The Boreal Owl is a cavity nester and depends above all on abandoned Black Woodpecker holes, but it also readily takes larger nest boxes put up in coniferous forest. The female usually lays 4–7 eggs, but the clutch size varies greatly with vole availability – good vole years can produce considerably larger clutches. The female incubates while the male provides the food during the early period, and the young leave the nest hole before they are fully fledged.