Tawny Owls pair off from the age of one year, and stay together in a usually monogamous relationship for life. An established pair's territory is defended year-round and maintained with little, if any, boundary change from year to year. The pair sit in cover on a branch close to a tree trunk during the day, and usually roost separately from July to October. Roosting owls may be discovered and "mobbed" by small birds during the day, but they normally ignore the disturbance.
The Tawny Owl typically nests in a hole in a tree, but will also use old European Magpie nests, squirrel dreys or holes in buildings, and readily takes to nest boxes. It nests from February onwards in the south of its range, but rarely before mid-March in Scandinavia. The glossy white eggs are 48 x 39 mm (1.89 x 1.54 in) in size and weigh 39.0 g (1.4 oz) of which 7% is shell. The typical clutch of two or three eggs is incubated by the female alone for 30 days to hatching, and the altricial, downy chicks fledge in a further 35–39 days. The young usually leave the nest up to ten days before fledging, and hide on nearby branches.