Spotted Owls give up to 13 different hooting, barking, and whistling calls, although only a few are common. The owl's signal call—used by adult males and females to mark and defend territory, and by males delivering food to females—is a series of four hooted notes, with the middle two closest together. The hoots have a deep, pure tone, with females' voices higher than males'. To stay in contact, mated pairs also emit a hollow whistling sound that rises in pitch at the end. Fledged young give a similar high-pitched whistle to beg for food.