Grey squirrels and red squirrels are known to strip the bark of trees but grey squirrels are known to do it more often than reds and on a larger scale this normally occurs between late April and the end of July.
Bark stripping damage reduces timber quality through staining (due to fungal infection) and structural defects and ultimately reduces timber value and yield. Weakened stems may break and trees that are ring-barked will die from that point up.
Damage varies across sites and between years and is difficult to predict. Thin barked species such as sycamore, beech, oak, sweet chestnut, pine, larch and Norway spruce are most at risk with trees aged between 10 and 40 years being most vulnerable.
This red is stripping a haw thorn that is heavily covered with ivy the thorn is part of a hedge row at the edge of the forest. We can see what shes doing but we cant see if it is sap or small insects she is getting from below the bark.