Grey squirrels will raid wild birds’ nests for their eggs and kill and eat fledglings. Studies have shown decreases in the fledging success rates of some woodland birds where numbers of grey squirrels are found, notably the blackbird, collared dove, green woodpecker, long-tailed tit and jay.
Grey squirrels also cause serious damage to woodland by stripping bark from the trunks and branches of trees. Bark-stripping damage reduces timber quality through staining (owing 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. 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.