape of fear’), or a combination of factors. Pine martens and red squirrels, however, have coevolved over tens of thousands of years, and though red squirrels are occasionally predated by pine martens, they coexist throughout their range in Ireland, the UK and Eurasia.
All-Ireland Squirrel and Pine Marten Survey
The All-Ireland Squirrel and Pine Marten Survey took place in 2019. Zoology researchers from the Ryan Institute in NUI Galway teamed up with Ulster Wildlife and Vincent Wildlife Trust to determine the latest distribution of red and grey squirrels and the pine marten in Ireland and to compare the current status of the animals with previous surveys conducted in 1997, 2007 and 2012. The results show that the dramatic decline in grey squirrel populations in the midlands of Ireland has continued and extended into new areas.
The survey report is available HERE
Further information and maps are also available on the project’s Facebook page.