There is a small dark portion between the eyes and the base of the bill. Eyes are pale to bright yellow, and the bill is yellowish horn. Upper parts are dark brown with bold white spotting. Underparts are off-white, with broad streaks of darkish brown, denser on the breast and trailing off at the lower belly. The legs and feet are covered with white feathers.
Claws are darkish horn to blackish brown, and have very sharp black tips.
This Owl is mainly nocturnal. The individual variation is in the number of notes and the pitch and speed at which the notes are uttered. This usually leads into a trill of up to 350 rapid notes, which is sung from potential nest sites to show the female. The female's call is infrequently heard, and similar to the male's, but fainter, higher pitched and not as clear. Boreal Owls usually hunt by perching on low branches or tree trunks.