Five species of owl regularly breed in Scotland though Little Owl(introduced to England & has spread north) only has a slim toe-hold whilst Eurasian Eagle Owl may also be poised to colonise (from an increasing population of escaped captive birds).
The spectacular Snowy Owl bred for a few years in Shetland but with the lack of new blood the population fizzled out though Snowy Owls are seen annually in Scotland, most notably in the Western Isles & the possibility of future breeding attempts remains.