What does the Northern Saw-whet Owl sound like at night?

A monotonous series of whistled toots given at about 2 notes per second. It's often likened to a backup alarm of a truck or a steady beeping. Typically, the male repeats this "too-too-too" for dozens, even hundreds of times, usually all on the same pitch. It carries well through the woods on calm nights and is used to attract females and declare territory.

“too-too-too...”

Birders often file this one under Song.

Deep in the night, mostly late winter into spring, when males advertise.

Males start singing as early as late winter (January/February in mild areas, March in colder areas) to attract a mate and establish territory. Breeding occurs from late winter into spring; they nest in cavities, laying eggs usually in April or May. Males bring food to the females and young. By summer, fledglings leave the nest and disperse. Saw-whets are quiet during summer and early fall, focusing on hunting. Come fall (October-November), many undertake migration at night; this is when they are often caught at banding stations using mist nets and audio lures. During winter, they roost in dense cover and are rarely vocal except sometimes making quiet calls on calm nights. As winter ends, the cycle of tooting songs begins anew. Throughout, they remain solitary except during breeding, and even then the male and female don't roost together (female stays at nest, male nearby).

A monotonous, endless too-too-too on one pitch, like a truck backing up somewhere in the woods. Saw-whets are tiny and easy to miss, and the song can run for minutes without a break — which is exactly why people notice it and go looking for what is beeping outside.