It is a bonding signal to coordinate family movements. In February, during courtship, the male will begin the single-note trill shortly before sunset and repeat it about once a minute for the next two hours. The female, who is the quieter of the two during courtship, picks up the slack during nesting and fledging. She uses the descending trill that is characteristically a nest-site territoriality defensive signal. She alerts the mate and fledglings to the possibility of danger and advertises to other screech owls that this is her home range.
Loud songs are by individuals of both sexes that are widely separated.
Muted versions are by family members that are close to one another. Both trills have variations that can be slurred, fast, slow, long, or short, and can be used in combinations. Screech owls also hoot, bark, and screech in increasing response to perceived danger. I have not heard these but have seen bill clapping, a fear response common to all owls. Gehlbach observed that Eastern Screech Owl calling is related to the gibbous cycle of the moon.