One subspecies in Arizona nests exclusively in saguaro cacti. No nest material is added and nests are kept cleaner than in Eastern Screech Owls. The average clutch size tends to increase from south to north and from the coast inland. The eggs are laid every 1 to 2 days and incubation begins after laying of the first. The incubation period is about 26 days and the fledging period about 35 days.
Females incubate eggs and brood young while males bring food to the nest.
The Western Screech Owl is single brooded, but may re-nest if first clutch is lost. Pairs will often reuse nest sites in consecutive years. Pairs mate for life but will accept a new mate if the previous mate is lost. Grey and red colour phases will mate together. Adults tend to remain near their breeding areas year-round while juveniles disperse in the autumn.