Grey squirrels were introduced into the UK from the US in the 1870s and they are blamed for the decline in the native reds.
It has been known for some time, but a recent study led by Joshua Twining, of the School of biological sciences at Queen’s University Belfast, supports the fact that red squirrels can benefit from an ally: the pine marten. Pine martens do occasionally eat red squirrels but they much prefer greys. Perhaps the word “prefer” is the wrong one. Some scientists believe that the red squirrel is more agile than the grey and rarely feeds on the ground. This removes them from the danger of attack by a pine marten.
However, it is said that pine martens raid the dreys of grey squirrels. “Dreys” are rough nests made by squirrels out of leaves, twigs and strips of bark which they build in the forks of branches high up in the tree canopy.
An earlier study published on March 7, 2018 also confirmed that pine martens can reverse the spread of the invasive grey squirrel and help the conservation of red squirrels in the UK.