Great spotted woodpecker

Woodpeckers build their nests in the hollows of large trees.

An excerpt from the article 19 facts about Great spotted woodpecker
They prefer damaged tree trunks as potential homes and treat digging a hole in a healthy tree as a last resort when they have no other choice. Digging a hollow takes from two to three weeks. Woodpeckers rarely inhabit the same hollow, usually creating a new one each year. They also like to occupy nesting boxes.