The primary function of great horned owl hooting is to attract a mate.
During the great horned owl mating season, the challenging, deep, rich tones of the males are occasionally interspersed with the higher and huskier notes of the females.
The hoots of female horned owls are not usually identified at any time except the mating and nesting period and there is doubt if they do much calling at other seasons. Even at that season they do not seem as vociferous as the males. The latter may call back and forth at regular intervals for hours at a time, while the female owl’s calling periods, at short and indefinite time intervals, seldom exceed more than fifteen to twenty minutes.