They may be doing it to impress the girls, but the mating ritual of grey squirrels that tear bark off trees is not impressing conservationists who monitor ancient woodland in the Forest of Dean, Glos.
The squirrels have caused unprecedented damage in the forest this summer, apparently because of their hormones.
The forest's wide range of trees, including oak, beech, chestnut, pine, fir and spruce, make it particularly attractive to squirrels. They strip bark from around the trunk, which means that the tree dies. If it is stripped on one side only, it weakens it until it snaps or allows fungus to set in.
Such damage occurs during the breeding season each year but the recent warm winters and a glut of autumn fruit has led to more squirrels breeding in the forest, leading to more damage.
The Forestry Commission estimates there are now around 20,000 squirrels there. Ben Lennon, of the commission, said: "If you walk around the forest at the moment you can start to see the damage. Some branches are bare on the trees and a lot of leaves are brown. The squirrels are an introduced species and their population just keeps growing and growing.
"There are several theories why the squirrels rip off the bark, but the most likely one is that it is linked to mating and the squirrels are trying to impress females."
Grey squirrels were introduced to Britain from America in the 19th century. The grey is bigger and more adaptable than the native red squirrel.
Mr Lennon added: "The animals have been in good condition to survive the winters in the past few years.
"We don't even bother planting some species in the forest now because it's not worth it - the squirrels just destroy them."