Article by Ed Snell – Project Support & Development at NatureSpy
Red squirrels play an important role in ecosystems by dispersing seeds which are a part of their diet, helping natural reforestation processes. However, without conservation, the future for Britain and Ireland’s red squirrels does not look good.
In recent years, research has been carried out that’s revealing the dynamics between pine martens, grey squirrels and red squirrels. This has captured a lot of attention, as pine marten conservation projects are currently helping this species return to the landscape following historic persecution and habitat loss. It now appears that pine martens could be part of the answer to helping the recovery of Britain and Ireland’s native red squirrels, which have suffered dramatic declines because of non-native grey squirrel presence.
Red squirrel footage from our project partners Alladale Wilderness Reserve, Bunloit and Aigas Field Centre.
Grey squirrels from North America were introduced to England in the late 1800s and Ireland in the early 1900s as an ornamental species to live in areas such as the grounds of stately homes. Grey squirrels outcompete the native red squirrel for food and space and also carry the squirrelpox virus, which grey squirrels are immune to, but is lethal to red squirrels. This has resulted in local extinctions of red squirrels across much of England and Wales, with strongholds remaining in Scotland and Ireland.
Grey squirrels also have a considerable economic impact. The vast number of grey squirrels currently in England and Wales is estimated to cost £37m a year in damage to trees due to bark stripping behaviour, which enables access to the sweet sap underneath.
As a result of the impact that grey squirrels have on red squirrels and woodlands, grey squirrel numbers are managed through methods such as trapping and shooting, yet there are an estimated 2.7m grey squirrels in Britain. Can pine martens lend a hand with controlling grey squirrels?
A grey squirrel scurries across a fallen tree in Yorkshire.
Pine martens have a varied omnivorous diet that commonly includes small and medium sized mammals, fruit, birds and insects. Studies across Europe have shown how varied a pine marten’s diet can be depending on factors such as food availability, seasonality and habitat. Part of what enables pine martens to access a wide variety of food is their excellent climbing abilities. They are able to climb quickly up and down trees as they have semi-retractable claws and their hind paws can rotate almost 180 degrees.
Dietary analysis and camera trap footage have provided evidence of pine martens preying on another nimble climber: grey squirrels. They occasionally prey on red squirrels too – although pine martens and red squirrels have coevolved and lived in the same habitats over thousands of years. Research has found pine martens prey significantly more on grey squirrels than red squirrels. This is where the dynamics between these three species gets interesting…
A red squirrel in the Scottish highlands cautiously approaches a pine marten feeding station and moves away without taking any peanuts from inside.
The presence of pine martens has been found to reduce grey squirrel numbers through predation. This suppression effect on grey squirrels gives red squirrels a chance to recover through competitive release: this means that red squirrels are avoiding the squirrelpox virus and have access to habitats once again. One reason for much greater predation of grey squirrels could be that they are not showing anti-predator responses to the scent of pine martens, unlike red squirrels that recognise pine martens as a threat and keep a distance.
Grey squirrels have been very successful in colonising large parts of Britain and Ireland due to their ability to thrive in a diverse range of habitats. From ancient woodlands to urban areas, so long as there’s trees where they can feed and den, they have what they need. However, in places such as urban areas where grey squirrels thrive and pine martens either avoid, cannot access or simply wouldn’t be able to survive in, grey squirrels are safe from pine marten predation. Research has also found that red squirrels persist better in certain habitat types (e.g. broadleaf woodland) and are likely more prone to pine marten predation in others (e.g. commercial conifer plantations). Shared, favourable habitats seem to be a key factor in how effectively pine martens can suppress grey squirrels while red squirrels recover. However, the affect that pine martens can have on suppressing grey squirrels shouldn’t be underestimated: research in Ireland has found that pine martens can cause grey squirrel populations to crash at the landscape scale.
Pine marten carrying a grey squirrel in Yorkshire
Research shows that pine martens are a viable part of an approach to managing grey squirrels and in turn helping red squirrels to recover. Pine martens alone are not likely to completely remove grey squirrels from the landscape, since grey squirrels live in a more diverse range of habitats. There are however certain habitat types such as woodlands where pine martens can have a significant impact on grey squirrel numbers. This has wider implications too, as it is an example of predators regulating prey, which is a fundamental part of maintaining healthy ecosystems.
Our footage of a pine marten preying on a grey squirrel in Yorkshire is a useful piece of evidence to confirm this behaviour in the region. This footage hints at the potential of pine martens to help with grey squirrel control in areas such as the North York Moors, which has completely lost its red squirrel populations and has an abundance of grey squirrels.
Learn more about our pine marten conservation work on our Project Pages.
