The Northern Hawk-Owl nests in cavities, preferably in a natural tree hole, in the top of a broken, rotten stump or in a nest box. The female lays a clutch of usually 5–9 eggs, and the clutch size is strongly governed by the supply of rodents. Good vole years produce large clutches and high productivity of young, while poor years can lead to breeding failing altogether. The Northern Hawk-Owl defends its nest forcefully against intruders.