Barn owls are sometimes called 'ghost owls' because of their pale colour and silent flight. The very edges of their feathers are fringed like soft combs, which break up the air as they fly. Other birds make a 'whoosh' when they flap. A barn owl makes almost no sound at all.
Their hearing is extraordinary. A barn owl can hear a mouse moving under thick grass - or even under snow - from many metres away. Its heart-shaped face works a bit like a satellite dish, catching the tiniest sounds and funnelling them into its ears.
Barn owls don't actually make a 'twit-twoo' sound. (That's the tawny owl.) Barn owls hiss and screech instead. The screech sounds a bit like a child shouting in the distance. People in the past sometimes thought it was a ghost.
They get their name because they often nest in old farm buildings - barns, sheds, ruined towers. In Ireland, organisations are putting up special nest boxes to help the barn owl population grow again.