Largely unmistakable. Male almost pure white with black dots. Female and juveniles white with heavy black barring, and may seem grey at a distance. Juveniles more finely barred than adult females, giving them a greyer appearance, with white neck and face. Body barrel-shaped, head small and rounded. Wing-tips more pointed than in other owls. Flight action both buzzard and owl-like, with surprising agility. Note that several species of owls may seem completely white to the untrained eye when suddenly appearing in car headlights etc.
Sound:Song consists of single utterances or series of "aooo", recalling Great Black-backed Gull, and is far carrying. Male warning call a deep and harsh "groat grat grat", with accented endings of each syllable. Female warning call higher pitched. Also various other high pitched calls.
Alarm call:
Distribution:
Wikipedia: map (se also Xeno-canto below)
Ecology:Birdlife ecology
Links:Observation.org Latest observations
Image search Flickr NB! May give other species
CCCC-sound:Niels Krabbe, Licence,Link.