What does the Great Horned Owl sound like at night?

The classic Great Horned Owl territorial song is a series of 3-8 deep hoots: often rendered as "hoo-h'HOO... hoo... hoo." The pattern is typically a longer first note, then two or more paired shorter hoots. Males have a lower-pitched hoot than females.

“hoo-h'HOO hoo-hoo”

Birders often file this one under Hooting.

Right at dusk and again in the hours before dawn, loudest on still winter nights.

This owl nests very early in the year. Courtship and mating happen in mid-winter (Dec–Feb), with pairs hooting duets. They often use old nests of other birds. Eggs are incubated in late winter, and owlets hatch by early spring. Through summer the young mature and disperse by fall. In winter, adults call frequently to establish territory. Primarily nocturnal year-round, but in winter they may be heard calling at dusk and dawn more often.

That deep, stuttering four- or five-note hoot carrying across a neighborhood is almost always a Great Horned Owl. Both sexes hoot and they duet, the female pitched noticeably higher than the male. Peak calling runs from late autumn through midwinter, when pairs court and claim nest sites long before anything else is nesting.