The Boobook is the smallest and most familiar of the Owls in Australia. It is more often heard than seen due to its familiar two note call, sometimes repeated for hours on end, which has been likened to that of a European Cuckoo. These sometimes playful little Owls are also known as Mopoke, Morepork, Spotted Owl, and Marbled Owl. Upperparts are pale to dark brown, depending on locality or individual variation, with white spots on the wings and back. The underparts are cream to buff with broad pale to dark brown streaks and mottling, the indistinct facial disc being much paler than general colour with a large dark patch behind eye.
Adults have a greenish-yellow iris, while a juvenile's is brown.
The females are slightly larger and more richly coloured. Immatures are paler than adults. Normal call is a brief double hoot with the second note pitched lower than the first, each note lasting for about a quarter of a second with a half second gap in between. There is usually a brief pause and then the call is repeated at a frequency of about twenty calls a minute. Calling may last for only a minute or two or may go on for hours.